Exercise as it relates to Disease/The Effect of Aerobic Exercise Intensity on Cardiovascular Risk in Coronary Heart Disease Patients

This is a review of the article 'Cardiovascular Risk of High- Versus Moderate-Intensity Aerobic Exercise in Coronary Heart Disease Patients' by Øivind Rognmo, et al published by Circulation in 2012.

Background
Coronary Heart Disease (CHD) involves the build-up of plaque inside the arteries that supply blood to the heart. This process is known as Atherosclerosis and results in a gradual narrowing of the arteries over many years, causing a decrease in the flow of blood to the heart. Blood clots may form in the artery, which can lead to Angina or an Acute Myocardial Infarction (Heart Attack).

Process of Atherosclerosis

The latest data shows that Coronary Heart Disease is the leading cause of death in Australia (19777 people in 2015). Despite continuing as the leading cause of death for the last ten years, the death rate is decreasing (23132 people in 2006).

When considering the risk factors for developing CHD, they can be broken in to two categories:

There have been several studies performed over the years that demonstrate that there is a strong inverse relationship between physical activity levels and cardiovascular mortality. A 1989 study by Slattery et al established that male US Railroad workers who were sedentary had a 39% greater risk of CHD compared to those who had higher levels of physical activity. This study and countless others since, demonstrate the importance of physical activity in its relation to CHD as it is able to “produce a host of positive morphological and physiological cardiovascular adaptations”. Whilst most studies focus on the avoidance of CHD incidence; there has been evidence to show that formal aerobic training programs also benefit those with established CHD (Secondary Prevention). Traditionally studies compare sedentary lifestyle with those that participate in moderate intensity exercise. This review aims to examine the possible benefits that high intensity exercise may also have for CHD rehabilitation.

Where is the research from?
This article was carried out by Øivind Rognmo along with Trine Moholdt, Hilde Bakken, Torstein Hole, Per Mølstad, Nils Erling Myhr, Jostein Grimsmo and Ulrik Wisløff in Norway. The research was conducted in collaboration with the Norwegian University of Science and Technology and American Heart Association. These are two very reputable institutions/organisations as well as the author’s PhD qualifications; demonstrates the reliability and validity of this article and a lack of any bias. No conflicts of interests were present and support was provided by grants from the K.G Jebson Foundation, The Research Council of Norway, and The Norwegian Council of Cardiovascular Disease.

What kind of research was this?
The study was performed as a Randomised Control Trial (RCT) analysis. This involved groups operating under different circumstances to then later compare the results. This sort of study and the number of participants is consistent with similar research investigations. Medical professionals referred participants and the total number of sessions provided was registered beforehand. Safety protocols were undertaken as all participants underwent a medical examination including a full-lead ECG before starting rehabilitation.

What did the research involve?
The study involved 4846 patients (70% Male, 30% Female) at three exercise-based cardiac rehabilitation centres between 2004 and 2011. The participants undertook interval-training sessions at High intensity (85-95% HRPeak) or Moderate Intensity (60-70% HRPeak) lasting approximately 60 minutes. The sessions usually involved treadmill exercise but also included biking sessions and cross-country skiing.

The intensity of the sessions were sometimes controlled by wearable Heart Rate monitors but mainly utilised Borg’s Rating of Perceived Exertion (RPE) Scale. Moderate intensity was classified as 12-14 on the Borg Scale and High Intensity was given as 15-17. The use of RPE is an easily understandable measure for the client and supervisor. However, it is only a subjective measure and in a CHD population absolute measures such as heart rate may be more preferable so as to have tighter control over safe exercising conditions.

Results and Conclusions
There was a low risk of adverse events occurring for both moderate and high intensity exercise.

The absolute event rates were extremely low however the authors identified that in order to detect a sufficient difference between the groups, a similar randomised study would require over 10,000 people in each group. The author’s acknowledge the increased risk of cardiac episodes occurring when participating in vigorous exercise however, believe that the benefits outweigh the risks, evidenced by the dose-response relationship between exercise and cardiac function.

Evidence from this study suggests that the beneficial adaptations of exercise are intensity dependent, signifying that high-intensity exercise should therefore be employed. A Dutch study performed the following year aligns with this concept as it suggests that High-Intensity training is recommended because it is more effective than moderate exercise. This research is a step in the right direction and as long as intensity levels can be monitored carefully and safety protocols maintained, then high-intensity exercise is more beneficial for Coronary Heart Disease Patients when compared with moderate exercise.

Practical Advice
It is highly important to consider that the low fatality rate seen during this research is a result of careful supervision and management by specialists. It is claimed that there would be 6 times as many deaths if this were not the case. Therefore, when reading this article, be aware that without qualified medical supervision these results may not be replicated and follow the suggestion by the author’s themselves for the need for further collection of data to assess the safety of using high-intensity exercise.

Further Information
Further information from trusted sources regarding CHD and exercise can be found below:


 * Heart Foundation- https://www.heartfoundation.org.au


 * National Heart, Lung, and Blood Institute- https://www.nhlbi.nih.gov/health


 * American College of Sports Medicine- http://www.acsm.org/public-information/articles/2016/10/07/exercising-with-coronary-heart-disease


 * Being Active When You Have Heart Disease- https://medlineplus.gov/ency/patientinstructions/000094.htm