A 69-year-old woman is in the Cardiac surgical ICU one day after aortic valve replacement because of severe aortic stenosis. Pre-op coronary angiography is normal:

• Sinus rhythm, 75/min, with AV dissociation due to a competing accelerated junctional rhythm (ventricular rate 82/min)
• One AV capture beat (with PR = 240 msec)
• Diffuse ST and T wave abnormality