Value of Detecting High Atrial Rates by Pacemaker Diagnostics

Abstract & Commentary

Synopsis: It is possible to use pacemakers to detect symptomatic and asymptomatic nonsustained atrial high-rate episodes, and detection of these atrial high-rate episodes identifies patients at higher risk for death, stroke, and atrial fibrillation.

Source: Glotzer TV, et al. Circulation. 2003;107: 1614-1619.

The Mode Selection Trial (MOST) was a 6-year prospective, randomized, multicenter trial that compared ventricular rate modulated pacing (VVIR) with dual chamber rate modulated pacing (DDDR) in patients with symptomatic sinus node dysfunction. Patients were eligible for the atrial diagnostics substudy of MOST if they had pacemakers capable of storing a record of atrial high-rate episodes. In these patients, atrial bipolar sensitivity was programmed to 0.5 mV, and the atrial high-rate episode diagnostic was programmed on. In patients who received only ventricular pacing, the atrial lead was used for only diagnostic purposes. The atrial detection rate was programmed to 220 bpm and only atrial high- rate episodes lasting at least 5 minutes were included in the analysis. The clinicians were blinded to the atrial diagnostics data. The number of atrial high-rate episodes were counted and entered into a model as a time-dependent covariate. Cox proportional hazards were used to examine the association between atrial high-rate episodes and the primary end point, which was a composite of death, nonfatal stroke, and atrial fibrillation.

MOST enrolled 2010 patients. The atrial diagnostic substudy enrolled 312 patients who were followed for a median of 27 months. Patients in the substudy had a higher prevalence of prior supraventricular arrhythmias (60% vs 51%) than patients not in the substudy. In the substudy, the median age was 74 years, and 55% were female. In 160 of the 312 patients at least 1 atrial high-rate episode was recorded by their pacemaker. A history of SVT, a history of atrioventricular block, antiarrhythmic drug use, and heart failure were predictors of atrial high-rate episodes. The primary trial end point of death or nonfatal stroke occurred in 33 of 160 (20.6%) of the patients with atrial high-rate episodes and in 16 of 152 (10.5%) patients without atrial high-rate episodes. However, of the 10 strokes in the ancillary study population, 8 occurred in the 160 patients with atrial high-rate episodes. The presence of any atrial high-rate episode was an independent predictor of the following: total mortality, death or nonfatal stroke, and atrial fibrillation.

A limited amount of ambulatory monitoring data were available from this study. Forty-one patients in the substudy had an ambulatory monitor that did not show atrial fibrillation. These 41 also had no atrial high-rate episodes detected during the monitoring. In 1 patient, the pacemaker stored an atrial high-rate episode that was not confirmed by the ambulatory monitor recordings. In 5 patients, an atrial high-rate episode detected by the pacemaker corresponded to atrial fibrillation seen on the ambulatory recording. There was no significant effect of pacing mode on the presence or absence of atrial highrate episodes. Of the 190 DDDR patients in the sample, 95 (50%) had atrial high-rate episodes. Of the 122 VVIR patients, 65 (53.3%) had atrial high-rate episodes.

Glotzer and colleagues conclude that it is possible to use pacemakers to detect symptomatic and asymptomatic nonsustained atrial high-rate episodes and that detection of these atrial high-rate episodes identifies patients at higher risk for death, stroke, and atrial fibrillation.

Comment by John DiMarco, MD, PhD

It has recently been possible to program certain cardiac pacemakers to detect atrial high-rate episodes and to store these events. It has been shown that there is a high false-positive rate if relatively slow atrial rate detection criteria are used (less than 220 bpm) or if brief durations (eg, 10-30 seconds) of high rates are required. This is probably due to oversensing of either far-field ventricular signals or of T waves by the atrial lead. It also is important to note that a conservative atrial sensitivity setting of 0.5 mV on the atrial lead was selected in this study. Increased sensitivity, sometimes required to detect true atrial fibrillation, would lead to many more false positives. The data here indicate that in patients with sinus node dysfunction, pacemakers can be used to detect episodes of atrial fibrillation that may be asymptomatic. Since much of the excess mortality in patients with sinus node dysfunction is due to stroke, this would constitute an indication for anticoagulation. It is, therefore, recommended that patients with sinus node dysfunction who are known to be at risk of atrial fibrillation have pacemakers with this capability inserted. Detection of atrial high-rate episodes during long-term follow-up would lead one to consider chronic anticoagulation for those patients who are either elderly or who had other risk factors for stroke.

Dr. DiMarco is Professor of Medicine Division of Cardiology University of Virginia, Charlottesville.