Mechanical efficiency in hypertrophic cardiomyopathy assessed by positron emission tomography with carbon 11 acetate

This study was performed to assess the relation between the regional work and oxidative metabolism in hypertrophic cardiomyopathy (HCM). By using carbon 11 acetate as a tracer of myocardial blood flow (%A(0)) and oxygen consumption (k value), 12 patients with HCM with asymmetric septal hypertrophy and 10 normal subjects were studied. Regional work rate (RWR) of the left ventricle was estimated by wall stress and wall thickness. %A(0) in hypertrophied septum was similar to that in nonhypertrophied free wall (92.6% +/- 2.8% vs 93.5% +/- 3.8%; p = not significant). However, oxygen consumption was significantly lower in hypertrophied septum than in nonhypertrophied free wall (0.043 +/- 0.011 vs 0.057 +/- 0.013 min(-1); p < 0.001). The k value in nonhypertrophied free wall was similar to the value observed in normal subjects (0.062 +/- 0.013). Average values for RWR in hypertrophied septum, nonhypertrophied free wall, and normal subjects were 0.26 +/- 0.07,0.62 +/- 0.02,and 1.98 +/- 0.15 J/cm3/ min, respectively. Furthermore, the analysis of covariance, in which the effect of RWR was removed as a covariate, revealed that the overall RWR-corrected k value was much larger in patients with HCM (0.109 vs 0.062, p < 0.0001) than expected from the decreased regional myocardial work, suggesting that there was a diffused inefficiency in oxygen consumption. We concluded, therefore, that the relative value of oxidative metabolism in patients with HCM is significantly higher than that of the normal subjects, suggesting the presence of reduced mechanical efficiency.