Background and Rationale

Cardiac rehabilitation (CR) following a cardiac event has been shown to reduce risk of mortality by 25% over three years¹.

While CR was originally centered around exercise and improving physical function, the current guidelines recommend that assessment and targeting of risk factors should be an integral part of CR¹.

Obesity is an established cardiovascular risk factor (CRF), and even patients who are overweight (BMI 25-29.9) are shown to be at an increased risk of cardiovascular events².

The majority of CR patients are overweight or obese³, and over half of CR patients are thought to have metabolic syndrome^4,5. Therefore, weight reduction and maintenance in an ideal weight range would seem a natural and prognostically relevant objective of CR.

Recent literature on the effects of CR in weight reduction has been inconclusive. While a few studies showed CR resulted in body weight reduction^1,6,7, others have not been able to demonstrate this⁸. None has provided ongoing long term supervised exercise program beyond 3 months.

Peak exercise capacity has been found to be the strongest predictor of mortality in men with cardiovascular disease⁹. While CR has been shown to markedly improve exercise capacity for patients of all weight ranges^3,10, the maintenance of fitness with long term CR is yet to be established.

We therefore undertake to determine the relationship of CR including an ongoing exercise program for over two years on weight reduction and fitness.

Method

Study population

Measurements

Intervention

Statistical Analyses

Results

The weight change experienced by patients during the Phase II program is shown in Table 2. The results showed no significant weight loss for overall population, nor for those who began the study with a BMI ≥30.

Similarly, no weight loss was found between entry and at 24 months of Phase III for the overall and obese populations (table 3).

When patients were categorized into three weight range groups (normal, overweight, and obese), there was no significant trend towards a lesser proportion of the study’s population being obese over the 24 months CR period (table 3).

Exercise capacity measured in maximum METs (Fig. 1) increased by 3.3±1.1 METs (P<0.0001) during Phase II CR, representing a relative increase of 66 percent. No significant change in exercise capacity was noted thereafter throughout the phase III program ( phase II to phase III: +0.6 METs, p=0.1).

Cardiac workload significantly improved during Phase II, increasing by 4921±4757 (table 2), representing a relative increase of 26 percent. No significant change was observed thereafter throughout the subsequent phase III program.

Resting heart rate and resting blood pressure did not change significantly throughout the Phase II or Phase III programs (table 2).

Figure 1

Table 1. Baseline Characteristics

Figure 2

Table 2. Results through phase II and phase III cardiac rehabilitation

Figure 3

Table 3. Patients’ BMI throughout cardiac rehabilitation

Discussions

In this study, supervised long-term CR (phase II followed by phase III) was associated with an improvement in physical fitness but did not result in significant weight loss.

In concordance with previous studies^3,4,5, most (75%) of our patients were overweight or obese at entry into the study (table 2). Among those who were obese at study entry there was a trend of 1.4% or 1.5 kg weight reduction at the completion of phase II program, although the loss was not statistically significant (p=0.79), possibly do to the small number of patients in this group (n:7). However, the group did show a greater trend of weight loss of close to 4% or 3.9 kg (p=0.46) between entry and ≥24 months. Other studies, employing a CR program of up to 3 months, have found obese patients tend to lose a greater percentage of their weight than non-obese patients^3,6,11, although not to the degree that satisfies recommendations for a 10% reduction of body weight over 6 months¹².

The literature on the influence of CR on weight loss remains inconclusive. While a few studies^1,6,7 found a modest weight loss (0-2% of total body weight), others have not found significant weight reduction following Phase II CR programs of up to 3 months^6,7,8,13. None, however, provided data on long-term supervised CR.

The failure of achieving significant weight loss by our patients and by patients in other studies may be related to inadequate energy expenditure during the exercise sessions. Savage, Brochu, Scott and Ades measured the energy expenditure by 112 patients during two Phase II CR sessions and found the average energy expenditure was 270±112 kcal per session¹⁴, below the recommended expenditure for cardiorespiratory benefits¹⁵.

Similar findings on patients attending maintenance CR program were reported by Schairer et al¹⁵. They found that despite most patients exercising at 60-80% of their maximum heart rate for an average of 47 minutes, the energy expenditure was only modest, at 230 kcal per session.

A recent study has also found that amongst patients 1 year after a coronary event, overall diet was poor¹⁶, suggesting a need for further dietary intervention.

Exercise capacity increased during Phase II, and plateaued throughout continuation of CR in Phase III. The findings indicate the effectiveness of the once per week supervised group exercise program per se, and possibly through its pleiotropic benefits (eg. keeping up with motivation to exercise, ability to discuss exercise routines with peers and exercise physiologists etc) in maintaining exercise capacity or physical fitness over 2 or more years of being in the program.

Cardiac workload improved in parallel with exercise capacity following phase II, and was maintained throughout Phase III (table 2).

Fitness has been found to be protective against all-cause mortality despite the presence of other risk factors⁹, and improved physical fitness has been found to reduce mortality by up to 44%¹⁷. Thus, the observed improvement in exercise capacity as a proxy of physical fitness following phase II and subsequent maintenance in phase III, establishes potential prognostic benefit of supervised long term CR.

Study limitation.

This is a retrospective study without a control group. Attendance rate throughout the CR program was not recorded. Thus variability in the frequency of session attendance may exist and dilute the effectiveness of the programs. Furthermore, the exercise capacity at entry does not necessarily reflect the patients’ physical fitness prior to cardiac events prompting enrollment into CR.

It would have been beneficial to measure the percent change in body fat throughout CR. Studies have found that CR can decrease body fat mass at a greater percentage than total weight^7,8. It is possible patients in our study experienced a change in body composition without a significant change in body weight.

A selection bias may exist in that only patients who had completed 2 or more years of CR were included, as their progress during Phase II may differ from those who chose not to continue into Phase III (eg. patients who successfully lost weight in Phase II may have chosen not to continue with Phase III). The selection bias questions the validity of the study’s findings on Phase II CR results more than the long term findings.

Conclusion

Our study results suggest that Phase II CR followed by 2 or more year long-term phase III CR program in its current model is not sufficient to produce significant weight loss, and further interventions, such as more exercise sessions or longer, more strenuous sessions, or dietary interventions should be considered. Out study did show benefits of Phase II CR in improving physical fitness, which is maintained throughout the long term Phase III CR. A long-term, prospective, controlled trial incorporating ongoing dietary guidance and surveillance with additional exercise sessions seems to be warranted.

Acknowledgments

No competing financial interests exist. The study was funded through an Educational Grant from Cardiac Health Institute, Sydney, Australia.