Association between cardiopulmonary exercise and dobutamine stress testing in ambulatory patients with idiopathic dilated cardiomyopathy: A comparison with peak VO₂ and VE/VCO₂ slope

Background: Both peak VO₂ and VE/VCO₂ slope are considered to be useful predictors of cardiovascular events. The left ventricular (LV) response to dobutamine stress testing (DST) also provides useful prognostic information. However, the relationship between these variables has not been fully investigated. Therefore, the aim of this study is to investigate the association between myocardial contractile reserve measured by DST and cardiopulmonary exercise testing (CPX) variables in patients with idiopathic dilated cardiomyopathy (IDCM). Methods: Thirty-eight patients were subjected to CPX as well as cardiac catheterization for measurement of LV pressure. The maximum first derivative of LV pressure (LV dP/dt_max) was measured at baseline and during dobutamine infusion at incremental doses of 5, 10, and 15 μg kg^{- 1} min^{- 1}. LV dP/dt_max at baseline and the percentage increase in LV dP/dt_max (ΔLV dP/dt_max) induced by DST served as indices of LV contractility and myocardial contractile reserve, respectively. Results: Peak VO₂, and VE/VCO₂ slope were 18.6 mL kg^{- 1} min^{- 1} and 32.3, respectively. Peak VO₂ was not correlated with LV dP/dt _max at baseline. However, peak VO₂ was significantly correlated with ΔLV dP/dt_max, and the correlation became more pronounced as the dose of dobutamine was increased. There was no correlation between VE/VCO₂ slope and ΔLV dP/dt_max. Multivariate regression analysis revealed that ΔLV dP/dt_max was independently correlated with peak VO₂ (p = 0.011). Conclusions: Peak VO₂, but not VE/VCO₂ slope, may reflect myocardial contractile reserve in ambulatory patients with IDCM. This study population is small, and therefore large confirmatory studies are needed.