When would you perform a viability study in patients with coronary artery disease (CAD) and what is its purpose?

Myocardial Viability Assessment in Coronary Artery Disease

Viability assessment should be performed before revascularization in patients with heart failure and reduced ejection fraction (HFrEF) who have coronary artery disease (CAD), particularly when left ventricular ejection fraction is ≤40% and there is dysfunctional but potentially recoverable myocardium. 1

What is a Viability Study?

A viability study identifies dysfunctional myocardium that remains metabolically active and capable of functional recovery after revascularization, distinguishing it from irreversibly scarred tissue. 2, 3

Key physiologic markers assessed include:

• Preserved cellular metabolism (glucose uptake) 4, 5
• Contractile reserve with inotropic stimulation 6
• Intact cell membrane integrity 2
• Preserved wall thickness (>5.5mm) 6
• Blood flow-metabolism mismatch patterns 4, 7

When to Perform Viability Testing

Class IIa Indications (Reasonable to Perform):

Primary indication: Patients with HFrEF (LVEF ≤40%) and known CAD being considered for revascularization (CABG or PCI). 1

Specific clinical scenarios:

• New-onset heart failure with documented CAD but no angina, unless the patient is ineligible for any revascularization 1
• Chronic ischemic cardiomyopathy with severe LV dysfunction being evaluated for revascularization versus transplantation 5, 7
• Patients with regional wall motion abnormalities and CAD where revascularization decision is uncertain 1

When NOT to Perform Viability Testing:

Do not perform viability studies in:

• Patients who are not candidates for revascularization of any kind 1, 8
• Patients with only coronary risk factors but no documented CAD or ischemic symptoms 8
• Routine screening without established CAD and LV dysfunction 1

Available Testing Modalities

Cardiac MRI with Late Gadolinium Enhancement (Preferred):

Most accurate single technique with 97% diagnostic accuracy for detecting ischemic damage. 8, 6

• Transmural extent of scar <75%: 91% likelihood of functional recovery after revascularization 1, 6
• Transmural extent of scar >75%: only 8% likelihood of recovery 1, 6
• Sensitivity 67-100%, specificity 96-100%, positive predictive value 100% 8
• Provides simultaneous assessment of wall thickness, contractility, and scar burden 1, 6

Dobutamine Stress Echocardiography:

• Contractile reserve present: 87% likelihood of functional recovery 6
• No contractile reserve: only 30% likelihood of recovery 6
• Widely available and lower cost than PET or MRI 2, 7

Nuclear Imaging (SPECT/PET):

FDG-PET with perfusion imaging:

• Flow-metabolism mismatch (preserved FDG uptake with reduced perfusion) indicates viable myocardium 4, 5, 7
• Matched defects (reduced FDG uptake and perfusion) suggest irreversible damage 4
• Historically considered gold standard but availability limited 2
• Led to revascularization decisions in approximately 50% of patients evaluated for transplant 5

Thallium or technetium SPECT:

• More widely available than PET 2
• Comparable performance to other modalities for predicting revascularization benefit 7

Clinical Decision Algorithm

Step 1: Confirm eligibility

• Document HFrEF with LVEF ≤40% on echocardiography 1
• Confirm CAD by prior angiography or high pretest probability 8
• Verify patient is revascularization candidate (acceptable surgical/procedural risk) 1, 8

Step 2: Select imaging modality

• First choice: Cardiac MRI with late gadolinium enhancement if available and no contraindications 8, 6
• Alternative: Dobutamine stress echocardiography for cost-effectiveness 2, 7
• Alternative: FDG-PET or SPECT if MRI contraindicated 4, 5

Step 3: Interpret results for revascularization decision

• Substantial viability present (>25% of dysfunctional myocardium viable): Proceed with revascularization—associated with 79.6% reduction in annual mortality (3.2% vs 16% with medical therapy alone) 7
• No viability or minimal viability: Continue medical therapy—revascularization shows no survival benefit and may trend toward higher mortality (7.7% vs 6.2%) 7
• Intermediate findings: Consider coronary angiography to assess anatomic revascularization feasibility 1, 8

Critical Caveats

Important limitations to recognize:

The STICH trial significantly tempered enthusiasm for routine viability testing in the United States, as it did not demonstrate that viability-guided revascularization improved outcomes compared to revascularization without viability testing. 1

However, the STICHES extension study (2016) showed CABG plus medical therapy was superior to medical therapy alone in HFrEF patients with CAD amenable to CABG for all-cause mortality and cardiovascular hospitalization. 1

Contemporary understanding: The primary benefit of revascularization may be preventing future acute coronary events in viable myocardium rather than recovering function in already dysfunctional segments. 3

False positives and negatives occur regularly:

• Positive viability does not guarantee functional recovery—successful revascularization is required 4
• Negative viability does not absolutely preclude benefit—clinical judgment remains essential 4, 7
• Non-cardiac conditions (fungal infections, inflammatory processes) can cause false-positive metabolic uptake 4

The severity of LV dysfunction directly correlates with magnitude of benefit: Patients with worse baseline LVEF derive greater survival benefit from revascularization when viability is present (p<0.001). 7