Rate-dependent T-wave alternans (TWA) is an index of vulnerability to ventricular tachyarrhythmias (VT) in pts with heart disease. However, false +ve TWA was reported to occur in relatively young normal subjects at high heart rates (HR). To establish optimal target HR for +veTWA, we evaluated 2 age –matched groups (Gr): Grl, 56 subjects (age 63 ± 6 yrs) considered normal by history, ECG, echo, stress test, and/or angiography. The subjects underwent symptom-limited (SL) bicycle exercise test.

Gr II, 27 pts (65 ± 8 yrs) with ischemic heart (n = 21) or dilated cardiomyopathy (n = 6) who received implantable defibrillator for VT. This group was selected to have +ve TWA at rest (HR = 50-93bpm,

n = 6) and/or during SL exercise (n = 21). We compared the HR-SL and the HR at onset of +ve TWA (HR-TWA) in the 2 Grs (CH 2000, Cambridge Heart, Inc.). RESULTS 1) HR-SL was 124 ± 18 bpm in Gr I compared to 108 ± 20 bpm in Gr II (p<0.0004). 2) 4 of Gr I developed +ve TWA at HR-TWA of 119 ± 12 bpm while the HR-TWA of Gr II was 84 ± 17 bpm. 3) A target HR-TWA of 110 bpm provided the best sensitivity (93%) and specificity (98%) [Fig.].

CONCLUSIONS 1) False +ve TWA developed in 7% of age-matched normal subjects at higher HR compared to Gr II pts. 2) A target HR-TWA of 110 bpm is highly sensitive and specific. However, because of their lower HR-SL (108 bpm), many Gr II-like pts will not be able to achieve target HR-TWA, resulting in indeterminate tests. In those pts, noninvasive or pharmacologic means to ­ HR may be considered.

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