3. T Wave Alternans
Microscopic T wave alternans characterized by microvolt changes in contour, amplitude, or polarity of the T wave unaccompanied by gross changes in cycle length, usually every other beat, appears to be the result of cellular and molecular alterations associated with repolarization hetero¬geneity. Small studies have indicated a relationship between T wave alternans and serious arrhythmias. These studies, however, have shown the specificity and positive predictive value of the test to be lower than the finding of a low ejection fraction (<30%) or nonsustained ventricular tachycardia.
In a study of 379 consecutive patients following acute infarction, T wave alternans was not present in any of the patients who died during follow up. It appears that the test is less sensitive in the presence of beta-blocking drugs, which must be used in patients following infarction. The value of this test is being assessed in ICD clinical trials.

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