Can kinetics of oxygen uptake at onset of exercise identify contractile reserve in patients with ischemic left ventricular dysfunction?

Background Prior studies demonstrated that kinetics of oxygen uptake (KVO2) at the onset of exercise is delayed in patients with ischemic left ventricular dysfunction (LVD), since it reflects a slower cardiac output increase. Given the myocardial contractile reserve elicited by endogenous catecholamines during exercise, it may be speculated that patients with a significant amount of myocardial viability (MV) could show a faster KVO2 at the onset of exercise attributable to a faster increase in stroke volume compared to patients without MV. Objectives To demonstrate a relationship between contractile reserve detected by low-dose dobutamine Echocardiography (LDDE) and KVO2 obtained during cardiopulmonary testing in patients with ischemic LVD. Methods Forty-one consecutive patients (62.5 ± 10.1 years) with ischemic LVD underwent LDDE and constant work rate exercise with KVO2 determination. The time constant for VO2 (tau) was determined by a curve fitting breath-by-breath data. Ten healthy subjects served as control group (59.5 ± 13.4 years). Results LDDE identified contractile reserve in 20 (48%) subjects. Patients without MV detected by LDDE showed a significantly longer tau compared to patients with MV and to healthy subjects (p = 0.03 and p = 0.01, respectively). Sensitivity, specificity, positive and negative predictive value of tau in detecting MV were 90%, 95%, 95% and 91%, respectively. Moreover, the percentage reduction of LV wall motion score index detected at LDDE was significantly related to KVO2 (r = 0.71, p < 0.01) Conclusions Our data suggest that KVO2 represents a reasonable initial approach to estimate presence of MV in patients with ischemic LVD.