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Patients with implantable cardioverter defibrillators (ICDs) who participated in exercise training programs showed significantly improved levels of cardiorespiratory fitness and had a lower likelihood of experiencing ICD shocks, according to research published in JACC: Clinical Electrophysiology.
A team of investigators from the UTSW Medical Center in Dallas, the Cleveland Clinic in Ohio, Duke Clinical Research Institute in Durham, North Carolina; and UCLA Medical Center in Los Angeles conducted a meta-analysis of current comparative, prospective studies in order to assess the efficacy and safety of exercise training in patients with ICDs.
Included in the meta-analysis were prospective, parallel-arm trials that had both control and exercise training groups. The studies evaluated the efficacy of exercise training in patients with ICDs; primary end points were differences in patients’ cardiorespiratory fitness and the likelihood of ICD shocks among participants in the 2 groups. Data were included from 5 randomized controlled trials and 1 nonrandomized controlled trial.
Within the selected studies, participants underwent exercise training with a median duration of 12 weeks (range: 8 to 24 weeks) and a median follow-up of 15 months (range: 2 to 26 months) for ICD-related events. All studies included patients with stable heart failure (HF) and depressed left ventricular ejection fraction; 98% of the pooled study participants had ICD implantation, and the majority of participants reported taking beta-blockers.
Peak exercise oxygen uptake was reported in all studies as a measure of cardiorespiratory fitness at baseline and after exercise training. Pooled analyses showed that participants who underwent exercise training demonstrated significant peak oxygen uptake improvement when compared with those in the usual care group (weighted mean difference [WMD]: 1.98 mL/kg/min; 95% confidence interval [CI]: 0.58 -3.38; I2 = 68.8%). Similar improvement was seen in sensitivity analyses limited to randomized controlled trials (n=5; WMD: 2.03 mL/kg/min; 95% CI: 0.47-3.60; I2=74.6%).
The likelihood of patients experiencing ICD shocks at follow-up was also significantly lower in the exercise training group (pooled odds ratio: 0.47; 95% CI: 0.24-0.91). Most ICD shock episodes were reported during long-term follow-up after completion of the exercise training protocol, and 5 of the 6 studies reported no exercise-associated ICD shocks.
“Patients with HF and ICDs represent a particularly challenging population for cardiac rehabilitation,” the researchers noted. “To our knowledge, the present study represents the most comprehensive evaluation of the efficacy and safety of supervised exercise training among this high-risk patient population with severe HF and an ICD.”
They went on to note the important clinical significance of the findings, pointing out that clinician concerns regarding the negative impacts of exercise on patients with HF and ICDs often create barriers in exercise counseling among patients with HF, as well as overall lower rates of regular physical activity and exercise.
“Findings from the present study provide strong evidence supporting the efficacy and safety of supervised exercise training in this patient population,” the authors concluded.
Larger trials with extended follow-up should be conducted to determine the clinical efficacy of exercise training in these patients.
Study Limitations
Due to limited literature on the topic, only 6 studies were included in the meta-analysis. Additionally, specific pooled-risk estimates could not be determined for inappropriate vs appropriate shocks among the two groups, which is of importance due to the pathophysiology differences of shocks. These findings should not be applied to certain conditions, such as inherited arrhythmia syndromes, where exercise is contraindicated. Finally, given the nature of the studies, the researchers were unable to determine the sustainability of patients’ cardiorespiratory fitness improvement after exercise training was discontinued.
Disclosures: Dr Fonarow reports research support from AHRQ and consultancy fees from Janssen and Medtronic. Dr Piccini reports receiving research grants and research support from Johnson & Johnson/Janssen Pharmaceuticals, research grants from Boston Scientific Corp., and consultant/advisory board fees from Forest Laboratories, Medtronic , and Johnson & Johnson/Janssen Pharmaceuticals.
