Exercise Can Keep ICD Patients Fit Without Raising Shock Risk

Deborah Brauser

March 27, 2015

Moderately strenuous aerobic exercise can improve cardiovascular health in patients who have received an implantable cardioverter-defibrillator (ICD)—without causing the device shocks that many patients fear working out might cause, according to researchers[1].

Their randomized study, which was published March 19, 2015 in Circulation, included 160 adults with an ICD for primary or secondary prevention of cardiac arrest. It showed that those who underwent an aerobics training and maintenance program in their homes for 6 months had significantly higher peak oxygen consumption (VO2 max) levels compared with those who received no clear exercise directives.

"The surprise finding was that in the aerobic maintenance phase of the study, the VO2 max continued to rise, indicating that patients gained more aerobic capacity after the prescription was cut in half," lead author Dr Cynthia M Dougherty (University of Washington School of Nursing, Seattle) told heartwire from Medscape by email.

Although ICD shocks were infrequent and did not differ significantly between the groups, there were slightly fewer occurrences in the aerobics group (3.5% vs 5.3%, respectively). There were also no significant between-group differences in any-cause hospitalizations or deaths.

"The number-one take-home message is that exercise at home is safe for patients with an ICD," said Dougherty, adding that clinicians shouldn't fear prescribing it to their patients.

Fear of Shocks

The investigators note that approximately 50% of the one million Americans who have an ICD change their behavior after implantation so as to not incur shocks from the new device. This includes participating less or not at all in daily household activities, exercise, and sexual activity.

"Such behavior not only fails to prevent ICD shocks but is likely to result in a cycle of decreased activity, increased shock anxiety, poor acceptance of the ICD, and decreased quality of life," they write.

In the study, participants with single- or dual-chamber ICDs (77.5% men; mean age 55 years; mean ejection fraction 40.6%) were enrolled between 2007 and 2012 in Washington State and randomly assigned to undergo a structured aerobics exercise program (n=84) or usual care (n=76).

The training portion of the aerobics program included 10 minutes of pre- and poststretching and 1 hour of walking at target heart rate 5 days per week for 8 weeks total. The maintenance portion then consisted of home walking at 80% of the target heart rate for 150 minutes/week for 16 additional weeks. Those assigned to usual care were told to stick with their usual exercise regimen.

At baseline and at weeks 8 and 24, peak VO2 was measured by cardiopulmonary exercise testing (CPET). Exercise adherence was monitored through a variety of methods, including exercise logs and weekly phone chats; the usual-care group was only monitored through monthly phone chats.

Results at 8 weeks showed that peak VO2 (the primary outcome) was significantly increased from baseline in the aerobics group (by 2.8 mL/kg/min, P<.001) vs the usual-care group.

"In addition, significant improvements were observed . . . in their exercise time, VO2 at anaerobic threshold, oxygen pulse, and metabolic equivalents," report the investigators. Plus, all of these measures were sustained or even improved during the maintenance phase. On the other hand, results at 24 weeks showed no significant changes in any of the outcomes for the usual-care group.

No deaths or sudden cardiac arrests occurred in either group. "Aerobic exercise that was strenuous enough to confer cardiopulmonary benefits was implemented without a concomitant increase in arrhythmias, ICD therapies, or hospitalizations," write the researchers.

"These observations should help dispel concerns," they add. "Having an ICD should not relegate persons to lifelong sedentary activity."

"Clear Demonstration of Benefit"

When asked for comment, Dr Rachel Lampert (Yale University School of Medicine, New Haven, CT) told heartwire that this is "a very exciting study."

"There are extensive data on the benefits of exercise in the general population and for people with all different types of heart disease. But there are surprisingly few data about the benefits of exercise and cardiac rehabilitation in patients who get ICDs," said Lampert.

In addition, she noted that these patients are often afraid that exercise will cause an arrhythmia "or their heart rate to go up and their ICD will go off, giving them a shock.

"So the demonstration of benefit from any type of exercise or rehabilitation program is important. Now, doctors will feel comfortable prescribing this and patients will feel comfortable doing it," she said.

Although the findings weren't really surprising, Lampert noted that the study was needed—especially because it clearly demonstrated the safety of these practices for this patient population.

"The data needed to be out there. And this was a good, careful, well-designed study," she said.

The study was funded by the National Institutes of Health, National Heart, Lung, and Blood Institute. The study authors report no relevant financial relationships. Lampert reports having received research grants from defibrillator companies, but no conflicts with this study.


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