Key result
Patients with mitochondrial disorders had similar rest (1.13 vs 0.85 ml/min/g) and adenosine-stimulated MBF to controls, though normalized rest MBF was elevated in a subset (P<0.05).
Why the study?
Does myocardial blood flow differ in patients with mitochondrial disorders compared to age-matched controls?
Case-Control (n=24)
Does myocardial blood flow differ in patients with mitochondrial disorders compared to age-matched controls?
Some patients with mitochondrial disorders and structurally normal hearts exhibit elevated basal myocardial blood flow when normalized to cardiac work, suggesting compensatory flow regulation due to inefficient aerobic metabolism.
Similar MBF does not support routine perfusion assessment in mitochondrial disorders; leaves open prognostic relevance of elevated normalized rest MBF in subsets.
OBJECTIVE: This study tests the hypothesis that elevated levels of rest myocardial blood flow (MBF), indicative of inefficient aerobic metabolism, will be present in some patients with mitochondrial disorders but structurally normal hearts. BACKGROUND: Regulation of MBF is a complex process closely linked to myocardial energy production. Aerobic metabolism in turn depends on normal mitochondrial function and so investigation of patients with mitochondrial disorders may provide important information regarding heritable mechanisms involved in regulation of myocardial flow. METHODS: Rest and adenosine-stimulated MBF was measured by the positron emission tomography (PET) 13NH(3) technique in nine patients with mitochondrial disorders and compared with 15 age-matched control participants. RESULTS: Basal heart rate (beats/min) and rate pressure product (mm Hg/min) were elevated in patients (76+/-13 and 9302+/-1910, mean+/-SD, respectively) compared with control participants (63+/-9 and 7411+/-1531, P<0.01 and P<0.05, respectively). However, rest and adenosine-stimulated MBF (ml/min per g) did not differ significantly between groups (patients, 1.13+/-0.52 and 4.17+/-0.84, respectively; control participants, 0.85+/-0.30 and 3.56+/-0.63, respectively). Normalization of rest MBF to rate pressure product, however, demonstrated three patients whose values exceeded that of all control participants (chi2=5.71, P<0.05, Fisher's exact test). CONCLUSIONS: Elevated basal MBF, in some patients with mitochondrial disorders but structurally normal hearts, suggests the level of basal flow is responsive to efficiency of aerobic metabolism, which closely reflects mitochondrial function. Mitochondrial heteroplasmy with relative sparing of myocardial mitochondria may account for normal basal flow in others with these disorders.
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Tawakol et al. (2003) conducted a case-control in Mitochondrial disorders (n=24). Mitochondrial disorders vs. Age-matched controls was evaluated on Rest myocardial blood flow (ml/min per g). Patients with mitochondrial disorders had similar rest (1.13 vs 0.85 ml/min/g) and adenosine-stimulated MBF to controls, though normalized rest MBF was elevated in a subset (P<0.05).
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