Dallas, TX

November 8-11, 1998

Beat-to-beat variations of the amplitude of the T-wave (T-wave alternans, TWA) has been associated with malignant arrhythmias in patients (pts) with structural heart disease. Physical exercise, rapid atrial pacing (P), and iv catecholamines have been proposed to attain critical heart rates for TWA measurements and to give concordant results. However, all of these tools have potential hazards and logistic drawbacks in pts with heart disease and/or arrhythmias. Therefore, we attempted to measure TWA during sinus tachycardia (105-120 bpm) induced by iv atropine (A, 0.5-2mg) and compare the results to TWA during P at the same rate. "TWA+" using the Cambridge Heart system 2000ä is defined as T-wave amplitude alternans of ³ 1.9m for ³ 1 minute with a background noise of £ 1.8m V at a rate >100 bpm. Heart rate >105 bpm was attained in 16/19 pts tested after A. Mean age was 46 ± 18 years, 6/16 pts had structural heart disease, 8 pts were female. Results: No pt was "TWA+" at rest. TWA measurements during P-induced and A-induced tachycardia gave concordant results in 15/16 pts (94%): 8/8 pts with P-induced "TWA+" were also "TWA+" after A and 7/8 pts who were "TWA-" during P were also "TWA-" after A (p<0.01). The alternans voltage in "TWA+" pts exceeded 3 m V in all pts irrespective of the induction mode. Conclusion: Whenever critical tachycardia is obtained by iv atropine, TWA measurements compare favorably to TWA measured during rapid atrial pacing.