abstract

presented

at the 1996 NASPE

Seattle, Washington

May 15 - 18, 1996

Heart Rate Threshold is Important for Detecting T Wave Alternans

PACE 1996;19:II-588

Stefan H. Hohnloser MD, Thomas Klingenheben MD, Markus Zabel MD, Yigang Li MD, Paul Albrecht PhD, Richard J. Cohen MD, PhD J.W. Goethe University Hospital, Frankfurt, Germany

Previous studies have shown that T wave alternans (TWA) is a marker of susceptibility to sustained ventricular tachycardia or fibrillation (VT/VF). We studied the heart rate (HR) threshold needed to detect TWA during exercise in 22 consecutive patients undergoing evaluation for ventricular ectopic activity (including 11 patients with a history of VT/VF).

METHODS: TWA trends were computed using the spectral method during rest and symptom limited exercise. Significant TWA was defined as > 1µV at rest or >1.9µV during exercise, with alternans ratio > 3 standard deviations.

RESULTS: 10 of 22 patients had significant TWA consistently during exercise (E+) when HR exceeded a patient specific HR threshold (97±10 bpm; see example). Three of the 10 E+ patients had a HR threshold >108 bpm. In E+ patients, TWA peaked at or close to the time of peak HR. Below the HR threshold, transient TWA was sometimes present during short periods of accelerated HR or immediately following ectopic beats. Five of the E+ patients also showed TWA consistently at rest, but at a significantly lower level than during exercise (p <0.001>). These 5 patients did not have a significantly different resting HR, peak exercise HR, or peak exercise TWA than the 5 E+ patients who were TWA negative at rest. The patients without exercise induced TWA were all TWA negative at rest. Their peak HR did no differ significantly from the E+ patients (112±17 vs. 114±12 bpm).

CONCLUSIONS: In this patient cohort undergoing non-invasive risk stratification, an exercise induced increase in HR above a threshold of approximately 100 bpm is required for reliable detection of TWA. These findings need to be considered in future large scale trials evaluating the utility of TWA for risk stratification.

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