Prognostic Value of Myocardial Viability by Delayed-Enhanced Magnetic Resonance in Patients With Coronary Artery Disease and Low Ejection Fraction: Impact of Revascularization Therapy

Study Questions:

What is the impact and interaction of assessment of myocardial viability by delayed-enhanced cardiac magnetic resonance imaging (DE-CMR) and revascularization in patients with coronary artery disease (CAD) and reduced left ventricular ejection fraction (LVEF)?

Methods:

One hundred forty-four consecutive patients with CAD and LV dysfunction (EF 24 ± 7%) underwent DE-CMR for assessment of myocardial viability. CMR was visually evaluated for regional wall motion on a 17-segment scale and graded as normal to dyskinetic and extent of fibrosis characterized as 0, 1-25%, 26-50%, 51-75%, and 76-100% transmurality in the same segments. A segment was considered viable when wall motion was hypokinetic or worse, and transmurality of scar/fibrosis was ≤50%. A patient was considered to have viable myocardium if there were ≥4 dysfunctional segments, each with transmurality ≤50%. Follow-up was complete in all 144 patients for 3 years.

Results:

All patients had obstructive CAD and none had undergone previous revascularization. Based on physician judgment, coronary artery bypass grafting (CABG) was performed in 79 patients and percutaneous coronary intervention (PCI) in 19 patients. Revascularization was considered complete in 86 patients, defined as fully revascularizing all diseased vessels and dysfunctional segments. Incomplete PCI was performed in 12 patients, revascularizing only nondysfunctional myocardium. Forty-six patients remained medically treated, all of whom had suitable CAD anatomy for revascularization. Over the 3-year follow-up, there were 49 deaths, 40 of which were attributable to cardiovascular disease and 7 of which were postoperative. Based on presence of viability and mode of treatment, six subgroups were identified, including 68 patients with completely revascularized myocardium, seven patients with viable myocardium who had incomplete revascularization not including the dysfunctional region, 26 patients with viable myocardium treated medically, 18 patients with completely revascularized nonviable myocardium, 20 patients with nonviable myocardium treated medically, and five patients with incomplete revascularization not including the dysfunctional nonviable myocardium. Three-year survival was 83% and 71% for the completely revascularized viable and nonviable myocardium subgroups, compared to 46% for subjects treated medically who had dysfunctional viable myocardium and 54% for those undergoing incomplete revascularization. Survival was 77% in medically treated patients without viable myocardium. Age, distribution of risk factors, comorbidities, LV volume, EF, and surgical risk scores were equivalent in patients undergoing complete revascularization and those treated medically. Medically treated or incompletely revascularized patients did have higher New York Heart Association functional class and more often two- rather than three-vessel CAD. For patients fully revascularized, the average number of dysfunctional viable segments was 9 ± 5 compared to 6 ± 5 for medically treated patients. Average transmurality was 15 ± 11% in fully revascularized subjects versus 27 ± 12% in medically treated patients (both p < 0.001). Propensity score matching was available for 43 pairs of patients undergoing complete revascularization or remaining under medical treatment or having incomplete revascularization. For the propensity-matched subsets, the hazard ratio for events for medically treated patients was 2.5 compared to revascularized patients (p = 0.02).

Conclusions:

The authors concluded that survival of patients with dysfunctional viable myocardium, as detected by DE-CMR, is improved with revascularization compared to medical therapy.

Perspective:

The issue of survival and benefit of revascularization versus medical therapy in patients with depressed LV function and viable myocardium has previously been addressed with dobutamine stress echocardiography, positron emission tomography, and standard perfusion imaging. More recently, using DE-CMR as a marker of myocardium fibrosis, this technique has also been used to identify viable myocardium based on the absence of scar implying permanent cell damage. Previous single studies using other techniques, as well as meta-analyses, have demonstrated the survival benefit for revascularizing viable myocardium compared to medical treatment alone. Many studies have also suggested a neutral effect for revascularization of nonviable myocardium. The study presented here provides a similar conclusion, that complete revascularization of viable myocardium confers a survival advantage over medical treatment of patients with significant viable myocardium. Outcomes were also poor in the presence of incomplete revascularizaton that did not address the dysfunctional segments. This study shares many of the limitations of previous work in this field with other modalities, including the nonrandomized nature of selection for revascularization versus medical therapy, but does nicely demonstrate that DE-CMR can be utilized not just for identification of scar, but by further assessment of transmurality and function identifying myocardium which is viable and likely to benefit with revascularization compared to continued medical therapy.

Clinical Topics: Cardiac Surgery, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Aortic Surgery, Cardiac Surgery and Heart Failure, Acute Heart Failure, Interventions and Imaging, Computed Tomography, Echocardiography/Ultrasound, Magnetic Resonance Imaging, Nuclear Imaging

Keywords: Propensity Score, Heart, Echocardiography, Stress, Comorbidity, Myocardium, New York, Magnetic Resonance Imaging, Perfusion Imaging, Positron-Emission Tomography, Percutaneous Coronary Intervention, Cicatrix, Myocardial Revascularization, Heart Failure, Stroke Volume, Coronary Artery Bypass


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