What is myocardial stunning and hibernation?

What is myocardial stunning and hibernation?

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Myocardium is the technical term for heart muscle. Just as you can get stunned for some time if hit on the head, part of the heart muscle can also stop functioning following transient blockage of blood supply. This usually occurs following a heart attack after which the blocked blood vessel gets opened up spontaneously by natural means or by medical treatment. Medical treatment can be in the form clot dissolving medications or mechanical clot removal by a procedure called angioplasty.

After a variable period of time, the stunned heart muscle usually recovers full function. During the period of stunning, if a large part of heart muscle is involved, the person may have features of heart failure due to decreased pumping function. Myocardial stunning is the reason for heart failure which recovers within hours to days after successful restoration of blood supply to the affected heart muscle in a heart attack.

Hibernation on the other hand is persistent poor function of the region of heart muscle due to long standing reduced blood supply. It is reversible after restoration of blood supply 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 heart muscle is dormant, but viable and can recover function when the blood supply is restored. Hibernation and stunning are related in a way that repetitive episodes of stunning due to reduced blood supply can lead on to hibernation of heart muscle as a protective mechanism. Presence of hibernating myocardium can be detected by the improvement in contraction of the region on giving medications which enlarge the blood vessels of the heart.

Similar improvement can also be documented by using medications which increase the contractile force of the heart in a test known as dobutamine stress echocardiography. Echocardiography is ultrasound imaging of the heart. 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 restoration of blood supply. 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 proteins needed for contraction of heart muscle may have decreased during the long period of decreased blood supply. New protein synthesis after successful restoration of blood supply takes a longer period.