Exercise testing and spirometry as predictors of mortality in congenital heart disease: Contrasting Fontan physiology with repaired tetralogy of Fallot.

OBJECTIVE: Risk prediction using cardiopulmonary exercise testing (CPET) in complex congenital heart disease tends to either focus on single diagnoses or complete cohorts. We aimed to evaluate patients with two distinct anatomies cared for at a single institution over the same time period to determine CPET variables associated with mortality.

DESIGN: All Fontan and tetralogy of Fallot (TOF) subjects with CPET between November 1, 2002 and December 31, 2014 and subsequently died were identified (cases). Cases were matched 1:3 to controls with similar age, underlying anatomy and timing of exercise test.

RESULTS: Of the 42 cases, 27 had a Fontan circulation and 15 with TOF. All Fontan patients had a low peak VO2 but there was no significant difference between cases and controls (52.5 ± 14.7 v. 57.4% ± 13.5% predicted, P = .11). Spirometry values were significantly lower in Fontan cases than controls (eg, FVC 67.4 ± 19.1 v 77.6% ± 14.9% predicted, P = .007). Spirometry values were also lower in TOF cases than controls (% predicted FVC 62.8 ± 16.7 v 75 ± 14, P = .006). In contrast to the Fontan analysis, both %peak predicted VO2 and VE/VCO2 slope were worse in TOF cases than controls (50.1 ± 13.5 v. 68.5% ± 15.0% predicted VO2 , P = .0004; 33.9 ± 12.9 v 26.6 ± 4.4, P = .002). Multivariable analysis also identified different predictors of mortality among the anatomic subgroups. Spirometric data (FVC) correlated most strongly with mortality in Fontan patients while the VE/VCO2 slope was most associated with outcome in TOF patients.

CONCLUSIONS: Variables most predictive of mortality in Fontan and TOF patients diverge but spirometry was abnormal and associated with mortality in both groups. When compared with age-matched controls, reduced FEV1 and FVC correlated most strongly with mortality in Fontan patients while VE/VCO2 slope correlated with mortality for TOF patients. These findings further support the importance of lung health in patients with complex congenital heart disease.