What is myocardial stunning and hibernation? Cardiology Basics

What is myocardial stunning and hibernation? Cardiology Basics

Just as you can get stunned for some time if hit on the head, part of the myocardium can also stop functioning following transient coronary obstruction. This usually occurs following a myocardial infarction after which the occluded coronary artery gets opened up spontaneously or by thrombolytic therapy or primary angioplasty.

After a variable period of time, the stunned myocardium usually recovers full function. During the period of stunning, if a large part of myocardium is involved, the person may have features of heart failure due to decreased left ventricular systolic function. Myocardial stunning is the reason for heart failure which recovers within hours to days after successful reperfusion after myocardial infarction.

Hibernation on the other hand is persistent contractile dysfunction of myocardium in response to chronic ischemia. It is reversible on revascularization by either coronary artery bypass surgery or coronary angioplasty. The term hibernation comes from the behaviour of animals which hibernate in winter like the bear, hedgehog, and some bats. In them it is a state of minimal metabolic activity with body temperatures dropping near to ambient temperature. They are able to survive in adverse conditions without food intake by hibernation.

Similarly, hibernating myocardium is dormant, but viable and can recover function after revascularization. Hibernation and stunning are related in a way that repetitive episodes of stunning due to ischemia can lead on to hibernation of myocardium as a protective mechanism. Presence of hibernating myocardium can be detected by the improvement in contraction of the region on giving nitrates.

Similar improvement can also be documented by using low dose dobutamine infusion during dobutamine stress echocardiography. Myocardial contrast echocardiography, single photon emission computed tomography and positron emission tomography are the more advanced and much more expensive tests for detecting hibernating myocardium.

Myocardial contractility recovers significantly in hibernating myocardium after successful revascularization. But the period needed for recovery varies depending on the duration and severity of disease which induced the hibernation. In long standing severe cases, it may take several weeks for the completion of recovery process. This is because the amount of contractile proteins in the myocardium may have decreased during the long period of ischemia. New protein synthesis after successful revascularization takes a longer period.