A 4-month-old infant presents with incessant tachycardia and a dilated cardiomyopathy. ECG shows a narrow complex tachycardia at 190 bpm with atrioventricular dissociation. The diagnosis of congenital junctional ectopic tachycardia (JET) is made. Chronic therapy is initiated. Which of the following is a known, important complication of catheter ablation for this condition?