Chronotropic incompetence and exercise capacity after cardiac surgery with left atrium incision

Type of funding sources: None.

Chronotropic incompetence (CI) is sometimes observed during exercise training of cardiac rehabilitation in patients who underwent cardiac surgery, however, little is known which factors affect to the incidence of CI and exercise capacity of those patients.

Because the possibility exists that cardiac sympathetic nerves might be impaired by surgical procedure, moreover CI is sometimes observed in patients after mitral valve surgery, we hypothesized that the incidence of CI was higher in patients with left atrium incision (LAI) during surgical operation as compared with those without LAI. And if so, which factor determines the exercise capacity of patients after cardiac surgery with LAI. We thus aimed this study to elucidate the hypothesis with cardiopulmonary exercise testing (CPX).

We performed CPX in total 153 patients who had undergone elective cardiac operation (45 patients with LAI, age 60.5±11.0; 108 patients without LAI, age 62.0±11.7). We analyzed chronotropic response index (CRI), peak oxygen uptake (peak VO2/W), anaerobic threshold (AT), and peak oxygen pulse (peak VO2/HR) with CPX, echocardiography, and blood hemoglobin concentration (Hb).

The value of CRI was significantly reduced in the patients with LAI as compared with those without LAI (with LAI 0.24±0.22 vs. without LAI; 0.44±0.18, p<0.001). Exercise capacity such as peak oxygen uptake (peak VO2), anaerobic threshold showed no significant difference between two groups. In patients with LAI, peak VO2 showed significant correlations between peak oxygen pulse (peak VO2/HR; r=0.36, p<0.05), Hb (r=0.40, p<0.01) and left atrium dimension (LAD) measured by echocardiography (r=-0.54, p<0.001).

The present study demonstrated that higher incidence of CI was shown in patients with LAI as compared with those without LAI. Moreover peak VO2 of patients with LAI showed significant correlations with peak VO2/HR, Hb and LAD. These results suggest that 1) left atrium incision impairs cardiac sympathetic nerves and causes CI, 2) peak VO2/HR and Hb which is essential element of oxygen pulse are important factors for exercise capacity in patients after LAI with CI. Left atrium enlargement may indicates pre-operative damages of left atrium, 3) LAD which may indicate left atrium function, also is an important factor of exercise capacity in those patients.