Middle cerebral artery blood velocity during exercise in patients with atrial fibrillation.

Atrial fibrillation limits the ability to increase cardiac output during exercise and may, in turn, affect the exercise-associated elevation in cerebral perfusion. In nine patients with atrial fibrillation (AF) and in five age-matched healthy subjects, middle cerebral artery blood velocity (MCA Vmean) was measured during incremental exercise using the transcranial Doppler. The AF patient group exhibited a lower aerobic capacity than the control group [peak work rate: 106 W (71-153 W; median and range) vs. 129 W (118-1.9 W) and maximal oxygen uptake: 1.4 l min-1 (1.0-1.9 l min-1) vs. 1.7 l min-1 (1.4-2.2 l min-1); P = 0.05]. At rest, MCA Vmean was not significantly different between the two groups [43 cm s-1 (39-56 cm s-1) vs. 52 cm s-1 (40-68 cm s-1)]. During intense cycling, the increase in MCA Vmean was to 51 cm s-1 (40-78 cm s-1) (9%) in the AF group and lower than in the healthy subjects [to 62 cm s-1 (50-81 cm s-1) 23%; P < 0.05], which corresponded with the smaller than expected increase in cardiac output [156% (130-169%) vs. 180%]. Thus, there was a correlation between the increase in MCA Vmean and the ability to increase cardiac output (r2 = 0.55, P < 0.01). We suggest that, during exercise with a large muscle mass, atrial fibrillation affects the ability to elevate cerebral perfusion, and this results from an impaired ability to increase cardiac output.