Non invasive assessment of myocardial viability

Heart failure (HF) is a major and growing public health problem in the United States of America (USA). Approximately 5 million patients in USA have HF, and over 550,000 new cases are diagnosed with HF each year. The current guidelines recommend cardiac catheterization to rule out Coronary Artery Disease (CAD) as the cause of newly diagnosed HF (Class I or IIa recommendation depending on the clinical scenario). Although cardiac catheterization is the gold standard in ruling out CAD, it does not provide information on viability and recovery of left ventricular function post revascularization. Determining the viability of myocardium is therefore of great clinical significance in clinical setting. Although presence of angina in patients with severe coronary vascular disease and severe left ventricular dysfunction can signify some viable myocardium, the absence of angina does not exclude the possibility of myocardial viability in similar patient population. Echocardiography and ventriculography by itself also cannot distinguish between viable and non-viable areas of myocardium as akinetic and dyskinetic areas have been seen to completely recover following revascularization. Several advanced non-invasive modalities have been developed to rule out CAD and to determine myocardial viability in patients with heart failure. The techniques most commonly used to identify viable myocardium include Thallium-201 Single-Photon Emission Computed Tomography (201Tl SPECT), Technetium-99m Sestamibi imaging (Tc-99m Sestamibi), Low Dose Dobutamine Echocardiography (LDDE), Positron Emission Tomography (PET) using a combination of flow and metabolic tracer and Cardiac Magnetic Resonance imaging (CMR). Coronary Computed Tomography Angiography (CCTA) is a non invasive tool to assess coronary anatomy. The strength of CCTA lies in its very high negative predictive value; however, it does not determine the functional significance of stenosis. CCTA use in assessment of viability is currently being evaluated in multiple research studies. Extent of myocardial Thallium-201 uptake on ²⁰¹Tl SPECT determines the viability of myocardial tissue and thereby helps in predicting recovery post revascularization. Flouro-I8 deoxyglucose (FDG) is a metabolic tracer used in PET for determination of viability of myocardial tissue. Normal FDG uptake in areas of decreased myocardial perfusion determines the probability of myocardial recovery in those areas post revascularization. LDDE helps to determine the myocardial viability by demonstrating stress induced contractile reserve with a high specificity. This section therefore focuses on the utilization of different imaging methods to assess the myocardial viability. It also discusses the advantages and the disadvantages of different imaging techniques. The best approach depends on the individual patient and on the expertise of the reader.