The electrocardiographic (ECG) signs used to differentiate ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberrancy are specific but not highly sensitive. The purpose of this study was to define the utility of an underappreciated form of atrioventricular (AV) dissociation at the onset of tachycardia, a single dissociated P wave, in the differentiation of non-sustained monomorphic wide complex tachycardia (WCT) in hospitalized patients.Methods and results
We prospectively analysed tracings from 102 consecutive hospitalized patients who had an episode of non-sustained (≥5 beats, <30 s), monomorphic, WCT (≥100 b.p.m.) on telemetry. WCT was classified as VT, SVT with aberrancy, or undifferentiated WCT based on predefined criteria. Of 102 patients with WCT, 3 (3%) had SVT with aberrancy, 43 (42%) had an undifferentiated WCT, and 56 (55%) had VT. ECG evidence of a single dissociated P wave at the onset of tachycardia (i.e. AV dissociation at the onset) was identified in 29 patients (28%) compared with less frequent traditional signs of VT including second-degree ventriculoatrial (VA) block in 18 patients (18%), AV dissociation during tachycardia in 17 patients (17%), fusion beats in 10 patients (10%), and capture beats in 3 patients (3%). On multivariate analysis, only the prematurity index predicted the occurrence of AV dissociation at the onset of the tachycardia (odds ratio 1.239, 95% confidence interval 1.033–1.486, P = 0.021).Conclusion
When evaluating WCT in hospitalized patients, a single dissociated P wave at the onset of tachycardia is an easily recognizable diagnostic sign of VT, and is observed more frequently than the other accepted criteria for VT.