The need for studies to evaluate the reproducibility of the T-wave alternans (TWA), and the rationale for a correction index of the TWA.

Sudden cardiac death (SCD) due to various cardiomyopathies is currently prevented by the implantation of an automated cardioverter/defibrillator (ICD). ICD impalntation in patients who are not survivors of SCD, or have not suffered potentially lethal ventricular arrhythmias, are based on the presence of cardiomyopathy with a reduced left ventricular ejection fraction. The bulk of patients who are considered suitable for an ICD implantation and receive such devices, do not experience device therapy shocks at follow-up ("false positives"), thus creating a climate of uncertainty among patients and physicians about the soundness of our current eligibility criteria for ICDs. In addition the cost of inappropriate ICDs is staggering, and the undue exposure of "false positive" patients to complications, and hardships is disconcerting. T-wave alternans (TWA) has emerged as a possible "risk detection of SCD" technology, but its reproducibility has not been tested. Peripheral edema (extracardiac) or other cardiac mechanisms, unrelated to the degree of SCD risk, alter the amplitude, and other attributes, of the T-waves. Since TWA may be T-wave amplitude-, or other T-wave attributes-dependent (this is still a speculation), a need may be emerging for its correction by the T-wave amplitude (TWA index); such an index may enhance the reproducibility, and evaluate the true sensitivity, specificity and predictive accuracy of the TWA in detecting future victims of SCD.