Size of the normal aortic root in normal subjects and in those with left ventricular outflow obstruction

CONGENITAL HEART DISEASE

Size of the Normal Aortic Root in Normal Subjects and in Those with Left Ventricular Outflow Obstruction Magdi El Habbal, MD, and Jane Somerville, MD

This study establishes normal values and growth curves of the aortic root to determine when it is unusually small. The aortic root diameter was measured by L-dimensional echocardiography in 188 normal subjects (group 1) and in 33 patients (group 2) with left ventricular outflow obstruction in whom the diagnosis of small aortic root was made during surgery for aortic root and valve replacement. In group 2 the aortic root was also measured by Mmode echocardiography and was compared to measurements during surgery. Growth curves of the normal aortic root were obtained. In group 2 the aortic root was smaller than normal except in 3 patients. When corrected for body surface area all were smaller than normal. The P-dimensional echocardiographic and surgical measurements were almost identical. M-mode values were higher (p
From the Pediatric and Adolescent Unit, The National Heart Hospital, London, England. Dr. El Habbal was supported by a grant from the World Congress of Pediatric Cardiology, London, England. Manuscript received July 19, 1988; revised manuscript received and accepted October 20, 1988. Address for reprints: Magdi El Habbal, MD, Pediatric and Adolescent Unit, National Heart Hospital, Westmoreland Street, London WlM SBA, England.

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efore surgery for relieving obstructive lesionsof the left ventricular outflow tract, it is imperative to know the size of the aortic root since surgical management and outcome differ among thosewith normal or small aortic roots.1-3However, normal values of the aortic root size during infancy, childhood and adolescencehave yet to be established. Data basedon Mmode echocardiography have been published,4-9but the accuracy of this approach for measuring the aortic root size is questionable. Autopsy data have also been published.‘O-l3Measurementsobtained from formalin-fixed heart specimensare expected to be smaller than those obtained in situ. Angiocardiography also has limitations related to magnification and distortion. This study determines the normal aortic root size using 2-dimensional echocardiography. By studying a wide spectrum of normal subjects,from infancy through late adulthood, our objective was to establish a reference base that can help to identify abnormal aortic roots, whether small or large, METHODS

We measuredthe aortic root size in 2 groups. Group 1 consisted of 188 normal healthy subjects (102 male and 86 female), with negative family history for systemic hypertension. Their ages ranged from 3 weeksto 60 years (Table I). Twenty-five were healthy subjectswith innocent heart murmurs and without any detectable cardiac abnormalities on clinical assessment,electrocardiography, chest radiography and echocardiography. The rest of group 1 were patients’ relatives, also healthy and without clinical evidence of heart disease,who accompanied the patients to the hospital and consentedto the echocardiographic examination. Group 2 consisted of 33 patients (20 male and 13 female), ranging in age from 7 to 35 years, with left ventricular outflow tract obstruction mainly at the valvular level (Table I). All had cardiac catheterization and angiocardiography. In only a few patients the aortic root was suspectedto be small. The diagnosisof small aortic root was made by an experienced surgeon who felt during operation that relief of the left ventricular outflow tract obstruction could only be achievedby replacing the whole aortic root. All thesepatients had aortic root and valve replacement by homograft. Two patients died in the early postoperative period. Measurements were made using ATL 2-dimensional echocardiographic equipment (Mark 600) and ATL transducers 5 MHz and 2.5 MHz. In the left paraster-

diameter was measured in the operating room by placing the aortic root, in its intact circular structure, on a OS-mm graded metal caliper. Body surface area was derived from height (in cm) and weight (in kg), using this equation.15Body surface X height0.3964 X 0.024265. The aorarea = weight0.5378 tic root diameter was also corrected for body surface area and expressedin mm/m2. The normal growth curves of the aortic root were obtained by plotting these measurements against age using a polynomial regression equation: Y = K + K,x’ + K,X* -k - - + K,X”, nal long-axis view, the aortic root was scanned and the where Y = aortic root diameter (in mm), X = age (in largest diameter was measured using a commercially years), K, Kt, K2, . . . , K, = constants and n = the available caliber on the television screen. The echocar- regressionorder. The order of regressionwas selected to diographic studies were recorded on video cassettes (VHS T120) using a Panasonicvideo cassetterecorder (NV 8200). The transducer was carefully manipulated to position the aortic root in the center of the screen, thus avoiding distortion of the image in the lateral fields. The aortic root diameter was measured (trailing edgeto leading edge) at the site of insertion of the aortic valve cusps at end-diastole (Figure 1). End-diastole was identified echocardiographically as the image immediately preceding closure of the mitral valve. The relative accuraciesof M-mode and 2-dimensional echocardiography were evaluated in the 33 patients 25 in group 2 in whom the aortic root size was also mea0 20 5 10 15 sured intraoperatively. Both echocardiographic recordSURGICAL MEASUREMENT mm ings were obtained in the same setting. The M-mode measurementswere made according to recommenda- FIGURE 2. A comparison between the M-mode, ?-dimensiontions of the American Society of Echocardiography.14 al echocardiographic and surgical measurements of the aortic Both the M-mode and a-dimensional echocardiographic root diameter. The P-dimensional and the surgical measuremeasurementswere compared to the direct measure- ments are almost identical. The M-mode measurements are significantly higher (p
and surgical

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FIGURE 1. A schematic diagram of the 2-dimensional longaxis view of the aortic root. The interrupted tine represents the site where the measurements are taken. ALMV = anterior leaflet of the mitral valve; Asc Ao = ascending aorta; LVOT = left ventricular outflow tract; VS = ventricular septum.

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FIGURE 3. The growth curve of the normal aortic root diameter from birth to 60 years. The solid line represents the mean; the interrupted line represents 1 standard deviation (SD) and the dotted line represents 2 standard deviations. R = 0.92. Y = 9.215 + 1.6432 X + (-1.3712 X 10-l) X2 + (7.3318 x lO-3)X3 + (-1.9776 x 1O-4)X4 + (2.5162 X 1O-6)X5 (-1.2025 x 1O-s)X6 = mm, where Y = aortic diameter in mm and X = age in years.

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TABLE II Formula for Predicting the Normal Aortic Root Diameter Aortic Root Diameter 0-W

Constants

Corrected Aortic Root Diameter (mm/m*)

9.2150 1.6432 -1.3712 x 7.3318 X -1.9776 X 2.5161 x -1.2025 x O.OOCO

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3.0058 x -3.4223 3.4872 x -2.3702 x 1.0126 x -2.4451 X 3.0053 x -1.4562 X

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and measuredthe aortic root diameter by 1 observeron 2 occasions(intraobserver variability). Another observer independently performed the measurements for the same 20 subjects (interobserver variability). RESULTS

10

The measurementsof the aortic root obtained by Mmode, 2-dimensional echocardiography and surgical 10-l 10-l measurementswere comparedand the results are shown K3 = 1O-3 lo-2 in Figure 2. There was no significant difference between K4= 1O-4 10-3 lo-6 K5 = 1O-5 the 2-dimensional echocardiographic and surgical mealo-8 Ks = 10-T surements. They were almost identical. The M-mode K7 = 1O-g measurementswere significantly higher than the surgiY (mm or mm/m2) = K + KIX’ + KzX* + . ..+ K7X’. where, K. KI, KP, K, = cal measurements(p 0.5). The relation between the aortic root diameter corHEIGHT IN Cm rected for body surface area and age is shown in Figure 7. A striking reduction of the corrected aortic root was FIGURE 4. The aortic root diameter plotted against height in a normal population. R = 0.92. observed during the first 15 years of life. Figure 8 shows the aortic root diameter of patients 1 in group 2 plotted against the normal curve derived THE NORMAL AORTIC ROOT

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FIGURE 5. The aortic root diameter a normal population. R = 0.94.

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plotted against weight in

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07 0.000

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FIGURE 6. The aortic root diameter plotted against body surface area in a normal population. R = 0.95.

from group 1 using age as the variable. The values were ameter is directly related to the left ventricular internal at or below 2 standard deviations from the normal. diameter at end-diastole, and that the aortic root/left However, there were 3 patients whose estimated aortic ventricular end-diastolic diameter ratio is almost conroot diameters were within 1 to 2 standard deviations stant. Therefore, the human heart, like the brain, is rellower than the normal mean. When corrected for body atively large at birth and continues to grow. The heart surface area and compared to normal subjects (Figure does not grow at the same rate as the body until it at9), they were all at or below 2 standard deviations from tains the adult heart size at or near puberty. Krovetz16 the mean. recalculated data gathered initially by Sutter’* and Kani19 and demonstrated that the size of the ascending DISCUSSION aorta, expressedas cross-sectionalarea/m2 of body surIt appears,as expected,that as the body grows in the face area, decreasesduring the first 20 years of life. first 3 decadesof life the aortic root also grows. ThereThe reported autopsy datalO- follow the same after, between 30 to 50 years of age, there is minimal growth pattern observedin our study (Figure 10). Howincreasein the size of the aortic root. After 50 years of ever, the values were consistently smaller than those age, there seemsto be a trend for the aortic root size to found by 2-dimensional echocardiography. The effect of again increase gradually. This latter observation has formalin fixation and fibrous tissue contracture, which been attributed to age-related changes in the collagen occur after death, may account for this discrepancy. and elastin content of the aorta.i6J7 In choosing a group of patients with left ventricular When the values are corrected for body surface area, outflow obstruction, in whom the surgeon defined the the curve obtained suggests that the aortic root de- aortic root as small becauseof its appearanceand difticreasesrelative to body size in the first 15 years of life. culties in relieving the obstruction, the value of normal Previousstudies4,5,7 have noticed that the aortic root di- identifying abnormal was tested. All aortic roots were small by j-dimensional echocardiography, except 3 patients in whom they were within normal range. When corrected for body surface area all aortic roots were small. Therefore, when evaluating the aortic root size in patients with left ventricular outflow tract obstruction, it is essential to take into consideration the body size. 45 ,

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FIGURE 7. The growth curve of the normal corrected aortic root diameter from birth to SO years. The aortic root diameter decreases relative to body growth in the first 15 years of life. R = 0.93. Y = 0.30058 + (-3.4223) X + (3.4972 X 10-l) X2

+ (-2.3702 x 10-Z) X3+(1.0126x 1O-3)X4 + (-2.4451 x 10-5)X5+ (3.0053 x lo-')X6 + (-1.4562 x 10-9) X7 = mm/m2, where Y = aortic root diameter age in years. SD = standard deviation.

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FIGURE 9. The corrected aortic root diameter of patients group 2 (A) plotted on the normal growth curve. All are emaller than normal. SD = standard deviation.

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IGURE 8. The aortic t diameter of pattents in group 2 (A) plotted on the normal growth curve. All are smaller than normal except 3 patients within the range of normal. SD = standard deviation.

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FIGURE 10. Published autopsy data of normal aortic root diameters plotted on the growth curve obtained by 2dimensional echocardiography. SD = standard deviation.

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Our experience suggeststhat these curves are useful for REFERENCES determining the critically small aortic root before sur- 1. Nicks R, Cartmill T, Bernstein L. Hypoplasia of the aortic root. The problem of valve replacement. Thorax 1970;25;339-346. gery. This knowledge should help with assessingrisks aortic 2. Westaby S, Karp RP, Blackstone EH, Bishop SP. Adult human valve dimenand planning prognosis. sions and their surgical significance. Am J Cardiol /984;53:552-556. Two-dimensional and M-mode echocardiography re- 3. Rahimtola SH. The problemofvalve prosthesis-patient mismatch. Circulation produced the actual aortic root size measuredintraoper- 4.1978;58:20-24. Henry WL, Ware J, Gardin JM, Hepner SI, McKay J, Weiner M. Echocardioatively differently becauseof the following reasons.The graphic measurements in normal subjects: growth-related changes that occur infancy and early adulthood. Circulation /978;57:278-284. actual plane and diameter measured by the M-mode between 5. Gardin JM, Henry WL, Savage DD, Ware JH, Burn C, Borer JS. Echocardioapproach are different from those measured by the sur- graphic measurements in normal subjects: evaluation of an adult population geon, whereas the 2-dimensional echocardiographic without clinically apparent heart disease. J Clin (Ntrosound 1979;7:439-445. Goldberg SJ, Allen HD, Sahn DJ. Pediatric and adolescent echocardiography. measurementsare basedon the samestructures that the 6.Chicago: Year Book Medical, 1975:43. surgeon measures. The American Society of Echocar- 7. Rage CL, Silverman NH, Hart PA, Ray RM. Cardiac structure growth diography’s recommendation for measuring the aortic pattern determined by echocardiography. Circulation 1978;57:285-290. 6. Feigenbaum H. Echocardiography. Third edition. Philadelphia: Lea and root includes the anterior wall of the aorta. The site of Febiger, 1981:549. insertion of the aortic valve cusps is deliberately chosen 9. Lester LA, Sodet PC, Hutcheon N, Arcilla RA. M-mode echocardiography in children and adolescents: some new perspectives. Pediatr Cardiol as the landmark for the aortic root size because it is normal 1987;8:27-31. easily recognized. Also, the aortic sinuses bulge above 10. Rowlatt UF, Rimoldi HJA, Lev M: The quantitative anatomy of the normal the root to a larger diameter but as long as the aortic child’s heart. Pediatric Clin North Am 1963:10:499-588. 11. Scholz DC, Kitzman DW, Hagen PT, II&up DM, Edwards WD. Ageroot is in situ it determines the difficulty and feasibility related changes in normal human hearts during the first 10 decades of life. Part I for valve replacement.1-3 (growth): a quantitative anatomic study of 200 specimens from subjects from It remains to be seen whether the upper limits of birth to 19 years old. Mayo Clin Proc 1988,63:126-136. 12. Kitzman DW, Scholz DG, Hagen PT, Ilstrup DM, Edwards WD. Agenormal aortic root size have been defined adequately to related changes in normal human heart during the first 10 decades of life. Part II use the curves in patients with a potential or definite (maturity): a quantitative anatomic study of 765 specimens from subjects from 20 to 99 years old. Mayo Clin Proc 1988;63:137-146. aortic root disease,such as Marfan’s syndrome. 13. Hutchins GM, Anaya OA. Measurements of cardiac size, chamber volumes We think the curves presented herein can be used to and valve orifices at autopsy. John Hopkins Med J 1973;133:96-106. evaluate the size of the aortic root in children and young 14. Sahn DJ, De Maria A, Kisslo J, Weyman A. Committee on M-mode standardization of the American Society of Echocardiography. Recommendations adults. The aortic root can easily be recognized as small regarding quantitation in M-mode echocardiography: results of a survey of echoif it is outside the range of normal. Evaluation should be cardiographic measurements. Circulation 1978;58:1072-1083. done before surgery becausespecial surgical techniques 15. Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring surface area: a height-weight formula validated in infants, children and may be required for relieving aortic stenosisat any level body adults. Pediatrics 1978,93:62-66. or of any type. Two-dimensional echocardiography is an 16. Krovetz LJ. Age-related changes in size of the aortic valve annulus in man. Am Heart J 1975,90:569-574. accurate method for measuring the aortic root. 17. Bashey RI, Torii S, Angrist A. Age-related collagen and elastin content of We acknowledge the surgeons who operated on our patients, Drs. D. Ross and M. de Leval. We thank Sue Stone who supplied us with the computer data, and Veronica E. Cullen and Joyce Jackovich for their secretarial assistance. Acknowledgment:

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human heart valves. J Gerontol 1967:2:203-208. 16. Sutter F. Uber das verhalten des aortenumfanges unter physiologischen und pathologischen bedingungen. Arch Exp Pathol Pharmacol l&87:39:289-

293. 19. Kani I. Systematische lichtungs and dickenmessungen des grossen arterien and ihre bedeutung fur die pathologic des getasse. Virchows Arch Pathol Anat 1910;201:45-51.