Myocardial Viability Assessment on Stress Echocardiography

Understanding Myocardial Viability Assessment on Stress Echocardiography

Myocardial viability assessment determines whether areas of the heart that aren't contracting well are still alive and could recover after restoring blood flow. This is crucial for patients with coronary artery disease and reduced heart function, as it helps decide whether bypass surgery or stenting would be beneficial.

Low-dose dobutamine stress echocardiography is the most commonly used technique for assessing viability, offering a non-invasive way to distinguish living but hibernating myocardium from scar tissue.

What Is Myocardial Viability?

When blood flow to the heart muscle is chronically reduced, the myocardium can adapt in different ways:

Types of Myocardial Dysfunction

Hibernating myocardium (viable):

• Chronically reduced blood flow
• Myocardium alive but not contracting
• Downregulated function to survive low flow
• Recovers function after revascularization
• Shows contractile reserve with dobutamine

Stunned myocardium (viable):

• Temporary dysfunction after ischemia
• Blood flow restored but function hasn't recovered
• Recovers function over days to weeks
• Shows contractile reserve with dobutamine

Scarred myocardium (non-viable):

• Dead heart tissue from previous infarction
• Replaced by fibrous tissue
• Will not recover function
• No contractile reserve with dobutamine

The Concept of Contractile Reserve

Contractile reserve refers to the ability of dysfunctional myocardium to improve contraction when stimulated:

Viable myocardium response:

• Improves with low-dose dobutamine (5-10 mcg/kg/min)
• Shows increased wall thickening
• May worsen at higher doses (biphasic response = ischemia)

Non-viable myocardium response:

• No improvement with dobutamine
• Remains akinetic or dyskinetic
• Scarred tissue cannot contract

Epidemiology and Clinical Context

Who needs viability assessment?

• Patients with reduced ejection fraction and coronary disease
• Those being considered for bypass surgery
• Patients with heart failure symptoms and coronary disease
• Determining recovery potential after revascularization

Expected findings:

• About 1/3 of patients have predominantly viable myocardium
• About 1/3 have predominantly scar
• About 1/3 have mixed viability and scar

Stress Echocardiography Protocol

Low-Dose Dobutamine Protocol

Unlike standard stress testing that uses high doses, viability testing uses lower doses:

Protocol stages:

1. Rest imaging: Baseline wall motion assessment
2. Low-dose dobutamine (5 mcg/kg/min): Early stimulation
3. Medium-dose dobutamine (10 mcg/kg/min): Peak for viability assessment
4. Optional higher doses (20-40 mcg/kg/min): To assess for ischemia
5. Recovery: Return to baseline

What we look for:

• Improved systolic thickening
• Reduced wall motion abnormality
• Biphasic response (improvement then worsening)

Imaging Appearances

Clinical Presentation

Typical Patient Scenario

Indications for Viability Testing

Viability assessment is performed when:

1. Reduced EF with coronary disease

   • EF typically ＜ 40%
   • Multivessel disease or significant proximal disease
   • Question of whether revascularization will help

2. Before considering bypass surgery

   • Determines potential benefit
   • Weighs risks vs. benefits
   • Guides patient and surgeon decision-making

3. Heart failure management

   • Distinguishes ischemic from non-ischemic cardiomyopathy
   • Identifies patients who may recover

4. After heart attack

   • Assess myocardial damage
   • Determine recovery potential

Differential Diagnosis

Diagnostic Performance and Management

Accuracy of Viability Assessment

Comparison with Other Modalities

Stress echocardiography:

• Widely available
• No radiation
• Good accuracy
• Lower cost than nuclear imaging

PET F-18 FDG (gold standard):

• Highest accuracy
• Expensive
• Limited availability
• Involves radiation

Cardiac MRI:

• Excellent accuracy
• Provides additional information (scar, function)
• Expensive
• Contraindicated with some devices

Management Based on Results

Prognosis and Outcomes

Impact of Viability on Outcomes

With significant viability:

• Revascularization improves survival
• 70-80% chance of functional recovery
• EF typically increases by 5-15%
• Symptom improvement common

Without viability (predominant scar):

• Medical therapy often preferred
• Revascularization has less benefit
• Higher mortality risk
• Heart failure management focus

Predictors of recovery:

• Extent of viable myocardium (＞ 5 segments)
• Degree of improvement with dobutamine
• Wall thickness ＞ 5.5 mm
• Absence of extensive scar

Frequently Asked Questions

What does viable myocardium mean?

Viable myocardium refers to heart muscle that is alive but not contracting properly. This occurs when blood flow has been chronically reduced, causing the muscle to hibernate (reduce function to survive). Importantly, this muscle can recover its function if blood flow is restored through bypass surgery or stenting.

How accurate is stress echo for viability?

Low-dose dobutamine stress echo has 80-90% sensitivity for detecting viable myocardium compared to PET scan (the gold standard). The positive predictive value is 70-80%, meaning that when echo shows viability, there's a high likelihood the muscle will recover after revascularization.

Will my heart function improve after bypass surgery?

If your echocardiogram shows significant viable myocardium (typically ＞ 5 segments with contractile reserve), there's a 70-80% chance your heart function will improve after bypass surgery. The ejection fraction typically increases by 5-15 percentage points, and symptoms often improve significantly.

References

1. American Society of Echocardiography. Guidelines for Stress Echocardiography. 2023.
2. Schinkel AF, et al. Prognostic Value of Dobutamine Stress Echocardiography. J Am Coll Cardiol. 2022.
3. Bax JJ, et al. Myocardial Viability: Detection and Clinical Relevance. Circulation. 2023.

Medical Disclaimer: This information is educational only. Always discuss findings with your healthcare provider for personalized medical advice.