The resting 12-lead electrocardiogram (ECG) is the oldest tool and the most widely adopted clinical test for detection of heart disease. Today, it is still one of the most useful methods for risk stratification for sudden cardiac death. A number of ECG repolarization measures have been assessed in large population studies, as well as in research focused on high-risk cohorts, for the purpose of estimating arrhythmic risk, and will be discussed in this chapter. They include static parameters, such as QT interval duration, as well as dynamic markers, such as QT variability, and computationally derived variables, such as T-wave alternans. It has become increasingly apparent that repolarization heterogeneity is present in a variety of cardiovascular diseases and syndromes and may also be predictive of sudden cardiac death in the general population. However, at the present time, there is no consensus on how to best measure repolarization heterogeneity in human subjects. A wider adoption of repolarization indices in clinical practice would require an improved diagnostic accuracy, as well as the implementation of standardized computational signal processing techniques.
