Effects of cardiac resynchronization therapy in heart failure patients

OBJECTIVIES AND BACKGROUND. Cardiac resynchronization therapy (CRT) is an established treatment for heart failure (HF) according to the most recent international guidelines. CRT was conceived by the observation that an enlargement of QRS is frequent in HF patients, it is often the expression of mechanical dyssynchrony of cardiac contraction and it is associated with poor prognosis. The effects of CRT are immediately evident in the acute setting as a reduction of QRS and left ventricular (LV) volumes and as an improvement of LV function. In the chronic setting, CRT is associated with NYHA class reduction, LV inverse remodelling, LV ejection fraction (EF) and peak oxygen uptake (VO2) increase, leading to mortality and morbidity improvement. However, the precise haemodynamic mechanism by which CRT improves HF patients’ condition, both at rest and during exercise, is still undefined, but measuring them at rest and during exercise could be crucial to clarify the effects of CRT and to optimize CRT patient selection and post-CRT treatment. METHODS. In 93 HF patients, before and 8±3 months after CRT, we assessed clinical conditions, ECG, and standard echocardiography and we performed maximal cardiopulmonary-exercise-test with non-invasive measurement of cardiac output (CO) by inert-gas-rebreathing method. RESULTS. At rest, CRT significantly shortened QRS, and it improved NYHA class and left ventricular ejection fraction (LVEF) but not CO and stroke volume (SV). At peak exercise, a significant improvement of peak 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) was detected. While all patients showed a similar peakCO increase, a significant post-CRT peakVO2 increase was observed only in patients with the lowest pre-CRT peakVO2 (5.9-11.3 ml/kg/min) and peakCO (24-43% predicted). DISCUSSION AND CONCLUSIONS.. . Our data showed that CRT improves exercise performance in HF patients by changing peak exercise CO and SV. The exercise performance improvement after CRT is significant only in patients with low peak VO2 and peak CO before implant, suggesting the use of CPET with haemodynamic evaluation in CRT selection and follow-up. Finally, blood flow distribution toward the muscles is probably crucial for post-CRT functional change, since peak CO increase is similar in all patients regardless of pre-CRT exercise performance while significant peak VO2 change is only evident in patients with a more severe exercise dysfunction. These data suggest the usefulness of pre-CRT peakVO2 and CO measurements for CRT patient selection and post-CRT follow-up and treatment.