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  • Researchers Identify Factors That May Keep Some Patients From Making Optimal Gains in Cardiac Rehab

    In brief:

    • Researchers studied 541 patients who underwent CR after a cardiac procedure (either percutaneous coronary intervention or coronary artery bypass graft).
    • Pre- and post-CR gains in 6MWT were compared with a range of demographic and health data to look for predictors of individuals who did not experience optimal exercise capacity (EC) gains from CR.
    • Findings: baseline 6MWT results, age, PCI, LDL-C levels, gender, use of statins, systolic at-rest BP, BMI, and triglyceride levels all identified as predictors of suboptimal EC post-CR.
    • Lower LDL-C and use of statins were associated with lower EC; higher LDL-C and no use of statins also were associated with suboptimal EC.
    • Researcher say predictors could help clinicians customize CR interventions for maximum effectiveness.

    Authors of a new study say they've found a set of predictors that could help providers identify which cardiac rehabilitation (CR) patients are at risk of making lower gains in exercise capacity (EC) from the intervention.

    Researchers analyzed before-and-after results from the 6-minute walk test (6MWT) among 541 patients enrolled in the Mayo Clinic Florida's CR program, tracking distance as well as heart rate and blood pressure before and after each test. Next they compared post-CR 6MWT results with a range of health and demographic data including type of initial cardiac procedure, age, sex, body mass index (BMI), total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (LDL), triglycerides, and use of lipid-lowering drugs (LLD) at baseline. Results were published in the American Journal of Cardiology (abstract only available for free).

    When they looked at who didn't achieve optimal EC after CR, researchers found a constellation of factors that they believe may be predictive of an individual's likelihood of making substandard gains. In all, 9 major predictors were identified (listed here in descending order of effect): baseline distance on 6MWT, age, percutaneous coronary intervention (or PCI, as opposed to coronary artery bypass graft, or CABG), LDL-C level, gender, the interaction of LDL-C while on LLDs, systolic BP at rest, BMI, and triglyceride levels.

    The CR protocol used in the program was built around 30 minutes of aerobic exercise within a prescribed heart rate range and 30 minutes of upper and lower body resistance exercise 3 times a week for 4 to 12 weeks. Patients were also given home exercise instructions that involved 30 to 60 minutes of exercise on non-rehabilitation days, and were provided with instruction on cardiovascular risks and nutrition.

    According to authors, some of the predictors—particularly age and gender—were already associated with lower post-CR EC gains among women and more elderly individuals. Other predictors, however, were more surprising. Among them:

    LDL-C levels and use of LLDs. Researchers found that the use of LLD and a lower LDL-C level while on the drugs was associated with lower post-CR exercise performance, while among participants without LLDs, higher LDL-C levels were associated with lower EC. Authors cite the need for more research on the effects of statins on a patient's ability to exercise, but they add that "if patients are showing signals of statin-related myopathy that limit their exercise performance, the clinician needs to have an open discussion with the patient about the benefit and risk involved in regards to EC and take the patient's preference into account."

    PCI vs CABG. Patients who received PCI—a nonsurgical procedure often involving angioplasty and stents—recorded less dramatic EC gains than those who received CABG, with the PCI improving their median 6MWT by 23.3 meters less than the CABG group. "This is probably due to the fact that patients are more deconditioned after CABG than after PCI and have more room to improve their functional capacity … but the possible effect of a more complete revascularization after CABG cannot be ruled out," authors write.

    BMI. While patients with higher BMI had lower EC improvements, authors noted that other studies have identified the so-called "obesity paradox"—a negative correlation between BMI and total cardiovascular mortality rates after a cardiac event—which makes BMI a bit less useful as a predictor of anything other than EC gain. Instead, authors advise paying careful attention to waist-to-hip ratio, beyond BMI, which they write "identifies more accurately those patients in CR who are in need of special attention with their preventive efforts."

    Researchers say that the case for the overall effectiveness of CR remains solid and was clearly supported by their own study, in which 92% of patients showed an increase in 6MWT results after CR. Rather than question CR itself, authors believe that their study points to the need for providers to weigh factors that might get in the way of success and then adjust interventions to suit, writing that "personalized treatment plans for such patients appear warranted in these groups to promote greater improvements in functional capacity and the related benefits."

    Research-related stories featured in PT in Motion News are intended to highlight a topic of interest only and do not constitute an endorsement by APTA. For synthesized research and evidence-based practice information, visit the association's PTNow website.

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