Myocardial blood flow and oxygen consumption in patients with Friedreichʼs ataxia prior to the onset of cardiomyopathy

OBJECTIVESWe tested the hypothesis, in patients with Friedreichʼs ataxia and no overt structural heart disease, that impairment of cardiac oxidative metabolism may be compensated for either by increased rest myocardial blood flow or more efficient oxygen consumption in performance of external work. BACKGROUNDFriedreichʼs ataxia is characterized by a mutant frataxin gene, which causes mitochondrial iron overload and impaired energy production. Further, it is frequently associated with cardiomyopathy. Studies using magnetic resonance spectroscopy, however, suggest impaired cardiac energetics even in the absence of structural heart disease. METHODSPositron emission tomography measured rest myocardial blood flow (N-13-ammonia method) and myocardial oxygen consumption (11-C-acetate, Kmono) in Friedreichʼs ataxia patients (n=8; 31±5 years, mean±SD, four women) and healthy controls (n=8; 30±7 years, five women) matched for stroke work index and age. Stroke work index and power were determined by electrocardiogram gated positron emission tomography N-13-ammonia using modified Simpsonʼs rule to compute left ventricular volumes. RESULTSNeither stroke work index nor rest myocardial blood flow differed significantly between the groups. Although myocardial oxygen consumption was lower in Friedreichʼs ataxia (P