Provocation of latent left ventricular outflow tract gradients with amyl nitrite and exercise in hypertrophic cardiomyopathy

Amyl nitrite may be used to provoke latent gradients in patients with hypertrophic cardiomyopathy (HC) without significant resting outflow tract gradients, but afterload reduction may not be comparable to a more physiologic Stressor such as symptom-limited exercise testing. This study compared the ability of amyl nitrite and exercise testing to provoke outflow tract gradients in 57 patients (40 men and 17 women, mean age ± SD 49 ± 16 years) with HC (septal thickness 19 ± 5 mm, average resting gradient 13 ± 10 mm Hg) who underwent echocardiography at rest, after amyl nitrite inhalation, and after maximal exercise. No significant gradient (< 50 mm Hg) was induced after either provocation in 26 patients (46%); in 15 patients (26%), inducibility was achieved after both stressors, in 6 (11%) after exercise only, and in 10 (18%) after amyl only. Patients with amyl-induced gradients differed from those in whom gradients were noninducible on the basis of smaller outflow tract dimensions (p < 0.001), larger resting gradients (p < 0.001), and a greater prevalence of “septal bulge” morphology (p = 0.02). Those with exercise-induced gradients were able to attain a greater workload (p = 0.07), have larger resting gradients (p = 0.02), and also tended to have a septal bulge morphology (p ≤0.01). Although outflow tract obstruction increased to similar levels after amyl nitrite (49 ± 39 mm Hg) and symptom-limited exercise (47 ± 39 mm Hg), gradients induced by exercise and amyl correlated poorly (r = 0.54). Gradients were the same (within 10%) with both stressors in 14 patients (25%), greater with exercise in 25 (44%), and greater with amyl in 18 patients (32%). Measurement of outflow tract gradients after exercise should be included in the assessment of patients with HC with suspected latent outflow obstruction, particularly in younger patients without amyl-induced outflow tract gradients.