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 \ub1 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 \ub1 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, pb0.01) Conclusions: Our data suggest that KVO2 represents a reasonable initial approach to estimate presence of MV in patients with ischemic LVD