This 76 year old woman is admitted to the cardiac ward for treatment of congestive heart failure. Of note, her QRS pattern has been unchanged since the time of her last admission four months ago:

•  Sinus rhythm, with isorhythmic AV dissociation due to an accelerated junctional rhythm (68/min)
•  Right bundle branch block
•  Anterolateral myocardial infarction, age undetermined

Isorhythmic dissociation: when the rate of the sinus node and the rate of the competing junctional pacemaker are almost identical