From the Guidelines
Stunned myocardium and hibernating myocardium are distinct conditions of cardiac dysfunction with different underlying mechanisms and clinical implications, where stunned myocardium typically recovers spontaneously, whereas hibernating myocardium requires revascularization to restore function. The key difference between the two conditions lies in their pathophysiology and the duration of reduced blood flow. Stunned myocardium occurs after a brief period of ischemia followed by reperfusion, resulting in temporary cardiac dysfunction that resolves within hours to days as the heart cells recover from the temporary injury 1. In contrast, hibernating myocardium represents chronically dysfunctional heart tissue due to persistently reduced blood flow, where the heart cells have adapted by reducing their function to match the decreased oxygen supply, essentially entering a "hibernating" state to survive 1.
Clinical Implications
The distinction between stunned and hibernating myocardium is crucial for guiding treatment decisions, as hibernating myocardium can benefit from revascularization procedures, such as coronary artery bypass grafting or angioplasty, to restore blood flow and improve function 1. On the other hand, stunned myocardium will recover on its own with supportive care. Imaging techniques like dobutamine stress echocardiography, cardiac MRI, or nuclear perfusion studies can help identify these conditions and guide appropriate treatment decisions for patients with heart failure or after myocardial infarction.
Diagnostic Considerations
The assessment of myocardial viability is essential in distinguishing between stunned and hibernating myocardium, as it can help identify viable tissue that can benefit from revascularization 1. The concept of "contractile reserve" is also important, as it refers to the ability of dysfunctional but viable myocardium to increase contractility for a brief period of time during an inotropic stimulus 1. However, the assessment of contractile reserve is limited in the setting of ischemic heart failure.
Treatment Strategies
Revascularization procedures can improve left ventricular function in patients with hibernating myocardium, and the choice of revascularization strategy depends on various factors, including the extent of coronary artery disease and the patient's overall clinical condition 1. In contrast, stunned myocardium typically does not require revascularization, and supportive care is usually sufficient to allow for spontaneous recovery. The choice of treatment strategy should be guided by a thorough assessment of myocardial viability and the underlying pathophysiology of the condition.
From the Research
Difference between Stunned and Hibernating Myocardium
- The main difference between stunned and hibernating myocardium is the presence or absence of ongoing ischemia. In hibernating myocardium, ischemia is still ongoing, whereas in stunned myocardium, blood flow is fully or almost fully restored 2.
- Both stunned and hibernating myocardium are characterized by reversible contractile dysfunction, but they have different pathophysiological mechanisms. Stunned myocardium is caused by a brief period of ischemia followed by reperfusion, which leads to a burst of reactive oxygen species formation and alterations in excitation-contraction coupling 3.
- Hibernating myocardium, on the other hand, is an adaptation of contractile function to reduced blood flow, which allows the myocardium to survive during periods of ischemia. Chronic myocardial hibernation is characterized by severe morphological alterations and altered expression of metabolic and pro-survival proteins 3.
- The therapy for hibernating myocardium is to restore blood flow to the hypoperfused tissue, whereas stunned myocardium per se requires no therapy at all, since blood flow is normal and contractile function will recover spontaneously 2.
- Inotropic stimulation in combination with metabolic imaging may help to identify viable, dysfunctional myocardium and distinguish between hibernating and stunned myocardium 2.
- The prevalence of stunned and hibernating myocardium can vary, with one study finding that stunned myocardium is more prevalent than hibernation in patients with severe ischemic left ventricular dysfunction 4.
- The time-course and extent of improvement after revascularization can also differ between stunned and hibernating myocardium, with stunned myocardium showing more complete functional restoration 4.
- Clinical parameters such as LV wall motion, myocardial perfusion, and myocardial metabolism can be used to differentiate between stunned and hibernating myocardium 5.
- Noninvasive imaging techniques such as positron emission tomography and exercise 201thallium scintigraphy can be used to identify hibernating myocardium 6.