- Email: [email protected]
Part I: Assessment of aortic regurgitation by noninvasive techniques
David Kandath, M.D., is a former Fellow in Cardiology at the State University of New York at Buflalo, and at the University of Alabama at Birmingham. He is currently in private practice at Saratoga Springs, NY.
Navin C. Nanda, MD., is Professor of Medicine and Director of the Heart Station and Echocardiography-Graphics laboratories at the University of Alabama School of Medicine, Birmingham, Division of Cardiovascular Disease. He is Editor-in-Chief of Echocardiography, and has authored or coauthored more than &IO articles.
D. Douglas Miller, M.D., is a member of the faculty of the University of Texas Health Science Center, San Antonio, in the Divisions of Cardiology and Radiolosy Dr. Miller received training in clinical cardiology and cardiovascular research at the Montreal Heart Institute, Emory University School of Medicine in Atlanta, and the Massachusetts General Hospital, Harvard Medical School in Boston. Dr. Miller is a graduate of McGill University Medical School in Montreal, Canada, and a Fellow of the Royal College of Physicians and Surgeons of Canada, the American College of Cardiology, and the American Heart Association. He serves as an editorial consultant and board member for ten medical journals, and has authored nearly 100 papers on cardiology-related topics. 42
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1990
Gregory B. Cranney, M.B., is Clinical Director of the Cardiovascular NMR Research Laboratory at the University of Alabama at Birmingham. He obtained his medical degree from the University of New South Wales in Sydney, and then completed his internship, residency and Cardiology Fellowship at the Prince of Wales and Prince Henry Hospitals in Sydney. He was then granted a National Heart Foundation of Australia postgraduate research scholarship to study ventricular mechanics in patients with valvular regurgitation. This work focused on noninvasive assessment using Doppler and radionuclide techniques. It became apparent to the author that NMR oflered a greater potential to accurately and noninvasively assess ventricular mechanics and thus he moved to the UAB to pursue this interest. Afler completing a fellowship in Cardiovascular Nuclear Magnetic Resonance at the University of Alabama at Birmingham, he was appointed to his current position as Assistant Professor of Medicine.
Chaim S. Lotan, M.D., is currently an attending physician in the Cardiovascular Division, the Hebrew VniversityHadassah Medical Center, Jerusalem, Israel. He received his medical degree from the Hebrew University medical school, and completed his internship, residency and cardiology fellowship at. the Hebrew University- Hadassah Medical Center, where he was involved in research regarding the early administration of thrombolytic therapy. As a recipient of an international Fulbright scholarship, Dr. Lotan spent 2 years at the Cardiovascular NMR laboratory at the University of Birmingham, where his research interests included NMR assessment of global and regional ventricular function and the identification and quantitation of post reperfiusion myocardial hemorrhage by NMR imaging. Curr
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1990
43
Gerald M. Pohost, M.D., graduated from the University of Maryland School of Medicine, Baltimore, in 1967. He completed his Internship at the Montejiore Hospital Medical Center in the Bron,x, New York. Dr. Pohost served his Residency in Medicine at the Montefiore Hospital Medical Center and the Bron,x Municipal Hospital, and was a Fellow in’Cardiology at the Massachusetts General Hospital in Boston. He is currently Professor of Medicine and Radiology and Director of the Division of Cardiovascular Disease at the University of Alabama School of Medicine in Birmingham. 44
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1990
PART
I: A&SESS~NT
OF ACWIW
REGURGPl’ATR3ly BY IWMWNVASIVE TECHWrQUES David Kandath, M.D. Navin C. Nanda, M.D.
Aortic regurgitation usually results from lesions of the aortic valve itself or of the aortic root. M-mode and two-dimensional echocardiography are useful in defining anatomy and are therefore accurate in detecting many of the causes of aortic regurgitation. These modalities are also useful in the measurement of left ventricular size and function. They are therefore valuable in the assessment of prognosis in patients with aortic regurgitation and in determining the optimal time for aortic valve replacement. However, it is impossible to accurately diagnose aortic regurgitation with these methods. High-frequency diastolic flutter of the anterior mitral valve leaflet (or the interventricular septum) on M-mode is the only reliable finding that suggests aortic regurgitation.’ This sign is not sensitive, because if the regurgitation jet is of a relatively low velocity or is not directed at one of those structures, flutter will not be observed. Moreover, even if flutter is present, this gives no indication of the severity of aortic regurgitation. Thus, until the recent arrival of Doppler technology, angiography was the only investigative mode available for the detection and quantitation of aortic regurgitation. Because it is invasive and expensive, this method is not widely applicable, especially as a screening tool. Doppler echocardiography now enables accurate noninvasive detection and semiquantitation of aortic regurgitation. This added dimension to the noninvasive examination, which was hitherto lacking, has improved the reliability of echocardiography in the assessment of aortic regurgitation. CONVENTIONAL DETECTION
DOPPLER
OF AORTIC
REGURGITATION
Both pulsed and continuous-wave Doppler can be used to detect aortic regurgitation. The first characteristic of the aortic regurgitation jet is that its velocity is high, due to the large pressure difference between the aorta and the left ventricle. It should be noted that Cur-r Probl
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1990
4s
this reversed gradient, however, is not so large as that between the left ventricle and the left atrium, and therefore the velocity of aortic regurgitation is less than that of mitral regurgitation. The second feature of the jet is that its flow is turbulent, because the high-velocity flow through a relatively small orifice causes a chaotic motion of the red blood cells. Thus high-velocity turbulent flow that occurs into the left ventricular outflow tract in diastole is the hallmark of aortic regurgitation on the Doppler examination.2-5 Pulsed Doppler Examination-The detection of the characteristic diastolic high-velocity turbulent flow into the left ventricular outflow tract requires close scrutiny of the Doppler spectral trace and of the audio signal. Because of the turbulent nature of the jet, its audio signal is harsh. It usually is holodiastolic. The spectral trace is boxlike and extends both above and below the zero line due to aliasing secondary to the high-velocity of the jet (Fig 11. The boxlike shape results because the spectral trace usually exceeds the Nyquist limit both above and below the zero line. This gives the appearance of the spectral trace being cut off at the site of the Nyquist limits for forward and reverse flow. Spectral broadening is present due to the turbulent flow. As with mitral regurgitation, the velocity of the jet has no relationship to the severity of the aortic regurgitation; it merely reflects the pressure difference between the aorta and left ventricle in diastole. The main views used in the pulsed Doppler examination are the apical (five chamber and long axis) and the parasternal (long axis and short axis) views. The pulsed Doppler examination is begun from the apical view. The apical five-chamber view is obtained first. The pulsed Doppler sample volume is then placed on the left ventricular aspect of the aortic valve just proximal to the cusps, and moved slowly and carefully from the medial aspect where the lowfrequency sounds of the septum are obtained, more laterally until mitral inflow is encountered. Each time the Doppler sample volume is moved the transducer should be angulated so that the azimuthal plane is interrogated. The same procedure is then repeated after rotating the transducer so that the apical long-axis view is obtained. In the parasternal long-axis view, the pulsed Doppler sample volume is placed in the left ventricular outflow tract just proximal to the aortic valve leaflets and moved from anterior to posterior. This view is less sensitive than the apical view because the flow of the regurgitation jet in most cases is perpendicular to the transducer. However, in the case of eccentrically directed jets, as might occur with paravalvular regurgitation in patients with prosthetic aortic valves, this view might allow a more parallel orientation with the regurgitation jet. Other views used in assessment of aortic regurgitation include the subcostal views (five chamber and short axis). Occasionally the su46
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1990
,“.,.
”
FIG 1. A, Doppler identification of aortic regurgitation. Top, Doppler sample volume (arrow) was placed in the left ventricular outflow tract just below the aortic valve (AV) imaged in the apical five-chamber view. LV = left ventricle. Boffom, Doppler tracing shows marked turbulence and aliasing in diastole characterized by large-frequency shifts (arrows), which reach the limits of the display on both sides of baseline (S) and produce a typical boxlike rectangular pattern. The systolic flow pattern (Sy) is normal. S = Doppler sample volume position in the A-mode. 8, Doppler baseline (S) has been shifted to the bottom of the display to more clearly delineate the characteristic rectangular pattern of diastolic signals (arrow) produced by aortic regurgitation. AV = aortic valve, B = Doppler base, LV = left ventricle, S = Doppler sample volume position on the A-mode. (From Nanda NC (ed): Doppler Echocardiography. New York, lgaku Shoin, 1985. Used by permission.)
prasternal and right parasternal views are used because the left ventricular outflow tract and aortic valve can be imaged. More commonly, however, these transducer positions allow visualization only of the ascending aorta and therefore are not particularly useful in the detection of aortic regurgitation.. Pulsed Doppler is nearly 100% sensitive and specific in the detection of aortic regurgitation.“‘ ’ As with mitral insufficiency, aortic regurgitation is often detected by Doppler examination in patients in whom a murmur cannot be auscultated. In such cases aortic insufficiency is usually confirmed by angiography. A potential source of confusion in the diagnosis of aortic regurgiCurr
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1990
47
tation occurs in the case of associated mitral stenosis, especially if the resultant diastolic jet is directed toward the septum. The velocity of a mitral stenosis jet, however, never approaches that of aortic regurgitation. In case of the latter, the spectral trace exceeds the Nyquist limit both above and below the zero line as a result of a severe degree of aliasing. This is responsible for the boxlike appearance of the spectral trace of aortic insufficiency. While the mitral stenosis jet might exceed the Nyquist limit once, it seldom is of sufficient velocity to cause abasing on both sides of the zero line. This fact helps distinguish the two conditions.’ Continuous-wave Doppler ExandnHion.--As with pulsed Doppler, diastolic flow into the lefk ventricular outflow tract, which is turbulent and of high velocity, is the characteristic of aortic regurgitation. The audio signal is similar to that seen on the pulsed wave examination. However, the spectral trace does not alias and is recorded as a somewhat rectangular holodiastolic pattern above the baseline. The apical view is mainly used because it is usually possible to orient the Doppler beam parallel to aortic regurgikttion flow from this position. If an imaging transducer is being utiBzed, the continuous-wave cursor is placed across the aortic valve in the apical five-chamber or long-axis view. The transducer is then angulated, as with the pulsed Doppler examination, until the highest veIocities are recorded. If a nonimaging transducer is being used, it is placed in the apical position and angulated until the aortic outflow tracing is recorded. Small changes in transducer position guided by the audio signal and the spectral trace will then result in the aortic regurgitation jet being interrogated. Using the continuous-wave Doppler spectral trace of aortic regurgitation, the left ventricular end-diastolic pressure can be calculated as follows: The velocity (V) at end-diastole can be converted into a pressure gradient (P) using the modified Bernoulli equation. Thus
P = 4v2 This is the gradient between the end-diastolic (AOEDP) and left ventricle (LVEDP). Therefore
pressures
in the aorta
P = AOEDP - LVEDP or LVEDP = AOEDP - P where AOEDP is diastolic pressure sure cuff. If there is no obstruction 4s
as measured with a blood presto left ventricular outflow, then Curr
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February
1999
LVEDP can be calculated using the above equation. When Doppler measurements are performed simultaneously or within 24 hours of cardiac catheterization, a good correlation (r = 0.84-0.98, standard error of estimate [SEE] 5.5-8 .mm Hg) was shown between the LVEDP measured by Doppler and cardiac catheterization!’ ’ It was found that the Doppler estimate could distinguish between a low (Cl5 mm Hg) and elevated P15 mm Hg) LVEDP with a high degree of specificity (90% 1.’ In another study where there was an interval between the Doppler examination and catheterization of greater than 24 hours, poor correlations were found between the LVEDP measurements obtained by the two methods.*’ There are a number of liniitations to the use of continuous-wave Doppler to calculate LVEDP. The major drawback is that in many instances the peak velocities on the spectral trace are not recorded, resulting in overestimation of LVEDP. The reason for this is that it is difficult to maintain the alignment of the ultrasonic beam parallel to flow throughout diastole, because of respiratory movements and because many aortic regurgitation jets are eccentric. Also, the SEE in the studies mentioned of 5.5 to 8 mm Hg is high, considering that the upper limit of normal for LVEDP is 12 to 15 mm Hg. Finally, determining the diastolic pressure fmm the cuff pressure by listening to Korotkov sounds may be problematic, especially in patients with severe aortic regurgitation, because the sounds completely disappear only at very low pressures, in which case th”e point at which there is a change in character of the sounds is probably a closer approximation of the true intra-arterial diastolic pressure. ASSESSMENT
OF SEVERITY
OF AORTZC
REGURGITATION
Flow Mapping.The most widely used and reproducible method is mapping of the extent of the flow disturbance. This requires the use of pulsed Doppler, because continuous-wave Doppler lacks the property of range gating. The views used are the apical five-chamber or long-axis views. The extent that the diastolic flow signal of aortic regurgitation extends back into the ventricular cavity is mapped. The regurgitation is then graded as follows:
Grade 1 (mild): The jet is detected just below the level of the aortic valve. Grade 2 (moderate): The flow disturbance extends up to the level of the tips of the mitral valve leaflet in diastole. Grade 3 (severe): The jet is detected below the tips of the mitral valve leaflets. This grading correlates fairly well with angiography.6 It should be emphasized that this method is semiquantitative, because even Curr
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February
1990
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though the jet is three dimensional, only its length is taken into account during quantitation by this approach. There are a number of other limitations to the estimation of aortic insufficiency by flow mapping. First, this system of grading is restricted to one particular imaging plane and does not take into consideration the fact that the flow, because it is three dimensional, might be maximally present in another two-dimensional echocardiogmphic plane even if the jet is not particularly eccentric. This plane might be one of the conventional two-dimensional echocardiographic views or “unconventional” in that the transducer position iYom which a parallel orientation of the ultrasonic beam with the flow jet is obtained lies between one of the standard two-dimensional echocardiagraphic planes. Second, if the aortic regurgitation jet is eccentric, this might result in underestimation of the severity, because the jet would not extend far enough lengthwise into the left ventricular cavity or might extend out of the imaging plane, resulting in a major portion of the flow disturbance not being detected. Also, in patients with low cardiac output the jet will not extend far back into the left ventricle because it is of low velocity even though its actual volume might be large. Further, in those patients with aortic regurgitation and an associated high-velocity jet directed toward the interventricular septum, as might occur with mitral stenosis or prosthetic mitral valves (especially metallic valves), confusion might occur when mapping the extent of the aortic regurgitation jet. Although the two jets can usually be distinguished at the level of the aortic valve leaflets, this is more of a problem as the pulse sample volume is moved further down into the left ventricular cavity during the process of mapping the aortic regurgitation jet. Finally, this method demands a high degree of technical expertise and is time consuming. Diastolic Slope ofSpectral Trace.-The slope of the spectral trace in aortic regurgitation reflects the rapidity with which the aortic diastolic pressure equalizes with the left ventricular diastolic pressure. If the left ventricular diastolic pressure is high, as in severe aortic regurgitation, then equalization of pressures is rapidly achieved, resulting in a steep slope. In contrast, in mild aortic regurgitation the slope is gradual. (NOTE: the opposite occurs in mitral stenosis; that is, the greater the degree of stenosis the more gradual the diastolic slope of the transmitral spectral trace). Several studies have shown that the rate of deceleration of the transaortic diastolic spectral trace reflects the degree of aortic regurgitation.” ’ In general, if the rate of deceleration is in excess of 3.0 m/se& then this correlates with the presence of severe a0r-k regurgitation (3+ to 4+) on angiography. A potential pitfall of this method is that in patients with severely diminished left ventricular compliance or in those with acute aortic regurgitation, rapid equalization of aortic - left ventricular diastolic ~RSSURS might occur, with a resultant steep slope on the regur50
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1990
FIG 4. Aort~c regurgitation. Left parasternal long-axis left ventricular outflow tract originating from t~on JAR), The mosaic slgnals turn to blue loses energy and the velocity decreases to aorta. LA = left atrium, iV = left ventricle, Textbook of Co/or Doppler Echocardiography. permission.)
plane shows diastolic mosaic signals in the the aortic valve, indlcatke of aortic regurgitadistally because the posteriorly directed jet below the Nyquist limit of 0.58 mkec A0 = RV = right ventricle. (From Nanda NC (ed): Philadelphia, Lea & Feblger, 1989. Used by
FIG 2. Color Doppler assessment indicated by a wide jet that valve level. A0 = aorta, AR (From Perry GJ, Nanda NC:
of seventy of aortic regurgitation Severe aortic Insufficiency is occupies 100% of the left ventricular outflow tract at the aortic = aortic regurgitant jet, LA = left atrium, RV = right ventricle. ini d Cardiac imag, 1988, Used by permlssion.)
FIG 3. Color Doppler assessment of aork regurgitation. Long thin let of aortic InsufficIency, VISUallred from the aplcal long-axis view, in a patient with moderate aortic insufficiency. Despite the length of the jet, its relative narrowness indicates that this is only moderate aortic insuffIciency. A0 = aorta, AR = aortic regurgitant jet, LA = left atrium, LV = left ventricle. (From Perry GJ and Nanda NC: Echocardiographyl986, 3:495. Used by permission.)
gitant spectral trace. On the other hand, in patients with extremely compliant ventricles the opposite might be noted. Another method of assessing the diastolic slope of the aortic regurgitation spectral trace is by measuring the pressure half-time, which is the time taken for the peak instantaneous pressure between the left ventricle and aorta to drop by half. The principle is the same as that used to assess the mitral valve area. Using the modified Bernoulli equation, the peak velocity (V,) of the aortic regurgitation spectral trace is converted to a pressure gradient (P,). The velocity (V,) at which P, drops to half of its initial value (PI,,) is given as PI/v?% Pressure half-time is the time taken for the velocity on the spectral trace to drop from V, to V,. The shorter the pressure halftime the more severe the degree of aortic regurgitation. When compared with angiography, aortic regurgitation (l+ to 4+) as estimated by the pressure half-time shows considerable overlap between grades. However, in one study, a value of 400 msec distinguished between mild (l+ to .Z+) and severe (3+ to 4-l-I aortic regurgitation.11 The major problem encountered during the evaluation of the diastolic slope is the difficulty in obtaining adequate spectral tracings. This is not possible in as many as 30% of patients.’ The reason for this is that in patients with aortic regurgitation the aortic valve is usually deformed as a result of fibrosis and calcification, resulting in an eccentric jet. Also, as pointed out earlier, it is difficult to maintain the ultrasonic beam parallel to flow throughout diastole because of the changing orientation between the jet and the Doppler cursor due to respiratory movements. Consequently, it is difficult to align the Doppler beam parallel to flow, resulting in underestimation of the maximal velocities. On the other hand, it has been found that adequate Doppler spectral traces are obtained in the majority of patients with severe aortic regurgitation, probably because the jet is wide. Estimation of the diastolic slope is another semiquantitative method of assessing the severity of aortic regurgitation.
Estimation of Reguqitant Fraction.-In aortic regurgitation, the total forward flow (total stroke volume, TSV) through the aortic valve includes the true stroke volume (SV, which is the effective for-ward flow) plus the volume of aortic regurgitation (regurgitant volume, RV). On the other hand, flow through any of the other valves (mitral, tricuspid, pulmonic), provided they are not regurgitant, consists solely of the true stroke volume. Regurgitant fraction is the mgurgitant volume expressed as a percentage of total stroke volume. From this the following equations can be derived: RV + SV = TSV RU = TSU - su Cow
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Cardiol,
February
1990
51
ThUS
Regurgitant
fraction (RF) =
TSV - SV TsV
If flow across the aortic valve is being measured, then the volume of forward flow that is calculated will be the TSV. The reverse flow, on the other hand, will consist solely of the regurgitant volume. Thus in equation 1 RF=
Reverse flow volume Forward flow volume
Two methods are used to estimate the regurgitant fraction in aortic regurgitation: 1. Forward flow through the aortic valve is used to calculate TSV, and flows through either the mitral or pulmonic valve are utilized to measure stroke volume. Regurgitant fraction can then be estimated from equation 1. Flow through an orifice, as estimated by Doppler echocardiography, is given by the product of the time-velocity integral (TVI) or area under the Doppler spectral trace and the cross-sectional area of flow. If the region of flow is circular, then this cross(Diameter12 sectional area = 77 Therefore, flow through an orifice (F) 4 can be expressed as F = TvI x
l-l
(Diameter? 4
In the case of the aortic valve, the time velocity integral of flow is obtained by placing a pulsed Doppler sample volume in the aortic orifice in the apical five-chamber view. The diameter of the aortic annulus is measured in the parasternal long-axis view as the inner diameter in mid-systole. For the pulmonic valve the time velocity integral is obtained by placing the pulsed Doppler sample volume in the valve orifice in the parasternal short-axis view. The orifice diameter is measured in the same view in mid-systole as the distance between the inner boundaries. To estimate flow through the mitral valve, the sample volume is placed in the mitral valve orifice in the apical four-chamber view. The mitral annulus is measured in the same view, as the distance between the inner borders in mid-diastole. All orifices are assumed to be circular. Good correlations have been obtained when compared with angiographic regurgitant fractions using either mitral (r = 0.9111’ or pulmonic flows (r = 0.94)‘3 to estimate stroke volume. However, this method of estimating regur52
curr~roblCardiol,
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gitant fractions has a number of limitations. In patients with turbulent flow through the aortic valve, as might occur in aortic stenosis Or severe aortic regurgitation, an adequate spectral trace is difficult to obtain. The same applies to the mitral or pulmonary valves. aso, in those with more than mild mitral insufficiency, the mitral valve cannot be used to estimate stroke volume, because the transmitral flow represents the total forward flow and not the effective forward flow. The situation is similar for the pulmonic valve in the case of more than mild pulmonic insufficiency. To overcome this limitation, the pulmonic valve can be used to estimate stroke volume if significant mitral regurgitation is present, and vice versa if significant pulmanic regurgitation is present. Since intracardiac or extracardiac shunt lesions also modify pulmonic and aortic flows, this method to estimate regurgitant fraction cannot be used in such cases. Thus significant mitral or pulmonic regurgitation and shunt lesions should be ruled out by careful Doppler examination prior to using these methods to assess aortic regurgitation. Another limitation is that an accurate and reproducible measure of the diameter of the orifice is diificult to obtain. Small errors in the diameter measurement are magnified because the diameter must be squared to obtain the area of flow. This is especially the case with the pulmonic annulus, where due to the limits of lateral resolution of the two-dimensional echocardiographic image, the lateral border of the pulmonic orifice is often difficult to determine. Finally, since the methods described involve the measurement of total stroke volume and stroke volume from two different anatomic sites, the potential for error in the diameter measurements and velocity measurements (as a result of varying angles of interrogation) is magnified. These drawbacks can be overcome by using forward and reverse flows in the aorta (see below) to determine total stroke volume (forward flow) and regurgitant volume (reverse flow). 2. The second method of calculating the regurgitant fraction in aortic regurgitation is by estimating the ratio of forward and reverse flows in the aorta. The best site at which to sample flow is the descending aorta at its junction with the arch (the aortic isthmus). Flow at this site is free of the turbulence caused by aortic stenosis or severe aortic regurgitation. Further, unlike the ascending aorta, this segment is easier to image from the suprasternal notch in adults. Finally, flow velocities are more uniform, and the peak velocity does not vary across the aortic diameter, depending on the sampling site, as is the case in the ascending aorta. Normally in the thoracic aorta flow is recorded away from the transducer in systole. If there is aortic regurgitation, significant retrograde diastolic flow might be present. Using pulse or continuouswave Doppler, flow in the descending thoracic aorta can be recorded from the suprasternal view. If pulsed Doppler is used, the Cur-r Probl
Cardiol,
February
1990
53
sample volume is positioned in the aortic isthmus. We know that the ratio of reverse and forward flows yields the regurgitant fraction. Thus anterograde or retrograde flow (F, or F,) = time velocity integral of anterograde or retrograde flow U’VI, or TvI,.) x cross-sectional area of flow (CSA, or CSA,). Therefore, F, = TVI, X CSA, F, = TVI, X CSA, Regurgitant
fraction
(RF) = 2 = zy ,” ,“zr a d d
If we assume that the area of the aorta does not change much tween diastole and systole, then
be-
The diameter of the aorta, however, does change during the cardiac cycle, and therefore, to be more accurate, the diameter of the aortic arch can be estimated in systole (D,) and diastole (D,) on the Mmode examination. The systolic diameter is the maximum diameter measured. The diastolic diameter is taken as the average of the maximum and minimum diameters. The aorta being circular, its crosssectional area is obtained by the formula. Substituting in equation 1, (Diameter? 5-r 4
RF =
TvI
a
x ,(Ds)’ 4
_ TVI, X (DJ2 - TVI, X (D,J’
Using this method, good correlations (r = 0.90) have been obtained with regurgitant fractions measured by cardiac catheterization.14 The estimation of regurgitant fractions offers a potentially attractive approach for assessing aortic regurgitation, because this is a truly quantitative method. The Doppler approach using different sites to quantitate the stroke volume and total forward flow has a number of limitations, as outlined previously. In addition, neither of the two Doppler methods is accurate in the presence of atrial fibrillation. Although excellent correlations have been obtained with cardiac catheterization using these Doppler methods, it should be noted that regurgitant fraction derived invasively also has several drawbacks. Different methods are used to estimate forward flow vol64
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1990
ume (which is done angiographically) and stroke volume (which is done by the Fick or thermodilution technique). During the angiographic measurement, assumptions are made regarding left ventricular geometry that might not be true in patients with severe aortic regurgitation. Further, when the Fick or thermodilution method is used to calculate stroke volume in the same patient, significantly different values might be obtained because the two methods are not strictly comparable. Also, the assessment of aortic regurgitation by the use of regurgitant fractions by cardiac catheterization cannot be used in patients with significant associated mitral regurgitation or in those with atrial fibrillation. Reverse Flow in Abdominal Aorta.-Normally in the abdominal aorta there is mainly systolic flow, which is recorded as flow away from the transducer and therefore below the zero line on the spectral trace. In diastole there is only a minimal amount of retrograde flow, which is due to distal runoff into the coronary arteries and systemic elastic recoil. Since this flow is toward the transducer, it is recorded above the zero line on the spectral pattern. In patients with mild aortic regurgitation there might be a significant amount of flow toward the transducer, but even so, this is still confined to early diastole. However, in patients with severe aortic regurgitation there is holodiastolic retrograde flow. Thus this manner of assessment differentiates mild from severe aortic insufficiency.15 In our laboratory it is used to confirm the degree of aortic regurgitation. A limitation of this method is that patients with left-to-right shunts from the aorta (e.g., patent ductus arteriosus) will also have holodiastolic retrograde flow in the abdominal aorta. Also, in obese patients the excessive depth of the aortic flow away from the transducer makes adequate velocity recordings impossible. Further, the angle the interrogating Doppler beam makes with abdominal aortic flow is large, which also decreases the sensitivity of the Doppler examination. Intensity of Spectral Wave Pattern.-The intensity of the gray scale of the spectral trace is proportional to the volume of red blood cells in the jet. Thus, the more severe the regurgitation the darker the spectral trace.16 The intensity of the retrograde aortic diastolic flow signal is compared with the anterograde flow through the aortic valve. In severe aortic regurgitation the intensity of the retrograde flow is equal to that of the anterograde flow. This method is highly subjective and offers only a rough estimate of the severity of aortic regurgitation. The various methods of quantitating aortic regurgitation listed above, with the exception of flow mapping by pulsed Doppler, are used in our laboratory in conjunction with color Doppler findings to arrive at a more precise estimate of the severity of the lesion. CurrProblCardiol,
February1990
66
COLOR
DOPPLER
DETECTION
OF AORTIC
REGURGITATION
Aortic regurgitation is diagnosed on color Doppler by visualizing diastolic mosaic colored signals originating from the aortic valve and extending into the left ventricular outflow tract. These can be noted in the parasternal (long or short axis) as well as the low parasternal, apical, and right parasternal imaging planes (Figs 2 through 4 [see color plates]). Color Doppler has a sensitivity of 88% and a specificity of 100% in the diagnosis of aortic regurgitation.17 ASSESSMENT
OF SEVERITY OF AORTZC
AEGURGITATZON
Color Doppler also enables the rapid mapping of the anatomic extent of the aortic regurgitant jet in the left ventricle. Previous reports suggested that the lengths of the jet correlated fairly well with the angiographic estimates of the degree of regurgitationl’ However, Switzer et all9 from our laboratory found that the length of the jet was a function of the pressure gradient across the aortic valve and bore little relation to the actual volume of regurgitation. Subsequently we found that the width of the jet, as measured at its origin at the level of the aortic valve, correlated well with the angiographic estimates of the severity of aortic regurgitation. This study17 demonstrated that the ratio of the aortic regurgitant jet width at the level of its issuance from the valve to the height of the left ventricular outflow tract at the same level correlated well with the semiquantitative angiographic grading system of Nagle et al?’ k = 0.791. A ratio of 1% to 24% predicted an angiographic grade of 1; 24% to 46% an angiographic grade of 2; 47% to 64%, grade 3; and greater than 64%) grade 4 or 5. It should be noted that the correlation of jet length to angiographic grade of severity, the standard pulsed Doppler criterion, correlated poorly (r = 0.321. The proximal width of the regurgitation jet tends to overestimate the size of the anatomic defect in the valve because of “entrainment” (blood outside the jet being set in motion by transfer of jet energy), but the overestimation is systematic, resulting in excellent correlation between the proximal jet width and the angiographic grade of severity of aortic regurgitation. It has also been shown that the area of the jet measured at the level of the aortic valve in the parasternal short axis view correlates well with the severity of aortic regurgitation measured at angiography.” Thus color Doppler may be reliably used to semiquantitatively assess the severity of aortic regurgitation noninvasively. Color M-mode Doppler is also useful in clarifymg ambiguous findings by allowing interrogation of the velocity and duration of any diastolic backflow in the distal aorta, although as mentioned previously, this may be done using pulsed or continuous-wave Doppler also. The descend66
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February
1990
ing aorta is imaged from the suprasternal view and the M-mode CUP SOTplaced through the flow within it. Holodiastolic flow toward the transducer (colored red) is an indication of significant aortic regurgitation.‘l Color Doppler also allows more accurate continuous-wave Doppler analysis of the diastolic waveform of aortic regurgitation. It enables the examiner to attempt to align the continuous-wave cursor parallel to the direction of the jet, as seen on real-time color Doppler. As mentioned, it has been said that the shorter the diastolic pressure half-time the more severe the aortic regurgitation, whereas a long pressure half-time suggests the presence of less severe regurgitation. In addition to the observations above, color Doppler, both realtime and M-mode, allows the immediate appreciation of the presence of diastolic mitral regurgitation, which in the absence of atrioventricular block suggests severe aortic regurgitation.22 Taken in combination, these findings indicate that color Doppler is at present the ultrasound modality of choice for the detection and assessment of aortic regurgitation. SUMMARY Detection and assessment of severity of aortic regurgitation by pulsed and continuous-wave Doppler techniques requires a lengthy period of examination and a high degree of expertise to approximate the sensitivity and specificity of angiography. This is a major limitation of this modality. Color Doppler, on the other hand, is less time consuming and more reproducible. However, when color Doppler is not available, conventional Doppler in the hands of an expert operator is useful for accurate detection and semiquantitation of aortic regurgitation. Also, it should be noted that color Doppler is not precise in estimation of the severity of aortic regurgitation. Color flow mapping of aortic regurgitation still remains a semiquantitative method. Thus conventional Doppler may need to be used to supplement the color Doppler examination, especially in the assessment of severity of aortic regurgitation, even when access to color flow mapping is readily available. REFERENCES 1. Estevez CN, Dillon JC, Waker PD, et al: Echocardiographic manifestations of aortic cusp rupture in a case of myxomatous degeneration of the aortic vdve.Chest1976;69;544. 2. Kwan OL, Handshoe R, Handshoe SD, et al: Sensitivity and specificity of Doppler ultrasound in the detection of valvular regurgitation: Comparison of continuous and pulsed wave techniques (abst). Circulation 1983; 68:111-229. 3. Ward JM, Baker DW, Rubenstein SA, et al: Detection of aortic insufficiency by pulse Doppler echocardiography. J Clin Ultrasound 1977; 5:5. CumProbl Cardiol,Febmary 1990 67
4. Esper RJ: Detection of mild aortic regurgitation by range-gated pulsed Doppler echocardiography. Am J Cardiol 1982; 50:1037. 5. Richards KL, Cannon SR, Crawford MH, et al: Noninvasive diagnosis of aortic and mitral valve disease with pulsed-Doppler spectral analysis. Am J Cardiol 1983; 51:1122. 6. Ciobanu M, Abbasi AS, Allen M, et al: Pulsed Doppler echocardiography in the diagnosis and estimation of severity of aortic insufficiency. Am J Cardiol 1982; 49:339-343. 7. Nanda NC fed): Doppler echocardiography. New York, Igaku-Shoin Medical Publishers, Inc., 1985; pp 229-230. 8. Grayburn PA, Handshoe R, Smith MD, et al: Quantitative assessment of the hemodynamic consequences of aortic regurgitation by means of continuous wave Doppler recordings. J Am Co11 Cardiol 1987; 10:135-141. 9. Nishimura RA, Tajik Al: Determination of left-sided pressure gradients by utilizing Doppler aortic and mitral regurgitant signals: Validation by simultaneous dual catheter and Doppler studies. J Am Co11 Cardiol 1988; 11:317-321. 10. Labovitz AI, Ferrara RP, Kern MJ, et al: Quantitative evaluation of aortic insufficiency by continuous wave Doppler echocardiography. J Am Co11 Cardial 1986; 8:1341-1347. 11. Teague SM, Heinsimer JA, Anderson JL, et al: Quantification of aortic regurgitation utilizing continuous wave Doppler ultrasound. J Am Co11 Cardiol 1986; 8:592-599. 12. Rokey R, Sterling LL, Zoghbi WA, et al: Determination of regurgitant fraction in isolated mitral or aortic regurgitation by pulsed Doppler two-dimensional echocardiography. J Am Co11 Cardioll986; 7:1273- 1278. 13. Kitabatake A, Ito H, moue M, et al: A new approach to noninvasive evaluation of aortic regurgitant fraction by two-dimensional Doppler echocardiography. Circulation 1985; 72:523-529. 14. Touche T, Prasquier R, Nitenberg A, et al: Assessment and follow-up of patients with aortic regurgitation by an updated Doppler echocardiographic measurement of the regurgitant fraction in the aortic arch. Circulation 1985; 72:819-824. 15. Takenaka K, Dabestani A, Gardin JM, et al: A simple Doppler echocardiographic method for estimating severity of aortic regurgitation. Am J Cardiol 1986; 57:1340. 16. Hatle L, Angelsen B: Doppler Ultrasound in Cardiology, ed 2. Philadelphia, Lea & Febiger, 1985, p 161. 17. Perry GJ, Helmcke F, Nanda NC, et al: Evaluation of aortic insufficiency by Doppler color flow mapping. J Am Call Cardiol 1987; 9:952-959. 18. Omoto KR, Yokote Y, Takamoto S, et al: The development of real-time twodimensional Doppler echocardiography and its clinical significance in acquired valvular diseases. Jpn Heart J 1984; 25:325-340. 19. Switzer DF, Yoganathan AP, Nanda NC, et al: Calibration of color Doppler flow mapping during extremes of hemodynamic conditions in vitro: A foundation for a reliable quantitative grading system for aortic incompetence, Circulation 1987; 75:837-846. 20. Nagle RE, Walker D, Grainger RG: The angiographic assessment of mitral incompetence. Clin Radio1 1968; 19:154. 21. Nanda NC ted): Textbook of Color Doppler Echocardiography. Philadelphia, Lea & Febiger, 1989. 22. Nanda NC: Atlas ofColor Doppler Echocardiography. Philadelphia, Lea & Febiger, 1989. 58
Cm-r
Prebt Car&o/, February
1390
Navin C. Nanda, MD., is Professor of Medicine and Director of the Heart Station and Echocardiography-Graphics laboratories at the University of Alabama School of Medicine, Birmingham, Division of Cardiovascular Disease. He is Editor-in-Chief of Echocardiography, and has authored or coauthored more than &IO articles.
D. Douglas Miller, M.D., is a member of the faculty of the University of Texas Health Science Center, San Antonio, in the Divisions of Cardiology and Radiolosy Dr. Miller received training in clinical cardiology and cardiovascular research at the Montreal Heart Institute, Emory University School of Medicine in Atlanta, and the Massachusetts General Hospital, Harvard Medical School in Boston. Dr. Miller is a graduate of McGill University Medical School in Montreal, Canada, and a Fellow of the Royal College of Physicians and Surgeons of Canada, the American College of Cardiology, and the American Heart Association. He serves as an editorial consultant and board member for ten medical journals, and has authored nearly 100 papers on cardiology-related topics. 42
Curr
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1990
Gregory B. Cranney, M.B., is Clinical Director of the Cardiovascular NMR Research Laboratory at the University of Alabama at Birmingham. He obtained his medical degree from the University of New South Wales in Sydney, and then completed his internship, residency and Cardiology Fellowship at the Prince of Wales and Prince Henry Hospitals in Sydney. He was then granted a National Heart Foundation of Australia postgraduate research scholarship to study ventricular mechanics in patients with valvular regurgitation. This work focused on noninvasive assessment using Doppler and radionuclide techniques. It became apparent to the author that NMR oflered a greater potential to accurately and noninvasively assess ventricular mechanics and thus he moved to the UAB to pursue this interest. Afler completing a fellowship in Cardiovascular Nuclear Magnetic Resonance at the University of Alabama at Birmingham, he was appointed to his current position as Assistant Professor of Medicine.
Chaim S. Lotan, M.D., is currently an attending physician in the Cardiovascular Division, the Hebrew VniversityHadassah Medical Center, Jerusalem, Israel. He received his medical degree from the Hebrew University medical school, and completed his internship, residency and cardiology fellowship at. the Hebrew University- Hadassah Medical Center, where he was involved in research regarding the early administration of thrombolytic therapy. As a recipient of an international Fulbright scholarship, Dr. Lotan spent 2 years at the Cardiovascular NMR laboratory at the University of Birmingham, where his research interests included NMR assessment of global and regional ventricular function and the identification and quantitation of post reperfiusion myocardial hemorrhage by NMR imaging. Curr
Probl
Cardiol,
February
1990
43
Gerald M. Pohost, M.D., graduated from the University of Maryland School of Medicine, Baltimore, in 1967. He completed his Internship at the Montejiore Hospital Medical Center in the Bron,x, New York. Dr. Pohost served his Residency in Medicine at the Montefiore Hospital Medical Center and the Bron,x Municipal Hospital, and was a Fellow in’Cardiology at the Massachusetts General Hospital in Boston. He is currently Professor of Medicine and Radiology and Director of the Division of Cardiovascular Disease at the University of Alabama School of Medicine in Birmingham. 44
Curr
Probl
Car-dial,
February
1990
PART
I: A&SESS~NT
OF ACWIW
REGURGPl’ATR3ly BY IWMWNVASIVE TECHWrQUES David Kandath, M.D. Navin C. Nanda, M.D.
Aortic regurgitation usually results from lesions of the aortic valve itself or of the aortic root. M-mode and two-dimensional echocardiography are useful in defining anatomy and are therefore accurate in detecting many of the causes of aortic regurgitation. These modalities are also useful in the measurement of left ventricular size and function. They are therefore valuable in the assessment of prognosis in patients with aortic regurgitation and in determining the optimal time for aortic valve replacement. However, it is impossible to accurately diagnose aortic regurgitation with these methods. High-frequency diastolic flutter of the anterior mitral valve leaflet (or the interventricular septum) on M-mode is the only reliable finding that suggests aortic regurgitation.’ This sign is not sensitive, because if the regurgitation jet is of a relatively low velocity or is not directed at one of those structures, flutter will not be observed. Moreover, even if flutter is present, this gives no indication of the severity of aortic regurgitation. Thus, until the recent arrival of Doppler technology, angiography was the only investigative mode available for the detection and quantitation of aortic regurgitation. Because it is invasive and expensive, this method is not widely applicable, especially as a screening tool. Doppler echocardiography now enables accurate noninvasive detection and semiquantitation of aortic regurgitation. This added dimension to the noninvasive examination, which was hitherto lacking, has improved the reliability of echocardiography in the assessment of aortic regurgitation. CONVENTIONAL DETECTION
DOPPLER
OF AORTIC
REGURGITATION
Both pulsed and continuous-wave Doppler can be used to detect aortic regurgitation. The first characteristic of the aortic regurgitation jet is that its velocity is high, due to the large pressure difference between the aorta and the left ventricle. It should be noted that Cur-r Probl
Cardiol,
February
1990
4s
this reversed gradient, however, is not so large as that between the left ventricle and the left atrium, and therefore the velocity of aortic regurgitation is less than that of mitral regurgitation. The second feature of the jet is that its flow is turbulent, because the high-velocity flow through a relatively small orifice causes a chaotic motion of the red blood cells. Thus high-velocity turbulent flow that occurs into the left ventricular outflow tract in diastole is the hallmark of aortic regurgitation on the Doppler examination.2-5 Pulsed Doppler Examination-The detection of the characteristic diastolic high-velocity turbulent flow into the left ventricular outflow tract requires close scrutiny of the Doppler spectral trace and of the audio signal. Because of the turbulent nature of the jet, its audio signal is harsh. It usually is holodiastolic. The spectral trace is boxlike and extends both above and below the zero line due to aliasing secondary to the high-velocity of the jet (Fig 11. The boxlike shape results because the spectral trace usually exceeds the Nyquist limit both above and below the zero line. This gives the appearance of the spectral trace being cut off at the site of the Nyquist limits for forward and reverse flow. Spectral broadening is present due to the turbulent flow. As with mitral regurgitation, the velocity of the jet has no relationship to the severity of the aortic regurgitation; it merely reflects the pressure difference between the aorta and left ventricle in diastole. The main views used in the pulsed Doppler examination are the apical (five chamber and long axis) and the parasternal (long axis and short axis) views. The pulsed Doppler examination is begun from the apical view. The apical five-chamber view is obtained first. The pulsed Doppler sample volume is then placed on the left ventricular aspect of the aortic valve just proximal to the cusps, and moved slowly and carefully from the medial aspect where the lowfrequency sounds of the septum are obtained, more laterally until mitral inflow is encountered. Each time the Doppler sample volume is moved the transducer should be angulated so that the azimuthal plane is interrogated. The same procedure is then repeated after rotating the transducer so that the apical long-axis view is obtained. In the parasternal long-axis view, the pulsed Doppler sample volume is placed in the left ventricular outflow tract just proximal to the aortic valve leaflets and moved from anterior to posterior. This view is less sensitive than the apical view because the flow of the regurgitation jet in most cases is perpendicular to the transducer. However, in the case of eccentrically directed jets, as might occur with paravalvular regurgitation in patients with prosthetic aortic valves, this view might allow a more parallel orientation with the regurgitation jet. Other views used in assessment of aortic regurgitation include the subcostal views (five chamber and short axis). Occasionally the su46
CurrProbl
Cardiol,
February
1990
,“.,.
”
FIG 1. A, Doppler identification of aortic regurgitation. Top, Doppler sample volume (arrow) was placed in the left ventricular outflow tract just below the aortic valve (AV) imaged in the apical five-chamber view. LV = left ventricle. Boffom, Doppler tracing shows marked turbulence and aliasing in diastole characterized by large-frequency shifts (arrows), which reach the limits of the display on both sides of baseline (S) and produce a typical boxlike rectangular pattern. The systolic flow pattern (Sy) is normal. S = Doppler sample volume position in the A-mode. 8, Doppler baseline (S) has been shifted to the bottom of the display to more clearly delineate the characteristic rectangular pattern of diastolic signals (arrow) produced by aortic regurgitation. AV = aortic valve, B = Doppler base, LV = left ventricle, S = Doppler sample volume position on the A-mode. (From Nanda NC (ed): Doppler Echocardiography. New York, lgaku Shoin, 1985. Used by permission.)
prasternal and right parasternal views are used because the left ventricular outflow tract and aortic valve can be imaged. More commonly, however, these transducer positions allow visualization only of the ascending aorta and therefore are not particularly useful in the detection of aortic regurgitation.. Pulsed Doppler is nearly 100% sensitive and specific in the detection of aortic regurgitation.“‘ ’ As with mitral insufficiency, aortic regurgitation is often detected by Doppler examination in patients in whom a murmur cannot be auscultated. In such cases aortic insufficiency is usually confirmed by angiography. A potential source of confusion in the diagnosis of aortic regurgiCurr
Probl
Cardiob
February
1990
47
tation occurs in the case of associated mitral stenosis, especially if the resultant diastolic jet is directed toward the septum. The velocity of a mitral stenosis jet, however, never approaches that of aortic regurgitation. In case of the latter, the spectral trace exceeds the Nyquist limit both above and below the zero line as a result of a severe degree of aliasing. This is responsible for the boxlike appearance of the spectral trace of aortic insufficiency. While the mitral stenosis jet might exceed the Nyquist limit once, it seldom is of sufficient velocity to cause abasing on both sides of the zero line. This fact helps distinguish the two conditions.’ Continuous-wave Doppler ExandnHion.--As with pulsed Doppler, diastolic flow into the lefk ventricular outflow tract, which is turbulent and of high velocity, is the characteristic of aortic regurgitation. The audio signal is similar to that seen on the pulsed wave examination. However, the spectral trace does not alias and is recorded as a somewhat rectangular holodiastolic pattern above the baseline. The apical view is mainly used because it is usually possible to orient the Doppler beam parallel to aortic regurgikttion flow from this position. If an imaging transducer is being utiBzed, the continuous-wave cursor is placed across the aortic valve in the apical five-chamber or long-axis view. The transducer is then angulated, as with the pulsed Doppler examination, until the highest veIocities are recorded. If a nonimaging transducer is being used, it is placed in the apical position and angulated until the aortic outflow tracing is recorded. Small changes in transducer position guided by the audio signal and the spectral trace will then result in the aortic regurgitation jet being interrogated. Using the continuous-wave Doppler spectral trace of aortic regurgitation, the left ventricular end-diastolic pressure can be calculated as follows: The velocity (V) at end-diastole can be converted into a pressure gradient (P) using the modified Bernoulli equation. Thus
P = 4v2 This is the gradient between the end-diastolic (AOEDP) and left ventricle (LVEDP). Therefore
pressures
in the aorta
P = AOEDP - LVEDP or LVEDP = AOEDP - P where AOEDP is diastolic pressure sure cuff. If there is no obstruction 4s
as measured with a blood presto left ventricular outflow, then Curr
Probl
Cardiol,
February
1999
LVEDP can be calculated using the above equation. When Doppler measurements are performed simultaneously or within 24 hours of cardiac catheterization, a good correlation (r = 0.84-0.98, standard error of estimate [SEE] 5.5-8 .mm Hg) was shown between the LVEDP measured by Doppler and cardiac catheterization!’ ’ It was found that the Doppler estimate could distinguish between a low (Cl5 mm Hg) and elevated P15 mm Hg) LVEDP with a high degree of specificity (90% 1.’ In another study where there was an interval between the Doppler examination and catheterization of greater than 24 hours, poor correlations were found between the LVEDP measurements obtained by the two methods.*’ There are a number of liniitations to the use of continuous-wave Doppler to calculate LVEDP. The major drawback is that in many instances the peak velocities on the spectral trace are not recorded, resulting in overestimation of LVEDP. The reason for this is that it is difficult to maintain the alignment of the ultrasonic beam parallel to flow throughout diastole, because of respiratory movements and because many aortic regurgitation jets are eccentric. Also, the SEE in the studies mentioned of 5.5 to 8 mm Hg is high, considering that the upper limit of normal for LVEDP is 12 to 15 mm Hg. Finally, determining the diastolic pressure fmm the cuff pressure by listening to Korotkov sounds may be problematic, especially in patients with severe aortic regurgitation, because the sounds completely disappear only at very low pressures, in which case th”e point at which there is a change in character of the sounds is probably a closer approximation of the true intra-arterial diastolic pressure. ASSESSMENT
OF SEVERITY
OF AORTZC
REGURGITATION
Flow Mapping.The most widely used and reproducible method is mapping of the extent of the flow disturbance. This requires the use of pulsed Doppler, because continuous-wave Doppler lacks the property of range gating. The views used are the apical five-chamber or long-axis views. The extent that the diastolic flow signal of aortic regurgitation extends back into the ventricular cavity is mapped. The regurgitation is then graded as follows:
Grade 1 (mild): The jet is detected just below the level of the aortic valve. Grade 2 (moderate): The flow disturbance extends up to the level of the tips of the mitral valve leaflet in diastole. Grade 3 (severe): The jet is detected below the tips of the mitral valve leaflets. This grading correlates fairly well with angiography.6 It should be emphasized that this method is semiquantitative, because even Curr
Probl
Cardiol,
February
1990
4s
though the jet is three dimensional, only its length is taken into account during quantitation by this approach. There are a number of other limitations to the estimation of aortic insufficiency by flow mapping. First, this system of grading is restricted to one particular imaging plane and does not take into consideration the fact that the flow, because it is three dimensional, might be maximally present in another two-dimensional echocardiogmphic plane even if the jet is not particularly eccentric. This plane might be one of the conventional two-dimensional echocardiographic views or “unconventional” in that the transducer position iYom which a parallel orientation of the ultrasonic beam with the flow jet is obtained lies between one of the standard two-dimensional echocardiagraphic planes. Second, if the aortic regurgitation jet is eccentric, this might result in underestimation of the severity, because the jet would not extend far enough lengthwise into the left ventricular cavity or might extend out of the imaging plane, resulting in a major portion of the flow disturbance not being detected. Also, in patients with low cardiac output the jet will not extend far back into the left ventricle because it is of low velocity even though its actual volume might be large. Further, in those patients with aortic regurgitation and an associated high-velocity jet directed toward the interventricular septum, as might occur with mitral stenosis or prosthetic mitral valves (especially metallic valves), confusion might occur when mapping the extent of the aortic regurgitation jet. Although the two jets can usually be distinguished at the level of the aortic valve leaflets, this is more of a problem as the pulse sample volume is moved further down into the left ventricular cavity during the process of mapping the aortic regurgitation jet. Finally, this method demands a high degree of technical expertise and is time consuming. Diastolic Slope ofSpectral Trace.-The slope of the spectral trace in aortic regurgitation reflects the rapidity with which the aortic diastolic pressure equalizes with the left ventricular diastolic pressure. If the left ventricular diastolic pressure is high, as in severe aortic regurgitation, then equalization of pressures is rapidly achieved, resulting in a steep slope. In contrast, in mild aortic regurgitation the slope is gradual. (NOTE: the opposite occurs in mitral stenosis; that is, the greater the degree of stenosis the more gradual the diastolic slope of the transmitral spectral trace). Several studies have shown that the rate of deceleration of the transaortic diastolic spectral trace reflects the degree of aortic regurgitation.” ’ In general, if the rate of deceleration is in excess of 3.0 m/se& then this correlates with the presence of severe a0r-k regurgitation (3+ to 4+) on angiography. A potential pitfall of this method is that in patients with severely diminished left ventricular compliance or in those with acute aortic regurgitation, rapid equalization of aortic - left ventricular diastolic ~RSSURS might occur, with a resultant steep slope on the regur50
Cur-r Probl
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February
1990
FIG 4. Aort~c regurgitation. Left parasternal long-axis left ventricular outflow tract originating from t~on JAR), The mosaic slgnals turn to blue loses energy and the velocity decreases to aorta. LA = left atrium, iV = left ventricle, Textbook of Co/or Doppler Echocardiography. permission.)
plane shows diastolic mosaic signals in the the aortic valve, indlcatke of aortic regurgitadistally because the posteriorly directed jet below the Nyquist limit of 0.58 mkec A0 = RV = right ventricle. (From Nanda NC (ed): Philadelphia, Lea & Feblger, 1989. Used by
FIG 2. Color Doppler assessment indicated by a wide jet that valve level. A0 = aorta, AR (From Perry GJ, Nanda NC:
of seventy of aortic regurgitation Severe aortic Insufficiency is occupies 100% of the left ventricular outflow tract at the aortic = aortic regurgitant jet, LA = left atrium, RV = right ventricle. ini d Cardiac imag, 1988, Used by permlssion.)
FIG 3. Color Doppler assessment of aork regurgitation. Long thin let of aortic InsufficIency, VISUallred from the aplcal long-axis view, in a patient with moderate aortic insufficiency. Despite the length of the jet, its relative narrowness indicates that this is only moderate aortic insuffIciency. A0 = aorta, AR = aortic regurgitant jet, LA = left atrium, LV = left ventricle. (From Perry GJ and Nanda NC: Echocardiographyl986, 3:495. Used by permission.)
gitant spectral trace. On the other hand, in patients with extremely compliant ventricles the opposite might be noted. Another method of assessing the diastolic slope of the aortic regurgitation spectral trace is by measuring the pressure half-time, which is the time taken for the peak instantaneous pressure between the left ventricle and aorta to drop by half. The principle is the same as that used to assess the mitral valve area. Using the modified Bernoulli equation, the peak velocity (V,) of the aortic regurgitation spectral trace is converted to a pressure gradient (P,). The velocity (V,) at which P, drops to half of its initial value (PI,,) is given as PI/v?% Pressure half-time is the time taken for the velocity on the spectral trace to drop from V, to V,. The shorter the pressure halftime the more severe the degree of aortic regurgitation. When compared with angiography, aortic regurgitation (l+ to 4+) as estimated by the pressure half-time shows considerable overlap between grades. However, in one study, a value of 400 msec distinguished between mild (l+ to .Z+) and severe (3+ to 4-l-I aortic regurgitation.11 The major problem encountered during the evaluation of the diastolic slope is the difficulty in obtaining adequate spectral tracings. This is not possible in as many as 30% of patients.’ The reason for this is that in patients with aortic regurgitation the aortic valve is usually deformed as a result of fibrosis and calcification, resulting in an eccentric jet. Also, as pointed out earlier, it is difficult to maintain the ultrasonic beam parallel to flow throughout diastole because of the changing orientation between the jet and the Doppler cursor due to respiratory movements. Consequently, it is difficult to align the Doppler beam parallel to flow, resulting in underestimation of the maximal velocities. On the other hand, it has been found that adequate Doppler spectral traces are obtained in the majority of patients with severe aortic regurgitation, probably because the jet is wide. Estimation of the diastolic slope is another semiquantitative method of assessing the severity of aortic regurgitation.
Estimation of Reguqitant Fraction.-In aortic regurgitation, the total forward flow (total stroke volume, TSV) through the aortic valve includes the true stroke volume (SV, which is the effective for-ward flow) plus the volume of aortic regurgitation (regurgitant volume, RV). On the other hand, flow through any of the other valves (mitral, tricuspid, pulmonic), provided they are not regurgitant, consists solely of the true stroke volume. Regurgitant fraction is the mgurgitant volume expressed as a percentage of total stroke volume. From this the following equations can be derived: RV + SV = TSV RU = TSU - su Cow
Probl
Cardiol,
February
1990
51
ThUS
Regurgitant
fraction (RF) =
TSV - SV TsV
If flow across the aortic valve is being measured, then the volume of forward flow that is calculated will be the TSV. The reverse flow, on the other hand, will consist solely of the regurgitant volume. Thus in equation 1 RF=
Reverse flow volume Forward flow volume
Two methods are used to estimate the regurgitant fraction in aortic regurgitation: 1. Forward flow through the aortic valve is used to calculate TSV, and flows through either the mitral or pulmonic valve are utilized to measure stroke volume. Regurgitant fraction can then be estimated from equation 1. Flow through an orifice, as estimated by Doppler echocardiography, is given by the product of the time-velocity integral (TVI) or area under the Doppler spectral trace and the cross-sectional area of flow. If the region of flow is circular, then this cross(Diameter12 sectional area = 77 Therefore, flow through an orifice (F) 4 can be expressed as F = TvI x
l-l
(Diameter? 4
In the case of the aortic valve, the time velocity integral of flow is obtained by placing a pulsed Doppler sample volume in the aortic orifice in the apical five-chamber view. The diameter of the aortic annulus is measured in the parasternal long-axis view as the inner diameter in mid-systole. For the pulmonic valve the time velocity integral is obtained by placing the pulsed Doppler sample volume in the valve orifice in the parasternal short-axis view. The orifice diameter is measured in the same view in mid-systole as the distance between the inner boundaries. To estimate flow through the mitral valve, the sample volume is placed in the mitral valve orifice in the apical four-chamber view. The mitral annulus is measured in the same view, as the distance between the inner borders in mid-diastole. All orifices are assumed to be circular. Good correlations have been obtained when compared with angiographic regurgitant fractions using either mitral (r = 0.9111’ or pulmonic flows (r = 0.94)‘3 to estimate stroke volume. However, this method of estimating regur52
curr~roblCardiol,
February1990
gitant fractions has a number of limitations. In patients with turbulent flow through the aortic valve, as might occur in aortic stenosis Or severe aortic regurgitation, an adequate spectral trace is difficult to obtain. The same applies to the mitral or pulmonary valves. aso, in those with more than mild mitral insufficiency, the mitral valve cannot be used to estimate stroke volume, because the transmitral flow represents the total forward flow and not the effective forward flow. The situation is similar for the pulmonic valve in the case of more than mild pulmonic insufficiency. To overcome this limitation, the pulmonic valve can be used to estimate stroke volume if significant mitral regurgitation is present, and vice versa if significant pulmanic regurgitation is present. Since intracardiac or extracardiac shunt lesions also modify pulmonic and aortic flows, this method to estimate regurgitant fraction cannot be used in such cases. Thus significant mitral or pulmonic regurgitation and shunt lesions should be ruled out by careful Doppler examination prior to using these methods to assess aortic regurgitation. Another limitation is that an accurate and reproducible measure of the diameter of the orifice is diificult to obtain. Small errors in the diameter measurement are magnified because the diameter must be squared to obtain the area of flow. This is especially the case with the pulmonic annulus, where due to the limits of lateral resolution of the two-dimensional echocardiographic image, the lateral border of the pulmonic orifice is often difficult to determine. Finally, since the methods described involve the measurement of total stroke volume and stroke volume from two different anatomic sites, the potential for error in the diameter measurements and velocity measurements (as a result of varying angles of interrogation) is magnified. These drawbacks can be overcome by using forward and reverse flows in the aorta (see below) to determine total stroke volume (forward flow) and regurgitant volume (reverse flow). 2. The second method of calculating the regurgitant fraction in aortic regurgitation is by estimating the ratio of forward and reverse flows in the aorta. The best site at which to sample flow is the descending aorta at its junction with the arch (the aortic isthmus). Flow at this site is free of the turbulence caused by aortic stenosis or severe aortic regurgitation. Further, unlike the ascending aorta, this segment is easier to image from the suprasternal notch in adults. Finally, flow velocities are more uniform, and the peak velocity does not vary across the aortic diameter, depending on the sampling site, as is the case in the ascending aorta. Normally in the thoracic aorta flow is recorded away from the transducer in systole. If there is aortic regurgitation, significant retrograde diastolic flow might be present. Using pulse or continuouswave Doppler, flow in the descending thoracic aorta can be recorded from the suprasternal view. If pulsed Doppler is used, the Cur-r Probl
Cardiol,
February
1990
53
sample volume is positioned in the aortic isthmus. We know that the ratio of reverse and forward flows yields the regurgitant fraction. Thus anterograde or retrograde flow (F, or F,) = time velocity integral of anterograde or retrograde flow U’VI, or TvI,.) x cross-sectional area of flow (CSA, or CSA,). Therefore, F, = TVI, X CSA, F, = TVI, X CSA, Regurgitant
fraction
(RF) = 2 = zy ,” ,“zr a d d
If we assume that the area of the aorta does not change much tween diastole and systole, then
be-
The diameter of the aorta, however, does change during the cardiac cycle, and therefore, to be more accurate, the diameter of the aortic arch can be estimated in systole (D,) and diastole (D,) on the Mmode examination. The systolic diameter is the maximum diameter measured. The diastolic diameter is taken as the average of the maximum and minimum diameters. The aorta being circular, its crosssectional area is obtained by the formula. Substituting in equation 1, (Diameter? 5-r 4
RF =
TvI
a
x ,(Ds)’ 4
_ TVI, X (DJ2 - TVI, X (D,J’
Using this method, good correlations (r = 0.90) have been obtained with regurgitant fractions measured by cardiac catheterization.14 The estimation of regurgitant fractions offers a potentially attractive approach for assessing aortic regurgitation, because this is a truly quantitative method. The Doppler approach using different sites to quantitate the stroke volume and total forward flow has a number of limitations, as outlined previously. In addition, neither of the two Doppler methods is accurate in the presence of atrial fibrillation. Although excellent correlations have been obtained with cardiac catheterization using these Doppler methods, it should be noted that regurgitant fraction derived invasively also has several drawbacks. Different methods are used to estimate forward flow vol64
Curt-
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Cardial,
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1990
ume (which is done angiographically) and stroke volume (which is done by the Fick or thermodilution technique). During the angiographic measurement, assumptions are made regarding left ventricular geometry that might not be true in patients with severe aortic regurgitation. Further, when the Fick or thermodilution method is used to calculate stroke volume in the same patient, significantly different values might be obtained because the two methods are not strictly comparable. Also, the assessment of aortic regurgitation by the use of regurgitant fractions by cardiac catheterization cannot be used in patients with significant associated mitral regurgitation or in those with atrial fibrillation. Reverse Flow in Abdominal Aorta.-Normally in the abdominal aorta there is mainly systolic flow, which is recorded as flow away from the transducer and therefore below the zero line on the spectral trace. In diastole there is only a minimal amount of retrograde flow, which is due to distal runoff into the coronary arteries and systemic elastic recoil. Since this flow is toward the transducer, it is recorded above the zero line on the spectral pattern. In patients with mild aortic regurgitation there might be a significant amount of flow toward the transducer, but even so, this is still confined to early diastole. However, in patients with severe aortic regurgitation there is holodiastolic retrograde flow. Thus this manner of assessment differentiates mild from severe aortic insufficiency.15 In our laboratory it is used to confirm the degree of aortic regurgitation. A limitation of this method is that patients with left-to-right shunts from the aorta (e.g., patent ductus arteriosus) will also have holodiastolic retrograde flow in the abdominal aorta. Also, in obese patients the excessive depth of the aortic flow away from the transducer makes adequate velocity recordings impossible. Further, the angle the interrogating Doppler beam makes with abdominal aortic flow is large, which also decreases the sensitivity of the Doppler examination. Intensity of Spectral Wave Pattern.-The intensity of the gray scale of the spectral trace is proportional to the volume of red blood cells in the jet. Thus, the more severe the regurgitation the darker the spectral trace.16 The intensity of the retrograde aortic diastolic flow signal is compared with the anterograde flow through the aortic valve. In severe aortic regurgitation the intensity of the retrograde flow is equal to that of the anterograde flow. This method is highly subjective and offers only a rough estimate of the severity of aortic regurgitation. The various methods of quantitating aortic regurgitation listed above, with the exception of flow mapping by pulsed Doppler, are used in our laboratory in conjunction with color Doppler findings to arrive at a more precise estimate of the severity of the lesion. CurrProblCardiol,
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COLOR
DOPPLER
DETECTION
OF AORTIC
REGURGITATION
Aortic regurgitation is diagnosed on color Doppler by visualizing diastolic mosaic colored signals originating from the aortic valve and extending into the left ventricular outflow tract. These can be noted in the parasternal (long or short axis) as well as the low parasternal, apical, and right parasternal imaging planes (Figs 2 through 4 [see color plates]). Color Doppler has a sensitivity of 88% and a specificity of 100% in the diagnosis of aortic regurgitation.17 ASSESSMENT
OF SEVERITY OF AORTZC
AEGURGITATZON
Color Doppler also enables the rapid mapping of the anatomic extent of the aortic regurgitant jet in the left ventricle. Previous reports suggested that the lengths of the jet correlated fairly well with the angiographic estimates of the degree of regurgitationl’ However, Switzer et all9 from our laboratory found that the length of the jet was a function of the pressure gradient across the aortic valve and bore little relation to the actual volume of regurgitation. Subsequently we found that the width of the jet, as measured at its origin at the level of the aortic valve, correlated well with the angiographic estimates of the severity of aortic regurgitation. This study17 demonstrated that the ratio of the aortic regurgitant jet width at the level of its issuance from the valve to the height of the left ventricular outflow tract at the same level correlated well with the semiquantitative angiographic grading system of Nagle et al?’ k = 0.791. A ratio of 1% to 24% predicted an angiographic grade of 1; 24% to 46% an angiographic grade of 2; 47% to 64%, grade 3; and greater than 64%) grade 4 or 5. It should be noted that the correlation of jet length to angiographic grade of severity, the standard pulsed Doppler criterion, correlated poorly (r = 0.321. The proximal width of the regurgitation jet tends to overestimate the size of the anatomic defect in the valve because of “entrainment” (blood outside the jet being set in motion by transfer of jet energy), but the overestimation is systematic, resulting in excellent correlation between the proximal jet width and the angiographic grade of severity of aortic regurgitation. It has also been shown that the area of the jet measured at the level of the aortic valve in the parasternal short axis view correlates well with the severity of aortic regurgitation measured at angiography.” Thus color Doppler may be reliably used to semiquantitatively assess the severity of aortic regurgitation noninvasively. Color M-mode Doppler is also useful in clarifymg ambiguous findings by allowing interrogation of the velocity and duration of any diastolic backflow in the distal aorta, although as mentioned previously, this may be done using pulsed or continuous-wave Doppler also. The descend66
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ing aorta is imaged from the suprasternal view and the M-mode CUP SOTplaced through the flow within it. Holodiastolic flow toward the transducer (colored red) is an indication of significant aortic regurgitation.‘l Color Doppler also allows more accurate continuous-wave Doppler analysis of the diastolic waveform of aortic regurgitation. It enables the examiner to attempt to align the continuous-wave cursor parallel to the direction of the jet, as seen on real-time color Doppler. As mentioned, it has been said that the shorter the diastolic pressure half-time the more severe the aortic regurgitation, whereas a long pressure half-time suggests the presence of less severe regurgitation. In addition to the observations above, color Doppler, both realtime and M-mode, allows the immediate appreciation of the presence of diastolic mitral regurgitation, which in the absence of atrioventricular block suggests severe aortic regurgitation.22 Taken in combination, these findings indicate that color Doppler is at present the ultrasound modality of choice for the detection and assessment of aortic regurgitation. SUMMARY Detection and assessment of severity of aortic regurgitation by pulsed and continuous-wave Doppler techniques requires a lengthy period of examination and a high degree of expertise to approximate the sensitivity and specificity of angiography. This is a major limitation of this modality. Color Doppler, on the other hand, is less time consuming and more reproducible. However, when color Doppler is not available, conventional Doppler in the hands of an expert operator is useful for accurate detection and semiquantitation of aortic regurgitation. Also, it should be noted that color Doppler is not precise in estimation of the severity of aortic regurgitation. Color flow mapping of aortic regurgitation still remains a semiquantitative method. Thus conventional Doppler may need to be used to supplement the color Doppler examination, especially in the assessment of severity of aortic regurgitation, even when access to color flow mapping is readily available. REFERENCES 1. Estevez CN, Dillon JC, Waker PD, et al: Echocardiographic manifestations of aortic cusp rupture in a case of myxomatous degeneration of the aortic vdve.Chest1976;69;544. 2. Kwan OL, Handshoe R, Handshoe SD, et al: Sensitivity and specificity of Doppler ultrasound in the detection of valvular regurgitation: Comparison of continuous and pulsed wave techniques (abst). Circulation 1983; 68:111-229. 3. Ward JM, Baker DW, Rubenstein SA, et al: Detection of aortic insufficiency by pulse Doppler echocardiography. J Clin Ultrasound 1977; 5:5. CumProbl Cardiol,Febmary 1990 67
4. Esper RJ: Detection of mild aortic regurgitation by range-gated pulsed Doppler echocardiography. Am J Cardiol 1982; 50:1037. 5. Richards KL, Cannon SR, Crawford MH, et al: Noninvasive diagnosis of aortic and mitral valve disease with pulsed-Doppler spectral analysis. Am J Cardiol 1983; 51:1122. 6. Ciobanu M, Abbasi AS, Allen M, et al: Pulsed Doppler echocardiography in the diagnosis and estimation of severity of aortic insufficiency. Am J Cardiol 1982; 49:339-343. 7. Nanda NC fed): Doppler echocardiography. New York, Igaku-Shoin Medical Publishers, Inc., 1985; pp 229-230. 8. Grayburn PA, Handshoe R, Smith MD, et al: Quantitative assessment of the hemodynamic consequences of aortic regurgitation by means of continuous wave Doppler recordings. J Am Co11 Cardiol 1987; 10:135-141. 9. Nishimura RA, Tajik Al: Determination of left-sided pressure gradients by utilizing Doppler aortic and mitral regurgitant signals: Validation by simultaneous dual catheter and Doppler studies. J Am Co11 Cardiol 1988; 11:317-321. 10. Labovitz AI, Ferrara RP, Kern MJ, et al: Quantitative evaluation of aortic insufficiency by continuous wave Doppler echocardiography. J Am Co11 Cardial 1986; 8:1341-1347. 11. Teague SM, Heinsimer JA, Anderson JL, et al: Quantification of aortic regurgitation utilizing continuous wave Doppler ultrasound. J Am Co11 Cardiol 1986; 8:592-599. 12. Rokey R, Sterling LL, Zoghbi WA, et al: Determination of regurgitant fraction in isolated mitral or aortic regurgitation by pulsed Doppler two-dimensional echocardiography. J Am Co11 Cardioll986; 7:1273- 1278. 13. Kitabatake A, Ito H, moue M, et al: A new approach to noninvasive evaluation of aortic regurgitant fraction by two-dimensional Doppler echocardiography. Circulation 1985; 72:523-529. 14. Touche T, Prasquier R, Nitenberg A, et al: Assessment and follow-up of patients with aortic regurgitation by an updated Doppler echocardiographic measurement of the regurgitant fraction in the aortic arch. Circulation 1985; 72:819-824. 15. Takenaka K, Dabestani A, Gardin JM, et al: A simple Doppler echocardiographic method for estimating severity of aortic regurgitation. Am J Cardiol 1986; 57:1340. 16. Hatle L, Angelsen B: Doppler Ultrasound in Cardiology, ed 2. Philadelphia, Lea & Febiger, 1985, p 161. 17. Perry GJ, Helmcke F, Nanda NC, et al: Evaluation of aortic insufficiency by Doppler color flow mapping. J Am Call Cardiol 1987; 9:952-959. 18. Omoto KR, Yokote Y, Takamoto S, et al: The development of real-time twodimensional Doppler echocardiography and its clinical significance in acquired valvular diseases. Jpn Heart J 1984; 25:325-340. 19. Switzer DF, Yoganathan AP, Nanda NC, et al: Calibration of color Doppler flow mapping during extremes of hemodynamic conditions in vitro: A foundation for a reliable quantitative grading system for aortic incompetence, Circulation 1987; 75:837-846. 20. Nagle RE, Walker D, Grainger RG: The angiographic assessment of mitral incompetence. Clin Radio1 1968; 19:154. 21. Nanda NC ted): Textbook of Color Doppler Echocardiography. Philadelphia, Lea & Febiger, 1989. 22. Nanda NC: Atlas ofColor Doppler Echocardiography. Philadelphia, Lea & Febiger, 1989. 58
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