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Abstract & Commentary
Synopsis: Physiologic pacing does not appear to be specific for preventing the development of atrial fibrillation in patients at highest risk.
Source: Skanes AC, et al. J Am Coll Cardiol. 2001;38:167-172.
The Canadian Trial of Physiologic Pacing (CTOPP) randomized 2568 patients undergoing first pacemaker implantation to physiologic, dual chamber, or atrial- vs. ventricular-based pacing. One of the major hypotheses in the trial was that physiologic pacing would reduce the incidence of atrial fibrillation (AF). This report describes those observations.
In CTOPP, 1474 patients received ventricular pacing only implants and 1094 patients received physiologic pacing implants. During the study, AF was defined as any ECG documented episode of AF lasting longer than 15 minutes. Chronic AF was defined to occur when a patient with new onset AF had continued AF on a second recording 1 week later. Physiologic pacing reduced the rate of development of chronic AF from 3.84% per year to 2.8% per year. This reduced risk was essentially linear over time with separation of the curves at approximately 6 months. Three clinical factors predicted the development of chronic AF. Age older than 74 years was associated with an annual risk of 3.83% vs. 2.95% for those younger than 74 years of age. The presence of sinoatrial node disease was associated with annual risk of 5.66% vs. 1.86% for those without sinoatrial node disease. A prior history of AF was associated with an annual risk of 9.64% vs. 2.04% for those without this history. The benefits of physiologic pacing were looked at in certain subgroups. There was a statistical trend for patients free of previous myocardial infarction (MI) or coronary disease and for patients with apparently normal ventricular function to derive the greatest relative risk reduction from physiologic pacing. However, the confidence intervals for the hazard ratios were broad in these groups. Interestingly, patients with prior AF and with sinoatrial node disease did not appear to derive greater relative benefit from physiologic pacing compared to those patients without these findings.
Skanes and colleagues conclude that physiologic pacing produces a small but statistically significant reduction in the annual rate of development of chronic AF. Unfortunately, physiologic pacing does not appear to be specific for preventing the development of AF in patients at highest risk.
Comment by John P. DiMarco, MD, PhD
It has only been in the last few years that randomized trials comparing physiologic pacing and ventricular pacing have been undertaken. In CTOPP and in another smaller trial—the Pacemaker Selection in the Elderly study—no benefit in overall mortality was observed in patients who recived physiologic pacing systems.1,2 In another study with patients only with sinatrial node dysfunction, atrial rate responsive pacing reduced the long-term incidence of chronic AF when compared to ventricular based rate response pacing.3 The data from CTOPP presented in this paper confirm that physiologic pacing reduces the incidence of AF but shows only a small, short-term clinical benefit. In this study, the overall reduction was 1% per year for a relative risk reduction of 27.1%. However, it is possible that if the event curves continue to diverge over time that even this small annual reduction can lead to a long-term reduction in stroke or cardiovascular death. This becomes more significant as pacemaker patients live longer due to improved therapy for heart failure and ischemic heart disease. However, it is somewhat disappointing that physiologic pacing seems to have the least significant relative effect in patients, one would suspect they are most likely to benefit from preservation of atrial contractility. In this study, patients with abnormal left ventricular function and prior MI had little benefit with atrial pacing. It is likely that the degree of myocardial dysfunction is so powerful that it overrides any changes that might be produced by atrial pacing alone.
At present, the decision to implant a dual chamber pacemaker or ventricular pacemaker continues to be up to the physician. There seems to be small but statistically significant benefits in terms of quality of life and development of AF. However, pacing is a lifelong therapy and even small annual benefits may be clinically significant when assessed over long intervals.
1. Connolly S, et al. N Engl J Med. 2000;342:1385-1391.
2. Lamas G, et al. N Engl J Med. 1998;338:1097-1104.
3. Andersen H, et al. Lancet. 1997;350:1210-1216.