Objectives. This study sought to evaluate the effects of autonomic stimulation and blockade on the signal-averaged P wave duration. Background. Signal-averaged P wave duration has been shown to have prognostic implications for patients prone to develop atrial fibrillation, but autonomic influences on the signal-averaged P wave duration have not been studied. Methods. In 14 healthy volunteers (8 men, 6 women; mean [±SD] age 28.5 ± 4.8 years, range 22 to 38), signal-averaged P wave duration was measured on day 1 at baseline, during sympathetic stimulation with infusions of epinephrine (50 ng/kg body weight per min) and isoproterenol (50 ng/kg per min), beta-blockade with propranolol (0.2 mg/kg) and autonomic blockade with propranolol followed by atropine (0.04 mg/kg). On a second day, 10 of the 14 subjects returned for repeat baseline recordings and recordings during parasympathetic blockade with atropine (0.04 mg/kg). Signal averaging was performed using a P wave template. Both unfiltered and filtered (least-squares fit filter with 100-ms window) P wave durations were measured. Day to day and interobserver variability were assessed by calculation of intraclass correlation coefficients. Results. The mean (±SD) baseline filtered P wave duration on day 1 was 141 ± 10 ms. Isoproterenol infusion significantly shortened the P wave duration to 110 ± 16 ms (p < 0.001), and epinephrine resulted in significant prolongation to 150 ± 10 ms (p < 0.05). Beta-adrenergic blockade increased the P wave duration to 153 ± 10 ms (p < 0.005). Autonomic blockade shortened the P wave duration to 143 ± 16 ms (p < 0.05 vs. beta-blockade). On the second day, the mean baseline P wave duration was slightly longer (144 ± 10 ms, p < 0.02). Parasympathetic blockade with atropine resulted in mild shortening of the P wave duration to 136 ± 15 ms (p < 0.1). Interobserver reproducibility was excellent (intraclass correlation coefficient 0.99). Day to day reproducibility was good (intraclass correlation coefficient 0.56). Conclusions. The signal-averaged P wave duration is not a fixed variable because it may change significantly under different autonomic conditions. This has important implications for the application of this test to the heterogeneous population susceptible to atrial fibrillation.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine