EFFECT OF LOW-DOSE SOTALOL ON THE SIGNAL-AVERAGED P-WAVE IN PATIENTS WITH PAROXYSMAL ATRIAL-FIBRILLATION

Objective-To investigate the effects of low dose sotalol on the signal averaged surface P wave in patients with paroxysmal atrial fibrillati on. Design-A longitudinal within patient crossover study. Setting-Card iac departments of a regional cardiothoracic centre and a district gen eral hospital. Patients-Sixteen patients with documented paroxysmal at rial fibrillation. The median (range) age of the patients was 65.5 (36 -70) years; 11 were men. Main outcome measures-Analysis of the signal averaged P wave recorded from patients not receiving antiarrhythmic me dication and after 4-6 weeks' treatment with sotalol. P wave Limits we re defined automatically by a computer algorithm. Filtered P wave dura tion and energies contained in frequency bands from 20, 30, 40, 60, an d 80 to 150 Hz of the P wave spectrum expressed as absolute values (P2 0, P30, etc) and as ratios of high to low frequency energy (PR20, PR30 , etc) were measured. Results-No difference in P wave duration was obs erved between the groups studied (mean (SEM) 149 (4) without medicatio n and 152 (3) ms with sotalol). Significant decreases in high frequenc y P wave energy (for example P60: 4.3 (0.4) v 3.3 (0.3) mu V-2.s, P = 0.003) and energy ratio (PR60: 5.6 (0.5) v 4.7 (0.6), P = 0.03) were o bserved during sotalol treatment. These changes were independent of he art rate. Conclusions-Treatment with low dose sotalol reduces high fre quency P wave energy but does not change P wave duration. These result s are consistent with the class III effect of the drug and suggest tha t signal averaging of the surface P wave may be a useful non-invasive measure of drug induced changes in atrial electrophysiology.