ABSTRACT
BACKGROUND: The slope of the minute ventilation versus CO2 production relationship (VE/VCO2 slope) is an index of gas exchange efficiency during exercise. In patients with repaired tetralogy of Fallot (rTOF), it correlates negatively with exercise capacity and is one of the best predictors of peak oxygen consumption (VO2). In these patients, the magnitude of the VE/VCO2 slope is related to the severity of pulmonary blood flow maldistribution (PBFM). The purpose of this study was to determine whether, in patients with rTOF, improvements in PBFM after a successful balloon angioplasty procedure (BAP) result in improvements in peak VO2 and gas exchange during exercise. METHODS: Seventeen patients with rTOF and residual pulmonary artery stenoses referred for BAP were recruited. Exercise tests were performed and PBFM determined before and after BAP. RESULTS: Nine patients (group 1) had a successful BAP (ie, improvement of >5 percentage points in PBFM); 8 did not (group 2). Patients in group 1 had significantly greater improvements in VE/VCO2 slope, peak VO2, and peak oxygen pulse (an index of forward stroke volume at peak exercise) than did patients in group 2. A significant correlation existed between the improvement in PBFM and the decline in the VE/VCO2 slope (r = -0.70, P = .002). Changes in peak oxygen pulse accounted for 89% of the improvement in peak VO2. CONCLUSIONS: In these patients, a successful BAP resulted in improved peak VO2 and more efficient gas exchange during exercise. The improvement in peak VO2 appeared to be mediated by an increase in forward stroke volume.