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Heart Transplantation: What Place for HIIT in Rehabilitation?

by P. Debraux | 9 October 2019

heart, transplantation, rehabilitation, HIIT, sport, science, disease, heart failure, exercise

Heart transplantation is a surgical procedure that involves replacing a diseased heart with a healthy one from a donor of the same blood type. It is usually a treatment of last resort for people with severe heart failure and whose life expectancy is very limited. Around the world, approximately 3500 heart transplants are performed every year, half of them in the United States. After this very heavy operation, life expectancy is on average about ten years (except complications due to rejection or immunosuppressive treatment).

Nevertheless, even if the new heart improves oxygen peak consumption (VO2PEAK), it usually remains 70% lower than that of a healthy person of the same age. This decrease is due to central problems (cardiac denervation and diastolic dysfunction) and peripheral (vascular dysfunction and reduction of oxidative fibers, enzymes and capillaries in skeletal muscle) which limit the supply of O2 and its extraction by skeletal muscles. As for a healthy person, it has been shown that long-term post-transplant survival is strongly linked to VO2PEAK.

In the case of heart transplantation, most studies have shown that conventional cardiovascular training (ie, moderate intensity and continuous training or MICT) improves VO2PEAK. This improvement is often dependent on the intensity of the stimulus. HIIT (High Intensity Interval Training) is a strong stimulus for the body and many studies show that these physiological effects are often equal to or greater than those seen in MICT (at same rate of work or not). Several meta-analyzes have already reported that HIIT is as safe as MICT, but is this the case with de novo heart transplant recipients ? And is HIIT feasible with these patients ?

The Study

To answer this question, a team consisting of Norwegian, Swedish and Danish researchers tested the introduction of HIIT in the rehabilitation that followed the heart transplantation of 81 patients. The aim was to compare this training method with the classic method, MICT, used in most cardiac rehabilitation programs. For this, the researchers selected 81 patients for whom the operation took place before 7 to 16 weeks. Patients were randomly assigned to a HIIT group (n = 39) and a MICT group (n = 42) and the trial lasted 9 months.

In both groups, patients were advised on healthy diet, regular exercise and no smoking. Regarding physical exercise, patients followed the experimental protocol in their local facility where they were looked after individually by a health professional who supervised each session. All patients had to perform two to three weekly sessions, for a total of approximately 72 supervised sessions, and each session lasted approximately 40 minutes for both groups.

Each HIIT session started with a 10-minute warm-up (60-70% FCPEAK) followed by 2-4 x 1-4 minute intervals (depending on the patient's fitness level) at 85-95% FCPEAK (or 16- 18 on the Borg scale) with 3 minutes of active recovery (60-70% FCPEAK or 11-13 on the Borg scale). Each session ended with 5 minutes of cool down at 60-70% FCPEAK. During the first three months of the protocol, the weekly program consisted of one HIIT session, one resistance training session and a session combining the two; during the next three months, two HIIT sessions and one resistance training session; and during the last three months, by 3 sessions of HIIT.

For the MICT group, after the same warm-up as the HIIT group, the patients performed 25 minutes of continuous effort at 60-80% FCPEAK (12-15 on the Borg scale) followed by 5 minutes of cool down ( 60-70% of FCPEAK).

To quantify the impact of the two training protocols, the patients performed a cardiopulmonary exercise test on a treadmill or on a bicycle ergometer between 7 and 16 weeks after the intervention, that is the beginning of the experiment, and after the 9 month of protocol, approximately 1 year after the intervention. The researchers also evaluated the isokinetic muscle strength of the lower limbs. Different cardiovascular functions were evaluated as well as quality of life related to health.

Of the 81 people tested at the beginning of the protocol, only 78 completed the experiment. In the HIIT group, one person was hospitalized for problems related to the throat and nose and one person did not follow the protocol and preferred to drop the study. In the MICT group, one person gave up because of an arteriovenous malformation in the brain.

Results & Analyzes

The MICT and HIIT sessions were well tolerated by the patients, and 81% of the scheduled sessions were performed. The main results of this study show that the two groups improved their VO2PEAK, 25% more for HIIT and 15% more for MICT, but it is HIIT which allowed a significantly greater improvement of VO2PEAK compared to MICT (+1.8 ml/kg/min). Patients in the HIIT group also improved their isokinetic strength of the lower limbs significantly more.

The magnitude of improvement of VO2PEAK is greater than or equal to that found in studies in patients with heart failure (+ 0.7mL/kg/min over one year) or that observed in patients treated with drugs. The high intensity of HIIT appears to be a key factor in improving central and peripheral factors. Multiple regression analysis showed that the mean change in VO2PEAK was mainly explained by central adaptations, whereas a recently published literature review concluded that in transplant patients, the increase in VO2PEAK was generally caused by peripheral adaptations.

Practical Applications

This randomized controlled trial is the first to show that it is possible to use HIIT very soon after heart transplantation for rehabilitation. If the oversight is adapted, this type of training is quite safe and feasible and allows cardiovascular gains greater than those observed with conventional MICT. The same team of researchers has shown in a previous study that improving VO2PEAK was an important factor for patient survival.

One of the main limitations of using HIIT is the level of intensity required. Patients must be able to reach the fixed levels (90-95% FCPEAK), this requires both a relatively good and stable medical condition given the circumstances but also a greater motivation. Some meta-analyzes showed contrasting results in the enjoyment of HIIT and MICT sessions. This depends strongly on the personal tastes of everyone, and contrary to some popular beliefs, the HIIT is not necessarily always the most appreciated. These researchers planned a follow-up 3 years after the heart transplantation, it will be interesting to see the long-term impact of training sessions in MICT and HIIT.

References

  1. Nytroen K, Rolid K, Andreassen AK, Yardley M, Gude E, Dahle DO, Bjorkelund E, Authen AR, Grov I, Wigh JP, Dall CH, Gustafsson F, Karason K and Gullestad L. Effect of high-intensity interval training in de novo heart transplant recipients in Scandinavia. Circulation 139 : 2198-2211, 2019.

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