THE ROLE OF SIGNAL-AVERAGED P-WAVE DURATION AND SERUM MAGNESIUM AS A COMBINED PREDICTOR OF ATRIAL-FIBRILLATION AFTER ELECTIVE CORONARY-ARTERY BYPASS-SURGERY

Objective-To investigate the role of low serum magnesium as a trigger for atrial fibrillation in patients with a substrate for the arrhythmi a (assessed by signal averaged P wave duration). Design-A case-control study. Setting-A regional referral cardiac centre. Patients and inter ventions-105 consecutive patients undergoing elective coronary artery bypass surgery had signal averaged P wave recordings before operation. Serum electrolytes were analysed preoperatively and on days 1, 2, and 5 after surgery. Main outcome measures-Any episode of electrocardiogr aphically recorded atrial fibrillation was taken as a study end point. Results-Of 102 patients discharged, 27 (26%) had documented episodes of atrial fibrillation at a mean of 2.7 days after surgery. A combinat ion of P wave duration >155 ms and serum magnesium on the first postop erative day of <0.7 mmol/l had a sensitivity of 75% and specificity of 80% for predicting atrial fibrillation. Duration of hospital stay (7. 9 v 6.8 days) was longer in the atrial fibrillation group (P<0.01). St epwise regression showed age, serum magnesium < 0.7 mmol/l on the firs t postoperative day (both P<0.001), angiotensin converting enzyme inhi bitor withdrawal (P<0.02), and signal averaged P wave duration (P=0.04 ) to be independent predictors. Conclusions-The combination of signal averaged P wave duration and low serum magnesium on the first postoper ative day identified the majority of patients with atrial fibrillation after coronary artery bypass surgery. Early identification and pharma cological treatment for selected patients may reduce the incidence of postoperative atrial fibrillation.