Arrhythmias and Conduction Disturbances
Electrical Alternans During Rest and Exercise as Predictors of Vulnerability to Ventricular Arrhythmias

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Abstract

This investigation was performed to evaluate the feasibility of detecting repolarization alternans with the heart rate elevated with a bicycle exercise protocol. Sensitive spectral signal-processing techniques are able to detect beat-to-beat alternation of the amplitude of the T wave, which is not visible on standard electrocardiogram. Previous animal and human investigations using atrial or ventricular pacing have demonstrated that T-wave alternans is a marker of vulnerability to ventricular arrhythmias. Using a spectral analysis technique incorporating noise reduction signal-processing software, we evaluated electrical alternans at rest and with the heart rate elevated during a bicycle exercise protocol. In this study we defined optimal criteria for electrical alternans to separate patients from those without inducible arrhythmias. Alternans and signal-averaged electrocardiographic results were compared with the results of vulnerability to ventricular arrhythmias as defined by induction of sustained ventricular tachycardia or fibrillation at electrophysiologic evaluation. In 27 patients alternans recorded at rest and with exercise had a sensitivity of 89%, specificity of 75%, and overall clinical accuracy of 80% (p <0.003). In this patient population the signal-averaged electrocardiogram was not a significant predictor of arrhythmia vulnerability. This is the first study to report that repolarization alternans can be detected with heart rate elevated with a bicycle exercise protocol. Alternans measured using this technique is an accurate predictor of arrhythmia inducibility.

Section snippets

Study Design:

All patients referred for invasive cardiac electrophysiologic evaluation for syncope, ventricular tachycardia, or fibrillation were eligible for this multicenter study. Patients were excluded if they were unable to complete a bicycle exercise protocol with an elevation of heart rate >100 beats/min or if they had excessive premature ventricular complexes (10%), atrial fibrillation, or a permanent pacemaker. Electrical alternans was successfully measured in 27 patients meeting these entry

Results

The characteristics of the 27 study patients are summarized in Table I. The 20 men and 7 women were an average age of 49 ± 19 years (mean ± SD). Coronary artery disease was present in 11, right ventricular dysplasia in 4, idiopathic-dilated cardiomyopathy in 5, and no structural heart disease in 7.

Discussion

Before the present study it was not known if microvolt level electrical alternans could be reliably measured during sinus rhythm with elevation of the heart rate with exercise or whether such measurements would be predictive of susceptibility to ventricular arrhythmias. Furthermore, it was not known whether the motion artifact of bicycle exercise would preclude the measurement of microvolt level electrical alternans during such exercise. The data in the present study indicate that

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This study was supported by Grant #NAGN-3927 from the National Aeronautics and Space Administration.

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