Peak exercise cardiac output but not oxygen uptake increases in all heart failure patients after successful resynchronization therapy

Objectives and Background: Hemodynamic changes at rest and during exercise in heart failure (HF) after cardiac resynchronization therapy (CRT) are still undefined. Methods: In 93 HF patients, before and 8 ± 3 months after CRT, we assessed clinical conditions, ECG and standard echocardiography and we performed a maximal cardiopulmonary exercise test with non-invasive measurement of cardiac output (CO) by inert gas rebreathing method. Results: At rest, CRT shortened QRS and improved NYHA class and left ventricular ejection fraction (LVEF), but not CO and stroke volume (SV). On average, at peak exercise, a significant improvement of oxygen uptake (VO2) (from 13.8 ± 3.8 ml/min/kg to 14.9 ± 4.6, p<0.0025), CO (from 6.19 ± 1.82 L/min to 6.97 ± 2.21, p<0.0001), and SV (from 62 ± 18 mL to 71 ± 19, p<0.0001) were detected. Regardless of HF severity, after CRT, patients showed a significant peak SV and CO increase, but a significant peak VO2 increase was observed only in patients with the lowest pre-CRT peak VO2 (5.9-11.3 ml/kg/min). Conclusions: Our data showed that: a) SV at rest was not affected by CRT, regardless of LVEF improvement; b) post-CRT peak VO2 improvement was limited to HF patients with low pre-CRT peak VO2; c) post-CRT, a similar peak CO increase was observed regardless of pre-CRT peak VO2. Consequently, the assessment of peak CO is preferable to analyze CRT effects on exercise.