Single ventricle physiology such as hypoplastic left heart syndrome remains one of the highest risk lesions in congenital heart disease, with a persistently high mortality rate, particularly between stage I and stage II palliative surgeries. In this issue of Heart Rhythm Journal, Czosek et al 1 Czosek R. Anderson J. Baskar S. et al. Predictors and outcomes of heart block during surgical stage I palliation of patients with a single ventricle: a report from the NPC-QIC.

Heart Rhythm. 2021; (XX:XX–XX)

explored the role that heart block might have in early mortality in single ventricle physiology. They were able to identify a higher mortality rate in the first year of life in those with a report of complete heart block. The data for this study were drawn from the National Pediatric Cardiology Quality Improvement Collaborative (NPC-QIC) single ventricle database. Database studies such as this can offer power in the number of participants they can gather, and this is no exception. A total of 1423 eligible infants were included in the initial study group, and identification of the rare event of heart block yielded 28 children with this finding. Interestingly, this was a lower incidence (2%) than what has typically reported in the literature (4%–11%), 2 Oster M.E. Chen S. Dagincourt N. et al. Development and impact of arrhythmias after the Norwood procedure: a report from the Pediatric Heart Network.

J Thorac Cardiovasc Surg. 2017; 153: 638-645.e642

,3 Mah D.Y. Cheng H. Alexander M.E. et al. Heart block following stage 1 palliation of hypoplastic left heart syndrome.

J Thorac Cardiovasc Surg. 2016; 152: 189-194

even including both second- and third-degree heart block as well as transient and permanent heart block. Given the high interstage mortality in this population, identification of any risk factors, such as heart block, are of great clinical interest. However, in a database study such as this, it is challenging to go beyond the surface correlation that has been identified, and understanding the meaning of this finding will require additional study, as the authors note.