Myocardial Viability Assessment, STICH Trial and STICHES, REVIVED-BCIS2

Assessing myocardial viability is a critical step in managing patients with chronic ischemic heart disease and left ventricular (LV) dysfunction. The primary goal is to distinguish between hibernating myocardium (dysfunctional but viable tissue that can improve after revascularization) and myocardial scar (fibrotic, non-viable tissue).

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1. Functional Concepts

• Stunning: Post-ischemic dysfunction that persists despite restored blood flow; typically recovers spontaneously over days or weeks.
• Hibernation: A chronic state of reduced LV function due to persistent low blood flow. The tissue remains metabolically active and can recover function if blood flow is restored via PCI or CABG.

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2. Primary Imaging Modalities

The choice of modality often depends on local expertise and specific clinical questions (e.g., “Is there scar?” vs. “Is there contractile reserve?”).

Modality	Marker	Strengths
Cardiac MRI (CMR)	Hyperenhancement (LGE)	The gold standard for anatomy and scar burden. High spatial resolution.
PET (FDG)	Glucose Metabolism	The gold standard for metabolic viability. Identifies “mismatch” (low flow/high uptake).
Dobutamine Stress Echo (DSE)	Contractile Reserve	Widely available. High specificity for functional recovery.
SPECT (Thallium-201)	Cell Membrane Integrity	Established protocols; assesses potassium analog uptake.

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3. Key Findings & Interpretation

Cardiac MRI (LGE)

CMR uses Gadolinium to identify the transmural extent of a scar.

Score 0: No hyperenhancement

Score 1: Hyperenhancement of 1 to 25 percent of the tissue

Score 2: Hyperenhancement of 26 to 50 percent of the tissue

Score 3: Hyperenhancement of 51 to 75 percent of the tissue

Score 4: Hyperenhancement of 76 to 100 percent of the tissue.

PET Metabolism (FDG-PET)

Often compared with perfusion scans (like Rubidium-82 or SPECT).

• Hibernating (Viable): Perfusion-Metabolism Mismatch (reduced blood flow but preserved glucose metabolism).
• Scar (Non-Viable): Perfusion-Metabolism Match (both blood flow and metabolism are absent).

Dobutamine Stress Echocardiography

The “Biphasic Response” is the most predictive sign of viability:

1. Low Dose: Improvement in wall motion (recruitment of reserve).
2. High Dose: Deterioration of wall motion (induced ischemia).

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4. Clinical Implications

The STICH Trial and its long-term extensions (STICHES) have provided significant data on this topic. While the presence of viability identifies suitable patients, the benefit of CABG over medical therapy in those with viability has been debated. However, current guidelines still generally support revascularization in patients with significant viable myocardium and amenable coronary anatomy. Assessment should always be integrated with the patient’s symptomatic status, coronary anatomy (SYNTAX score), and overall surgical or procedural risk.

The Original STICH Trial (5-Year Results)

This study evaluated whether CABG plus Medical Therapy (610 patients) was superior to medical therapy (602 patients) alone in patients with an EF of ≤ 35% and CAD amenable to surgery. The study concluded that there was no significant difference between medical therapy alone and medical therapy plus CABG with respect to the primary end point of death from any cause. Those assigned to CABG had lower rates of death from cardiovascular causes and of death from any cause or hospitalization for cardiovascular causes.

The STICHES Extension Study (10-Year Results)

The STICH Extension Study (STICHES) followed the original cohort for a median of nearly 10 years to see if the benefits of surgery emerged over time. At 10 years, CABG was associated with a significant reduction in all-cause mortality (58.9% vs. 66.1%) and cardiovascular mortality compared to medical therapy alone. This confirmed that the benefits of CABG in HFrEF are realized in the long term. In effect, early surgical risk offsets short term benefit while long-term survival favors surgery.

STICH Viability Sub-study

This specific sub-analysis addressed whether the presence of viable myocardium (assessed by SPECT or Dobutamine Echo) predicted better outcomes with CABG. Of the 1212 patients enrolled in the STICH randomized trial, 601 underwent assessment of myocardial viability. Of these patients, 298 were randomly assigned to receive medical therapy plus CABG and 303 to receive medical therapy alone. Though presence of viable myocardium was associated with a greater likelihood of survival, this relationship was not significant after adjustment for other baseline variables. In short, myocardial viability assessment did not identify patients with a survival benefit from CABG as compared with medical therapy.

Long term follow up of this sub study was published in 2019. The median duration of follow-up was 10.4 years. Findings did not support the concept that myocardial viability is associated with a long-term benefit of CABG in patients with ischemic cardiomyopathy. Presence of viable myocardium was associated with improvement in left ventricular systolic function irrespective of treatment option. But such improvement was not related to long-term survival.

REVIVED-BCIS2 Trial

This newer trial, published in NEJM in 2022 studied patients with EF ≤ 35% AND substantial viable myocardium (assessed primarily by CMR) and randomized them to PCI + medical therapy vs. medical therapy alone. The primary composite outcome evaluated was death from any cause or hospitalization for heart failure. Study had a total of 700 patients. REVIVED found NO benefit for PCI over medical therapy, even in a cohort defined by viability. This has reinforced the idea that identifying hibernation might not be the key to selecting candidates for revascularization.