Two-dimensional echocardiography in discrete subaortic stenosis

Two-Dimensional Echocardiography in Discrete Subaortic Stenosis MICHAEL MOTRO, MD, ADAM SCHNEEWEISS, MD, ABRAHAM SHEM-TOV, MD, ZVI VERED, MD, JULIUS HEGESH, MD, HENRY N. NEUFELD, MD, and SHEMUEL RATH, MD

Thirty-seven patients with discrete subaortic stenosis (DSS) underwent 2-dimensional echocardiography (2-D echo) and cardiac catheterization. The peak systolic pressure gradients ranged from 0 to 150 mm Hg. Thirty-two patients had membranous DSS and 5 had fibromuscular DSS. Of 37 patients with DSS, 2-D echo diagnosed the presence and type in 35; in 2, a membrane was demonstrated by angiography. Of the 35 patients accurately diagnosed by 2-D echo, angiography corroborated the diagnosis in 33, but failed to show the membrane in 2. Subsequent cardiac surgery confirmed the accuracy of the echocardiographic diagnosis in these 2 patients. In all patients with membranous DSS, the anterior insertion of the membrane was demonstrated. In 9 of them the posterior insertion was

demonstrated by tilt of the transducer but the anterior insertion disappeared. In 4 patients both insertions were demonstrated simultaneously and in 3 patients the membrane was demonstrated as a continuous line. In 4 of the 5 patients with fibromuscular DSS, both insertions of the lesion were demonstrated simultaneously. However, 2-D echo was unsuccessful in assessing the severity of obstruction. In only 1 patient did demonstration of the whole subaortic membrane as a continuous line below the aortic valve correlate with severe obstruction. Thus, the presence and type of DSS, but not the degree and severity, can be accurately and reliably diagnosed by means of 2-D echo.

Discrete subaortic stenosis (DSS) is one of the important types of left ventricular (LV) outflow obstruction. Several series of echocardiographic diagnosis of DSS have been reported.1-7 Echocardiography (echo) has changed the known pattern of this disease in that many mild cases of DSS can now be diagnosed. Previously, without the aid of echo, many mild cases were probably misdiagnosed as functional murmurs. This article describes the advantages and limitations of 2-dimensional (2-D) echo in diagnosing different types8 of DSS, based on our experience with 37 patients.

available for review. The 2-D echo was performed before cardiac catheterization by an Aloka SSD 110 echograph equipped with a 3.5-MHz mechanical sector scanner. All patients were studied in the long-axis parasternal view to determine the presence of DSS and the type of obstruction. These echocardiograms were compared with the findings of left ventriculograms. The diameter of maximal LV outflow narrowing (subaortic) in systole, as well as the thickness of the membrane, were measured and plotted against the systolic pressure gradient, measured by pullback of the catheter from the left ventricle to the aorta.

Methods In 37 patients with DSS, clinical history, physical examination, ECG, thoracic roentgenogram, Z-D echocardiogram, cardiac catheterization data and angiocardiogram were From the Heart institute, Chaim Sheba Medical Center, Tel-Hashomer, Israel, and Sackler School of Medicine-University of Tel-Aviv, Tel-Aviv, Israel. Manuscript received May 11, 1983; revised manuscript received November 16, 1983, accepted November 23, 1983. Address for reprints: Henry N. Neufeld, MD, Chaim Sheba Medical Center, Tel Hashomer 52621, Israel.

(Am J Cardiol 1984;53:896-898)

Results The 37 patients included 26 males and 12 females, aged 1 to 66 years (mean 10.5). The pressure gradients ranged from 0 to 150 mm Hg across the subaortic obstruction. Two patients had associated congenital valvular aortic stenosis. Thirty-two patients had membranous DSS and 5 had fibromuscular DSS. Two patients had no pressure gradients, 4 had gradients of 5 to 25 mm Hg, 12 had gradients of 26 to 50 mm Hg, 16 had gradients of 51 to 100 mm Hg and 3 had gradients of 101 to 150 mm Hg.

March 15, 1984

THE AMERICAN JOURNAL OF CARDIOLOGY

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FIGURE 1. Two-dimensional echocardiogram of membranous discrete subaortic stenosis. Left, only the anterior insertion of the membrane is visible. Middle, both anterior and posterior insertions of the membrane are demonstrated. Right, the membrane is demonstrated as a continuous line. LA = left atrium; LV = left v&icle.

Detection of discrete subaortic stenosis: DSS was diagnosed by 2-D echo in 35 of the 37 cases. In 2 patients in whom angiocardiography revealed membranous DSS, 2-D echocardiography failed to demonstrate the lesion. In 2 of the 37 patients, membranous DSS was accurately diagnosed by echocardiography, whereas angiocardiography failed to demonstrate the membrane. These 2 patients had pressure gradients of 65 and 30 mm Hg, respectively. Diagnosis of the anatomic type of discrete subaortic stenosis: Membranous DSS was accurately diagnosed by echocardiography in 30 of 32 patients with the condition. In all 30, the anterior insertion of the membrane was demonstrated (Fig. 1A). In 13 posterior insertion was also demonstrable by tilt of the transducer, but was achieved at the expense of loss of the echo of the anterior insertion in 9 of the cases. In only 4 of the 13 patients were both insertions simultaneously demonstrated (Fig. 1s). In 3 other cases the membrane was demonstrated as a continuous line (Fig. 10. In 4 of the 5 cases of fibromuscular collar, both the anterior and posterior portions of the lesions were demonstrated (Fig. 2). The anterior insertion was demonstrated in 1 case only. This type of DSS was differentiated from membranous DSS by the w:idth of the obstructing tissue. Estimation of severity: In the membranous obstruction it was difficult to estimate the severity of the lesion. In most patients only 1 insertion of the membrane was visualized at ,atime and the accurate diameter of the lumen could not be measured. There was no correlation between measurements of the narrowest luminal diameter (either from the anterior or posterior insertion of the membrane) and the pressure gradients across the obstruction. In the patients in whom both insertions were simultaneously demonstrated, the peak pressure gradient ranged from 35 to 72 mm Hg. The thickness of the obstructive tissue did not correlate with the pressure gradient. The only direct echocardiographic sign of severe obstruction was simultaneous demonstration of the aortic valve. All 3 patients had pressure gradients ove:r 65 mm Hg. The number of patients with fibromuscular collar DSS was too small to make significant calcu:lations.

Discussion Two-dimensional echocardiographic findings have been reported in small series of DSS.1-3 Imaging from the left parasternal view demonstrated the subaortic lesion in about two-thirds of the patients.2,3 In other patients, the apical long-axis view revealed a subaortic membrane that was not demonstrated in the left parasternal long-axis view.2 In our series the lesion was demonstrated by the left parasternal long-axis view in 35 of our 37 patients. The other 2 apical views also failed to demonstrate the lesion. Our results indicate that careful examination from the parasternal long-axis view is highly sensitive in detecting DSS and may be used as the standard echocardiographic view in this disease. However, it appears reasonable to include the apical long-axis view in the examination of patients suspected to have DSS because this view enables a good direct visualization of LV outflow. DiSessa et al2 reported that membranous DSS produces linear echoes adjacent and parallel to the inter-

FIGURE 2. Two-dimensional echocardiogram in fibromuscular discrete subaortic stenosis. Wide masses of tissue are demonstrated in the anterior and posterior aspect of the left ventricular outflow tract.

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ventricular septum beneath the aortic valve. In several of their illustrations only the anterior aspect of the membrane is demonstrated. Weyman et al’ demonstrated both aspects of the obstructive lesion in 7 patients. However, 5 of their patients had fibromuscular collar and only 2 had membranous DSS. Khan et al” demonstrated the lesion in all 7 of their patients in whom 2-D echocardiography was performed. They did not specify if the whole lesion or only portions of it. were demonstrated. Our results indicate that 2-D echo is as effective as angiocardiography in demonstrating DSS. Although only a portion of the lesion is found, the experienced examiner should have no difficulty in diagnosis. In some cases the whole lesion may be demonstrated. Many pathologic and surgical reports of DSS describe it not as a circular membrane, but as a crescent. Therefore, it is not surprising that only 1 aspect of the obstructive lesion was demonstrated echocardiographically in most cases. No reports of estimation of the LV pressure or the pressure gradient across the obstruction by 2-D echocardiography were reported in DSS. Our results indicate that such an estimation can not be made from direct evaluation of the lesion by this technique. It may be argued, however, that such an estimation is essential. Until recently, criteria for surgery in DSS were similar to those of other forms of congenital aortic stenosis. In recent years, however, it has been recognized that in a high proportion of the patients, the anomaly is associated with severe complications such as aortic insufficiency and subacute bacterial endocarditis and possible development of myocardial abnormality. Moreover, it was reported that these complications may also develop in the presence of mild obstruction and even in the absence of pressure gradient altogether.%12 Cases of DSS with mild obstruction may progress within a short period and be present with severe stenosis.‘” Therefore,

the measurement of pressure gradient may lose its significance in evaluating patients with this anomaly scheduled for surgery. Because 2-D echo is, qualitatively, a near-optimal noninvasive diagnostic tool in DSS, some patients with definite 2-D echocardiographic diagnosis of DSS may not need cardiac catheterization. The diagnosis of 2 patients with 2-D echocardiographic and angiographic signs of DSS but without pressure gradients suggests the presence of DSS without stenosis. This type of stenosis has yet to be recognized as a separate entity. Two-dimensional echocardiography provides an excellent tool for screenihg and identifying such patients. References 1. Wyman 2. 3. 4.

5. 6. 7.

8. 9. IO. 11. 12. 13. 14.

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