Echocardiographic observations in a case of discrete membranous subaortic stenosis with a stenotic bicuspid aortic valve--a pre- and post-operative study (a case report).
Amongst the various congenital cardiac disorders that can be diagnosed echocardiographically, subvalvular aortic stenosis forms an important group. We have encountered three cases of discrete membranous subaortic stenosis at the Bombay Hospital and of these one has been studied in detail echocardiographically. We are reporting herewith this case which had, in addition, a congenital Stenotic bicuspid aortic valve. We have so far not come across an echocardiographic report of this combination.
A 21 year old girl was known to have a `heart murmur' since the age of 5 for which surgery was advised in her childhood. For the last 5 years she complained of grade II exertional dyspnoea, palpitations and occasional blackouts after exertion, lasting for 1 to 2 minutes. There had been no loss of consciousness during the attack. She neither had congestive cardiac failure nor rheumatic fever in the past.
On physical examination, she was found to be well built and nourished. She had a regular pulse of 90/minute with a delayed upstroke and low volume. Blood pressure was recorded thus, RUL 124/90 mm Hg, LUL 112/90 mm Hg, RLL 110/80 mm Hg and LLL 116/90 mm Hg. No oedema of feet, clubbing or cyanosis was present. Her jugular venous pulse was unremarkable. Her apex impulse was in the 5th left intercostal space in the midclavicular line and was forceful with a single continuous thrust. A systolic thrill was palpable in the 4th left intercostal space. Auscultation revealed normal heart sounds with no click. A long harsh ejection systolic murmur of grade 4/6 was heard best at the 3rd and 4th left intercostal spaces in the parasternal region, conducted to apex. it diminished with isometric exercise and was better heard in expiration. Her lungs were clear; the liver was not palpable.
Her chest X-ray showed a cardiothoracic ratio of 0.5 with prominent left ventricular contour. The aortic shadow was normal. No aortic calcification or pulmonary congestion was seen. The electrocardiograms showed a progressive left ventricular hypertrophy with strain which developed over the last 10 years.
The echocardiogram was recorded in the supine position with a SKI echocardiograph, EKO line 20, with an universal transducer mode Cl, 01684 ZH, on polaroid films. It showed a normal mitral valve. The aortic root dimensions at the onset of systole were normal (1.6 cm), [Fig. 1]. In systole, both the aortic cusps were faintly seen opening incompletely with no midsystolic closure or fluttering. The diastolic portion showed a prominent closure line which was clearly eccentric. Eccentricity index was 1.6 suggestive of bicuspid aortic valve. A thin bright linear echo was recorded in the region of the left ventricular outflow tract [Fig. 2]. It started just above the level of the mitral valve and extended to just below the aorta. It moved anteriorly in systole and posteriorly in diastole. The minimum left ventricular outflow tract dimensions were normal (3.6 cm). [Fig. 3]
Surgery wag and undertaken under cardiopulmonary bypass, where a stenotic bicuspid aortic valve was detected. The valve was not calcified. The pressure gradient across the left ventricular outflow tract was 140 mm Hg. A pliable fibrous membrane was found situated 5 mm below the aortic valve and encircling the left ventricular outflow tract with an opening of 0.5 cm. The aortic valve cusps were separated, sand membrane incised as completely as possible. A gredient of 50 mm Hg was recorded across the left ventricular outflow tract postoperatively. The significant post-operative clinical findings were reduction of blood pressure in RUM: 120/80 mm Hg, in LUL: 116/80 mm Hg and in legs: 110/80 mm Hg. An attenuation of systolic murmur also occurred. No aortic diastolic murmur was detected.
The echogram recorded 7 days later revealed a normal mitral valve and remnants of the subaortic membrane in the form of persistence of the linear echo in the region of the left ventricular outflow tract[Fig. 4]. The aortic cusps were seen opening fully without a midsystolic closure or flutter. The closure line was central, the eccentricity index was 1.1 and within normal limits [Fig. 5].
There are several forms of obstruction to the left ventricular outflow and discrete membranous subaortic stenosis constitutes an important member of the group.,  In the membranous type, a thin fibrous membrane encircles the left ventricular outflow tract below the aortic valve, leaving an opening with a diameter from 5 to 15 mm.
The clinical diagnosis of discrete membranous subaortic stenosis is suspected when the systolic murmur of aortic stenosis is heard lower than at the usual site.,  It is also well known that the membrane as in our case may not be demonstrated on angiography.,  However, the echocardiographic findings when present are conclusive. There are two important echo signs of this condition; the first is the presence of a linear structure in the left ventricular outflow tract and second important sign is an early, mid-systolic closure with fluttering of the aortic cusps.
Ultan et al were the first to report the findings of a membranous subaortic stenosis; but, according to Popp et al, their structure resembles a mitral annulus, both in position and in movement. Popp et al are of the opinion that the diagnosis of discrete membranous subaortic stenosis requires the demonstration of three separate structures as we have shown in our cases [Fig. 2] i.e. mitral annulus, interventricular septum and an additional linear echo in the left ventricular outflow tract. However, Popp et al did not have surgical proof of this membrane in their case. Laurenceau et al demonstrated a linear echo in the left ventricular outflow tract in 4 of their 7 patients. In 3 patients, the echo persisted post-operatively; this is understandable as most surgeons do not remove the membrane completely for fear of damaging the AV conduction system. Lundstrom et al had similar findings; in our case also, the echo persisted after surgery [Fig. 4]
The other sign of discrete subaortic stenosis is early or mid-systolic closure of the aortic cusps associated with systolic fluttering. This has been first described by Davis et al. The diagnostic importance of this sign has been stressed by Krajcer et alb in their report of 9 cases and also by Nanda and Gramiac, in more than 20 patients. It is interesting to note that no author has described the existence of both the signs in the same patient.
We have not been able to demonstrate early mid-systolic closure in our case though it was carefully looked for. According to Nanda and Gramiac, aortic preclosure is due to the Bernoulli effect i.e. fall in the lateral pressure beyond the obstruction in the stenosed outflow tract, In our case, though the pressure gradient at the valvular level was 142 mm Hg pre-operatively, and 50 mm Hg postoperatively, there was no early systolic closure. We feel that the absence of narrowing of the left ventricular outflow tract may be responsible for the absence of aortic preclosure.
Aortic preclosure can be obtained in a non-stenotic bicuspid valve with a discrete subaortic membrane if the valve is not damaged, or calcified. If however, the bicuspid aortic valve is severely stenosed and calcified, the systolic opening of the cusps is limited and aortic preclosure may not be obtained in this combination. Absence of stenosis of the left ventricular outflow tract may also play a role as discussed above.
The signs of bicuspid aortic valve are clearly demonstrated in our case, e.g., eccentric diastolic closure line and increased eccentricity index. [Fig. 1]. The latter came to near normal after surgery. [Fig. 5]. Our case did not show multiple echoes in diastole as reported by Nanda et al because their presence depends on the valve morphology and the accommodation of the redundant cuspal tissue in diastole. Its demonstration also depends on the beam orientation and is only present in 50% of cases.
Hess et al were the first to describe a combination of descrete membranous subaortic stenosis with acquired valvular disease but ours is the first case where the combination of a discrete subaortic membranous stenosis and a congenital bicuspid stenotic aortic valve had been demonstrated echo cardiographically in the same patient. We propose the following explanation for the absence of aortic preclosure occurring in our case.
In conclusion the demonstration of a linear echo in the left ventricular outflow tract is a pathognomonic sign of discrete membranous subaortic stenosis while aortic preclosure is not so specific as it has been reported in other conditions as well.
We wish to thank Prof, Nanda from the University of Rochester (N.Y.) for his useful comments.