In a study of patients with AVNRT with short versus long ventriculoatrial intervals, there was no significant difference in tachycardia cycle ; however, the induction of typical AVNRT caused a marked initial fall in systemic BP, followed by only partial recovery that resulted in stable hypotension and a reduction in cardiac output due to a decrease in stroke volume. In comparison, atypical AVNRT, having a longer ventriculoatrial interval, exhibited a lesser degree of initial hypotension, a complete recovery of BP, and no significant change in cardiac output.70 The contrasting hemodynamic responses without sig- nificant differences in heart rate during SVT confirm that rate alone does not account for these hemodynamic changes. Atrial contraction on a closed valve might impair pulmonary drain- age and lead to neural factors that account for these observa- tions. These findings were confirmed in a study performed in the electrophysiological (EP) laboratory: When pacing was used to replicate the timing of ventricular and atrial activation during SVT, the decrease in BP was greatest with simultane- ous ventriculoatrial timing, smaller with a short vertriculoatrial interval, and smallest with a long ventriculoatrial interval.71 An increase in central venous pressure followed the same trend. Sympathetic nerve activity increased with all 3 pacing modali- ties but was most pronounced with simultaneous atrial and ventricular pacing or a short ventriculoatrial interval. In a study of the relationship of SVT with driving, 57% of patients with SVT experienced an episode while driving, and 24% of these considered it to be an obstacle to driving.72 This sentiment was most common in patients who had experienced syncope or near-syncope. Among patients who experienced SVT while driving, 77% felt fatigue, 50% had symptoms of near-syncope, and 14% experienced syncope. Women had more symptoms in each category. 