Hibernating and Stunned Myocardium

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• Stunned: prolonged myocardial contractile dysfunction after a brief period of absent or reduced blood flow

• Hibernating: myocardial contractile dysfunction associated with chronic reduced blood flow that reverses with revascularization

• Imaging evidence of myocardial viability in areas of reduced myocardial contractility:

  • – Absence of thin scarred myocardial segment on echocardiography

  • – Wall motion response to dobutamine infusion

  • – Metabolic activity but reduced perfusion on positron emission tomography scan

  • – Lack of late gadolinium enhancement on cardiac MRI

GENERAL CONSIDERATIONS

• Affects both systolic and diastolic function

• Stunned myocardium recognized by persistent wall motion abnormalities even after chest pain, ST-segment deviation, and regional perfusion have recovered

• Lack of recovery after a few weeks suggestive of true infarction or scar formation

• Hibernating myocardium is recognized by improvement of left ventricular function after revascularization of chronic ischemia

• Hibernation related to chronically reduced myocardial perfusion

• Recovery of function may occur over days to weeks in both situations

• Transient improvement occurs in both situations with inotropic stimulation

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Stunned myocardium:

  • – Persistent shortness of breath after an infarction despite evidence of reperfusion

  • – A similar situation may occur with cardioplegia during cardiopulmonary bypass (lack of recovery after a few weeks suggests true infarction)

• Hibernation:

  • – Persistent dyspnea in chronic coronary artery disease

PHYSICAL EXAM FINDINGS

• Hypotension may be present

• S₃ may be present

• Occasionally an S₄ may be present

DIFFERENTIAL DIAGNOSIS

• Stunned: acute ischemia with compromised blood flow

• Hibernating: infarcted myocardium

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• CBC, brain natriuretic peptide, troponin

ELECTROCARDIOGRAPHY

• ECG may show infarction or ischemia

IMAGING STUDIES

• Resting echocardiogram to evaluate left ventricular function after adequate revascularization or reperfusion

• Thinned hyperechoic and akinetic wall segment indicates scar (nonviable)

• Technetium-99m sestamibi single-photon emission cardiac tomography (SPECT) stress imaging for regional myocardial ischemia (presumably due to reduced perfusion)

• Dobutamine echocardiogram: improvement in function in areas of resting regional wall motion at low doses, followed at higher doses by deterioration due to ischemia, so-called biphasic response

• Positron emission tomography (PET):

  • – Perfusion: ¹³NH₃-labeled ammonia, ¹⁵O₂-labeled water, and ⁸²Rb-labeled PET

  • – Metabolism: fluorodeoxyglucose PET

  • – Reduced perfusion and metabolism suggest infarction (matched defects)

  • – Reduced perfusion with intact metabolism (flow metabolism mismatch) suggests viable or hibernating myocardium

• Cardiac magnetic resonance

  • – Myocardial late gadolinium uptake indicates myocardial scar (nonviable)

DIAGNOSTIC PROCEDURES

• Coronary angiography to define anatomy in hibernation before revascularization

TREATMENT

CARDIOLOGY REFERRAL