High-intensity interval training can help clinically stable heart transplant recipients achieve increased exercise capacity, maintain control of blood pressure and gain improved resting heart rate when compared with moderate exercise, according to a new study published in the American Journal of Transplantation.

A heart transplant is an operation to replace a damaged or failing heart with a healthy human heart from a donor who has recently died. A heart transplant may be needed when a person's heart can no longer work effectively, potentially putting their life at risk.

A heart transplant is usually recommended if a person:

  • Has severe heart failure - when the heart is having trouble pumping enough blood around the body
  • Is expected to die within in a year without a transplant
  • Has not responded to conventional treatments for heart failure.

There are over 2,000 heart transplants that take place in the US annually, most occurring between the ages of 50-64 years, with around 70% of cases male.

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High-intensity exercise has been deemed safe in heart transplant patients, with the effect on exercise capacity and blood pressure control superior to moderate-intensity training.

Survival rates in solid organ transplant - for example heart, liver and kidney - have improved significantly, with around 88% of patients surviving the first year after transplant surgery and 75% surviving for 5 years. The 10-year survival rate is around 56%.

After surgery, most heart transplant patients can return to their normal levels of activity. However, less than 30% return to work for many different reasons.

With these improved survival rates, there has been an increased focus on long-term outcomes following transplant including physical function, health-related quality-of-life and cardiovascular mortality.

Exercise has the potential to affect these outcomes; however, research on the optimal timing, type, dose of exercise, mode of delivery and relevant outcomes is limited.

These observations were reported in the summary of a 2-day meeting held in April 2013 in Toronto, Canada, in which a multi-disciplinary group of clinicians, researchers, administrators and patient representatives engaged in knowledge exchange and discussion of key issues in exercise in solid organ transplant.

The new study, a randomized crossover trial led by Christian Dall, PhD fellow, MSc, of the Bispebjerg Hospital at the University of Copenhagen, Denmark, aimed to investigate whether high-intensity interval training would lend similar benefits to heart transplant recipients as it had with heart disease patients previously.

The heart disease patients trained for a few minutes close to maximum heart rate, and results indicated the high-intensity exercise was more efficient than the currently recommended continued moderate exercise for improving exercise capacity.

Training sessions compared over 12-week period

The research team compared the effects of supervised exercise sessions, three times a week for a 12-week period. After exclusions, there were 16 stable heart transplant participants who had been living with their new heart for more than 1 year, separated randomly into two groups to partake in either high-intensity interval exercise or moderate-intensity exercise.

The high-intensity interval training sessions consisted of:

  • 10-minutes warm-up
  • 16-minute total upright bicycle interval training with intervals of 4-, 2- and 1-min duration at >80% of peak oxygen uptake
  • Each interval was separated by a 2-minute active rest period at approximately 60% of peak oxygen uptake
  • 10-minutes cool-down.

The continued moderate exercise training sessions consisted of:

  • 10-minutes warm-up
  • 45-minutes upright bicycle training at 60-70% of peak oxygen uptake
  • 10-minutes cool-down.

After 12 weeks, the participants were instructed to resume their usual lifestyle for a 5 month "washout" before swapping to the opposite session.

Peak oxygen uptake enhanced by high-intensity interval sessions

The study is one of the first to directly compare high-intensity interval training with continued moderate exercise in heart transplant recipients. The main finding is the enhanced effect of high-intensity training versus moderate training on peak oxygen uptake.

High-intensity exercise has been deemed safe in heart transplant patients with the effect on exercise capacity and blood pressure control superior to moderate-intensity training.

The researchers observed:

  • Maximum oxygen uptake was increased by 17% in the group performing high-intensity interval training, compared with 10% in the moderate-intensity group
  • Systolic blood pressure decreased considerably in the high-intensity group while remaining unchanged in the moderate-intensity group
  • Peak heart rate and heart rate reserve improved in the high-intensity group only
  • Heart rate recovery improved across both groups.

"Today, people who have been given a new heart experience increased physical function, quality of life, and overall life span; however, most patients continue to have limitations in their physical function and reduced quality of life compared to the general population due to side-effects from anti-rejection medications and because heart rate regulation is impaired after heart transplantation," comments Dall. He continues:

"The impaired heart rate response has been considered a hindrance for more demanding high-intensity training, but this new study documents that stable heart transplant recipients benefit from this type of training more than from the moderate training that has been recommended so far. Importantly, the training is also safe and well received by patients."

There was a marked loss of effect documented after the 5-month "washout," emphasizing the need for repeated intervention programs and lifelong change in exercise habits.

The investigators note that there were limitations within the study due to the small sample size and the results should be confirmed in other, larger studies.

The attendees of the meeting in Toronto have developed a list of top research priorities and agenda for exercise in solid organ transplant, which includes the requirement to organize significant multicenter intervention studies, standardize measures of physical function in clinical trials, examine the benefits of innovative types of exercise, and assess the effects of exercise on measures such as immunity, infection and cognition.

Earlier this year, a study suggested motion prolongs survival while waiting for a donor heart - patients who remain active and stay in good shape psychologically while waiting for a donor heart can significantly increase their chances of surviving this period.