Diuretics and arrhythmias in the Medical Research Council trial.

Direct visual interpretation of a daytime and night-time hour of ambulatory ECG recording was possible in 287 of 324 Medical Research Council mild hypertension trial participants. The prevalence of arrhythmias in 103 unselected participants was similar before and 8 weeks after initiation of placebo or thiazide treatment. However, in 164 unselected participants studied during long term therapy (average, 24 months) the prevalence of daytime and night-time ventricular ectopic beats (VEBs) greater than or equal to 5/hour was greater in thiazide recipients (32% and 23%, respectively) than in their placebo counterparts (20% and 9%, respectively). In addition, special VEBs such as multifocal beats, couplets. R-on-T beats and bigeminy were more common during long term thiazide (33%) than placebo (15%) treatment. Ventricular ectopic beats greater than or equal to 5/hour and special VEBs were also common (45% and 40%, respectively) in 20 selected hypokalaemic participants studied during long term thiazide therapy. In pooled data, daytime and night-time VEBs were negatively correlated with serum potassium (p = 0.04 and p = 0.03, respectively) but the correlation coefficients were small (r = -0.11 and r = -0.12, respectively).