What is myocardial hibernation?

What is myocardial hibernation?

Abstract: Myocardial hibernation is reversible left ventricular dysfunction which occurs in a chronically ischemic myocardium, which improves after revascularization.

Hibernating myocardium is a chronically ischemic myocardium, the function of which improves after successful revascularization. Short of revascularization, presence of hibernating myocardium can be documented by improvement in regional / global function of the left ventricle in response to nitrates, inotropes and postextrasystolic potentiation.¹ Nitrates delivered sublingually or as an infusion during a wall motion study either by echocardiography or by nuclear perfusion imaging can document improvement in wall motion due to improvement in the circulation. Inotropic stimulation during echocardiography can also document similar improvement in wall motion during low dose stimulation. Postextrasystolic potentiation is a simpler method as it does not involve any additional measures, only just longer period of imaging. The beat after a ventricular premature beat has natural augmentation of inotropic state of the myocardium due to increased availability of intracellular calcium. The ectopic beat though it releases calcium does not utilize it fully. Hence part of it is available during the postextrasystolic beat in addition to the regular amount of calcium being released during the index beat. The extra calcium invokes an inotropic response in the hibernating myocardium which manifests as an improvement in wall motion during echocardiography or perfusion imaging.

Adaptive response for survival of myocytes

Myocardial hibernation can be considered as an adaptive response of the myocardium to chronic ischemia to improve survival of the myocytes. As the chronic ischemia progresses, there seems to be a perfusion-contraction mismatch which occurs to preserve viability. A non contracting myocardium needs only less amount of aerobic metabolism to maintain viability.²

Documentation of viability in hibernating myocardium

Dobutamine stress echocardiography, myocardial contrast echocardiography, single photon emission computed tomography and positron emission tomography are the important modalities of assessing myocardial viability and thereby establishing the possibility of hibernating myocardium in the setting of chronic ischemia.

Recovery from hibernation

Myocardial contractility recovers significantly in hibernating myocardium after successful revascularization. But the period needed for recovery varies depending on the duration and severity of ischemia which induced the hibernation. In chronic severe hypoperfusion it may take several weeks for the completion of recovery process.³ This is because the amount of contractile proteins may have decreased due to the catabolic wasting which occurred during the chronic ischemia. New protein synthesis after successful revascularization takes a longer period.

References

1. Conti CR. The stunned and hibernating myocardium: a brief review. Clin Cardiol. 1991 Sep;14(9):708-12.
2. Ferrari R, Cargnoni A, Bernocchi P, Pasini E, Curello S, Ceconi C, Ruigrok TJ. Metabolic adaptation during a sequence of no-flow and low-flow ischemia. A possible trigger for hibernation. Circulation. 1996 Nov 15;94(10):2587-96.
3. Hamm CW. Recovery of myocardial function in the hibernating heart. Cardiovasc Drugs Ther. 1992 Jun;6(3):281-5.