Timing of the right ventricular apical electrogram during sustained ventricular tachycardia: relation to surface QRS morphology and potential clinical implications.

To evaluate the timing of the right ventricular (RV) apical electrogram in relation to the QRS complex during ventricular tachycardia (VT), 94 episodes of sustained uniform VT were analyzed in 56 patients. The timing of the RV apical electrogram varied and could be recorded from 33 ms before to 180 ms (mean 77 +/- 44 ms) after the onset of the QRS complex. The timing of the RV apical electrogram, expressed both as an absolute value and as a percentage of a QRS width, was significantly different when right bundle branch block (BBB) morphology VT (95 +/- 37 ms) and left BBB morphology VT (40 +/- 341) were compared (p less than 0.001). The timing of the RV apical electrogram, expressed as a percentage of the QRS width, was significantly different when VT with different axes were compared in the right BBB VT group (p less than 0.01). A left BBB VT, as compared to a right BBB VT, predicted an RV apical electrogram occurring in the first 35% of the QRS with a sensitivity of 74%, a specificity of 91%, and a positive predictive value of 84%. Right BBB VT with a right and inferior axis were usually associated with the latest occurring RV apical electrogram. A right BBB VT with a right and inferior axis predicted an RV apical electrogram inscribed in the latter half of the QRS with a sensitivity of 65%, a specificity of 84% and a positive predictive value of 80%.(ABSTRACT TRUNCATED AT 250 WORDS)