Signal averaging of the surface QRS complex predicts inducibility of ventricular tachycardia in patients with syncope of unknown origin: a prospective study.

Forty patients with syncope of unknown origin underwent quantitative signal averaging of the surface QRS complex before invasive electrophysiologic testing with programmed ventricular stimulation. Of 34 patients without bundle branch block, 12 had inducible ventricular tachycardia (Group I) and 22 did not (Group II). The duration of low amplitude signals, the root mean square voltage of the terminal 40 ms and the signal-averaged QRS vector duration were measured in each case. One or more abnormal signal averaging variables were present in 92% of patients in Group I, but in only 27% of patients in Group II (p less than 0.005). An abnormal root mean square voltage of the terminal 40 ms was the most significant distinguishing variable, being present in 83% of Group I patients and in only 14% of Group II patients (p less than 0.005). The QRS vector duration was prolonged in 58% of Group I patients, but in only 9% of Group II patients (p less than 0.05). Likewise, the duration of low amplitude signals was prolonged in 58% of Group I patients, but in only 19% of Group II patients (p less than 0.05). When compared with 24 hour ambulatory electrocardiographic monitoring, the presence of abnormal signal averaging variables was more predictive of inducible ventricular tachycardia. Seven (32%) Group II patients had greater than or equal to 10 ventricular premature beats/h, couplets or episodes of nonsustained ventricular tachycardia; however, none had abnormal late potentials recorded. In contrast, three patients (25%) in Group I had less than 10 ventricular premature beats/h, although all in that group had one or more abnormal signal-averaged variables.(ABSTRACT TRUNCATED AT 250 WORDS)