Exercise as it relates to Disease/The reliability of HIIT as a worthwhile accessory to standard cardiac rehabilitation

This is a critique of the research article: Keteyian, S., Hibner, B., Bronsteen, K., Kerrigan, D., Aldred, H., & Reasons, L. et al. (2014). Greater Improvement in Cardiorespiratory Fitness Using Higher-Intensity Interval Training in the Standard Cardiac Rehabilitation Setting. Journal Of Cardiopulmonary Rehabilitation And Prevention, 34(2), 98-105.

The critique was written as an assignment in the unit; Health, Disease and Exercise at University of Canberra, August-September 2020.

1) What is the background to this research?
Cardiovascular Disease (CVD) accounts for more deaths world-wide each year than any other cause. More than 75% of CVD's occur in low to middle income countries. CVD's are a set of often highly preventable diseases via modifying physical activity, diet, tobacco and alcohol use. CVD relate to a group of diseases/conditions of the heart and the vascular system. Coronary heart disease (disease of blood vessels supplying the heart) is a type of CVD and is the focus of the present study. The pathophysiology of coronary heart disease primarily occurs with the development of plaque within the arteries. The formation of plaque is primarily caused by elevated levels of LDL (low-density lipoproteins) circulating in blood. Consuming unhealthy/fatty foods regularly can keep blood-LDL levels consistently elevated, and thus increase the risk of plaque development (also known as atherosclerosis). The narrowing of arteries associated with atherosclerosis causes reduced blood flow and consequently reduced heart-oxygen availability. This process can impair cardiac (myocardium) function. Due to the discussed global prevalence of CVD, modifiable risk factors/ lifestyle changes to attenuate CVD's should be of strong interest in current/on-going research.

2) What is the research from?
The article of interest was published in the Journal of Cardiopulmonary Rehabilitation and Prevention (JCRP) in 2014. 13 authors collaborated on the present study; their credentials follow. Steven J. Keteyian, PhD; Brooks A. Hibner, BS; Kyle Bronsteen, MS; Dennis Kerrigan, PhD; Heather A. Aldred, PhD; Lisa M. Reasons, BS; Mathew A. Saval, MS; Clinton A. Brawner, PhD; John R. Schairer, DO; Tracey MS. Thompson, MSA; Jason Hill, BS; Derek McCulloch, BS; Jonathon K. Ehrman, PhD.

3) What kind of research is it?
The present study was a randomised controlled clinical trial. Patients were randomly assigned to either a control group (MCT - Moderate Continuous Exercise) or the intervention group (HIIT - High Intensity Interval Training). The length of the experiment lasted 10 weeks from baseline to follow-up. Randomisation of patients occurred via a computerised random number generator. A total of 39 subjects were randomised (HIIT; 21, MCT; 18) with 15 and 13 patients completing the testing protocol respectively. Resistance training was disallowed for all patients involved in the study (a measure designed to control a potential confounding variable). The present study compares a proposed intervention (integration of HIIT into standard CR practice) against a standard CR 'control'(MCT) group. The randomisation of patients to a certain group eliminates allocation bias. This in turn leads to a stronger level of evidence, the strongest level of evidence for studies of this design.

4) What did the research involve?
Men and women between the ages of 18-75 years participating in one of the Henry Ford Health Systems phase 2 CR programs were screened for participation. The study involved 39 patients; all patients involved were considered to have 'stable' coronary heart disease. The following eligibility criteria was defined. Patients must have a sinus rhythm; ejection fraction > 40% > 3 weeks following myocardial infarction or percutaneous coronary intervention > 4 weeks following coronary bypass surgery. One of the above conditions must be coupled with both of the following; a) the successful completion of the run-in period (attending greater than or equal to 4 of the 6 first CR sessions without complications using MCT), b) free of a co-morbidity which might limit treadmill exercise. Also note that patients with Canadian cardiovascular society class 2-4 angina, significant Arrhythmia, or >1 mm horizontal or down-sloping ST segment depression during CPX were excluded. The present study monitored the following physiological variables (as markers of cardiovascular fitness) over time. These included HR and blood pressure as a response to exercise testing and exercise training. Although, the main focus of the study was to monitor changes to sub-maximal endurance over time as a response to an exercise training intervention. Consequently, peak VO2 was monitored at baseline and finish. Peak VO2 was also calculated via ventilatory-derived anaerobic threshold using the CPX cole LAB protocol and was completed with 3 reviewers blinded to group assignment.

5) What were the basic results?
In both the control (MCT) and intervention (HIIT) groups there were similar changes in resting HR and blood pressure from baseline to follow-up. At follow-up sub-maximal HR determined at the exercise test was significantly lower for both groups (there was no significant difference between groups). Peak VO2 improved more in the intervention (HIIT) group (3.6 ± 3.1 mL/kg/min - P<0.05) versus the control (MCT) group (1.7 ± 1.7 mL/kg/min - P<0.05). VO2 at ventilatory-derived anaerobic threshold increased more with the intervention group (3.0 ± 2.8 mL/kg/min - P<0.05) than with the control group (0.7 ± 2.2 mL/kg/min - P<0.05).

6) what conclusions can we take from the research?
The sample size of the study was relatively small with 39 patients; therefore, replication by others across other CVD brackets (with different demographics and eligibility criteria) is warranted to fortify conclusions made. Furthermore, patients were generally younger and male. As a consequence, possessing a higher exercise capacity. With this granted, additional studies should aim to address older patients, women, or those with lower functional capacities. Eligibility criteria limits applicability to other CVD patients; therefore, impact of findings is limited to those meeting criterion. Considering the previous limitations, further studies which address patients with different backgrounds, eligibility criteria, pathophysiology, age, gender, and physical ability must be made when considering integrating HIIT into standard CR regimes. Conclusions made regarding the interventions' impact on improving both peak exercise capacity and sub-maximal endurance cannot safely be extrapolated to patients excluded from study criterion. Moreover, the clinical safety and efficacy of HIIT in patients outside study criterion has not been clearly elucidated. A key weakness of the study was that relevant CVD health parameters were not measured and so impact of the intervention upon quality of life for CVD patients remains unclear.

7) Practical Advice:
Generally, when possible prevention through lifestyle intervention (such as physical activity, and nutrition) is most effective in minimising risk of acquiring CVD. If you are a patient with coronary heart disease that does not meet the discussed study criterion, do not attempt HIIT variety exercise until discussed and approved by your doctor and associated cardiac rehabilitation team. Additionally, note that patients involved in the study were considered 'stable' meaning that a number of associated symptoms and severity of symptoms patients experienced had to meet certain limitations. In general, patients should undergo symptom-limited testing prior to engaging in unfamiliar exercise in order to identify potential complications and/or suitability of the exercise prescription.

8) Further Information/Resources:
Exercise and Cardiovascular Health

Lifestyle Changes for Heart Attack Prevention

Cardiac Rehab

Overview of Exercise Stress Testing

[https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.119.042160#:~:text=Another%20meta%2Danalysis%20found%20that,with%20cardiovascular%20disease%2C%20Keech%20said. Evidence for HIIT Benefits for Cardiac Rehabilitation]