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. 2 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 2
- Stunned myocardium: Transient contractile depression following acute ischemic insult that typically recovers within 2 weeks if reperfusion is established 3
- Mixed patterns: Alternating regions of irreversibly scarred myocardium and viable tissue within the same ventricular territory 2
Key Distinguishing Feature: Contractile Reserve
A defining property of viable myocardium is "contractile reserve"—the ability to transiently increase contractility during inotropic stimulation. 1, 4 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 2
- If dysfunction is predominantly scar: Revascularization confers no benefit, and procedural risks outweigh potential gains 1, 4
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. 5 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 5
- Bypass viability testing entirely in patients who cannot undergo revascularization due to comorbidities, surgical risk, or patient preference 5
Diagnostic Markers of Viability
Multiple imaging modalities can detect viable myocardium by assessing different physiologic properties: 6
- Preserved wall thickness 6
- Contractile reserve during inotropic stimulation 6
- Blood perfusion reserve 6
- Cellular membrane integrity 6
- Preserved cellular metabolism 6
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. 2 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, 5, 7
- The REVIVED-BCIS2 trial showed no benefit of PCI in patients with viable myocardium and modern heart failure therapy 2
- 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 2
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. 2 This requires an integrative approach involving specialized imaging, heart failure, arrhythmia, and revascularization specialists. 2