T-wave alternans: does size matter. PMID: 16302917

摘要

In the current issue, Klingenheben, Ptaszynski, and Hohnloserresurface an important question relevant to employing T-wave alternans (TWA) analysis for sudden death risk stratification. Specifically, they explore the possibility that quantitative assessment of the magnitude of TWA may provide complementary information beyond the results of a standardized cutpoint for a positive microvolt TWA (MTWA) test. The concept that the magnitude of TWA may be important is supported by multiple experimental studies demonstrating that higher TWA levels are associated with greater likelihood of ventricular fibrillation. Moreover, TWA undergoes an orderly progression in magnitude en route to ventricular fibrillation that includes discordant TWA, T-wave multupling, and more complex oscillatory behavior. The importance of TWA magnitude clinically is suggested by a prospective analysis of archived ambulatory ECG records demonstrating that patients with a recent myocardial infarction who subsequently experienced cardiac arrest or arrhythmic death exhibited higher levels of TWA at 8:00 a.m. and during periods of peak activity indicated by maximum heart rates than did matched study participants without subsequent events. TWA magnitude is also elevated in patients with implantable cardioverterdefibrillators (ICDs) but not in normal volunteers in response to mental stress as well as to mild and maximum exercise. Kodama and coworkers recently reported that TWA was sufficiently large as to be visible in 8-10% of patients with cardiomyopathy, especially during episodes of emerging tachycardia or adrenergic stimulation with dobutamine.Raeder and coworkers and Hohnloser reported cases of spontaneous ventricular fibrillation emerging from a background of macroscopic TWA during telemetered clinical monitoring.