The circadian variation of atrial defibrillation thresholds

Background: A circadian variation exists for ventricular defibrillation thresholds (DFTs) with a morning peak and a corresponding decrease in therapy success rates from implantable cardioverter defibrillators. Such a variation in atrial DFTs may have implications for the timing of internal cardioversion of atrial arrhythmias. The aim of this study was therefore to determine the circadian variation of atrial DFTs in patents with recurrent atrial fibrillation (AF). Methods and results: Data were collected as part of the worldwide Jewel AF-only study. Patients had recurrent persistent AF and no history of ventricular arrhythmias. The atrial DFT was assessed at device implantation using a step-up protocol and was recorded for 100 patients (age 63.0 +/- 11.7, 74% male, ejection fraction 49.6 +/- 17.8%, left atrial diameter 46 +/- 9 mm). The mean atrial DFT was 6.3 +/- 4.3 J. For the most commonly tested lead configuration (right atrium to coronary sinus in 56 patients), the atrial DFT for patients implanted in the morning (3.3 +/- 1.5 J) was significantly lower than for both the DFT measured in the afternoon (5.8 +/- 3.4 J, p < 0.01) and the DFT measured in the evening (7.4 +/- 5.9 J, p = 0.01). Conclusion: There may be a significant variation in measured atrial DFT for the right atrium to coronary sinus configuration, with a nadir in the morning. This is the converse to measurements of ventricular DFTs suggesting different regulatory electrophysiological mechanisms. Further investigation of this possible variation is warranted.