An increased minute ventilation ( e)/carbon dioxide production (Vco2) relationship, an expression of ventilatory inefficiency (VI), is associated with increased morbidity and mortality in patients with left ventricular systolic dysfunction (LVSD). A direct link between VI and a specific cardiac abnormality has not been established.
We analyzed cardiopulmonary exercise test (CPET) data from patients (N = 83) with severe LVSD (ischemic and nonischemic; left ventricular ejection fraction [LVEF] 19% ± 7%) and at least moderate exercise intolerance. Subjects were stratified into two groups based on the ( e/Vco2 ratio at anaerobic threshold ( e/Vco2@AT) (group 1 e/Vco2@AT ≤ 34; group 2 e/Vco2@AT > 34). Clinical, CPET, echocardiographic, and hemodynamic data were compared between groups.
Group 2 subjects had lower exercise capacity (peak ( o2, 45.7% ± 11.8% vs 50.4 ± 8.9% predicted; P < .05), with a significantly lower oxygen pulse (71.6% ± 24.5% vs 85.4 ± 18.5% predicted) and maximum systolic BP (122 ± 19 mm Hg vs 138 ± 22 mm Hg; P < .001 for both), suggesting a more blunted stroke volume to exercise vs group 1. There were no differences in left ventricular (LV) size, LVEF, or mitral regurgitation between the two groups. In sharp contrast, group 2 had larger right ventricular (RV) dimensions (4.5 ± 1.1 cm vs 3.9 ± 0.8 cm) and more severe RV systolic dysfunction (RV fractional area change 26% ± 11% vs 33% ± 12%; tricuspid annular plane systolic excursion [TAPSE] 1.6 ± 0.5 cm vs 2.0 ± 0.5 cm; all P < .001) vs group 1. Multivariable analysis revealed that only TAPSE and Doppler-estimated pulmonary artery systolic pressure were independently associated with e/Vco2@AT and the ( e/Vco2slope. The e/Vco2@AT, e/Vco2 slope, and TAPSE had nearly identical predictive value for death or transplant.
The present study suggests that VI is a functional, noninvasive marker of more advanced right-sided heart dysfunction in patients with severe LVSD.