Myocardial Stunning and Hibernation

Coronary artery disease can result in acute and chronic myocardial perfusion deficits. This hypoperfusion can result in impaired myocardial contractility and decreased left ventricular function. Restoration of myocardial function is sometimes achievable by percutaneous coronary intervention or coronary artery bypass grafting. Identification of viable tissue that can be successfully revascularized is an area of active research. "Stunned" myocardium is myocardium that suffers transient reversible myocardial contractile dysfunction induced by acute ischemia wherein the blood supply is almost completely restored on reperfusion and suffers no metabolic deterioration. The term was coined originally to describe a laboratory situation in canine experiments, where total occlusion of the coronary artery for 5-15 minutes resulted in abnormalities in LV wall motion that persisted for several days despite prompt reperfusion, demonstrating the phenomenon of "stunning." "Hibernating" myocardium is also used to indicate chronic myocardial contractile dysfunction due to ischemia, where there is reduced coronary blood flow at rest and increased myocardial demand will result in impaired contractility. It is, in effect, ischemic myocardium supplied by a narrowed coronary artery in which ischemic cells remain viable, but contraction is chronically depressed. Here, the contractile function of the involved myocardium can be partially or even totally restored by improving the coronary blood flow or reducing the oxygen demand of the myocardium. Any patient with chronic LV dysfunction, which encompasses a wide clinical spectrum ranging from regional dysfunction to ischemic cardiomyopathy could be having hibernating myocardium. Many of these patients could be having pre-existing collateral channels and newly formed vessels in the coronary circulation which maintain the contractility and function of the LV. Hence, the degree of LV dysfunction may not always be directly proportional to the severity of the CAD. The fact that hibernating myocardium is viable establishes that LV function could have partial or complete restoration with successful, timely revascularisation. A wide range of diagnostic techniques like dobutamine echocardiography, PET scanning, radionuclide myocardial perfusion imaging (rMPI), and cardiovascular magnetic resonance (CMR) imaging can determine the presence of myocardial tissue that contracts if stimulated or existence of metabolic activity in that dysfunctional myocardial segment. Therefore, distinguishing between myocardium with potential for improvement in contractility and that with irreversible damage which does not react after revascularization is vital. Both stunned and hibernating myocardium can retain their inotropic capacity with reperfusion.