Hibernating myocardium is myocardial tissue that has reduced contractility due to poor perfusion, but remains viable. It is important as hibernating myocardium can recover normal contractility with revascularisation.
Hibernating myocardium is most commonly seen in the setting of chronic ischaemia when myocardial cells adapt to longstanding poor perfusion by entering a state of low metabolic activity. This includes loss of myocardial contractility in the tissue affected. This can result from progression of chronic coronary atherosclerosis or as a result of an acute ischemic event. In the later it is analagous to stunned myocardium.
On stress and rest, a perfusion defect will be present (e.g. on both stress-rest images using Tc-99m-sestamibi or Tc-99-m-tetrofosmin SPECT or Rb-82 or N-13 ammonia PET/CT). However, due to retained viability, the tissue will demonstrate uptake of FDG, often more intense than the normal myocardium, and will also demonstrate redistribution of Tl-201 upon delayed imaging, which will discriminate between infarction and hibernating myocardium.
Dobutamine stress MRI has become an established method of assessing myocardial viability. Hibernating mycoardium is suggested by poor resting wall motion in the affected region which improves with dobutamine stress. There is also absence of delayed enhancement post-contrast, the presence of which indicates infarction.
- matched rest and stress perfusion abnormality which does not normalize upon FDG-PET/CT. Hibernating myocardium represents a viable target for revascularization and should be distinguished from infarcted myocardium, where an attempt to revascularize would be futile.
- myocardial ischaemia: rest images will demonstrate reversal of stress perfusion abnormality.
- differentiation from stunned myocardium can be difficult, but can sometimes be made on the basis of maintained, or nearly maintained, perfusion with a wall motion abnormality (hibernating myocardium will have abnormal perfusion and a wall motion abnormality).
- hibernating myocardium typically represents a chronic process whereas stunned myocardium is typically related to an acute infarction or ischaemic insult resulting in altered wall motion.
- repetitive stunning may evolve into hibernating myocardium.