Background: Cardiac resynchronisation therapy (CRT) has become a valuable therapeutic tool in patients with advanced chronic heart failure (CHF). The search for optimal methods for the assessment of CRT efficacy is still underway.
Aim: To evaluate the impact of implantation of CRT devices in patients with CHF on adaptation of circulatory and respiratory systems to maximal exercise assessed by cardiopulmonary exercise tests (CPX) and 6-minute walking tests (6MWT).
Methods: We investigated 27 patients (22 males, 5 females, 61.2±9.1 years) with a CRT device implanted due to advanced CHF, which resulted from ischaemic or dilated cardiomyopathy. All patients before implantation underwent echocardiography, CPX with expired gas analysis and 6MWT. Investigations were repeated at 3-6 months after CRT implantation. In CPX we evaluated peak oxygen uptake (peak VO₂), oxygen pulse, maximal minute ventilation-carbon dioxide production (VE/VCO₂ max), and its slope (VE/VCO₂ slope) and VE/VO₂ slope, VO₂ in anaerobic threshold (AT), and cardiac and respiratory reserve. In 6MWT we evaluated walking distance and heart rate and blood pressure response to exercise.
Results: We noted statistically higher mean peak VO₂ after CRT implantation in the studied group: 11.34±3.38 vs. 14.56±3.99 ml/kg/min (p <0.0001) and 1.01 ±0.44 vs. 1.4±0.55 l/min (p=0.003) and higher values of expired CO₂: 1.00±0.43 vs. 1.43±0.67 l/min (p=0.004). The O₂ pulse rose from 9.65±3.39 to 13.23±5.43 ml/beat (p=0.015). We also observed a significant reduction of VE/VCO₂ slope from 42.34±13.35 before CRT to 34.77±6.04 after CRT (p=0.0196) and a significant decrease of VE/VO₂ slope from 41.32 ±15.46 to 34.01±6.27 (p=0.037). VE/VCO₂ max fell from 58.02±15.86 to 50.1±13.14 (p=0.009). Patients estimated their dyspnoea on the Borg scale at peak exercise at 4.75±0.75 points before CRT and at 3.67±1.15 points (p=0.002) after CRT. Patients could walk a longer distance during 6MWT than before CRT (367±154.9 vs. 231.1±170.3 m, p <0.001).
Conclusions: Cardiac resynchronisation therapy improves exercise tolerance measured by means of CPX and 6MWT, improves respiratory system efficiency and restores its adaptive mechanisms during exercise in patients with advanced CHF. Better exercise adaptation after CRT may be objectively measured with CPX parameters, and corelates with improvement of clinical symptoms. CPX seems to be a very helpful tool in assessing the results of CRT.