INTRODUCTION
Sudden cardiac death (SCD) is a major cause of preventable mortality, estimated to be responsible for over 6 million deaths per year worldwide.1{{86 Myerburg, M Risk stratification of patients for implantable cardioverter defibrillator (ICD) therapy has major limitations, particularly for patients at risk due to a non-ischemic cardiomyopathy, who make up 20% of SCD cases.2 Current electrophysiological (EP) and non-invasive predictive methods for the identification of non-ischemic patients at high risk for SCD have been shown to be inaccurate.3 The recent DANISH study has further highlighted the need for better risk stratification in this patient group.4
Action potential duration (APD) restitution describes the property that myocardial APD is determined by the length of the preceding diastolic interval (DI). In silico models suggest that abnormal APD restitution is arrhythmogenic through two mechanisms: increased heterogeneity of APD restitution and increased APD restitution slope steepness.5–8 Body surface electrocardiogram (ECG) surrogates for APD and DI have been used to successfully plot APD restitution in dog and swine models and have been shown to correlate with epicardial unipolar electrograms.9,10 Our research group has developed two novel, independent, high resolution 12-lead ECG measures of APD restitution pathology: Regional Restitution Instability Index (R2I2, a measure of APD restitution heterogeneity) and Peak Electrocardiogram Restitution Slope (PERS, a measure of APD restitution slope).11 R2I2 and PERS have been shown to be predictive of ventricular arrhythmia (VA)/death in three cohorts of patients with ischemic cardiomyopathy, and to be independent of standard risk markers.11,12 The aim of this study was to explore the application of R2I2 and PERS as risk stratification markers in a cohort of patients with non-ischemic cardiomyopathy.