Diagnostic information in implantable devices that pertain to endpoints in atrial fibrillation studies

Implantable devices can store significant information about physiologic parameters relating to rhythm and rate control. The primary objective of our analysis was to evaluate the relationship between changes in these parameters and changes in clinical outcomes in patients with atrial tachyarrhythmias (AT). Because the present guidelines do not provide quantitative definition of rhythm and rate control, we used the percent of time in AT and frequency of such episodes as measures of rhythm control. Rate control was measured as the percent of time spent at a ventricular rate >120 beats/min, as well as the median ventricular rate during AT. Analysis was conducted in 643 patients with a history of AT and bradycardia receiving pacemakers to evaluate whether changes in these parameters were correlated with changes in cardiac hospitalization rates and SF-36 and symptom checklist scores. All patients were followed at 1, 4, and 7 months postimplant, during which rhythm and rate control data were collected. Positive correlation was observed between changes in cardiac hospitalization rate and changes in AT burden, as well as frequency of AT (P = 0.01, r = 0.08 for each). Changes in SF-36 or symptom checklist scores did not correlate with changes in rhythm and rate control measures. This patient cohort had relatively asymptomatic atrial fibrillation (symptom checklist frequency and severity scores of 14.3 +/- 9.5 and 11.5 +/- 7.9, respectively), and this may have contributed to the lack of correlation with SF-36 and symptom scores. Data stored in implantable devices offer a unique opportunity to monitor parameters of rhythm as well as rate control in patients with AT. In patients implanted with pacemakers for management of bradyarrhythmias who have a history of AT, a significantly positive but weak correlation was observed between changes in rhythm control measures (AT burden and frequency) and changes in cardiac hospitalization rate.