Reader Response: Association of Ventricular Arrhythmias With Dementia: The Atherosclerosis Risk in Communities (ARIC) Study

Norby et al.¹ report their interesting findings on the relationship between ventricular arrhythmias and dementia. As they note, speculative mechanisms underlying the observed relationship may include brain hypoperfusion. We previously had the opportunity to directly measure the effects of premature ventricular contractions (PVC) on intracranial hemodynamics.² Using simultaneous transcranial Doppler ultrasound and electrocardiography, we measured middle cerebral artery blood flow velocity during PVC in comparison to blood flow velocity before and after PVC. Compared with the preceding beat, we found significant reductions in peak, mean, and diastolic velocities (30.7%, 34.2%, and 29.6%, respectively) for PVC. Compared with the following beat, we also found significant reductions in peak, mean, and diastolic velocities (37.1%, 30.3%, and 36.2%, respectively) for PVC. Moreover, using similar measurement techniques, we found substantial intracranial hemodynamic effects of atrial fibrillation, including dramatic changes before and immediately after cardioversion.³ We believe that these findings offer some mechanistic perspectives on the epidemiologic observations of the link between cardiac arrhythmias and dementia.^1,4