Contractile Dysfunction in Sarcomeric Hypertrophic Cardiomyopathy

• Contractile abnormalities are common and progressive in hypertrophic cardiomyopathy (HCM).
• Abnormal cardiomyocyte disarray results in reduced contractile stress.
• The development of hypertrophy helps normalize resting contractile forces.
• The normal or increased ejection fraction is explained by the presence of hypertrophy.
• The different phenotypes of HCM may be explained by the distribution of contractile stresses and strains.

The pathophysiological mechanisms underlying the clinical phenotype of sarcomeric hypertrophic cardiomyopathy are controversial. The development of cardiac hypertrophy in hypertension and aortic stenosis is usually described as a compensatory mechanism that normalizes wall stress. We suggest that an important abnormality in hypertrophic cardiomyopathy is reduced contractile stress (the force per unit area) generated by myocardial tissue secondary to abnormalities such as cardiomyocyte disarray. In turn, a progressive deterioration in contractile stress provokes worsening hypertrophy and disarray. A maintained or even exaggerated ejection fraction is explained by the increased end-diastolic wall thickness producing augmented thickening. We propose that the nature of the hemodynamic load in an individual with hypertrophic cardiomyopathy could determine its phenotype. Hypertensive patients with hypertrophic cardiomyopathy are more likely to develop exaggerated concentric hypertrophy; athletic individuals an asymmetric pattern; and inactive individuals a more apical hypertrophy. The development of a left ventricular outflow tract gradient and mitral regurgitation may be explained by differential regional strain resulting in mitral annular rotation.