Alternative aerobic training session in coronary artery disease patients in cardiac rehabilitation. A new stone thrown in the pond Free

Cardiovascular disease (CVD), including coronary artery disease (CAD), is currently the leading cause of death worldwide,¹ and cardiac rehabilitation is an important secondary prevention service.² Exercise-based cardiac rehabilitation typically involves CAD patients engaging in low- to moderate-intensity continuous training (MICT), and it is effective for reducing cardiovascular mortality and all-cause mortality.³ High-intensity interval training (HIIT) has also been proposed in CVD,^4,–6 particularly in CAD patients.^7,–9 An aerobic exercise programme should be progressive and this progression should be modulated according to the FITT principles, which include: the frequency (sessions per week), intensity (fraction of peak oxygen consumption (⁠$V·$O₂)), time (or duration of each session) and type of exercise session (HIIT or MICT), adjusted to the goals and characteristics of the individual.¹⁰ Training periodization is a manipulation of the FITT parameters which increases variation in training with the aims to optimize training adaptations, to avoid a plateau and to prevent overtraining and injuries. Traditional periodization typically begins with low exercise intensity and short duration and focuses on a gradual increase.

In the present issue of this journal, Boidin et al. provide a meritorious paper¹¹ and they compare two different periodized aerobic sessions, linear (LP) versus non-linear (NLP), blindly randomized, in a 12-week supervised exercise programme on the cardiopulmonary exercise response in patients with CAD. All patients completed cardiopulmonary exercise testing (CPET): peak oxygen uptake (peak VO₂), oxygen uptake, efficiency slope, ventilatory efficiency slope (VE/VCO₂ slope), VO₂ at the first (VT1) and second (VT2) ventilatory thresholds, and oxygen pulse (O₂ pulse) were measured. These were including criteria: all study testing at baseline and study-end were completed, and all CAD patients were in the same condition. Boidin et al. evaluated the proportion of responders according to training protocols, as well.¹¹

Boidin et al. concluded that more variation was observed in NLP, but this does not seem necessary for greater cardiopulmonary adaptations in CAD patients (+1.7 ml/kg per min for LP and 0.2 ml/kg per min for NLP). CAD patients were highly selected, as none had a reduced left ventricular ejection fraction or severe co-morbidities (respiratory or kidney disorders). All CAD patients were similar in demographic aspects, were on optimal medical therapy and pharmacological therapy was homogenous between exercise programme groups. In short, the study compares the exercise response and aerobic function in CAD patients who underwent two different training protocols and no difference was found for LP versus a NLP increase in energy expenditure. In the HIIT, the workloads reached 100% of peak power. Boidin’s paper¹¹ elicits also some points:

1. Although the study was not planned to address the issue of safety of HIIT in CAD patients, as the population was limited (39 CAD patients were enrolled over two years), older and female CAD patients did not favour HIIT prescription. Patients’ preferences should be met in order to optimize adherence and increase intrinsic motivation to exercise (i.e. sedentary and low-fitness patients).

2. In some CAD patients, optimization of pharmacological therapy takes a long time while in others this medical process is rapid. How long was this process and for how long should the patient be clinically stable or on optimal pharmacological therapy?

3. In Table 1, half of the CAD population are treated with beta-blockers; changes in peak VO₂ are hardly achievable when this therapy is in the background in CAD patients.

4. Although the aetiology of CAD was the same in the two exercise programme groups, some patients, however, had a combined myocardial revascularization procedure (percutaneous coronary intervention and coronary artery bypass grafting (CABG)), and soon after CABG, peak ventilatory CPET parameters are constrained due to mechanical thoracic abnormalities;^12,13 the increment of VE/VCO₂ and in VE was low in both exercise testing groups (less than 10%). Moreover, inadequate VE parameters regulate a lower peak VO₂ as well.¹⁴

5. Although CPETs were conducted in the same clinical and experimental conditions, maximality of tests is not explained in the text: nevertheless, a high respiratory exchange ratio can be detected at peak, after a careful inspect of Table 2.¹¹

6. Upgrading of CPET is influenced by time of intervention: this should be explained.

7. Improvement of CPET parameters is influenced by age and gender (see above). Usually, women have a reduced first anaerobic ventilatory threshold (VT1) and they might not achieve the second one (VT2);^12,13 this unsteadiness might provide misleading results.

These aspects should be acknowledged when CPET is used as reference; however, the number of CAD patients in this experimental study prohibits subgrouping analysis or individual enquiry.

Boidin et al.¹¹ also evaluated different sessions’ intensity during exercise programmes in CAD patients; high-responders and low-responders were based on the change in peak VO₂. Patients above the median (Δ peak VO₂ > 1.3 mL.min^–1.kg^–1) were considered as high-responders; patients under or equal to the median or with a decrease in peak VO₂ were considered as low-responders or as non-responders. Boidin et al.¹¹ found that, in the LP and NLP groups, five and three patients were considered as non-responders, respectively, three and seven patients as low-responders, and 12 and nine patients as high-responders; no significant statistically difference between the two exercise programme groups was observed. Boidin et al.¹¹ provide an important contribution to test different individualized progressive exercise testing models to optimize adaptations in CAD patients.

In conclusion, the authors should be congratulated for addressing this interesting topic. Because of the methodological limitations regarding CPET pre/post evaluations, caution is needed when translating these findings to the regular CAD patient. Prior to advocating it, we need properly designed trials; HIIT should be more fully and systematically integrated, while reinforcing existing evidence on the long-term safety and efficacy of this training modality.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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