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The effects of amyl nitrite inhalation were observed in 12 patients with aortic valve stenosis and five patients with muscular subaortic stenosis during left heart catheterization. In aortic valve stenosis the left ventricular systolic pressure always fell, although less than the brachial arterial pressure, and the transaortic systolic pressure gradient rose by an average of 25% due to the increase in left ventricular ejection rate. In muscular subaortic stenosis, the left ventricular pressure always remained the same or rose despite a marked fall in brachial arterial pressure, and the average increase in transaortic systolic pressure gradient was more than fourfold. This effect was associated with a significant increase in the degree of outflow tract obstruction. The increase in outflow tract obstruction is thought to be due to a decrease in left ventricular volume, causing the hypertrophied walls of the left ventricle to become more closely apposed. We believe that inhalation of amyl nitrite is superior to infusion of isoproterenol as a provocative test for muscular subaortic stenosis during cardiac catheterization and is probably the most potent stimulus available for this purpose.
Hancock et al. (Tue,) studied this question.