A 51-year-old man with good exercise tolerance and no symptoms or abnormal findings on physical examination suggesting cardiac disease, is in the pre-op clinic prior to a scheduled urology procedure:

• Ectopic atrial rhythm
• Atrial rate 85/min. – PR 90 msec
• No other abnormalities

Comment: When the P waves are negative in the inferior leads, the atrial rhythm is likely originating from the low atrium causing a superior axis to the P-wave.  Because the atrial rhythm is originating closer to the AV node, the PR interval may be shorter than usual.