Chronic Adaptations in Cardiovagal Modulation and Cardiorespiratory Fitness in Patients With Coronary Artery Disease to a 12-week Heart Rate Variability-guided Training vs Traditional Aerobic Prescription Program: Study Protocol for a Randomized Controlled Trial

Background

Coronary artery disease (CAD) is characterized by the inability to adequately supply blood and oxygen to the heart, often resulting from the formation of atherosclerotic plaques within the arterial lumen. This inflammatory, multifactorial condition can impair the autonomic nervous system (ANS), disrupting the balance between the sympathetic and parasympathetic pathways and leading to autonomic dysfunction. Key indicators of this dysfunction include reduced heart rate variability (HRV) and delayed heart rate recovery, both of which signify heightened sympathetic activity and diminished parasympathetic activity. These changes predict worse cardiovascular outcomes in CAD patients, as the ANS compensates for myocardial ischemia and hypoxia by increasing sympathetic drive and reducing vagal activity to preserve cardiac contractility and output. This imbalance triggers a cascade of neurohumoral alterations affecting the cardiovascular, peripheral vascular, and renal systems, further exacerbating disease progression.

Regular exercise is known to play an important role in the prevention, management, and treatment of CAD, mainly through the preservation of endothelial function but also through the improvement of cardiovagal modulation and neurocardiovascular stress reactivity and by the increase in cardiorespiratory fitness. Patients with stable CAD should undergo a cardiac rehabilitation program to fulfill exercise guidelines. Protocols may vary in mode, intensity, frequency, and duration, whereas the most recommended types of exercise are walking and cycling, with intensities between 40-80% of VO2peak associated with increases in exercise capacity by 11-36%. Recent studies demonstrated that high-intensity interval training (HIIT) compared with moderate-intensity continuous training (MICT) promotes higher adaptation in VO2max and in post-exercise heart rate recovery, HIIT has also demonstrated to contribute to the restoration of endothelial function and autonomic balance, inducing reverse cardiac remodeling and increasing left ventricle morphology and function. However, MICT demonstrates higher adherence because it is a safer and more effective approach. Nevertheless, despite the known non-pharmacological benefits of exercise, recent studies demonstrate that more than 15% of the patients with CAD are exercise non-responders to increases in VO2max , i.e., an increase of 3.5 ml/kg/min in VO2max, which has been associated with a 10% decrease in all-cause of mortality and cardiovascular mortality, however the greater the increases in VO2max the greater the reduction in the risk.

Exercise individualization is increasing among apparently healthy populations due to the ease of the use of cellphone applications. Recently, HRV-guided training has been identified as an alternative prescription technique for cardiovascular endurance exercise prescription, this prescription technique demonstrated to contribute to greater improvements in endurance athletes. HRV-guided training concerns to exercise prescribed based on daily changes in HRV, depending on thresholds constructed at the individual level. After an initial characterization period, where the HRV after waking up is measured, the individual HRV profile is defined. Then, considering the resting values of HRV, exercise intensity will be determined for the training session, i.e., if LnRMSSD7day-roll-avg remained inside the smallest worthwhile change (SWC) (+), high-intensity or moderate-intensity training sessions is prescribed, and if LnRMSSD7day-roll-avg fell outside SWC (-), low intensity or rest is prescribed. This prescription technique leads to different workloads from the predefined training programs.

To the best of our knowledge, no study has yet compared the chronic effects of two different exercise protocols on cardiovagal modulation, and cardiorespiratory fitness in patients with CAD. Thus, this research aims to compare the chronic adaptations on cardiorespiratory fitness, cardiovagal modulation, baroreflex sensitivity (BRS), and arterial stiffness (AS) of two different techniques of exercise prescription (traditional vs individualized) and two training methods (HIIT vs MICT) in patients with CAD. We hypothesize that exercise individualization will promote higher adaptations in cardiovagal modulation, cardiorespiratory fitness, BRS and AS in patients with CAD, compared with traditional prescription.