Improving lung function capacity in patients with chronotropic incompetence using closed loop stimulation: A randomized crossover study.

Background: Chronotropic incompetence (CI) severely limits exercise tolerance due to impaired heart rate responses. This study investigated whether pacemaker with closed-loop stimulation (DDD-CLS) pacing, which provides rate acceleration in response to exertion, could enhance lung function and cardiopulmonary capacity compared pacemaker without CLS pacing in patients with CI.

Methods: This randomized crossover trial included 32 patients with CI who were compared to each CLS and DDD pacing over 2 months. Spirometry was used to assess the forced vital capacity (FVC). Cycling-based cardiopulmonary exercise testing (CPET) measured peak oxygen uptake (peak VO₂).

Results: DDD-CLS pacing yielded significantly higher FVC (2.2 ± 0.8 L) versus DDD pacing (2.0 ± 0.7 L), p = 0.036, a 3.2% improvement. Moreover, those in the DDD-CLS mode showed a significantly higher FEV1 of 1.8 ± 0.6 L compared to the DDD mode of 1.7 ± 0.5 L (p = 0.03). Compared with DDD pacing, DDD-CLS pacing also achieved superior peak VO₂ (14.9 ± 4.0 vs 12.2 ± 3.7 mlO₂/kg/min, p < 0.001) and peak heart rate (106.9 ± 9.7 vs 98.3 ± 19.8 bpm, p = 0.013). DDD-CLS and DDD pacing modes showed significant correlations between FVC and peak VO₂ and between peak VO₂ and peak heart rate during CPET.

Conclusions: Compared with DDD mode, DDD-CLS pacing provided physiological chronotropic support to improve cardiopulmonary function during exertion, which enhanced lung capacity in patients with CI.