An unusual ECG after spinal surgery.

Dr. Hancock is Professor of (Cardiovascular) Medicine Emeritus. Stanford University School of Medicine, Stanford. Calif. A 91-year-old man with leg weakness and pseudoclaudication of four months' duration underwent lumbar laminectomy for intervertebral disc disease and spinal stenosis. He did not have heart disease or cardiac symptoms-the preoperative cardiovascular examination and ECG were normal. The operation was uneventful, and the patient's initial recovery was satisfactory. However, his stay in the intensive care unit was prolonged because of cough, fever, and pulmonary infiltrates. Borderline respiratory failure and intermittent hypoxemia developed On the sixth postoperative day, an arrhythmia was noted on the monitor. The 12-lead ECG recorded at this time is shown. What explains the differing QRS complexes? What explains the intermittent pauses in rhythm? Is a cardiologic intervention indicated?