So far, cardiac resynchronization therapy (CRT) has only been studied during resting conditions. The aim of our study was to elucidate the immediate effects of CRT during submaximal exercise in patients with chronic heart failure.
Eleven patients (age 69±5, NYHA II-III, LVEF<30%, sinus rhythm, QRS>130msec, CRT for at least 3 months) underwent a cardiopulmonary exercise test using the modified bruce protocol (treadmill; 4.6 METS). Heart rate (HR), the rate of increase of minute ventilation per unit of increase of oxygen consumption (VE/VO2 slope), respiratory exchange ratio (RER), and respiratory minute ventilation (VE) were evaluated during a 3 minute exercise period followed by a 10-minute resting period. Measurements were taken during right- (RV), left- (LV), and biventricular pacing (CRT)as well as during sinus rhythm. Physical recovery in-between the different pacing modes was proven by normalized blood lactate levels.
VE/VO2 was highest during sinus rhythm and decreased significantly during CRT (from 34.2±5.6 to 30.7±4.2; P<0.05). By contrast, RV and LV pacing did not show significant effects. Interestingly, responders to CRT (n=6, defined as a > 10% decrease in VE/VO2) had significant higher basal VE/VO2 levels (37.6±6.9) as compared to non-responders (30.0±4.9; P<0.05; n=5). RER was higher during sinus rhythm (0.81±0.07) as compared to CRT (0.76±0.04; P<0.05). VE, HR and blood lactate levels did not show any changes within different pacing modes as compared to sinus rhythm.
Cardiac resynchronization therapy exerts an increase in oxygen uptake during submaximal exercise. This effect is due to an improvement in cardiac performance.
Thus, hemodynamic responders to CRT may be identified by spiroergometry.
R.H. Zwick, None.