Myocardial blood flow in patients with hibernating myocardium

The debate on whether resting myocardial blood flow (MBF) to hibernating myocardium is reduced or not has attracted a lot of interest and has contributed to stimulate new research on heart failure in patients with coronary artery disease (CAD). Positron emission tomography with oxygen-15 labeled water (H₂¹⁵O) or nitrogen-13 labeled ammonia (¹³NH₃) has been used for the absolute quantification of regional MBF in human hibernating myocardium. When hibernating myocardium is properly identified, i.e. a dysfunctional segment subtended by a stenotic coronary artery that improves function upon reperfusion, the following conclusions can be reached based on the available literature: (a) in the majority of these studies resting MBF in hibernating myocardium is not different from either flow in remote tissue in the same patient or MBF in normal healthy volunteers; (b) a reduction in MBF of ∼20% compared to MBF in remote myocardium or age matched normal subjects has been demonstrated in a minority of truly hibernating segments; (c) hibernating myocardium is characterized by a severely impaired coronary flow reserve which improves after revascularization in parallel with contractile function. Thus, the pathophysiology of hibernation in humans is more complex than initially postulated. The recent evidence that repetitive ischemia in patients with coronary artery disease can be cumulative and lead to more severe and prolonged stunning, lends further support to the hypothesis that, at least initially, stunning and hibernation are two facets of the same coin.