Delayed untwisting: the mechanistic link between dynamic obstruction and exercise tolerance in patients with hypertrophic obstructive cardiomyopathy.
OBJECTIVE
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 (VO2max) 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 VO2max (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 VO2max (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 VO2max. After septal reduction, untwisting occurs earlier and leads to an improvement in LV filling and exercise tolerance.
Department of Cardiology, Methodist DeBakey Heart and Vascular Center, The Methodist Hospital, Houston, Texas 77030, USA.
Jianwen
J
Wang
John M
JM
Buergler
Kumuthavally
K
Veerasamy
Yelena P
YP
Ashton
Sherif F
SF
Nagueh
D006328:Cardiac Catheterization; D002306:Cardiac Volume / Q000502:physiology; D002312:Cardiomyopathy, Hypertrophic / Q000503:physiopathology* / Q000628:therapy*; D003971:Diastole / Q000502:physiology; D004452:Echocardiography; D000431:Ethanol / Q000008:administration & dosage; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006346:Heart Septum; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D014102:Torsion Abnormality / Q000000981:diagnostic imaging* / Q000503:physiopathology
D000431:Ethanol