SKELETAL-MUSCLE MYOSIN HEAVY-CHAINS IN HEART-FAILURE - CORRELATION BETWEEN MAGNITUDE OF THE ISOZYME SHIFT, EXERCISE CAPACITY, AND GAS-EXCHANGE MEASUREMENTS

Background Patients with congestive heart failure (CHF) have a reduced exercise capacity because of the early appearance of fatigue and dysp nea. Qualitative changes in the skeletal muscle composition and metabo lism can be responsible for the origin of symptoms Methods We correlat ed the myosin heavy chain (MHC) composition of the gastrocnemius in 20 patients with different degrees of CHF to NYHA class, diuretic consum ption, echocardiographic parameters, and expiratory gases measured dur ing cardiopulmonary exercise testing. MHC composition was determined e lectrophoretically in skeletal muscle needle microbiopsies and the per cent distribution was calculated by densitometry. Maximal cardiopulmon ary exercise testing was performed on a treadmill with a modified Naug hton protocol. A capnograph was used.Results There was no correlation between election fraction, left ventricular end systolic diameter, lef t ventricular end diastolic diameter, and MHC composition. We found a significant positive correlation between the percentage of MHC1 (slow aerobic isoform) and NYHA class (r(2) = 0.62, p < 0.0001), peak VO2 (r (2) = 0.5, p < 0.0004), ventilatory threshold (VT) (r(2) = 0.33, p = 0 .008) and O-2 pulse (peak VO2/HR) (r(2) = 0.40, p = 0.003). There was a negative correlation between both MHC2a (Fast oxidative) and MHC2b ( fast glycolytic) with peak VO2 (r(2) = 0.38, p = 0.004 and r(2) = 0.37 , p = 0.004, respectively), VT (r(2) = 0.2, p = 0.046 and r(2) = 0.34, p = 0.007, respectively), and O-2 pulse (peek VO2/HR) (r(2) = 0.39, p = 0.003 and r(2) = 0.23, p = 0.03). NYHA class was also correlated po sitively with MHC2a and MHC2b (r(2) = 0.46, p = 0.001 and r(2) = 0.41, p < 0.006, respectively) and negatively with the same clinical and fu nctional parameters. Conclusions The correlation between the magnitude of the MHC shift from the slow aerobic to the fast glycolytic and fas t oxidative with both functional and objective measurements of exercis e capacity (peak VO2, VT, O-2 pulse) seem to suggest that changes in s keletal muscle composition may play a determining role in exercise tol erance in patients with CHF.