Evaluation of novel measurement methods for detecting heterogeneous repolarization

There exists a well-documented link between heterogeneity of cardiac recovery characteristics and vulnerability to arrhythmia; however, electrocardiographic detection of this heterogeneity remains problematic. The only modalities suitable for measuring variation of repolarization are electrophysiologic in nature, with action potential duration in single cells the most direct method and QT intervals from the body surface electrocardiogram the most common clinical approach. The authors have shown previously, however, that the QT interval is a poor measure of regional change in repolarization, especially when shortening occurs. Here, the authors discuss an experimental preparation based on an isolated canine heart suspended in a human-shaped, instrumented, electrolytic tank and describe a method of applying cold to create local, transient changes in recovery characteristics. The authors have simultaneously recorded epicardial and torso tank surface potentials before, during, and after intervention, and from them have generated isopotential and isointegral maps and computed activation-recovery intervals (ARIs). In all cases, epicardial potentials revealed changes in recovery associated with localized heating and cooling. The changes were visible from tank surface potential distributions in some, but not all, cases. The results also suggest that epicardial ARIs are sensitive to changes in recovery and that, at least for a subset of tank surface leads, ARIs can be used to create noninvasive indices of disparity of repolarization characteristics.