A randomized controlled trial of a controlled breathing protocol on heart rate variability following myocardial infarction or coronary artery bypass graft surgery.

OBJECTIVES: To determine whether a controlled breathing programme increases heart rate variability following an acute myocardial infarction and/or coronary artery bypass graft surgery. RATIONALE: Heart rate variability is reduced following a myocardial infarction, and low heart rate variability is associated with a high mortality risk. By changing tidal volume and rate of breathing, individuals can alter beat-to-beat heart rate variability. It is hypothesized that heart rate increases with inspiration and decreases with exhalation, and that deep slow breathing enhances respiratory sinus arrhythmia, increasing heart rate variability. DESIGN: Randomized controlled trial. SETTING: Cardiac rehabilitation programme at a large academic medical centre in North Texas. SUBJECTS: From 2001 to 2005, 44 patients, age 46-65 years, who had a myocardial infarction and/or undergone coronary artery bypass graft surgery 1-8 weeks previously and were referred to the Cardiac Rehabilitation Program. INTERVENTION: Patients were randomized to either usual cardiac rehabilitation or cardiac rehabilitation with controlled breathing (6 breaths/min for 10 minutes twice daily during the eight-week treatment period). MAIN MEASURES: Weekly measurements of total power and standard deviation of the mean normal to normal RR interval (SDNN), and fortnightly measurements of respiratory sinus arrhythmia were taken using Biocom Technologies Heart Rhythm Scanner and Tracker software. RESULTS: No significant difference in change were seen between groups in SDNN (P = 0.3984), baseline respiratory sinus arrhythmia (P = 0.6556) or total power (P = 0.6184). CONCLUSION: Results suggest participation in the controlled breathing programme offered no additional benefit in increasing heart rate variability following myocardial infarction or coronary artery bypass graft surgery. However, 77% of study patients were on heart rate-lowering medications, which may have masked changes in heart rate variability.