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CLINICAL RESEARCH: LEFT VENTRICULAR DEFORMATION

Delayed Untwisting

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

Methodist DeBakey Heart and Vascular Center, The Methodist Hospital, Houston, Texas

Manuscript received March 17, 2009; revised manuscript received May 14, 2009, accepted May 25, 2009.

^_* Reprint requests and correspondence: Dr. Sherif F. Nagueh, Department of Cardiology, The Methodist DeBakey Heart and Vascular Center, 6550 Fannin Street, Suite 677, Houston, Texas, 77030 (Email: snagueh{at}tmhs.org).

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 (VO _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 < 0.05) after septal reduction. Twist and untwisting rate were not different between patients with HCM and control patients, but untwisting was significantly delayed in HCM patients and longest in HOCM patients. The delay related well with LV end-diastolic pressure (r = 0.76) and volume (r = –0.73), and VO _2max (r = –0.75, all p < 0.01). After septal reduction, untwisting occurred earlier and accounted for the increase in end-diastolic volume (r = 0.65), and VO _2max (r = 0.74, both p < 0.05).

Conclusions: Dynamic obstruction leads to delayed untwisting in HOCM, which accounts well for the increased LV filling pressures, the reduced LV volumes, and VO _2max. After septal reduction, untwisting occurs earlier and leads to an improvement in LV filling and exercise tolerance.

Key Words: diastole • hypertrophic cardiomyopathy • mechanics • exercise

Abbreviations and Acronyms   E/e' = ratio of mitral peak E velocity to annular early diastolic velocity   HCM = hypertrophic cardiomyopathy   HOCM = hypertrophic obstructive cardiomyopathy   LA = left atrial   LV = left ventricular   LVEF = left ventricular ejection fraction   LVOT = left ventricular outflow tract   PA = pulmonary artery   VO 2max = peak oxygen consumption

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