Concealed accessary pathway manifesting clinically only after pacemaker implantation

A 66-year-old man with coronary artery disease and persistent left superior vena cava received a DDDR pacemaker for symptomatic 2:1 heart block. There was no previous history of tachyarrhythmias. Endless loop tachycardia and repetitive nonreentrant ventriculoatrial synchrony occurred afterwards and were triggered by a late coupled atrial premature beat. ECGs suggested a co ncealed left posterior accessory pathway that was confirmed during electrop hysiological study. Effective palliation was achieved with extension of the PVARP and enabling noncompetitive atrial pacing operation.