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Cerebral hemodynamics during induced tachycardia in routine electrophysiologic studies: a transcranial Doppler study.

Supraventricular and ventricular tachyarrhythmia are established causes of syncope. We investigated the mean blood flow velocities (Vmean) of the middle cerebral arteries (MCA) during routine cardiac electrophysiologic studies in patients with supraventricular and ventricular tachyarrhythmias in order to evaluate the changes in cerebral hemodynamics associated with pre-syncopal and syncopal states. Thirty-two patients with a history of supraventricular (n = 14) or ventricular (n = 18) tachyarrhythmias were investigated in the nonsedated, post-absorptive state in supine position. Vmean was assessed in both MCAs by means of transcranial Doppler under resting conditions, during atrial and ventricular pacing at constant rates (n = 28) and during induction of tachyarrhythmia (n = 4). Mean arterial blood pressure (MABP) and heart rate were also recorded. Seven patients suffered pre-syncope at a heart rate of 187 +/- 45 bpm (mean +/- SD) with an average drop of 44% in the Vmean MCA, and statistically insignificant changes in MABP. Five patients suffered syncope during tachyarrhythmia (mean heart rate 283 +/- 42 bpm) with a reduction of 69% in the Vmean MCA. MABP could be assessed in two of those patients and showed a drop of 15 and 43 mmHg, respectively. During tachyarrhythmia pre-syncope and syncope are associated with an average reduction in Vmean MCA by 44% and 69%, respectively. The decrease in MCA blood flow velocity is a more important predictive factor for the development of pre-syncope and syncope than the MABP.