Natural History and Determinants of Conduction Defects Following Coronary Artery Bypass Surgery

Ninety-three consecutive patients undergoing coronary artery bypass grafting (CABG) were followed prospectively to ascertain the natural history and determinants of new postoperative conduction defects. Each patient was followed in the postoperative period with serial electrocardiograms and continuous monitoring. In the last 70 patients, a technetium pyrophosphate scan was obtained 48 to 72 hours after operation. Postoperatively, new bundle-branch or fascicular block developed in 42 patients (45%) and third-degree atrioventricular (AV) block, in 4 (4%). The occurrence was compared with patient age, preoperative bundle-branch block or fascicular block, number of diseased arteries, number of bypassed arteries, total time of cardiopulmonary bypass, aortic cross-clamping time, occurrence of a preoperative or perioperative myocardial infarction, and presence of disease in the left anterior descending or right coronary artery. Only the number of bypassed arteries, the total time of cardiopulmonary bypass, and the aortic cross-clamping time were related to the development of postoperative conduction defects (all, p < .05). The conduction defect resolved partially or completely by the time of hospital discharge in 54% of patients. In the 4 patients with third-degree AV block, AV block resolved on postoperative day 2 in 1 patient and resolved transiently for up to 5 days or persisted in 3 patients. At two months of follow-up, all 3 patients discharged in third-degree AV block with a permanent pacemaker were no longer in AV block. In conclusion, following CABG, (1) the occurrence of new AV conduction defects is related to the number of vessels bypassed, the cardiopulmonary bypass pump time, and the aortic cross-clamping time; (2) new conduction defects occur frequently, but the resolution rate is high and third-degree AV block is rare if it is not present by postoperative day 1; (3) because resolution of third-degree AV block may be only transient, patients who have recovered from AV block should be observed for several days before discharge; and (4) ventricular demand pacing may be adequate in patients who require a pacemaker at the time of discharge, because the AV block may resolve by two months of follow-up.