Electrocardiogram of the month intracardiac electrogram. Paradoxic slowing of ventricular rate with intravenous isoproterenol in a patient with A V block

Recently, a report demonstrating facilitation of conduction in the A V node and His Purkinje system with intravenous isoproterenol was published. Despite this facilitation of conduction, it was anticipated that paradoxic worsening of conduction could occur in patients with bilateral bundle branch disease, due to increase in atrial rate with this agent. In this report, the authors document paradoxic worsening of heart block and slowing of ventricular rate during isoproterenol infusion in a patient with 2:1 A V block distal to the His bundle. The implications of these findings are briefly discussed.