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The Role of Cardiac Pacing

atrial fibrillationAtrial conduction delay and triggering events, such as atrial premature beats (APBs), may predispose patients to the genesis of new-onset atrial fibrillation (AF) after cardiac surgery. A prolonged P-wave duration on the signal-averaged ECG (a measure of atrial conduction delay) is a predictor of post-coronary artery bypass graft AF. Likewise, APBs are more common in the minutes and hours preceding the onset of AF in cardiac surgery patients. These observations support the concept that reducing atrial conduction time and suppressing APBs with atrial pacing may decrease the incidence of AF after cardiac surgery.

Evidence Review and Recommendations

Evidence was compiled, reviewed, and graded, and recommendations were formulated as described in the “Methodological Approach” article in this supplement. It was found that a number of randomized controlled trials have investigated the utility of atrial pacing after cardiac surgery. Each utilized either atrial pacing at a moderate rate (ie, 90 to 100 beats/min) or an atrial overdrive pacing algorithm that was designed to pace the atrium slightly faster than the underlying sinus rhythm. In all cases, pacing was performed via epicardial wires that were placed at the time of cardiac surgery. Right atrial (RA) electrodes were most often placed on the high RA near the sinus node. Left atrial (LA) electrodes were usually placed on the posterior LA between the pulmonary veins or on the roof of the LA at the Bachman bundle. Patients received RA pacing only, LA pacing only, biatrial pacing (BAP), or no atrial pacing, depending on the study design. Patients also received backup epicardial ventricular pacing electrodes. Pacing was initiated within 24 h postoperatively and generally continued for 3 to 4 days.

RA Pacing

The trials that investigated the utility of RA pacing alone for the reduction of AF after cardiac surgery have yielded mixed results. Blommaert et al2 studied 96 patients and demonstrated a reduction in AF from 27.1 to 10.4% with RA pacing compared with control treatment. Similarly, Greenberg et al randomized 154 patients to RA pacing, LA pacing, both, or neither and showed a reduction from 37.5 to 7.5%, respectively, with RA pacing compared with no pacing. A number of other studies, however, involving a total of 411 patients, have demonstrated no significant benefit of RA pacing alone compared with the control treatment.

BAP after cardiac surgeryLA Pacing

The utility of LA pacing after cardiac surgery has not been as extensively studied. Two trials randomized patients to RA pacing, LA pacing, both, or neither. LA pacing alone (provided to a total of 88 patients) did not significantly reduce the incidence of AF after cardiac surgery compared to no pacing or backup pacing,

BAP

BAP after cardiac surgery appears to offer the most promise. Gerstenfeld et al and Levy et al conducted separate trials involving a total of 248 patients comparing BAP to control treatment (ie, no pacing or backup pacing). The rate of postoperative AF was reduced from 35.0 to 20.7% and from 38.5 to 13.8%, respectively. Four other trials randomized patients to BAP, control, RA pacing alone, and/or LA pacing alone. Two of these trials” (250 patients) showed a significant reduction in AF with BAP compared with the control treatment, and two other studies (215 patients) showed no benefit. BAP also reduced the incidence of AF compared with RA pacing alone in two of the four trials’ that compared them directly and in one of two trials that compared BAP directly with LA pacing alone.

The risks of temporary atrial pacing via epicardial wires are small. Placing the wires requires minimal time. Diaphragmatic pacing can occasionally occur but usually can be overcome by pacemaker reprogramming. The loss of capture (ie, > 50% by the fifth postoperative day in one study) and atrial undersensing can affect treatment efficacy. Atrial proarrhythmia resulting in an increase in ABPs rather than a decrease also has been reportedA The removal of the temporary atrial wires was performed without significant complication in every study, although pericardial effusion with tamponade, saphenous vein graft injury, and the occasional inability to remove an entrapped epicardial wire may rarely occur. The use of BAP to prevent postoperative AF after cardiac surgery may find limited application because of the need for additional intensive monitoring and potential prolongation of the hospital stay, but may have a prophylactic role in those patients in whom there is a particularly high incidence of postoperative AF (eg, those who have undergone mitral valve and coronary bypass surgery). The recommendation summary follows and is presented in Table 1.

Summary of Recommendations

Atrial pacing appears to reduce the incidence of AF after cardiac surgery in some studies. BAP appears to be the most efficacious. RA pacing alone may reduce the incidence of AF, while LA pacing alone does not appear to reduce the incidence, at least based on the limited data currently available. The recommendations are also summarized in Table 1.

1. We do not recommend RA pacing alone to reduce postoperative AF after cardiac surgery (strength of recommendation, I; evidence grade, fair; net benefit, small/weak).

2. We do not recommend isolated LA pacing to prevent postoperative AF following cardiac surgery (strength of recommendation, I; evidence grade, fair; net benefit, none).

3. We recommend BAP to help prevent postoperative AF (strength of recommendation, B; evidence grade, good; net benefit, small/ weak)

Table 1—Recommendation Summary for Cardiac Pacing To Prevent Atrial Fibrillation After Cardiac Surgery

Intervention Evidence

Grade

Net

Benefit

Overall Strength of Recommendation
RA pacing Fair Small/weak I
LA pacing Fair None I
Biatrial Pacing Good Small/weak B