Delayed Untwisting: The Mechanistic Link Between Dynamic Obstruction and Exercise Tolerance in Patients With Hypertrophic Obstructive Cardiomyopathy

Objectives We sought to determine the mechanisms linking dynamic obstruction and exercise tolerance in patients with hypertrophic obstructive cardiomyopathy (HOCM). Background Patients with HOCM have reduced exercise tolerance. However, the association between dynamic obstruction and peak oxygen consumption (V o 2max ) is weak. Methods We enrolled 25 patients with HOCM, 20 with hypertrophic cardiomyopathy (HCM), and 20 normal control patients. Two-dimensional, Doppler, strain, and left ventricular (LV) twist mechanics by speckle tracking echocardiography were obtained. The 25 HOCM patients had left heart catheterization, and 16 were re-examined after septal reduction. Results Deformation measurements were the lowest in HOCM patients and increased (p o 2max (r = −0.75, all p o 2max (r = 0.74, both p Conclusions Dynamic obstruction leads to delayed untwisting in HOCM, which accounts well for the increased LV filling pressures, the reduced LV volumes, and V o 2max . After septal reduction, untwisting occurs earlier and leads to an improvement in LV filling and exercise tolerance.