To the Editor,

We read with interest the article by Khiabani et al,1 where the authors examine the relationship between power loss in the total cavopulmonary connection (TCPC) and clinical exercise testing. Using an indexed power loss, ‘iPL’, they report that higher iPL correlates with worse minute oxygen consumption and exercise work at anaerobic threshold. Based on this, the authors suggest that power loss in the TCPC could affect exercise performance in a patient with Fontan circulation. In the manuscript, the authors attempt to discover a correlation of the hydraulics of the Fontan circulation with exercise performance. In doing so, they use the unique parameter, iPL, instead of the unadjusted power loss. We believe that this approach is misleading and leads to the wrong conclusion.

The term iPL was defined as: where PL, ρ, Q …