Correspondence
Effects of Physiologic Pacing versus Ventricular Pacing
N Engl J Med 2000; 343:1417-1418November 9, 2000
- Article
To the Editor:
The article by Connolly et al. (May 11 issue)1 on physiologic pacing as compared with ventricular pacing was published prematurely, since the period of follow-up (range, two to five years) was simply too short for the true advantages of one type of pacing over the other to become fully manifest. The physiologic virtues of normally timed atrial transport were described in 1911,2 and the consequences of retrograde ventriculoatrial conduction (a harbinger of symptoms of the “pacemaker syndrome” in the recipients of antiarrhythmia devices and in all likelihood the mechanism that triggers subsequent atrial fibrillation) in 1913.3 More recent studies have confirmed that the incidence of retrograde ventriculoatrial conduction is 50 percent in patients with complete antegrade heart block and 90 percent in those with the sick sinus syndrome. Nielsen et al.4 randomly assigned 225 consecutive patients with sinus-node disease to single-chamber atrial pacing or single-chamber ventricular pacing and recorded deleterious effects of the left atrial size, left ventricular end-diastolic dimension, diuretic requirements, and New York Heart Association class in the ventricular-pacing group. Preliminary data suggested a reduction in atrial fibrillation and death from atrial pacing. The physiologic advantages of dual-chamber pacing include an increase in cardiac output of 19 to 40 percent5 through the restitution of properly timed atrial transport.
I hope Connolly et al. will document serial echocardiographic measurements of chamber size in the two groups in this large sample of pacemaker recipients and will note the results among the patients who declined participation or were not randomly assigned to a treatment group for another reason.
5 ReferencesJ. Warren Harthorne, M.D.
Massachusetts General Hospital, Boston, MA 021141
Connolly SJ ,Kerr CR ,Gent M , et al. Effects of physiologic pacing versus ventricular pacing on the risk of stroke and death due to cardiovascular causes. N Engl J Med 2000;342:1385-1391
Full Text | Web of Science | Medline2
Gesell RA . Auricular systole and its relation to ventricular output. Am J Physiol 1911;29:32-63
Web of Science3
Mines GR . On the dynamic equilibrium in the heart. J Physiol 1913;46:349-383
Web of Science | Medline4
Nielsen JC ,Andersen HR ,Thomsen PEB , et al. Heart failure and echocardiographic changes during long-term follow-up of patients with sick sinus syndrome randomized to single-chamber atrial or ventricular pacing. Circulation 1998;97:987-995
Web of Science | Medline5
Stewart WJ ,DiCola VC ,Harthorne JW ,Gillam LD ,Weyman AE . Doppler ultrasound measurement of cardiac output in patients with physiologic pacemakers: effects of left ventricular function and retrograde ventriculoatrial conduction. Am J Cardiol 1984;54:308-312
CrossRef | Web of Science | Medline
To the Editor:
In the well-conducted study by Connolly et al., a few points need clarification. The authors state that the rate of lead dislodgment was 4.2 percent in the physiologic-pacing group, accounting for approximately 45 patients. The standard procedure in these cases is to perform a repeated operation in order to attach the dislodged lead, thus increasing the rate of complications. It is unclear whether this factor was taken into account in the analysis.
In addition, the rate of infection was not reported among the 2568 patients who underwent implantation of a pacemaker. Infection of the implantation site and bacteremia cause major morbidity in pacemaker recipients, since prolonged antibiotic treatment and sometimes removal of the device are required. Since infection is correlated with the duration of the procedure, infection would be expected to occur more frequently with physiologic pacing.
The study did not show a decrease in the rate of stroke or death in the physiologic-pacing group. We believe that when there are differences between treatment groups only in “soft” end points, more emphasis should be given to associated complications. Doctors who must decide which pacemaker to choose for their patients need to know whether a device causes major complications as the price of preventing atrial fibrillation.
Oren Shibolet, M.D.
Guy Amit, M.D.
Hadassah University Hospital, Jerusalem 91120, IsraelAuthor/Editor Response
The authors reply:
To the Editor: We agree with Dr. Harthorne that there is considerable evidence from physiologic studies that physiologic pacing may be superior to ventricular pacing. This was the rationale for the Canadian Trial of Physiologic Pacing, which was conducted in order to obtain the best estimate of the benefit of physiologic pacing. To the surprise of some observers, the trial did not show a significant benefit of physiologic pacing in regard to the composite outcome of stroke or death from cardiovascular causes. The findings do not rule out a small benefit of physiologic pacing.
Our results indicate that the benefit of physiologic pacing has been overestimated. One can speculate that the mean follow-up period of three years in our study may have been too short for a benefit of physiologic pacing to emerge. Prolonged follow-up should provide a definite answer. We are continuing to follow the patients, and since there has been very little crossover from the randomly assigned treatment to the other treatment, we expect to be able to answer this question. Echocardiographic measurements were not routinely performed in the study and will not be available for analysis. Patients who declined participation were not routinely followed, and the results for those patients are not known.
We agree with Drs. Shibolet and Amit that, in the light of the minimal benefit of physiologic pacing observed in our trial, physicians should be concerned about the higher rate of complications with more complex pacemakers. Of the 45 patients in the physiologic-pacing group who had a dislodged lead, 12 underwent a repeated procedure during their initial hospitalization to correct the problem. The risk of infection during the whole period of follow-up was 0.8 percent for the physiologic-pacing group and 0.3 percent for the ventricular-pacing group.
Stuart J. Connolly, M.D.
Michael Gent, D.Sc.
McMaster University, Hamilton, ON L8L 2X2, CanadaCharles R. Kerr, M.D.
University of British Columbia, Vancouver, BC V6Z 1Y6, Canadafor the Canadian Trial of Physiologic Pacing Investigators
