Background:
One-third of HCM patients without left ventricular outflow tract obstruction under resting conditions have the propensity to develop an outflow gradient with physiologic exercise. However, the natural history and management implications of exercise-induced (i.e., provocable) obstruction is unresolved.
Methods:
We prospectively studied 533 consecutive HCM patients without outflow obstruction at rest (<30mmHg) who underwent a symptom limiting stress (exercise) echocardiogram to assess development of outflow obstruction following physiologic provocation and followed for 6.5 ± 2.0 years. Of the 533 patients, obstruction ≥ 30 mmHg was present following exercise in 262 patients (49%; provocable obstruction), and was absent both at rest and with exercise in 271 (51%; nonobstructive).
Results:
Over the follow-up period, 43 out of 220 (20%) HCM patients with provocable obstruction and baseline NYHA class I/II symptoms developed progressive limiting heart failure symptoms to class III/IV, compared to 24 of 249 (10%) nonobstructive patients. Rate of heart failure progression was significantly greater in patients with provocable obstruction vs. nonobstructive patients (3.1%/year vs. 1.5%/year; RR=2.0, 95% CI of 1.3-3.2; p=0.003). However, the vast majority of patients with provocable obstruction who developed advanced heart failure symptoms achieved substantial improvement in symptoms to class I / II following relief of obstruction with invasive septal reduction therapy (n=30/32; 94%). In comparison, the majority of nonobstructive patients who developed advanced heart failure remained in class III/IV (16/24;67%), including 10 (42%) currently listed for heart transplant.
Conclusions:
Stress (exercise) echocardiogram identifies physiological provocable outflow tract obstruction in HCM, and is a predictor of future risk for progressive heart failure (3.1%/year), in patients who become candidates for invasive septal reduction therapy. Therefore, exercise echocardiography should be considered in all HCM patients without obstruction under resting conditions.
Heart failure—emerging roles for the mitochondrial pyruvate carrier
