Objectives—To study the differences between endocardial bipolar and unipolar ventricular paced evoked responses and surface electrocardiograms.Patients—10 patients with conduction system disease awaiting insertion of a permanent pacemaker were studied with temporary ventricular pacing from the right ventricular apex.Main outcome measure—Comparison of the durations of the QRS complexes and QTa and QTe intervals of the endocardial bipolar paced evoked response and the surface electrocardiogram with those of the reference unipolar paced evoked response.Results—By comparison with the unipolar reference, the mean durations of the QRS complexes of the bipolar signal and the surface electrocardiogram were 41·8% and 132·1% respectively. The mean QTa interval was 85·9% and 112·2% respectively and the mean QTe interval was 86·9% and 109·5% respectively. All these differences were significant. The amplitudes of the unipolar QRS complexes and T waves were significantly larger than those recorded in the bipolar configuration.Conclusions—Differences between the unipolar and bipolar ventricular paced evoked responses are significant. The time course of the unipolar signal is closer to that of the surface electrocardiogram. This indicates that the unipolar paced evoked response does not reflect local electrophysiological events, as has been suggested previously.
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