Resting myocardial blood flow in patients with hibernating myocardium quantified by positron emission tomography

Conclusion

The results of the PET studies reported in Table 1 and Table 2 demonstrate that on average resting myocardial blood flow in hibernating segments is within the range of flows measured in normal subjects and on average is only slightly reduced (approximately by 15–20%) compared with normal remote regions in the same patients. Direct measurements in conscious animals have demonstrated that a 20% reduction in transmural flow (which in dogs involves no decrease in subepicardial flow) accounts for less than a 40% reduction in function (5) which is far less severe than the functional impairment seen in most patients.

Therefore, some other phenomenon must account for the severe ventricular dysfunction observed in most patients with hibernating myocardium. In patients with coronary artery disease, coronary flow reserve decreases as the degree of stenosis is increased and is abolished for stenoses equal to 80% or more of the luminal diameter. Under these circumstances, any increase in cardiac workload above baseline conditions cannot be met by an adequate increase in myocardial blood flow, leading to myocardial ischemia. In their pioneering study, Vanoverschelde et al. (12) have demonstrated that in patients with proximal occlusion of the left anterior descending (LAD) coronary artery and normal resting myocardial blood flow, the only discriminant between those with normal wall motion and those with severe dysfunction in the territory subtended by the LAD was the inability to increase flow following dipyridamole administration in the latter group They conclude (12) that “in these patients, impaired function probably results from repetitive episodes of ischemia with a persistent stunning effect ...”.