Differentiation of supravalvar aortic stenosis from valvular and subvalvular

Differentiation of supravalvar aortic stenosis from valvular and subvalvular

Differentiation of supravalvar aortic stenosis from valvular and subvalvular: Supravalvar aortic stenosis is often part of Williams syndrome, with associated elfin facies, hypercalcemia and often learning disability. Various points for differentiation of supravalvar AS from other varieties can be considered under the following headings:

Murmur in different types of aortic stenosis

Murmur of subvalvular AS is unlikely to radiate to the carotids. Murmur of supravalvar aortic stenosis may radiate more to the right carotid. Murmur of valvular aortic stenosis radiates to both carotids.

Ejection click

Ejection click is in favor valvular aortic stenosis. Ejection click in valvular aortic stenosis is non-phasic or constant, meaning that it does not vary with respiration.

Associated aortic regurgitation

Supravalvar AS is unlikely to be associated with aortic regurgitation, while it can occur in valvular and subvalvular variety. In fact aortic regurgitation may be seen in almost half of those with subvalvular membranous aortic stenosis. Aortic regurgitation in subvalvular aortic stenosis is due to damage to the aortic cusps because of the jet from the subaortic narrowing [1]. It may be noted that discrete subvalvular membranous aortic stenosis is different from dynamic subaortic obstruction seen in hypertrophic obstructive cardiomyopathy.

Pulse asymmetry or anisosphygmia

Anisosphygmia with right brachial pulse more prominent than left, may occur in supravalvar aortic stenosis, due to the direction of the jet towards the right brachiocephalic artery. There may be a corresponding difference of blood pressure more than 10 mm Hg between the two upper limbs. Anisosphygmia is not a feature of subvalvular or valvular aortic stenosis.

Anisosphygmia in supravalvular aortic stenosis is due to Coanda effect [2]. Coanda effect is the tendency of a jet stream to adhere to a wall. French JW et al evaluated 56 patients with supravalvular aortic stenosis. 48 patients had unequal blood pressure in upper extremities. Mean difference in pressure was 18 mm Hg between the upper limbs. In valvular aortic stenosis the velocity of the jet is quickly dissipated beyond the stenotic orifice. In supravalvular aortic stenosis, smooth narrowing causes the jet to adhere to the ascending aortic wall. The high velocity stream along the right aortic wall causes a disproportionately high blood pressure in the right arm in most patients with supravalvular aortic stenosis. In that study, 40 patients had right upper limb pressure greater than left while 8 patients had left upper limb pressure greater than right. The mean difference in pressure between the upper extremities in valvar aortic stenosis was only 3.5 mm Hg.

References

1. Sharma BD, Mittal S, Kasliwal RR, Trehan N, Kohli V. Discrete subvalvular aortic stenosis. J Assoc Physicians India. 2000 Nov;48(11):1103-6.
2. French JW, Guntheroth WG. An explanation of asymmetric upper extremity blood pressures in supravalvular aortic stenosis: the Coanda effect. Circulation. 1970 Jul;42(1):31-6.