Transcranial Doppler evaluation of cerebral blood flow in patients with paroxysmal atrial fibrillation.

Cerebral blood flow was measured by transcranial Doppler sonography (TCD) in 15 patients during and after an attack of paroxysmal atrial fibrillation. During the attack the mean flow velocity (MFV) was reduced significantly in the middle cerebral artery (p < 0.05) and nonsignificantly in the other arteries. The pulsatility index (PI) was reduced in all the arteries but not significantly. During the fibrillation phase the MFV and PI tended to decrease as the heart rate increased. None of the patients showed clinical signs of cerebral ischemia during the attacks. The absence of such signs despite the reduced cerebral blood flow in atrial fibrillation is probably due to the activation of mechanisms of autoregulation.