Relation of Norwood Shunt Type and Frequency of Arrhythmias at 6 Years (from the Single Ventricle Reconstruction Trial)

Abstract

The Norwood procedure with a right ventricular to pulmonary artery shunt (RVPAS) decreases early mortality, but requires a ventriculotomy, possibly increasing risk of ventricular arrhythmias (VAs) compared with the modified Blalock-Taussig shunt (MBTS). The effect of shunt and Fontan type on arrhythmias by 6 years of age in the SVRII (Single Ventricle Reconstruction Extension Study) was assessed. SVRII data collected on 324 patients pre-/post-Fontan and annually at 2 to 6 years included antiarrhythmic medications, electrocardiography (ECG) at Fontan, and Holter/ECG at 6 years. ECGs and Holters were reviewed for morphology, intervals, atrioventricular conduction, and arrhythmias. Isolated VA were seen on 6-year Holter in >50% of both cohorts (MBTS 54% vs RVPAS 60%), whereas nonsustained ventricular tachycardia was rare and observed in RVPAS only (2.7%). First-degree atrioventricular block was more common in RVPAS than MBTS (21% vs 8%, p = 0.01), whereas right bundle branch block, QRS duration, and QTc were similar. Antiarrhythmic medication usage was common in both groups, but most agents also supported ventricular function (e.g., digoxin, carvedilol). Of the 7 patients with death or transplant between 2 and 6 years, none had documented VAs, but compared with transplant-free survivors, they had somewhat longer QRS (106 vs 93 ms, p = 0.05). Atrial tachyarrhythmias varied little between MBTS and RVPAS but did vary by Fontan type (lateral tunnel 41% vs extracardiac conduit 29%). VAs did not vary by Fontan type. In conclusion, at 6-year follow-up, benign VAs were common in the SVRII population. However, despite the potential for increased VAs and sudden death in the RVPAS cohort, these data do not support significant differences or increased risk at 6 years. The findings highlight the need for ongoing surveillance for arrhythmias in the SVR population.

Figure 1.

Non-sustained ventricular tachycardia episodes in 2 subjects in the RVPAS cohort on 6-year Holter. Both episodes are monomorphic, with the left panel showing a 7-beat run at 136 beats/minute, and the right panel showing an 8-beat run at an average rate of about 120 beats/minute.

Figure 2.

Prescribed drugs with antiarrhythmic actions by follow-up age in the MBTS and RVPAS cohorts. The Y-axis represents the percentage of each age/cohort receiving each of the agents, with the number of subjects noted on each bar.