Assessment of cardiac autonomic functions by heart rate recovery indices in patients with myocardial bridge

Background: Heart rate (HR) recovery (HRR) reflects autonomic activity and predicts cardiovascular events. The aim of this study was to assess HRR in patients with myocardial bridge (MB). Methods: Medical recordings of 93 patients with MB and appropriate age, compared to 78 sex-matched healthy subjects were analyzed. MB was diagnosed via coronary computed tomography angiography after a positive exercise stress test (EST). HRR indices were calculated by subtracting 1st (HRR1), 2nd (HRR2) and 3rd (HRR3) minute HR from the maximal HR during EST. Results: HRR1 (30.2 +/- 13.3 bpm vs. 35.8 +/- 10.4 bpm, p = 0.001) and HRR2 (52.3 +/- 13.3 bpm vs. 57.1 +/- 11.6 bpm, p = 0.013) were lower in patients with MB. In addition, HRR1 was lower in patients with left anterior descending (LAD) MB than non-LAD MB (28.5 +/- 13.2 vs. 37.1 +/- 11.4, p = 0.013). Presence of MB, deep MB, LAD MB and multi-vessel MB were predictors of HRR1 (p < 0.01 for all). In a multivariate analysis, LAD MB was the only significant independent predictor of HRR1 (b = -8.524, p = 0.009). Conclusions: Patients with MB have impairment in HRR indices which is more pronounced among patients with LAD MB. Cardiac autonomic dysfunction in MB might be due to recurrent myocardial ischemia.