Relation of functional and morphological changes in mitochondria to myocardial contractile and relaxation reserves in asymptomatic to mildly symptomatic patients with hypertrophic cardiomyopathy

Abstract

Aims: To examine the relation between mitochondrial dysfunction and myocardial contractile and relaxation reserves in hypertrophic cardiomyopathy (HCM).

Methods and results: Thirty HCM patients (LVEF >or=60%) underwent biventricular cardiac catheterization analysis both at rest and during atrial pacing as well as myocardial (99m)Tc-sestamibi scintigraphy at rest to calculate washout rate. Endomyocardial biopsy specimens were obtained for quantitative mRNA analysis and electron microscopy. The HCM patients were divided into two groups-group A: normal force-frequency relation and a pressure half-time (T(1/2)) of <30 ms (n = 15); group B: abnormal force-frequency relation or T(1/2) of >or=30 ms (n = 15). The (99m)Tc-sestamibi washout rate was significantly correlated with T(1/2) for all patients (r = 0.74, P < 0.01) and was also significantly greater in group B (29.2 +/- 6.3%) than in group A (19.3 +/- 3.1%). The abundance of mRNAs for mitochondrial electron transport-related enzymes was significantly higher in group A than in group B. Mitochondria showed a greater variation in size and were more disorganized in group B than in group A.

Conclusion: Mitochondria showed functional impairment and morphological disorganization in the left ventricle of HCM patients without baseline systolic dysfunction. These mitochondrial changes were associated with impaired myocardial contractile and relaxation reserves.