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Exercise that focuses on building cardiorespiratory fitness, rather than resistance or strength training, provides the best shot at reducing mortality, researchers found.

In the meta-analysis, rehabilitation significantly increased fitness by more than one and a half metabolic equivalents (P<0.001), Gavin Sandercock, PhD, of the University of Essex in Colchester, England, and colleagues reported.

Specifically, aerobic or mixed exercise programs were equally effective and significantly more so than the few which prescribed resistance exercise, according to the study published online in the International Journal of Cardiology.

"Higher cardiorespiratory fitness is associated with reduced risk of cardiovascular mortality and morbidity, as is the multitude of gains in fitness due to exercise training," they wrote.

It's been shown that cardiac rehabilitation reduces morbidity and mortality in heart disease patients, but it's less clear whether it can specifically improve cardiorespiratory fitness -- one potential explanation for the benefits of rehabilitation, the researchers said.

So to assess whether studies of cardiac rehabilitation have shown improvements in cardiopulmonary fitness, Sandercock and colleagues conducted a literature review of 31 studies totaling 3,827 patients.

Patients were referred for cardiac rehabilitation following a myocardial infarction (MI), revascularization (coronary angiography or bypass grafting), or a combination of revascularization and MI, valvuloplasty or angina.

The investigators chose to use the metric of metabolic equivalents as a gauge of fitness for several reasons:

• It is easily understood by researchers and clinicians.
• It is transferable across a number of exercise modalities and patient groups.
• It is used to describe aerobic exercise as well as everyday tasks.

Overall, they found a mean improvement in fitness of 1.55 metabolic equivalents across all studies (95% CI 1.21 to 1.89, P<0.001).

"This is an impressive and clinically important increase and provides further evidence for the efficacy of cardiac rehabilitation as a therapeutic tool to increase exercise capacity, decrease mortality and morbidity, and to increase patients' quality of life," they wrote.

The improvement could translate to an estimated reduction in mortality of 16% to 54%, Sandercock and colleagues reported.

They noted, however, that the findings were highly heterogeneous (P<0.001), as patient response to rehab is highly variable.

To assess those variations, they conducted subgroup analyses, and found that characteristics associated with greatest fitness gains were age -- being younger (under age 55) and sex (being male, training in a male-only exercise group).

"It may be that male-only groups provide a more competitive environment in which male patients 'push' themselves more," the researchers wrote.

They also found that gains were highest in patients who completed at least 36 exercise sessions, typically given in three weekly exercise sessions over 12 weeks.

Changes in fitness weren't related to program type or duration, and there was no association with the patient's baseline fitness level, they added, though they noted there was a "clear trend toward larger gains in exercise-only programs" rather than comprehensive programs that also incorporate psychological or educational aspects.

"We recommend that cardiac rehabilitation should focus primarily on delivery of exercise sessions," they wrote.

The study was limited by its inclusion of nonrandomized and cohort-based study designs.

In an accompanying editorial, Chetan Shenoy, MD, of Tufts University in Boston, and Mahesh Patel, MD, of Duke University, wrote that the study "quantifies the degree of improvement to be expected with conventional programs, providing guidance for judging an individual's response to cardiac rehabilitation."

They said further work is needed to find an adequate threshold that can help determine whether patients need further rehabilitation, and these thresholds likely vary based on patient profiles.

"With a reliable metric of response to cardiac rehabilitation, new strategies can then be tested and incorporated into programs to optimize the benefits for individual patients and to improve the overall efficacy of cardiac rehabilitation programs," they concluded.

From the American Heart Association: