Abstract 4366: Relation of Functional and Morphological Changes in Mitochondria to Myocardial Contractile and Relaxation Reserves in Asymptomatic to Mildly Symptomatic Patients with Hypertrophic Cardiomyopathy
Impairment of myocardial relaxation reserve and subsequent impairment of contractile reserve constitute a primary manifestation of hypertrophic cardiomyopathy (HCM). Although these reserves reflect energy-consuming processes, the relation between their impairment and mitochondrial function in HCM has remained unclear. Thirty HCM patients underwent biventricular cardiac catheterization analysis both at rest and during atrial pacing as well as myocardial 99mTc-sestamibi (MIBI) scintigraphy at rest. MIBI washout rate (WR) was calculated from initial and delayed left ventricular (LV) planar images. Endomyocardial biopsy specimens were obtained for quantitative mRNA analysis and electron microscopic observation. The HCM patients were divided into two groups: Group A consisted of 15 patients showing a normal force-frequency relation (FFR) and pressure half-time (T1/2) of <30 ms, whereas group B consisted of 15 patients showing an abnormal FFR or T1/2 of ≥30 ms. The MIBI WR was significantly correlated with T1/2 at the peak pacing rate for all patients (r = 0.74, P <0.01). It 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. 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.