A Simple Echocardiographic Method to Detect Atrioventricular Dissociation: A Useful Aid in the Differential Diagnosis of Regular Tachycardia with Wide QRS Complexes

Abstract

Regular tachycardia with wide QRS complexes may be difficult to classify as supraventricular (SVT) or ventricular (VT) without electrophysiologic studies. We felt that hemodynamic differences between VT and SVT should allow their distinction by echocardiography. In this study, we utilized high speed M-mode echocardiography in the usual projections in eight patients during tachycardia. Two patients had spontaneous VT and three had spontaneous SVT with aberrant conduction. The remaining three were patients in sinus rhythm undergoing electrophysiologic studies in whom right ventricular (RV) pacing (induced VT), right atrial (RA) pacing (induced SVT) and sequential RV-RA pacing (induced VT with 1:1 retrograde conduction) were carried out. The echocardiographic parameters studied included: left ventricular internal dimensions, time during which the mitral valve remained open (MVOT), left ventricular ejection time (LVET) and pre-ejection period. We measured 20 consecutive beats and for each parameter defined its variability. During A-V dissociation (VT, RV pacing) there was always a striking beat-to-beat variability in the values of MVOT (68 percent to 129 percent) and in LVET (41 percent to 175 percent). In contrast, during A-V association (SVT, sequential RV-RA pacing, sinus rhythm) the maximal variability of MVOT and LVET was 22 percent and 12 percent, respectively. Variability during A-V dissociation could be explained by asynchronous timing of atrial systole. We conclude that echocardiography can readily identify atrioventricular dissociation, a feature heavily in favor of a diagnosis of VT.