Wide and narrow QRS complexes after arthroscopy.

A n obese (5 feet 5 inches, 224 pounds) 57-year-old woman with high blood pressure, diabetes mellitus, and arthritis underwent arthroscopy for a painful left knee. After the procedure, the electrocardiographic monitor in the recovery room showed alternately narrowing and widening QRS complexes, and a 12-lead electrocardiogram was obtained (Figure). e first three QRS complexes are wide (0.17 seconds) and occur regularly (R-R interval = 1.09 seconds; rate = 55/minute), and no P waves are seen. e next three QRS complexes become progressively more narrow, and a P wave can be seen in front of each, with a steadily lengthening P-R interval. ese QRSs are fusion beats. e next four complexes (7–10) are completely sinus-initiated with normal P waves, a P-R interval of 0.17 seconds, and a QRS duration of 0.09 seconds. e last four complexes show gradually shortening P-R intervals and widening QRSs that once again are fusion complexes. us, at times sinus rhythm completely captures the ventricles and at other times shows isorhythmic atrioventricular dissociation from an idioventricular rhythm. During each transition in rhythm, there are numerous ventricular fusion beats. What allows the idioventricular rhythm to emerge and then disappear is sinus bradycardia with slight sinus arrhythmia. As P waves first appear on the left side of the tracing, the P-P intervals are as short as 1.00 seconds, whereas toward the right side of the tracing where the Ps disappear into the wide QRSs, Wide and narrow QRS complexes after arthroscopy