Arrhythmias in mitral valve prolapse. Effect of selection bias.

To assess the contribution of bias in subject selection to the prevalence of arrhythmias in cases of mitral valve prolapse (MVP), we compared ambulatory arrhythmias in 63 patients with MVP and 28 symptom-matched control subjects. All subjects were in sinus rhythm. Mean 24-hour heart rate of the prolapse population was lower than that of the control group (76 v 82 beats per minute). Mean atrial premature complex (APC) density per 1,000 beats (0.9 v 0.7 for patients with MVP and control subjects, respectively) and mean ventricular premature complex (VPC) density per 1,000 total beats (1.2 v 1.5) did not differ between groups. Small differences between groups in APC and VPC complexity did not reach statistical significance. Our findings suggest that, compared with similarly symptomatic controls, patients with MVP do not have as high an excess prevalence of arrhythmias as previously believed.