Ischemic Cardiomyopathy: Myocardial Viability Assessment and Revascularization

Definition and pathophysiology

Ischemic cardiomyopathy is severe myocardial dysfunction caused by coronary artery disease (CAD). The clinical syndrome may resemble primary dilated cardiomyopathy, particularly when angina or a previous myocardial infarction (MI) is absent. Heart failure (HF) symptoms may result from several overlapping processes:

• Recurrent or extensive MI with necrosis and scar formation

• Diffuse myocardial fibrosis

• Reversible ischemic dysfunction

• Chronic hypoperfusion with hibernating myocardium

• Post-ischemic stunning

• Adverse left ventricular (LV) remodeling

Ischemic cardiomyopathy is the leading cause of heart failure with reduced ejection fraction (HFrEF) in developed countries. New ischemic events are major determinants of subsequent LV deterioration and long-term survival.

Viable, stunned, and hibernating myocardium

Viable dysfunctional myocardium is myocardial tissue whose contractile function improves after coronary revascularization. This functional definition encompasses several physiological states.

Brief coronary occlusion or relatively prolonged moderate ischemia may produce post-ischemic stunning. In the absence of infarction, contractile recovery can occur rapidly after reperfusion, with recovery generally occurring within one week. By contrast, chronic hypoperfusion may result in hibernating myocardium: a persistently dysfunctional but potentially recoverable state.

The chronically dysfunctional myocardium in ischemic cardiomyopathy is therefore heterogeneous. Irreversibly scarred regions may alternate with viable segments that are dysfunctional because of repeated ischemic episodes or chronic reductions in perfusion. The amount and distribution of both viable and nonviable myocardium, together with coronary anatomy and the feasibility of revascularization, determine the clinical significance of imaging findings.

Historically, revascularization was considered capable of improving LV systolic function and prognosis by restoring perfusion to viable dysfunctional myocardium while preventing further ischemic events. However, the presumed relationship between viability, recovery of ejection fraction, and survival has been challenged by randomized trials.

Relationship between viability and LV recovery

Observational studies and positron emission tomography (PET) studies have shown that meaningful improvement in global LV ejection fraction (LVEF) after revascularization is most likely when a relatively large amount of hibernating or stunned myocardium is present, approximately 20% of LV mass. Conversely, a greater burden of nonviable or scarred myocardium is associated with less improvement in LVEF.

Nevertheless, improvement in LVEF is not the only possible objective of revascularization. Contemporary evidence suggests that protection of jeopardized myocardium from future ischemic events, and prevention of their potentially lethal arrhythmic consequences, may be more important than restoration of global LV function.

Clinical presentation and symptoms

The presentation is variable and may evolve over time.

Some patients initially have angina as the dominant manifestation of CAD. As LV dysfunction and HF become more prominent, angina may diminish or disappear. Others have no recognized history of angina or MI, making the distinction from primary dilated cardiomyopathy particularly difficult.

When present, the clinical picture may include:

• Symptoms attributable to chronic LV systolic dysfunction and HF

• Angina, although its absence does not exclude ischemic cardiomyopathy

• Symptoms related to recurrent ischemia

• Symptoms associated with ventricular arrhythmias

The prognosis is especially unfavorable when ischemic cardiomyopathy is associated with recurrent MI, ventricular arrhythmias, or a large burden of hibernating myocardium.

Evaluation and physical examination

The assessment should establish three complementary features:

• The severity of LV dysfunction

• The extent and anatomical distribution of CAD

• The amount and location of ischemic, viable, and nonviable myocardium

Clinical evaluation alone may not distinguish ischemic cardiomyopathy from nonischemic dilated cardiomyopathy, particularly in patients without angina or a prior MI. Symptoms, previous coronary events, known CAD, and the presence of ventricular arrhythmias are important components of risk assessment, but they must be integrated with anatomical and functional data.

The source material does not provide a detailed physical-examination profile or specific examination findings that reliably distinguish viable from nonviable myocardium.

Diagnostic assessment

Electrocardiography

The ECG remains important in the broader assessment of ischemic heart disease, but Q waves cannot be used as a direct surrogate for transmural infarction. Late gadolinium enhancement (LGE) studies have shown that Q waves may occur with large subendocardial infarctions, whereas non-Q-wave infarction may occasionally be transmural. Q-wave formation is more closely related to total infarct size than to infarct transmurality.

The source material does not provide a specific ECG diagnostic pattern for ischemic cardiomyopathy or myocardial viability.

Echocardiography

Transthoracic echocardiography assesses:

• LV systolic function

• Regional wall motion

• Wall thickness

• Valve function

• Associated structural abnormalities

A resting diastolic wall thickness below 6 mm is highly suggestive of nonviable scar, although wall thinning does not invariably indicate irreversible damage. Even segments with wall thickness ≤5.5 mm may improve in regional thickness and contractility after revascularization when the scar burden is limited to 50% or less of wall thickness.

Low-dose dobutamine stress echocardiography

Low-dose dobutamine echocardiography evaluates contractile reserve. Improvement in regional wall motion suggests viable myocardium. A biphasic response—initial improvement at low dose followed by deterioration at higher dose—is particularly specific for viability.

An improvement in wall motion by at least one grade in two or more segments during stress is also likely to indicate viability, whether the underlying process is stunning or hibernation. Compared with nuclear and CMR approaches, dobutamine stress echocardiography has somewhat lower sensitivity but greater specificity for predicting recovery of systolic function in viable segments.

Cardiac magnetic resonance

Cardiac magnetic resonance (CMR) provides high-resolution assessment of LV structure, function, perfusion, and myocardial tissue characteristics. It is particularly useful when echocardiographic image quality is inadequate and for distinguishing ischemic from nonischemic myocardial damage.

LGE assessment

In acute MI, gadolinium-based contrast agents accumulate in areas with ruptured cardiomyocytes and expanded extracellular space. In chronic infarction, replacement of cardiomyocytes by collagen-rich extracellular matrix produces a similar increase in extracellular volume and delayed contrast accumulation.

Ischemic LGE generally follows a coronary distribution and is subendocardial or transmural. The extent of transmural LGE can be used to estimate the likelihood of functional recovery:

In segments with 50–75% transmurality, stress perfusion imaging may help identify peri-infarct ischemia, while low-dose dobutamine CMR can assess contractile reserve.

LGE can detect small, focal infarctions that may be missed by other approaches. The presence of LGE in patients with known or suspected CAD is associated with increased mortality and major adverse cardiovascular events. The peri-infarct zone, representing heterogeneous tissue at the interface between scar and normal myocardium, is an arrhythmogenic substrate. Its quantification has been associated with long-term mortality and appropriate implantable cardioverter-defibrillator therapy in ischemic cardiomyopathy.

Nuclear imaging

The principal nuclear techniques are single-photon emission computed tomography (SPECT) and PET. Nuclear methods assess perfusion and, in the case of PET, myocardial metabolism.

SPECT

SPECT myocardial perfusion imaging can define the extent and severity of ischemia during exercise or pharmacological stress. For viability assessment, attenuation-corrected SPECT is preferred.

Technetium-labelled tracers and thallium-201 can be used. Thallium-201 may be particularly useful in severe resting hypoperfusion because it provides a more accurate assessment of viable myocardium. Nitrates may be used to improve collateral perfusion at rest and enhance tracer uptake in severely hypoperfused regions.

Late redistribution or redistribution after a second tracer injection suggests viability.

PET

PET provides quantitative assessment of ischemia and metabolic imaging of myocardial viability. The usual metabolic approach uses 18F-fluorodeoxyglucose (18F-FDG). Viability is suggested by a perfusion–metabolism mismatch: reduced perfusion with preserved glucose uptake.

PET protocols require careful patient preparation. PET can also quantify the burden of ischemia and myocardial blood-flow reserve, although the source material does not specify preparation protocols or numerical diagnostic thresholds beyond the approximate 20% LV mass of viable or hibernating myocardium associated with clinically meaningful global LV recovery.

Computed tomography

Computed tomography can provide alternative assessment of wall thickness, regional function, perfusion, and myocardial fibrosis, although the source material emphasizes CMR, echocardiography, SPECT, and PET for viability assessment.

CT coronary angiography should be considered in patients with a low-to-intermediate pre-test probability of CAD or equivocal noninvasive stress-test findings, principally to exclude coronary stenosis.

Summary of imaging indicators

Biomarkers and laboratory findings

The source material does not provide a specific biomarker strategy for chronic ischemic cardiomyopathy or myocardial viability assessment.

Natriuretic peptides are mentioned as biomarkers of HF severity in the broader HF context, but no specific threshold or role in selecting patients for viability-guided revascularization is provided. In acute coronary syndromes, troponin elevation identifies myocardial injury and is associated with increased risk, but this does not constitute a chronic viability test.

Revascularization and medical management

Guiding principles

Management requires integration of:

• Clinical status and symptoms

• Coronary anatomy

• Severity of LV dysfunction

• Ischemia and viability findings

• The anatomical correspondence between viable myocardium and a revascularizable supplying artery

• Procedural risk, particularly in severe LV dysfunction

• Age, frailty, kidney dysfunction, respiratory disease, and other comorbidities

• The likely benefit of preventing future ischemic events and arrhythmias

All patients require guideline-directed medical therapy (GDMT) for HFrEF and CAD. Revascularization should not be based on viability imaging in isolation.

Coronary artery bypass grafting

The available evidence supports consideration of CABG in selected patients with ischemic cardiomyopathy, especially those with significant multivessel CAD and severely reduced LVEF.

The STICH trial enrolled patients with CAD and LVEF <35% who were eligible for CABG and randomized them to CABG plus GDMT or GDMT alone. CABG did not significantly reduce all-cause mortality at a median follow-up of four years. At a median follow-up of 9.8 years, however, CABG was associated with lower all-cause mortality and cardiovascular mortality than medical therapy alone:

• All-cause mortality decreased from 66.1% to 58.9%

• Cardiovascular mortality decreased from 49.3% to 40.5%

The survival benefit was more pronounced in patients with three-vessel disease and the reduction in all-cause mortality was greater in younger patients. An early mortality hazard reflects the operative risk of CABG in patients with severe LV dysfunction.

In observational data involving patients with severe LV dysfunction, CABG was associated with an operative mortality of 5.4% and a five-year actuarial survival of 75%, although these findings are not equivalent to randomized evidence.

Percutaneous coronary intervention

REVIVED-BCIS2 randomized 700 patients with LVEF ≤35%, extensive CAD suitable for PCI, and viable myocardium in at least four dysfunctional segments to PCI plus GDMT or GDMT alone. After a median follow-up of 3.4 years, PCI did not reduce the composite of all-cause death or HF hospitalization. It also produced no overall improvement in LV function compared with GDMT.

Symptoms improved slightly and temporarily after PCI, but there was no incremental improvement in global LV function.

In a prespecified analysis, the extent of viable myocardium did not predict benefit from PCI. In contrast, a larger burden of nonviable myocardium was associated with a higher risk of death or HF hospitalization regardless of whether PCI was performed.

There are no randomized trials directly comparing CABG with PCI in patients with ischemic HF. Observational comparisons have generally suggested lower long-term mortality and fewer myocardial infarctions or repeat revascularizations with CABG than PCI, at the cost of a somewhat higher stroke risk. These findings are confounded by differences in patient age, prior MI, CAD severity, and completeness of revascularization.

Revascularization in high-risk clinical settings

Revascularization carries increased periprocedural risk when LVEF is severely depressed, particularly at or below 35%. In patients with extensive ischemia and severe LV systolic dysfunction, temporary LV mechanical support may be required during PCI for hemodynamic support.

In the setting of cardiogenic shock complicating an acute coronary syndrome, immediate PCI is recommended when feasible. Emergency CABG may be required when coronary anatomy is unsuitable for PCI.

The role of viability testing

Viability testing has an intuitive appeal because it can identify dysfunctional myocardium that might recover after restoration of perfusion. However, randomized evidence does not establish that viability testing improves survival by selecting patients for revascularization.

The PARR-2 trial randomized 430 patients with suspected ischemic cardiomyopathy to PET-assisted management or standard care. There was no overall reduction in cardiac events with the PET strategy. Post hoc analyses suggested benefit when clinical decisions adhered to PET recommendations, but these analyses excluded protocol violations and did not preserve the strength of an intention-to-treat comparison.

The STICH viability substudy likewise found no significant interaction between the presence or absence of viability and the effects of CABG on LV recovery or long-term survival. In REVIVED-BCIS2, the extent of viable myocardium did not identify patients who benefited from PCI.

Accordingly, viability imaging should be regarded as one component of an integrated assessment rather than as a stand-alone gatekeeper for revascularization. It may be particularly useful when the balance between procedural risk and potential benefit is uncertain, including patients with frailty, chronic kidney dysfunction, or severe respiratory disease. Its value may lie more in risk stratification, scar characterization, and assessment of the anatomical plausibility of recovery than in predicting a survival advantage from revascularization.

Guideline recommendations

The following recommendations are supported by the source material:

• Coronary revascularization has a class I recommendation in patients with LVEF ≤35% and significant two- or three-vessel disease to improve prognosis, according to the cited 2023 ACC/AHA chronic coronary disease guidance.

• Noninvasive stress imaging with CMR, stress echocardiography, SPECT, or PET may be considered for assessment of ischemia and viability in patients with CAD who are considered suitable for revascularization: class IIb, level B.

• Invasive coronary angiography is recommended in patients with angina despite pharmacological therapy or symptomatic ventricular arrhythmias: class I, level B.

• Invasive coronary angiography may be considered in HFrEF when the pre-test probability of CAD is intermediate to high and ischemia is present on noninvasive stress testing: class IIb, level B.

• CT coronary angiography should be considered in patients with a low-to-intermediate pre-test probability of CAD or equivocal noninvasive stress tests to exclude coronary stenosis: class IIa, level C.

• CMR is recommended for assessment of cardiac structure and function when echocardiographic acoustic windows are poor: class I, level C.

• CMR with LGE should be considered in dilated cardiomyopathy to distinguish ischemic from nonischemic myocardial damage: class IIa, level C.

• In patients with severe HF being assessed for transplantation or mechanical circulatory support, cardiopulmonary exercise testing and right-heart catheterization are recommended as part of the evaluation.

These recommendations do not imply that viability imaging alone should determine whether CABG or PCI is performed. Decisions should incorporate anatomy, ischemia, scar burden, comorbidity, procedural risk, and the expected ability to revascularize the relevant myocardial territory.

Prognosis

The prognosis of medically treated ischemic cardiomyopathy is poor. Outcomes are particularly unfavorable in the presence of:

• Recurrent MI

• Ventricular arrhythmias

• Extensive hibernating myocardium

• Extensive nonviable or scarred myocardium

• Severe LV dysfunction

The amount of scar has prognostic importance independent of the likelihood of functional recovery. In REVIVED-BCIS2, a larger burden of nonviable myocardium predicted worse outcomes regardless of PCI. CMR-detected LGE is associated with increased all-cause mortality, cardiovascular mortality, and major adverse cardiovascular events. The peri-infarct zone is associated with long-term mortality and appropriate ICD therapy, reflecting its role as an arrhythmogenic substrate.

Revascularization may improve long-term survival in selected patients, particularly after CABG, but the benefit may be mediated primarily by prevention of future ischemic events rather than by improvement in LVEF. CABG also carries an early procedural mortality hazard, especially in patients with severe LV dysfunction.

Follow-up and reassessment

Follow-up should include continued assessment of:

• HF symptoms and functional status

• Angina or recurrent ischemic symptoms

• Ventricular arrhythmias

• LV systolic function

• Response to GDMT

• The occurrence of new ischemic events

• Revascularization completeness and durability when intervention has been performed

In patients with a pre-discharge LVEF <40% after acute coronary syndrome, repeat LVEF assessment is recommended 6–12 weeks after complete revascularization and optimal medical therapy to determine whether primary-prevention ICD implantation should be considered.

After an acute MI, echocardiography is recommended to evaluate resting LV and right ventricular function, valvular function, mechanical complications, and LV thrombus. CMR is a useful alternative when echocardiography is suboptimal or inconclusive.

The heterogeneous evidence base, different definitions of viability, variation in imaging methods, and uncertain relationship between viability and outcome mean that follow-up should remain individualized. Complex cases are best managed through coordinated evaluation by heart-failure, imaging, arrhythmia, and revascularization specialists.