763-5 Provocation of Latent Left Ventricular Outflow Tract Gradients with Amyl Nitrite and Exercise in Patients with Hypertrophic Cardiomyopathy

Abstract

In pts with hypertrophic cardiomyopathy (HCM) who have obstructive symptoms without significant resting outflow tract gradients, amyl nitrite may be used to provoke latent obstruction. However, the provocative effect of afterload reduction may not be comparable to a more physiologic method such as symptom-limited exercise stress testing. This study compared the ability of amyl nitrite and exercise testing to provoke outflow tract gradients in the same pts. Sixty-one pts (age 49 ± 17y, 43 male) with non-obstructive HCM (septal thickness 19 ± 5 mm, resting outflow tract gradient 15 ± 14 mmHg) underwent echocardiography at rest, following amyl nitrite inhalation, and after maximal exercise. Twenty-six pts (43%) remained without significant inducible gradients «50 mmHg) after either provocation, 17 (28%) became inducible after both stressors, 7 (11%) after exercise only, and 11 (18%) after amyl only. Although obstruction increased to similar levels after amyl nitrite (50 ± 38 mmHg) and after symptom-limited exercise (49 ± 39 mmHg), gradients induced by exercise and amyl correlated poorly (r = 0.54). Gradients were the same with both stressors in 15 patients (EO group), greater with exercise in 26 (EX group), and greater with amyl in 20 patients (AM group). Differences between amyl and exercise were unrelated to drug therapy. EQ(n = 15) EX(n = 26) AM (n = 20) p Age (ys) 37 ± 15 47 ± 17 61 ± 9 p < 0.001 EQ vs AM Septum (mm) 21 ± 5 20 ± 6 17 ± 3 p < 0.01 EQ vs AM Ex HR (% predicted) 73 ± 23 96 ± 9 82 ± 16 p < 0.001 EQ vs EX Exercise RPP (× 10 3 ) 21.4±8.2 33.9 ± 7.7 24.3 ± 85 p < 0.001 EQ vs EX Amyl gradient (mmHg) 40 ± 39 37 ± 33 76 ± 34 p < 0.001 EQ vs AM Ex gradient (mmHg) 40 ± 39 67 ± 42 33 ± 25 p < 0.03 EQ vs EX Over 50% of pts with non-obstructive HCM at rest have inducible gradients which may explain inlermittent symptoms. Measurement of gradients after AM and EX should be included in the assessment of pts with HCM with suspected latent outflow obstruction. Pts with a preponderant AM response are older and have less hypertrophy. EX is particularly indicated in younger patients without AM-induced gradients.