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Echocardiogram of the porcine aortic bioprosthesis in the mitral position
Echocardiogram
of the Porcine Aortic Bioprosthesis
In the Mitral Position
WINSTON N. BLOCH, Jr., MD* JOEL M. FELNER, MD* CHARLES WICKLIFFE, MD* PANAGIOTIS N. SYMBAS, MD, FACC+ ROBERT C. SCHLANT, MD, FACC’ Atlanta, Georgia
Echocardiography was performed in 10 consecutive patients who had a clinically normally functioning porcine aortic bioprosthesis in the mitral
position. Strong well defined echoes were recorded from the anterior and posterior aspects of the xenograft stent. The maximal separation of the anterior and posterior stent echoes approximated the diameter of the stent at its base. The maximal excursion of the anterior stent was 5 to 10 mm (mean 7.5) with a mean systolic slope of 15 to 35 mm/set (mean 22.2) and diastolic slope of 11 to 59 mm/set (mean 21.5). In all 10 patients it was possible to record an anterior xenograft leaflet with anterior movement at the onset of diastole and posterior movement at the onset of systole and with appropriately steep (more than 200 mm/set) slopes. The diastolic (E-F) slope of the anterior leaflet in g of the 10 patients ranged from g to 38 mm/set (mean 19). In 6 of the 10 patients a posterior xenograft leaflet with a movement pattern symmetric with that of the anterior leaflet was recorded. In two patients, the central aortic leaflet was recorded with little diastolic displacement. These two patients also had mild aortic regurgitation, which was associated with diastolic shudder of the the xenograft leaflets. Echocardiography was also performed in one patient who was later shown to have a 10 cm3 thrombus on the ventricular surface of a xenografl valve. The echocardiogram in this patient revealed the following abnormalities: (1) excessive anterior stent movement and systolic slope suggesting paravalvular leak in the presence of abnormal cinefluoroscopic valve tilt, and (2) multiple dense nonhomogeneous echoes between the anterior and posterior aspects of the valve stent, with an early diastolic clear Space behind the anterior stent and abnormal echoes behind the Posterior stent during systole. Echocardiography therefore appears to be useful in evaluating the porcine aortic bioprosthesis in the mitral tion.
posi-
From the Division of Cardiology, Department of Medicine* and The Division of Cardio-Thoracic Surgery,+ Department of Surgery, Emory University School of Medicine and Grady Memorial Hospital, Atlanta, Ga. This study was supported in part by Training Grant HE-05731 from the National Heart and Lung Institute. National Institutes of Health, Bethesda, Md. Manuscript received January 5, 1976; revised manuscript received February 9, 1976, accepted February 11, 1976. Address for reprints: Joel M. Felner, MD, Department of Medicine (Cardiology), Emory University School of Medicine, 69 Butler St., S.E., Atlanta, Ga. 30303.
Recent reports indicate favorable long-term survival rates of patients with a xenograft aortic valve in the mitral positi0n.l Since widespread use of such valves is possible, knowledge of their normal echocardiographic appearance will be useful. Material
and Methods
Eleven adult patients were studied consecutively. Their ages ranged from 20 (mean 34.7). Ten patients had a clinically normally functioning
to 72 years
flexible stented porcine aortic bioprosthesis in the mitral position and one patient had a 10 cm3 thrombus within the valve leaflets, primarily on the ventricular side of the valve. Two of the 10 patients had mild aortic regurgitation. Ten patients were studied at least 1 month after surgical placement of the valve. The longest interval between operation and the echocardiographic study was 16 months. All patients were thoroughly examined with a series C-100 Unirad echoscope using a 2.25 megahertz 518 inch (1.59 cm) diameter transducer focused at 10 cm.
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Volume 36
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ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
Recordings were made on a model 174 Tektronix strip chart recorder, using either heat- or light-sensitive paper. A standard M mode heart scan was performed by placing the transducer in the left parasternal interspace where the mitral valve echoes were best seen. The transducer was then rotated in a partial arc, from the mitral valve to the ascending aorta and to the cardiac apex. To record the xenograft mitral valve leaflets it was usually necessary to keep the focus on the anterior and posterior aspects of the bioprosthetic stent (Fig. 1) while slowly increasing or decreasing the gain and “sweeping” from the superolateral to the inferomedial position and back again. Since the structure (stent) that supports the leaflets resembles a cylinder when it is examined echocardiographitally near its diameter, it appears as two parallel discontinuous structures that will be described as “anterior” and “posterior” stent, respectively.
--cw
Echocardiographic measurements: The diameter of the stent was measured as the distance between the anterior echoes of the anterior and posterior stent (Fig. 1). Use of the distance from the anterior echoes of the anterior stent to the posterior echoes of the posterior stent had proved an unreliable measure of stent diameter because the latter echoes often overlapped those of other structures or reverberations (Fig. 2 to 4). A range of values for stent diameter resulted from making measurements wherever the anterior and posterior stent could be defined by appropriate damping. The “true” stent diameter was obtained by subtracting 3 mm (the in vitro estimate of stent thickness) from the manufacturer’s stated anulus diameter. This gave the ultrasonically detectable maximal stent diameter, located at the nadir (or base) of the stent, measured from the anterior side of the anterior stent to the anterior side of the posterior stent (Fig. 1). The maximal
-
FIGURE 1. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position. Linear echoes of the valve leaflets (PL) separate during diastole and reunite
-PL H?3 1 ‘_
d
/_._A
_i
--CW -
...__ -k,
..4
-ARVW C -EGG
FIGURE 2. Echocardlogram of the porcine aortic bioprosthesis in the mitral position with thrombus. Multiple dense nonhomogeneous echoes are present mostly between the valve stent (arrow). They are most prominent behind the posterior stent during systole (AE). LAW = left atrial wall; other abbreviations as in Figure 1.
294
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ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
Stent -:
Stent -:
FIGURE 3. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position in a patient with aortic regurgitation. A, left to right scan from the bioprosthesis with its three leaflets at the level of the atrioventricular junction to the left ventricular cavity. As the scan proceeds, the bioprosthetic echoes disappear abruptly. The interventricular septum moves paradoxically during systole. B, schematic diagram of the echocardiogram of the bioprosthesis. The arrows and cylinder indicate the direction and location of the ultrasonic beam as it traverses the bioprosthesis. All three leaflets are visualized in the echocardiogram. partly because of the diastolic shudder caused by aortic regurgitation. C, scan from the aortic root to the porcine aortic bioprosthesis in the mitral position. The posterior aortic wall (PAW) is continuous with the anterior stent. AAW = anterior aortic wall: Ant. = anterior; CW = chest wall: ECG = electrocardiogram: IVS = interventricular septum; LA = left atrium; LV = left ventricle; PAW = posterior aortic wall; PL = anterior and posterior bioprosthetic leaflets; Post. = posterior; RV = right ventricle; RVOT = right ventricle outflow tract.
September 1976
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ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
FIGURE 4. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position in a second patient with aortic regurgitation. The diastolic shudder is greatest on the posterior leaflet although present on all three leaflets. During attenuation, the weaker leaflet echoes disappear before the stronger echoes of the stent. AS = anterior stent; CW = chest wall; ECG = electrocardiogram: IVS = interventricular septum; LVPW = left ventricular posterior wall; PS = posterior stent.
excursion of the anterior stent and its systolic and diastolic slopes were measured as shown in Figure 1. The slope of the anterior movement of the anterior stent during systole will be referred to as the systolic slope, and the slope of the posterior movement of this stent during diastole as the diastolic slope. Since the movements and slopes of the anterior and posterior stent were virtually identical, we have measured the anterior stent only. The internal diameter of the stent was measured as the maximal observed distance from the posterior echo of the anterior stent to the anterior echo of the posterior stent during appropriate damping. The opening and closing slopes of the xenograft leaflets were measured. The mid-diastolic closure rate (E-F slope) of the anterior leaflet and the maximal diastolic separation of the leaflets (from their closest borders) were measured whenever appropriate visualization was obtained (Fig. 1).
Results Stent measurements: Strong well defined echoes were always observed from the anterior and posterior
TABLE
I
Echocardiographic Measurements of the Porcine Bioprosthesis in the Mitral Position Stem diameter Case no. It 2 3 4 5t 6 7t 9” IO? Mean ll?S
“True”* External
Anterior
(mm)
Ultrasonic External
Internal
20
Aortic
Stent Movement
Excursion (mm)
Systolic Slope (mm/set)
Diastolic Slope (mm/set)
6 6
19 19
17 15
z
15 26 15
:“2 15 59 15 11 34
TABLE
z 26 $8” 28 ? 33
30 ;: 27 24 29 2’:
InIdefinite
18 17 ;:, ::
9” 1:
;:
23 20
1:
22.5 2’: 22.2
21
7.5 61
if.5 26
September
1976
The American Journal of CARDIOLOGY
II
Ultrasonic Measurements of the Leaflets of the Normal Porcine Aortic Bioprosthesis in the Mitral Position
2242
*Derived by subtracting 3 mm from the anulus size used by the manufacturer and surgeons. TPatients with sinus rhythm. SPatient with thrombus attached to inner surfaces of xenograft leaflets.
296
stent of the normally functioning xenografts (Fig. 1). Maximal measurements of stent diameter are given in Table I. The stent diameter of the heterograft with thrombus could not be measured unless the true stent dimensions were used as a guide. When this was done, extraneous echoes were evident behind the stent during systole (Fig. 2). The maximal stent diameter measurement in eight of the nine patients with a normal prosthesis was within 2 mm (mean 1.9 mm) of the “true” stent diameter (Table I). The internal diameter of the stent ranged from 16 to 24 mm and corresponded closely with the maximal stent diameter when allowance was made for stent thickness (Table I). Maximal movement of the anterior stent ranged from 6 to 10 mm (mean 7.5). The maximal systolic slope of this stent ranged from 15 to 35 mm/set (mean 22.2) and the maximal diastolic slope from 11 to 59 mm/set (mean 21.5). In the patient whose xenograft had thrombus, values were abormally high for both maximal systolic anterior stent movement (21 mm) and slope (61 mm/set). In this patient the maximal bioprosthetic valve anulus tilt along the valve’s long axis was 14’ as measured in successive frames of the cinefluoroscopic filmstrip.
Case no. :
Manufacturer’s Anulus Diameter (mm)
Opening
E-F
Closing
23
329 266
15
>600 354
12 lo 10 14
Slopes of Anterior-Leaflet (mm/set)
Maximal Diastolic Leaflet Separation (mm)
3 4 :
if; 27 29
326 383 209 276
16 26 38 16
300 279 424 523
; 9
z’1’ 31
280 253 378
18 9 22
340 244 >600
lo -
?
285 299
13 19
255 392
11
10 Mean
Volume 36
ECH~ARDi~AM
Valve leaflet echoes: Echoes from all three valve leaflets occasionally were seen between the thick parallel lines of echoes from the circular stent. Except for timing, the excursions of the xenograft valve leaflets resembled those of the normal human aortic valve. An anterior xenograft leaflet was recorded in all 10 patients with a normally functioning bioprosthesis (Fig. 1 and 3). Opening slopes in early diastole ranged from 209 to 383 mm/set. The E-F slopes corresponded closely with the diastolic slopes of the stent (Tables I and II), ranging from 9 to 38 mm/set. Closing slopes in early systole ranged from 244 to more than 600 mmlsec. A posterior xenograft leaflet (Fig. 3 and 4) was recorded in 6 of the 10 patients. Five of these patients had a measurable opening slope in early diastole of 207 to 561 mmlsec. Closing slopes of the posterior leaflet in early systole, measured in three patients, ranged from 269 to more than 600 mm/set. Maximal diastolic leaflet separation, measured in five patients, ranged from 10 to 14 mm. In the two patients with coexisting mild aortic regurgitation, a third centrally located leaflet was seen in association with moderate diastolic puttering of all three leaflets (Fig. 3 and 4). Xenograft with superimposed thrombus: In the patient whose xenograft had thrombus confirmed at operation, multiple dense nonhomogeneous echoes were recorded from between the anterior and posterior stent instead of the leaflets (Fig. 2).2 In addition, a clear space just behind the anterior stent in early diastole mimicked the clear space ch~acteristic of an atrial myxoma. A flat (4 to 11 mm thick) triangular (18 to 21 mm per side) thrombus was attached to the internal aspect of two of the leaflets, and its mobility allowed slight protrusion into the atrium only. This patient with a history of bacterial endocarditis was studied 16 months after insertion of the porcine xenograft in the mitral position. His bioprosthesis was replaced with a disc prosthesis when the thrombus was discovered. In each patient the M mode scan from the aortic root to the porcine aortic bioprosthesis in the mitral position revealed continuity between the posterior aortic wall and the anterior stent of the bioprosthesis (Fig. 3C). During further scanning from the prosthesis toward the apex of the left ventricle, the bioprosthetic stent and leaflet echoes disappeared abruptly (Fig. 3A). Paradoxic interventricular septal motion was uniformly present (Fig. I,3 and 4).
Discussion
Echocardiography has been useful in evaluating normal and abnormal mitral valves and mitral valve prostheses.s-” It also appears to be useful in evaluating porcine aortic heterografts in the mitral position. Nonquantitative echocardiographic descriptions of the normal and at least one abnormal homograft aortic valve in the mitral position have been published.6 The thick parallel bands of echoes from the anterior and posterior valve stent can be simultaneously recorded with appropriate focusing and damping. Figure 3B shows the relation of the ultrasonic beam and the prosthetic valve and the resulting echocardiogram. In most patients, echocardiograms were recorded from
September
OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
several transducer positions, resulting in many instances in different measurements for stent diameter. In each instance the maximal diameter from any transducer position was the value used. The maximal distance between the anterior echoes from the two stent components approximated the calculated diameter at the base of the stent (Table I). Submaximal measurements were attributable to ultrasonic transection of the stent at less than the maximal diameter. The ability of the flexible stent apexes to bend inward slightly probably also contributed to making ultrasonic measurements of diameter smaller than those in vitro.7 Since the internal diameter of the stent could be easily determined, inability to demonstrate this diameter may suggest that the stent lumen is occupied by extraneous material, as occurred in the xenograft with thrombus. The interventricular septum lies in front of the stent, and the posterior wall of the left atrium or left ventricle is behind it. Comparison with normal aortic and mitral valves: The ech~~diographic excursions of the porcine bioprosthetic valve leaflets resemble those of the normal human aortic valve.s The linear echoes from the porcine leaflets separate early in diastole and rejoin each other at the beginning of systole. To be recorded, they require a higher gain setting than the stent, presumably because they are less reflective than the polypropylene and Dacron@ stent. The anterior xenograft leaflet was recorded in all patients with a normally functioning bioprosthesis, thus suggesting that failure to visualize this leaflet is abnormal, as in the patient with thrombus on the xenograft. It is also possible that a decrease in the uniformly rapid maximal diastolic opening and systolic closing slopes of the anterior and posterior valve leaflets indicates abnormal function, as in patients with a calcified homograft aortic valve.6 The close correspondence of the normal anterior leaflet EdF slopes with that of the anterior stent in mid-dimple suggests that there is only slight closure of the leaflets in early and mid-diastole. This possibility is in accord with reports of a mild diastolic hemodynamic gradient even when these valves are functioning’ normallys The maximal amplitude of diastolic leaflet separation (averaging 11 mm) could be accurately recorded in only five patients because of difficulty in adequately visualizing the posterior leaflet. The extent of valve leaflet separation of the porcine aortic xenograft during diastole is moderately less than that of either the normal human aortic valve during systole, which ranges from 16 to 26 mm,‘0 or the normal mitral valve during diastole.ll The relatively smaller leaflet separations of the normal porcine aortic xenografts may account for the mild diastolic hemodynamic gradient reported across them. Although the maximal diastolic leaflet separations show some correspondence with values for internal diameter of the stent, they aren’t always proportional (Tables I and II). This may be due to lack of optimal ultrasonic beam orientation or to relative stenosis of the valve. A final conclusion should await further data. Identification of xenograft leaflets and aortic regurgitation: The difficulty in adequately visualizing
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ECHOCARDIOGRAM
OF BIOPROSTHESIS
IN MITRAL POSITION-BLOCH
the posterior xenograft leaflet in many patients is probably due to the obliquity of its ultrasonic beam transection with respect to the posterior stent in diastole. In both patients with aortic rugurgitation this leaflet was made apparent by diastolic shuddering (Fig. 3 and 4). The diastolic shudder due to aortic regurgitation also made the echocardiographically central (third) aortic leaflet easily identifiable. In most other patients, only two valve leaflets were well identified. Echocardiographic scanning from the aorta to the mitral bioprosthesis revealed the continuity of the posterior aortic wall with the anterior stent. Continuing the scan to the apex of the left ventricle revealed paradoxic systolic motion of the interventricular septum, which has previously been observed in many patients with a prosthetic mitral valve. Its mechanism is uncertain, and it usually resolves within 6 months after operation.i2J3 Identification of graft thrombus: The xenograft with thrombus was abnormal as revealed by the abnormally high values for maximal systolic anterior movement and systolic slope of the stent.2 Normally, movement of the stent can be considered to coincide with movement of the mitral anulus, with both structures moving anteriorly during systole and posteriorly during diastole. The diastolic slopes of backward stent movement were greatest in patients with atria1 fibrillation, in whom they varied inversely with the length of
ET AL.
the R-R interval. The normal diastolic posterior slope of the anterior stent in the xenograft with thrombus makes it uncertain whether there was increased obstruction to left ventricular filling.13 The combination of absent leaflet echoes and dense nonhomogeneous echoes from the stent on repeated examinations suggested abnormal material such as thrombus within the stent. Additional clues to a myxoma-like mass in the space between the xenograft leaflets were the early diastolic clear space and the abnormal systolic echoes behind the anterior stent. At operation, the prosthetic valve with a thrombus on the leaflets was excised intact. The mobile thrombus protruded slightly from the atria1 side of the valve. However, its attachment did not appear to allow anterior protrusion, thus making a paravalvular leak or mitral anulus aneurysm the presumed explanation for the excessive maximal anterior stent movement and slope. Since the maximal prosthetic valve tilt of 14’ exceeded l2O, it strongly suggested a paravalvular leak,14 but such a leak could not be demonstrated when the bioprosthesis was later replaced. Acknowledgment We express our appreciation to Dr. J. Willis Hurst for his comments and suggestions. We thank Drs. John Douglas, Charles R. Hatcher, Jr., Ellis L. Jones, and Paul H. Robinson for referring patients for evaluation.
References 1.
2.
3. 4.
5.
6.
7.
298
CarpentierA, Deloche A, Relland J, et al: Six-year follow-up of glutaraldehyde-preserved heterografts; with particular reference to the treatment of congenital valve malformations. J Thorac Cardiovasc Surg 88:771-781, 1974 Bloch WN, Felner JM, Wlckllffe C, et al: Echocardiographic diagnosis of thrombus on a heterograft aortic valve in the mitral position. Chest, in press Feigenbaum H: Echocardiography. Philadelphia, Lea & Febiger, 1973, p 43-73 Winters WL, Glmlnez J, Soloff LA: Clinical application of ultrasound in the analysis of prosthetic ball valve function. Am J Cardiol 19: 97-107, 1967 Johnson ML, Holmes JH, Paton BC: Echocardiographic determination of mitral disc valve excursion. Circulation 47:1274-1280, 1973 Horowitz MS, Goodman DJ, Popp RL: Echocardiographic diagnosis of calcific stenosis of a stented aortic homograft in the mitral position. J Clin Ultrasound 2:179-183, 1974 Zuhdi N, Hawley W, Voehl V, et al: Porcine aortic valves as re-
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8. 9.
10. 11. 12.
13.
14.
placements for human heart valves. Ann Thorac Surg 12479-49 1, 1974 Gramiak R, Shah PM: Echocardiography of the normal and diseased aortic valve. Radiology 96: 1-8, 1970 Johnson AD, Daily PO, Peterson KL, et al: Functional evaluation of the porcine heterograft in the mitral position. Circulation 50, 51:Suppl l:l-140-I-147, 1975 Felgenbaum H: In Ref 3, p 86 Gramlak R, Shah PM Cardiac ultrasonography. Radio1 Clin North Am 9:469-490, 1971 Miller HC, Gibson DG, Stephens JD: Role of echocardiography and phonocardiography in diagnosis of mitral paraprosthetic regurgitation with Starr-Edwards prosthesis. Br Heart J 35:12171225, 1973 Burggraf GW, Cralge E: Echocardiographic studies of left ventricular wall motion and dimensions after valvular heart surgery. Am J Cardiol 35:473-480, 1975 Whlte AF, Dlnsrnore RE, Buokley MJ: Cineradiographic evaluation of prosthetic cardiac valves. Circulation 48:882-889, 1973
Volume 36
of the Porcine Aortic Bioprosthesis
In the Mitral Position
WINSTON N. BLOCH, Jr., MD* JOEL M. FELNER, MD* CHARLES WICKLIFFE, MD* PANAGIOTIS N. SYMBAS, MD, FACC+ ROBERT C. SCHLANT, MD, FACC’ Atlanta, Georgia
Echocardiography was performed in 10 consecutive patients who had a clinically normally functioning porcine aortic bioprosthesis in the mitral
position. Strong well defined echoes were recorded from the anterior and posterior aspects of the xenograft stent. The maximal separation of the anterior and posterior stent echoes approximated the diameter of the stent at its base. The maximal excursion of the anterior stent was 5 to 10 mm (mean 7.5) with a mean systolic slope of 15 to 35 mm/set (mean 22.2) and diastolic slope of 11 to 59 mm/set (mean 21.5). In all 10 patients it was possible to record an anterior xenograft leaflet with anterior movement at the onset of diastole and posterior movement at the onset of systole and with appropriately steep (more than 200 mm/set) slopes. The diastolic (E-F) slope of the anterior leaflet in g of the 10 patients ranged from g to 38 mm/set (mean 19). In 6 of the 10 patients a posterior xenograft leaflet with a movement pattern symmetric with that of the anterior leaflet was recorded. In two patients, the central aortic leaflet was recorded with little diastolic displacement. These two patients also had mild aortic regurgitation, which was associated with diastolic shudder of the the xenograft leaflets. Echocardiography was also performed in one patient who was later shown to have a 10 cm3 thrombus on the ventricular surface of a xenografl valve. The echocardiogram in this patient revealed the following abnormalities: (1) excessive anterior stent movement and systolic slope suggesting paravalvular leak in the presence of abnormal cinefluoroscopic valve tilt, and (2) multiple dense nonhomogeneous echoes between the anterior and posterior aspects of the valve stent, with an early diastolic clear Space behind the anterior stent and abnormal echoes behind the Posterior stent during systole. Echocardiography therefore appears to be useful in evaluating the porcine aortic bioprosthesis in the mitral tion.
posi-
From the Division of Cardiology, Department of Medicine* and The Division of Cardio-Thoracic Surgery,+ Department of Surgery, Emory University School of Medicine and Grady Memorial Hospital, Atlanta, Ga. This study was supported in part by Training Grant HE-05731 from the National Heart and Lung Institute. National Institutes of Health, Bethesda, Md. Manuscript received January 5, 1976; revised manuscript received February 9, 1976, accepted February 11, 1976. Address for reprints: Joel M. Felner, MD, Department of Medicine (Cardiology), Emory University School of Medicine, 69 Butler St., S.E., Atlanta, Ga. 30303.
Recent reports indicate favorable long-term survival rates of patients with a xenograft aortic valve in the mitral positi0n.l Since widespread use of such valves is possible, knowledge of their normal echocardiographic appearance will be useful. Material
and Methods
Eleven adult patients were studied consecutively. Their ages ranged from 20 (mean 34.7). Ten patients had a clinically normally functioning
to 72 years
flexible stented porcine aortic bioprosthesis in the mitral position and one patient had a 10 cm3 thrombus within the valve leaflets, primarily on the ventricular side of the valve. Two of the 10 patients had mild aortic regurgitation. Ten patients were studied at least 1 month after surgical placement of the valve. The longest interval between operation and the echocardiographic study was 16 months. All patients were thoroughly examined with a series C-100 Unirad echoscope using a 2.25 megahertz 518 inch (1.59 cm) diameter transducer focused at 10 cm.
September 1976
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Volume 36
293
ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
Recordings were made on a model 174 Tektronix strip chart recorder, using either heat- or light-sensitive paper. A standard M mode heart scan was performed by placing the transducer in the left parasternal interspace where the mitral valve echoes were best seen. The transducer was then rotated in a partial arc, from the mitral valve to the ascending aorta and to the cardiac apex. To record the xenograft mitral valve leaflets it was usually necessary to keep the focus on the anterior and posterior aspects of the bioprosthetic stent (Fig. 1) while slowly increasing or decreasing the gain and “sweeping” from the superolateral to the inferomedial position and back again. Since the structure (stent) that supports the leaflets resembles a cylinder when it is examined echocardiographitally near its diameter, it appears as two parallel discontinuous structures that will be described as “anterior” and “posterior” stent, respectively.
--cw
Echocardiographic measurements: The diameter of the stent was measured as the distance between the anterior echoes of the anterior and posterior stent (Fig. 1). Use of the distance from the anterior echoes of the anterior stent to the posterior echoes of the posterior stent had proved an unreliable measure of stent diameter because the latter echoes often overlapped those of other structures or reverberations (Fig. 2 to 4). A range of values for stent diameter resulted from making measurements wherever the anterior and posterior stent could be defined by appropriate damping. The “true” stent diameter was obtained by subtracting 3 mm (the in vitro estimate of stent thickness) from the manufacturer’s stated anulus diameter. This gave the ultrasonically detectable maximal stent diameter, located at the nadir (or base) of the stent, measured from the anterior side of the anterior stent to the anterior side of the posterior stent (Fig. 1). The maximal
-
FIGURE 1. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position. Linear echoes of the valve leaflets (PL) separate during diastole and reunite
-PL H?3 1 ‘_
d
/_._A
_i
--CW -
...__ -k,
..4
-ARVW C -EGG
FIGURE 2. Echocardlogram of the porcine aortic bioprosthesis in the mitral position with thrombus. Multiple dense nonhomogeneous echoes are present mostly between the valve stent (arrow). They are most prominent behind the posterior stent during systole (AE). LAW = left atrial wall; other abbreviations as in Figure 1.
294
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ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
ET AL.
Stent -:
Stent -:
FIGURE 3. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position in a patient with aortic regurgitation. A, left to right scan from the bioprosthesis with its three leaflets at the level of the atrioventricular junction to the left ventricular cavity. As the scan proceeds, the bioprosthetic echoes disappear abruptly. The interventricular septum moves paradoxically during systole. B, schematic diagram of the echocardiogram of the bioprosthesis. The arrows and cylinder indicate the direction and location of the ultrasonic beam as it traverses the bioprosthesis. All three leaflets are visualized in the echocardiogram. partly because of the diastolic shudder caused by aortic regurgitation. C, scan from the aortic root to the porcine aortic bioprosthesis in the mitral position. The posterior aortic wall (PAW) is continuous with the anterior stent. AAW = anterior aortic wall: Ant. = anterior; CW = chest wall: ECG = electrocardiogram: IVS = interventricular septum; LA = left atrium; LV = left ventricle; PAW = posterior aortic wall; PL = anterior and posterior bioprosthetic leaflets; Post. = posterior; RV = right ventricle; RVOT = right ventricle outflow tract.
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ECHOCARDIOGRAM OF BIOPROSTHESIS IN MITRAL POSITION-BLOCH
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FIGURE 4. Echocardiogram of a normally functioning porcine aortic bioprosthesis in the mitral position in a second patient with aortic regurgitation. The diastolic shudder is greatest on the posterior leaflet although present on all three leaflets. During attenuation, the weaker leaflet echoes disappear before the stronger echoes of the stent. AS = anterior stent; CW = chest wall; ECG = electrocardiogram: IVS = interventricular septum; LVPW = left ventricular posterior wall; PS = posterior stent.
excursion of the anterior stent and its systolic and diastolic slopes were measured as shown in Figure 1. The slope of the anterior movement of the anterior stent during systole will be referred to as the systolic slope, and the slope of the posterior movement of this stent during diastole as the diastolic slope. Since the movements and slopes of the anterior and posterior stent were virtually identical, we have measured the anterior stent only. The internal diameter of the stent was measured as the maximal observed distance from the posterior echo of the anterior stent to the anterior echo of the posterior stent during appropriate damping. The opening and closing slopes of the xenograft leaflets were measured. The mid-diastolic closure rate (E-F slope) of the anterior leaflet and the maximal diastolic separation of the leaflets (from their closest borders) were measured whenever appropriate visualization was obtained (Fig. 1).
Results Stent measurements: Strong well defined echoes were always observed from the anterior and posterior
TABLE
I
Echocardiographic Measurements of the Porcine Bioprosthesis in the Mitral Position Stem diameter Case no. It 2 3 4 5t 6 7t 9” IO? Mean ll?S
“True”* External
Anterior
(mm)
Ultrasonic External
Internal
20
Aortic
Stent Movement
Excursion (mm)
Systolic Slope (mm/set)
Diastolic Slope (mm/set)
6 6
19 19
17 15
z
15 26 15
:“2 15 59 15 11 34
TABLE
z 26 $8” 28 ? 33
30 ;: 27 24 29 2’:
InIdefinite
18 17 ;:, ::
9” 1:
;:
23 20
1:
22.5 2’: 22.2
21
7.5 61
if.5 26
September
1976
The American Journal of CARDIOLOGY
II
Ultrasonic Measurements of the Leaflets of the Normal Porcine Aortic Bioprosthesis in the Mitral Position
2242
*Derived by subtracting 3 mm from the anulus size used by the manufacturer and surgeons. TPatients with sinus rhythm. SPatient with thrombus attached to inner surfaces of xenograft leaflets.
296
stent of the normally functioning xenografts (Fig. 1). Maximal measurements of stent diameter are given in Table I. The stent diameter of the heterograft with thrombus could not be measured unless the true stent dimensions were used as a guide. When this was done, extraneous echoes were evident behind the stent during systole (Fig. 2). The maximal stent diameter measurement in eight of the nine patients with a normal prosthesis was within 2 mm (mean 1.9 mm) of the “true” stent diameter (Table I). The internal diameter of the stent ranged from 16 to 24 mm and corresponded closely with the maximal stent diameter when allowance was made for stent thickness (Table I). Maximal movement of the anterior stent ranged from 6 to 10 mm (mean 7.5). The maximal systolic slope of this stent ranged from 15 to 35 mm/set (mean 22.2) and the maximal diastolic slope from 11 to 59 mm/set (mean 21.5). In the patient whose xenograft had thrombus, values were abormally high for both maximal systolic anterior stent movement (21 mm) and slope (61 mm/set). In this patient the maximal bioprosthetic valve anulus tilt along the valve’s long axis was 14’ as measured in successive frames of the cinefluoroscopic filmstrip.
Case no. :
Manufacturer’s Anulus Diameter (mm)
Opening
E-F
Closing
23
329 266
15
>600 354
12 lo 10 14
Slopes of Anterior-Leaflet (mm/set)
Maximal Diastolic Leaflet Separation (mm)
3 4 :
if; 27 29
326 383 209 276
16 26 38 16
300 279 424 523
; 9
z’1’ 31
280 253 378
18 9 22
340 244 >600
lo -
?
285 299
13 19
255 392
11
10 Mean
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Valve leaflet echoes: Echoes from all three valve leaflets occasionally were seen between the thick parallel lines of echoes from the circular stent. Except for timing, the excursions of the xenograft valve leaflets resembled those of the normal human aortic valve. An anterior xenograft leaflet was recorded in all 10 patients with a normally functioning bioprosthesis (Fig. 1 and 3). Opening slopes in early diastole ranged from 209 to 383 mm/set. The E-F slopes corresponded closely with the diastolic slopes of the stent (Tables I and II), ranging from 9 to 38 mm/set. Closing slopes in early systole ranged from 244 to more than 600 mmlsec. A posterior xenograft leaflet (Fig. 3 and 4) was recorded in 6 of the 10 patients. Five of these patients had a measurable opening slope in early diastole of 207 to 561 mmlsec. Closing slopes of the posterior leaflet in early systole, measured in three patients, ranged from 269 to more than 600 mm/set. Maximal diastolic leaflet separation, measured in five patients, ranged from 10 to 14 mm. In the two patients with coexisting mild aortic regurgitation, a third centrally located leaflet was seen in association with moderate diastolic puttering of all three leaflets (Fig. 3 and 4). Xenograft with superimposed thrombus: In the patient whose xenograft had thrombus confirmed at operation, multiple dense nonhomogeneous echoes were recorded from between the anterior and posterior stent instead of the leaflets (Fig. 2).2 In addition, a clear space just behind the anterior stent in early diastole mimicked the clear space ch~acteristic of an atrial myxoma. A flat (4 to 11 mm thick) triangular (18 to 21 mm per side) thrombus was attached to the internal aspect of two of the leaflets, and its mobility allowed slight protrusion into the atrium only. This patient with a history of bacterial endocarditis was studied 16 months after insertion of the porcine xenograft in the mitral position. His bioprosthesis was replaced with a disc prosthesis when the thrombus was discovered. In each patient the M mode scan from the aortic root to the porcine aortic bioprosthesis in the mitral position revealed continuity between the posterior aortic wall and the anterior stent of the bioprosthesis (Fig. 3C). During further scanning from the prosthesis toward the apex of the left ventricle, the bioprosthetic stent and leaflet echoes disappeared abruptly (Fig. 3A). Paradoxic interventricular septal motion was uniformly present (Fig. I,3 and 4).
Discussion
Echocardiography has been useful in evaluating normal and abnormal mitral valves and mitral valve prostheses.s-” It also appears to be useful in evaluating porcine aortic heterografts in the mitral position. Nonquantitative echocardiographic descriptions of the normal and at least one abnormal homograft aortic valve in the mitral position have been published.6 The thick parallel bands of echoes from the anterior and posterior valve stent can be simultaneously recorded with appropriate focusing and damping. Figure 3B shows the relation of the ultrasonic beam and the prosthetic valve and the resulting echocardiogram. In most patients, echocardiograms were recorded from
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ET AL.
several transducer positions, resulting in many instances in different measurements for stent diameter. In each instance the maximal diameter from any transducer position was the value used. The maximal distance between the anterior echoes from the two stent components approximated the calculated diameter at the base of the stent (Table I). Submaximal measurements were attributable to ultrasonic transection of the stent at less than the maximal diameter. The ability of the flexible stent apexes to bend inward slightly probably also contributed to making ultrasonic measurements of diameter smaller than those in vitro.7 Since the internal diameter of the stent could be easily determined, inability to demonstrate this diameter may suggest that the stent lumen is occupied by extraneous material, as occurred in the xenograft with thrombus. The interventricular septum lies in front of the stent, and the posterior wall of the left atrium or left ventricle is behind it. Comparison with normal aortic and mitral valves: The ech~~diographic excursions of the porcine bioprosthetic valve leaflets resemble those of the normal human aortic valve.s The linear echoes from the porcine leaflets separate early in diastole and rejoin each other at the beginning of systole. To be recorded, they require a higher gain setting than the stent, presumably because they are less reflective than the polypropylene and Dacron@ stent. The anterior xenograft leaflet was recorded in all patients with a normally functioning bioprosthesis, thus suggesting that failure to visualize this leaflet is abnormal, as in the patient with thrombus on the xenograft. It is also possible that a decrease in the uniformly rapid maximal diastolic opening and systolic closing slopes of the anterior and posterior valve leaflets indicates abnormal function, as in patients with a calcified homograft aortic valve.6 The close correspondence of the normal anterior leaflet EdF slopes with that of the anterior stent in mid-dimple suggests that there is only slight closure of the leaflets in early and mid-diastole. This possibility is in accord with reports of a mild diastolic hemodynamic gradient even when these valves are functioning’ normallys The maximal amplitude of diastolic leaflet separation (averaging 11 mm) could be accurately recorded in only five patients because of difficulty in adequately visualizing the posterior leaflet. The extent of valve leaflet separation of the porcine aortic xenograft during diastole is moderately less than that of either the normal human aortic valve during systole, which ranges from 16 to 26 mm,‘0 or the normal mitral valve during diastole.ll The relatively smaller leaflet separations of the normal porcine aortic xenografts may account for the mild diastolic hemodynamic gradient reported across them. Although the maximal diastolic leaflet separations show some correspondence with values for internal diameter of the stent, they aren’t always proportional (Tables I and II). This may be due to lack of optimal ultrasonic beam orientation or to relative stenosis of the valve. A final conclusion should await further data. Identification of xenograft leaflets and aortic regurgitation: The difficulty in adequately visualizing
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the posterior xenograft leaflet in many patients is probably due to the obliquity of its ultrasonic beam transection with respect to the posterior stent in diastole. In both patients with aortic rugurgitation this leaflet was made apparent by diastolic shuddering (Fig. 3 and 4). The diastolic shudder due to aortic regurgitation also made the echocardiographically central (third) aortic leaflet easily identifiable. In most other patients, only two valve leaflets were well identified. Echocardiographic scanning from the aorta to the mitral bioprosthesis revealed the continuity of the posterior aortic wall with the anterior stent. Continuing the scan to the apex of the left ventricle revealed paradoxic systolic motion of the interventricular septum, which has previously been observed in many patients with a prosthetic mitral valve. Its mechanism is uncertain, and it usually resolves within 6 months after operation.i2J3 Identification of graft thrombus: The xenograft with thrombus was abnormal as revealed by the abnormally high values for maximal systolic anterior movement and systolic slope of the stent.2 Normally, movement of the stent can be considered to coincide with movement of the mitral anulus, with both structures moving anteriorly during systole and posteriorly during diastole. The diastolic slopes of backward stent movement were greatest in patients with atria1 fibrillation, in whom they varied inversely with the length of
ET AL.
the R-R interval. The normal diastolic posterior slope of the anterior stent in the xenograft with thrombus makes it uncertain whether there was increased obstruction to left ventricular filling.13 The combination of absent leaflet echoes and dense nonhomogeneous echoes from the stent on repeated examinations suggested abnormal material such as thrombus within the stent. Additional clues to a myxoma-like mass in the space between the xenograft leaflets were the early diastolic clear space and the abnormal systolic echoes behind the anterior stent. At operation, the prosthetic valve with a thrombus on the leaflets was excised intact. The mobile thrombus protruded slightly from the atria1 side of the valve. However, its attachment did not appear to allow anterior protrusion, thus making a paravalvular leak or mitral anulus aneurysm the presumed explanation for the excessive maximal anterior stent movement and slope. Since the maximal prosthetic valve tilt of 14’ exceeded l2O, it strongly suggested a paravalvular leak,14 but such a leak could not be demonstrated when the bioprosthesis was later replaced. Acknowledgment We express our appreciation to Dr. J. Willis Hurst for his comments and suggestions. We thank Drs. John Douglas, Charles R. Hatcher, Jr., Ellis L. Jones, and Paul H. Robinson for referring patients for evaluation.
References 1.
2.
3. 4.
5.
6.
7.
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CarpentierA, Deloche A, Relland J, et al: Six-year follow-up of glutaraldehyde-preserved heterografts; with particular reference to the treatment of congenital valve malformations. J Thorac Cardiovasc Surg 88:771-781, 1974 Bloch WN, Felner JM, Wlckllffe C, et al: Echocardiographic diagnosis of thrombus on a heterograft aortic valve in the mitral position. Chest, in press Feigenbaum H: Echocardiography. Philadelphia, Lea & Febiger, 1973, p 43-73 Winters WL, Glmlnez J, Soloff LA: Clinical application of ultrasound in the analysis of prosthetic ball valve function. Am J Cardiol 19: 97-107, 1967 Johnson ML, Holmes JH, Paton BC: Echocardiographic determination of mitral disc valve excursion. Circulation 47:1274-1280, 1973 Horowitz MS, Goodman DJ, Popp RL: Echocardiographic diagnosis of calcific stenosis of a stented aortic homograft in the mitral position. J Clin Ultrasound 2:179-183, 1974 Zuhdi N, Hawley W, Voehl V, et al: Porcine aortic valves as re-
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8. 9.
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placements for human heart valves. Ann Thorac Surg 12479-49 1, 1974 Gramiak R, Shah PM: Echocardiography of the normal and diseased aortic valve. Radiology 96: 1-8, 1970 Johnson AD, Daily PO, Peterson KL, et al: Functional evaluation of the porcine heterograft in the mitral position. Circulation 50, 51:Suppl l:l-140-I-147, 1975 Felgenbaum H: In Ref 3, p 86 Gramlak R, Shah PM Cardiac ultrasonography. Radio1 Clin North Am 9:469-490, 1971 Miller HC, Gibson DG, Stephens JD: Role of echocardiography and phonocardiography in diagnosis of mitral paraprosthetic regurgitation with Starr-Edwards prosthesis. Br Heart J 35:12171225, 1973 Burggraf GW, Cralge E: Echocardiographic studies of left ventricular wall motion and dimensions after valvular heart surgery. Am J Cardiol 35:473-480, 1975 Whlte AF, Dlnsrnore RE, Buokley MJ: Cineradiographic evaluation of prosthetic cardiac valves. Circulation 48:882-889, 1973
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