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As part of cardiac rehabilitation for patients with coronary artery disease, high-intensity interval training (HIIT) couldn't outperform standard exercise training beyond a few weeks, according to the from Australia.

Cardiopulmonary exercise test (CPET) results showed that individuals randomized to HIIT had a 10% boost in VO₂ peak from baseline to 4 weeks, compared with 4% improvement among peers receiving moderate-intensity continuous training (MICT) during this time instead (P=0.02).

By 12 months, however, improvement was similar between study arms (10% vs 7%, P=0.30), reported a group led by Jenna Taylor, PhD, now a postdoc fellow at Mayo Clinic in Rochester, Minnesota, in .

On the other hand, those HIIT participants who followed program rigorously did show more durable benefit.

"These findings support the inclusion of HIIT in CR [cardiac rehab] programs as an alternative or an adjunct to standard moderate-intensity exercise, allowing for prescription based on patient goals, preferences, and capabilities," the authors wrote. "This should have broad applicability for traditional CR and home-based programs."

Their small, single-center trial had 93 patients undergo 4 weeks of supervised HIIT or MICT training in a private hospital cardiac rehabilitation program (three sessions per week: two supervised and one at home), with subsequent home-based training for the next 11 months (three sessions per week).

Heart rate monitoring suggested similarly low rates of adherence between groups during the home-based phase of the trial (HIIT 53% vs MICT 41%, compared with 91% for both groups during the supervised exercise stage).

"The frequency and reasons stated for being unable to complete the exercise protocol were similar between groups, as well as unpleasant symptoms and injuries reported in relation to the exercise protocols," Taylor and colleagues reported.

As well, they indicated, "[f]urther improvement in cardiorespiratory fitness after 12 months in patients undertaking HIIT was limited to those with good exercise adherence."

The 93 patients had been medically cleared for participation in the FITR Heart Study following a CPET. Mean age was 65 years, and 84% were men. Baseline VO₂ peak was approximately 27.5 mL/kg/min.

HIIT and MICT were both associated with high feasibility, and there were no deaths or cardiovascular events determined to be a result of either type of exercise training. The sole case of post-exercise hypotension in the HIIT group was found to be caused by diuretic-induced dehydration.

Generally, supervised MICT was associated with a greater decrease in systolic and diastolic blood pressure (BP; -3/2 mmHg vs +2/+1 mmHg with supervised HIIT, P<0.05). However, people with hypertension at baseline experienced similar reductions in BP after exercise.

"There were no group differences for any other cardiovascular risk factors or measures related to diet and physical activity. All quality of life domains improved over the study period, with no differences between groups," Taylor's team noted.

Limitations of the trial include the questionable generalizability to other centers and the inclusion of few women and people with left ventricular dysfunction, type 2 diabetes, and a history of tobacco smoking, the investigators acknowledged.

"In the current study, medical exclusion following baseline CPET (3%) and further coronary intervention (1%) were very low. However, these safety data should still be interpreted in the context of the small size of the study and the requirement that all patients have CPET prior to enrollment, which is not routinely done for all patients referred for CR," they also cautioned.

Notably, cardiac rehab participation among heart disease patients remains low in the U.S.

Tai chi and other types of exercise have been suggested in lieu of full-blown cardiac rehabilitation.

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