The patient is a 54-year-old woman with a history of tetralogy of Fallot. At age 18 months, she underwent placement of a left end-to-end Blalock-Taussig shunt. Two years later, she required a right end-to-side Blalock-Taussig shunt. The patient was then lost to follow-up until age 29. 

At that point, after relocating and reestablishing medical care for increasing fatigue, the patient was found to have a murmur. Subsequent work-up revealed a persistent ventricular septal defect, and she underwent near-complete repair of the tetralogy of Fallot, which included placement of a transannular right ventricular outflow patch, closure of the ventricular septal defect, and takedown of the right Blalock-Taussig shunt. The left pulmonary artery was allowed to remain discontinuous from the main pulmonary artery.

The patient fared well until three years ago, when she began experiencing abdominal pain and atrial arrhythmias. Further evaluation revealed right heart failure and severe right-sided pulmonary artery hypertension. Left pulmonary artery pressures were normal, presumably due to anastomosis of the stenotic left subclavian artery to the left pulmonary artery. She was also found to have severe right atrial and ventricular enlargement, with moderate tricuspid regurgitation and wide-open pulmonic valve regurgitation. The patient has been treated with diuretics, ACE inhibitors, and beta-blockers to control her right-sided heart failure and systemic hypertension. 

As part of her current evaluation to determine whether further surgical intervention is warranted, an ECG is obtained and shows the following: a ventricular rate of 47 beats/min; PR interval, 266 ms; QRS duration, 172 ms; QT/QTc interval, 528/467 ms; P axis, 67°; R axis, 9°; and T axis, 5°. What is your interpretation of this ECG?

ANSWER

The ECG is remarkable for marked sinus bradycardia with a first-degree atrioventricular (AV) block and a right bundle-branch block (RBBB). Sinus bradycardia impulses originate in the sinus node at rates of less than 60 beats/min. In first-degree AV block, a P wave precedes each QRS complex at an interval exceeding 200 ms.

Criteria for an RBBB include a prolonged QRS complex (> 120 ms) and an abnormal late portion of the QRS manifested by a broad terminal S wave in lead I as well as the precordial leads, a terminal broad R wave in lead aVR, and the characteristic RSR’ in lead V1. The later positive deflection (R’) may be either smaller or larger in amplitude than the initial R wave.

The above findings are common in postoperative complex congenital heart disease.