From the Guidelines
Stunned myocardium is a temporary and reversible condition of the heart muscle that occurs after a period of reduced blood flow, characterized by impaired function without permanent damage, and typically recovers within 2 weeks of reperfusion. This condition is often seen after events such as a heart attack, cardiac surgery, or unstable angina, where the heart tissue experiences a brief interruption in its oxygen supply 1. The affected heart muscle doesn't immediately recover its normal contractile function despite the absence of permanent damage, and this delayed recovery can last hours to days, sometimes even weeks, depending on the severity and duration of the initial ischemic insult.
Some key points to consider about stunned myocardium include:
- It is a temporary dysfunction of the heart muscle that occurs after a period of reduced blood flow 1
- The condition typically follows events like a heart attack, cardiac surgery, or unstable angina 1
- Once blood flow is restored, the affected heart muscle doesn't immediately recover its normal contractile function despite the absence of permanent damage 1
- The underlying mechanism involves calcium handling abnormalities within cardiac cells, oxidative stress from free radicals generated during reperfusion, and disruption of cellular structures 1
- Unlike permanently damaged heart tissue (infarction), stunned myocardium will eventually recover completely with supportive care 1
Treatment of stunned myocardium focuses on maintaining adequate blood pressure and cardiac output with medications like inotropes if needed, while allowing time for the heart muscle to naturally recover its function 1. It is essential to differentiate stunned myocardium from hibernating myocardium, which involves chronic rather than acute dysfunction due to persistently reduced blood flow 1. Diagnostic techniques such as conventional myocardial perfusion scintigraphy or stress echocardiography can help detect myocardial viability and guide treatment decisions 1.
From the Research
Definition of Stunned Myocardium
- Stunned myocardium is viable myocardium salvaged by coronary reperfusion that exhibits prolonged postischemic dysfunction after reperfusion 2.
- It is characterized by temporary depression of myocardial contractility, causing symptoms similar to those of cardiogenic shock 3.
- Stunned myocardium can occur after an episode of prolonged or transient ischemia, and can be identified in various patient groups, including those with acute evolving infarction, unstable angina, exercise-induced angina, and coronary artery spasm 2, 4.
Clinical Characteristics
- Stunned myocardium has abnormal wall motion that tends to normalize in response to inotropes and postextrasystolic potentiation 2.
- Perfusion is adequate and metabolism is also adequate in stunned myocardium 2.
- Stunned myocardium returns to normal after a prolonged period of time, ranging from hours to weeks 2.
Differentiation from Hibernating Myocardium
- Stunned myocardium can be differentiated from hibernating myocardium by three clinical parameters: LV wall motion, myocardial perfusion, and myocardial metabolism 2.
- Hibernating myocardium has abnormal wall motion, reduced myocardial perfusion, and adequate metabolism, whereas stunned myocardium has abnormal wall motion, adequate perfusion, and adequate metabolism 2, 5.
Mechanisms and Treatment
- The mechanisms determining the slow recovery of function after ischemia are still not completely understood, but experimental data suggest a reduced Ca++ affinity of the myofibrils and a reduced maximal calcium-activated force 5.
- Angiotensin converting enzyme (ACE) inhibitors have been shown to improve contractile function of stunned myocardium by different mechanisms of action, including stimulation of cardioprotective prostaglandins and antioxidant properties 6.