Detection of myocardial viability by low-dose dobutamine cine MR imaging

Abstract

The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity.

Introduction

Acute myocardial infarction often leaves an infarct-associated region with impaired contractile function. Three mechanisms may be responsible for this: Chronic scar formation, hibernation due to chronic underperfusion or prolonged stunning following ischemia and reperfusion. While scar tissue is non-viable and cannot resume contractile function, stunned or hibernating myocardium is viable and may resume contractile function after revascularization. Therefore, clinical methods that allow the distinction of viable and non-viable myocardium are important to select those patients who will benefit from interventional or surgical revascularization.

Several methods have been used for distinction of viable and non-viable myocardium: Radionuclide imaging techniques include Thallium-201 single photon emission computed tomography (Thallium-201 SPECT) with reinjection and [18F]fluorodeoxyglucose positron emission tomography (FDG-PET), the latter being considered the “gold standard”. Due to high costs, however, FDG-PET does not have widespread clinical availability. Experimental and clinical studies have shown that myocardial dysfunction caused by hibernation or stunning can be transiently reversed by positive inotropic stimulation.1, 2, 3 During dobutamine infusion, systolic wall thickness increases in viable, but not in scarred myocardium. The response to dobutamine was mostly studied by echocardiography,4, 5, 6 with three studies also comparing cine magnetic resonance (MR) imaging during dobutamine stress to echocardiography or radionuclide imaging modalities.7, 8, 9 A comparison of the prediction of viability and of long-term functional recovery after revascularization was performed for echocardiography and FDG-PET5, 6, 10 and, using MRI, for patients with chronic infarction (>= 4 months since ischemic event).11 Most patients are referred to revascularization in the first few weeks after myocardial infarction, whereas some patients with wall motion abnormalities have no history of myocardial infarction. The purpose of this prospective study was, therefore, to assess the value of dobutamine stress MR imaging in predicting myocardial viability in all patients with wall motion abnormalities. Due to clinical relevance, restoration of regional function re-examined by MR imaging after revascularization therapy was used as the criterion of viability.