Atrial fibrillation: profit from cardiac pacing?

Rationale and design of a randomized clinical trial to assess the role of overdrive and triggered prevention pacing therapies in reducing atrial fibrillation: the Study of Atrial Fibrillation Reduction (SAFARI)

BACKGROUND

Rhythm control in selected patients diagnosed with paroxysmal atrial fibrillation (AF) remains a clinically important goal. The role of pacing therapies for maintaining that goal remains unclear, despite considerable study effort. Several pacing strategies have been evaluated to treat AF, including various prevention pacing therapies (PPTs) designed to suppress known triggers of AF. The inconsistent results and difficulty interpreting the results of past studies stems in part from variability in trial designs, patient populations, and end points.

METHODS

The SAFARI is the largest, multicenter, prospective, randomized clinical trial that aims to address many of the design limitations of previous trials to delineate better the role of PPTs. The primary end point for the study is total AF burden as reported by the device. Patients are selected to include only those with paroxysmal AF and to exclude those without documented arrhythmias. A 1-month postimplant lead stabilization period followed by a 3-month run-in period is incorporated into the design to help exclude patients with no AF after implantation or patients in whom the accuracy of the device reported AF burden is suspect. A suite of 6 PPTs is used to treat multiple different triggers of arrhythmia. Data will be gathered for 10 months. Enrollment of 546 patients was completed in January 2005; patient follow-up visits are expected to be completed in November 2005.

CONCLUSION

By using a study design that addresses the limitations of previous trials, SAFARI will help significantly refine our understanding of the role of pacing to prevent AF.

Identification of “substrate fibrillators” and “trigger fibrillators” by pacemaker diagnostics

BACKGROUND

The population of patients likely to respond to selected pacing algorithms for maintenance of sinus rhythm is unknown.

OBJECTIVES

The purpose of this study was to identify patients with specific onset patterns of paroxysmal atrial fibrillation (AF).

METHODS

Dual-chamber pacemakers with advanced diagnostic functions were implanted in 112 patients with conventional indications for antibradycardia pacing and a history of paroxysmal AF. Pacemaker diagnostic data were analyzed after 97.5 +/- 40.9 days. According to the frequency of premature atrial contractions (PACs) during the 5 minutes before AF onset, patients were assigned to one of three groups: group A (high PAC activity), group B (moderate PAC activity), or group C (low PAC activity).

RESULTS

AF burden was lower in group A (4.6% +/- 2.4%) than group B (15.8% +/- 3.0%, P = .003) and group C (15.5% +/- 3.1%, P = .003). Fewer AF episodes occurred in group A (2.1 +/- 1.3 per day) than group B (3.8 +/- 1.2 per day, P = .006). Mean AF episode duration was shorter in group A (11.4 +/- 10.2 hours) than group C (41.4 +/- 27.5 hours, P = .03).

CONCLUSION

The coincidence of low PAC activity before AF onset, high AF burden, and extended arrhythmia episode duration appears to be the consequence of a high atrial substrate factor. In these "substrate fibrillators," the efficacy of pacing algorithms for maintenance of sinus rhythm may be limited. In contrast, "trigger fibrillators" exhibiting low AF burden despite high PAC incidence may represent the target population for specific PAC-suppressing pacing algorithms.