Relationship between extracellular T-wave height, T-wave alternans amplitude, and tissue action potential alternans: a 1-dimensional computer modeling study.

T-wave alternans (TWA) is a useful marker of cardiac instability, but not much is known about the factors that affect its measurement, such as electrode placement. We used a 1-dimensional myocardial fiber computer model of alternans to investigate the effect of electrode position on TWA measurement. Results demonstrated that TWA amplitude and T-wave amplitude change proportionally if both recording electrodes are symmetrically moved toward or away from the tissue. However, TWA amplitude and T-wave amplitude change out of proportion to one another when one electrode is moved while the other electrode remains stationary. These disproportionate changes result from beatwise alternation in the asymmetric potential field around the tissue. In summary, nonlinear changes in tissue repolarization during alternans result in nonlinear changes in T-wave amplitude and TWA amplitude.