What is myocardial viability in a patient with a history of coronary artery disease (CAD) and impaired ventricular function?

What is Myocardial Viability?

Myocardial viability refers to dysfunctional but living heart muscle that has the potential to recover contractile function if adequate blood flow is restored through revascularization. 1

Core Pathophysiologic Concept

Myocardial viability represents a spectrum of reversible myocardial dysfunction in patients with coronary artery disease and impaired ventricular function. 1 The underlying substrate includes:

• Hibernating myocardium: Chronically dysfunctional but viable tissue resulting from persistent hypoperfusion or repetitive ischemic episodes that can recover function after revascularization 1
• Stunned myocardium: Transient contractile depression following acute ischemic insult that typically recovers within 2 weeks if reperfusion is established 1
• Mixed patterns: Alternating regions of irreversibly scarred myocardium and viable tissue within the same ventricular territory 1

Key Distinguishing Feature: Contractile Reserve

A defining property of viable myocardium is "contractile reserve"—the ability to transiently increase contractility during inotropic stimulation. 1, 2 This distinguishes viable tissue from irreversibly infarcted myocardium, which cannot respond to inotropic challenge. 1

Clinical Significance in CAD with LV Dysfunction

The critical distinction between viable and non-viable myocardium determines treatment strategy:

• If sufficient viability exists: Revascularization combined with guideline-directed medical therapy may restore function, prevent new ischemic events, and improve prognosis 1
• If dysfunction is predominantly scar: Revascularization confers no benefit, and procedural risks outweigh potential gains 1, 2

When to Assess Viability

Viability assessment should only be performed in patients who are actual revascularization candidates and present with de novo heart failure, known CAD, but no anginal symptoms. 3 The American Heart Association specifically recommends:

• Bypass viability testing entirely in patients with angina—proceed directly to coronary angiography, as revascularization is indicated for significant ischemic chest pain regardless of viability status 3
• Bypass viability testing entirely in patients who cannot undergo revascularization due to comorbidities, surgical risk, or patient preference 3

Diagnostic Markers of Viability

Multiple imaging modalities can detect viable myocardium by assessing different physiologic properties: 4

• Preserved wall thickness 4
• Contractile reserve during inotropic stimulation 4
• Blood perfusion reserve 4
• Cellular membrane integrity 4
• Preserved cellular metabolism 4

Contemporary Controversies

The classical binary definition of myocardial viability may benefit from more contemporary paradigms with greater focus on anatomic alignment between viable myocardial regions and arteries. 1 Recent evidence challenges traditional concepts:

• The STICH trial substudy found that viability assessment did not identify patients with differential survival benefit from CABG compared to medical therapy alone 1, 3, 5
• The REVIVED-BCIS2 trial showed no benefit of PCI in patients with viable myocardium and modern heart failure therapy 1
• Heterogeneous methods of viability assessment (metabolism-based, contractile reserve-based, or scar extent-based) and variable quantification leave open questions about optimal definition and application 1

Therapeutic Implications Beyond Function

Therapeutic aims should extend beyond enhancing local and overall LV function to include safeguarding against new ischemic events and their potentially lethal arrhythmias. 1 This requires an integrative approach involving specialized imaging, heart failure, arrhythmia, and revascularization specialists. 1