Sudden cardiac death: The role of imaging

Sudden cardiac death (SCD) is defined as “a non-traumatic, unexpected, fatal event occurring within one hour of the onset of symptoms in an apparently healthy subject”, and it causes a fifth of all deaths worldwide. It often occurs in individuals not previously known with cardiac disease, which makes prevention challenging. The mechanism underlying SCD is thought to be a trigger (e.g. ischemia) acting upon a substrate (e.g. scar), causing a lethal arrhythmia. Primary prevention refers to patients at high risk of SCD and secondary prevention to those who have had an aborted episode of SCD. Insertion of an implantable, cardioverter-defibrillator (ICD) is the most effective approach to primary prevention; currently ICD candidate selection is based on a left ventricular ejection fraction (LVEF) ≤ 35%. The LVEF is neither sensitive nor specific in identifying individuals who will benefit from ICD therapy, and therefore alternative strategies are required. The present review article summarizes the evidence on various non-imaging (e.g. microvolt T-wave alternans, signal-averaged ECG, QRS fragmentation and measures of autonomic function) and imaging (echocardiography, cardiac magnetic resonance and radionuclide) modalities showing incremental value over LVEF to identify the patients who will benefit from an ICD.