Introduction There is a need for better sudden cardiac death (SCD) risk markers. Mounting evidence suggests that the mechanism underlying risk of ventricular arrhythmia (VA) is increased heterogeneity of electrical restitution. We investigated a novel measure of action potential duration (APD) restitution heterogeneity: the Regional Repolarisation Instability Index (R2I2) and correlated it with peri-infarct zone (PIZ) a cardiac magnetic resonance (CMR) anatomic marker of VA risk.
Methods Blinded retrospective study of 30 patients with ischaemic cardiomyopathy assessed for an implantable cardioverter defibrillator. The R2I2 was derived from high resolution 12 lead ECG recorded during programmed electrical stimulation (PES). ECG surrogates were used to plot APD as a function of diastolic interval; the R2I2 was the maximal value of the mean squared residuals of the mean points for anterior, inferior and lateral leads normalised to the mean value for the total population. PIZ was measured from late gadolinium enhanced CMR images using the full width half maximum technique.
Results Seven patients reached the endpoint of VA/death (median follow-up 24 months). R2I2 > median was found to be predictive of VA/death independent of PES result, left ventricular ejection fraction and QRS duration (6/14 vs 1/15 p=0.031). Modest correlation was seen between the R2I2 and PIZ (r=0.41 p=0.057) (Abstract 159 figure 1).
Conclusions In this pilot study of ischaemic cardiomyopathy patients, the R2I2 was shown to be an electrical measure of VA/death risk with a moderately strong correlation with an anatomic measure of arrhythmic substrate, the extent of PIZ. The R2I2 may add value to existing markers of VA/death and merits further investigation.
- Implantable cardioverter defibrillator
- sudden cardiac death
- risk stratification