Changes in short-term measures of heart rate variability after eight weeks of cardiac rehabilitation

Area of Science:

• Cardiology
• Autonomic Nervous System Research
• Rehabilitation Medicine

Background:

• Autonomic nervous system activity is altered in coronary artery disease (CAD) and post-myocardial infarction (MI).
• Reduced heart rate variability (HRV) is a known risk factor for future cardiac events.
• Previous studies on HRV changes post-cardiac rehabilitation (CR) show inconsistent results due to varied protocols.

Purpose of the Study:

• To evaluate changes in spectral measures of HRV using short-term (5-minute) ECG recordings.
• To assess the impact of an 8-week CR program on HRV in patients with CAD.
• To determine if CR leads to favorable alterations in autonomic control.

Main Methods:

• Thirty-eight patients undergoing an 8-week CR program had 5-minute supine ECGs recorded pre- and post-rehabilitation.
• A control group of 23 patients also underwent ECG recordings.
• Key outcome measures included low frequency power (LF), high frequency power (HF), LF:HF ratio, and mean RR interval, analyzed using ANCOVA and paired t-tests.

Main Results:

• Patients in the CR group demonstrated significant increases in SDNN, HF power (HFln), LF power (LFln), and mean RR interval compared to the control group.
• Specifically, CR led to increases of +6 ms in SDNN, +0.4 log units in HFln, +0.6 log units in LFln, and +30 ms in RR interval.
• These increases were statistically significant when compared to minimal changes observed in the control group.

Conclusions:

• This study is the first to report significant increases in raw LF and HF power from short-term ECG recordings in CR patients.
• The observed increases in HRV measures, which are risk factors for future cardiac events, suggest CR's efficacy.
• CR is associated with favorable alterations in autonomic control, positioning it as an effective therapeutic intervention for cardiovascular health.