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Reviewing the research: Safe sports participation with an implantable defibrillator

Many patients with implantable defibrillators can safely participate in sport.

Larmpert R, Olshansky B et al.  Safety of Sports for Athletes With Implantable Cardioverter-Defibrillators:  Results of a Prospective, Multinational Registry.  Circulation. 2013; 127:2021-30.


Sudden cardiac death is the leading cause of non-traumatic death in sport.   The advent of implantable defibrillators, which detect potentially-fatal heart rhythms and deliver an electrical shock directly to the patient, has improved survivability for patients with cardiac conditions that have a high arrhythmia risk.  The advantage of an implantable defibrillator is that it works much more quickly than the time it takes for a first responder to recognize the problem, call for the defibrillator (such as an AED) and use it.  In some cardiac conditions, survival drops below 5% when more than three minutes have passed from the time of patient collapse.  Thus, time is of the essence.

Because implantable defibrillators carry a theoretical risk of injury to the device with contact sports, and because sports participation can provoke the arrhythmia in many patients with potentially fatal arrhythmia problems, return to activity guidelines for these patients have tended to be conservative, lacking definitive safety data.

The Implantable Cardioverter-Defibrillator (ICD) Sports Safety Registry was started in 2006 in an effort to track patients with these devices and determine safety recommendations based upon real data.  This study – a report on registry findings – sheds light on the questions raised above.  For this study, 372 patients with ICDs who were participating in organized (328) or high-risk (44) sports were selected for observation.  94% of patients on the registry were Caucasian – perhaps indicating a lack of access for African-American athletes into the registry (3% of registrants).  In descending order, the most common reasons for ICD implantation in these patients were Long QT Syndrome (a genetic disorder that leads to fatal ventricular arrhythmias), hypertrophic cardiomyopathy (the same congenital condition that killed Reggie Lewis and Hank Gathers) and ARVD (a condition where the right ventricle is under-developed and has a higher risk of arrhythmia).  155 of these patients had ventricular arrhythmias that preceded implantation – 42 during sports participation.  The heart rate threshold for when these devices trigger can be set, and in this patient group the low setting was 200 bpm, with the low setting in the competitive subgroup 217 bpm.  Average time from implantation was 27 months.  62% of all subjects were taking beta-blocker medications to control heart rate, including 67% of competitive athletes.  Average ejection fraction (a measure of cardiac function) was 66% — which is good.

The most common organized sports that registrants were participating in were running, basketball and soccer.  The most common high-risk sport was skiing.  Competitive athlete levels ranged from junior high to national team competition.  Subjects in the competitive subgroup averaged 13 hours of practice per week (range 7-19).   Subjects were followed for an average of 31 months.  Twenty-one patients did not complete the study, including two patients who died.  One of these two patients was a 52 year old cyclist who died at work (desk job) despite receiving multiple shocks.  The other fatality was a 32 year old volleyball and softball player who died after being hospitalized for congestive heart failure.  During the study period there were no occurrences of death related to rapid heart rhythm, death during or immediately after sports participation, or injury related to shock or arrhythmia-related blackouts (the primary endpoints of the study).

During the observation period, 77 subjects (21% of patients) received shocks from their ICD.  40 (11%) received at least one inappropriate shock.  Thirty-six subjects (10%) received shocks during practice or competition (a total of 47 shocks), 29 subjects received shocks (total = 39) during other physical activity and 23 subjects received shocks (33) at rest.   There was a higher likelihood of receiving a shock during competition or physical activity compared to rest, but there was no higher chance of a shock being delivered in competition versus being just generally active.  Shocks delivered during activity were statistically more likely to be delivered appropriately.

Patients who received shocks tended to re-evaluate sports participation.  Of the 36 patients receiving shocks during sports participation, four ceased participation in all sports, while seven stopped participation in at least one sport (30% of this subgroup).  Five other patients stopped at least one sport after receiving a shock at rest.

Two patients developed ventricular tachycardia below the threshold of the ICD and ended up being externally cardioverted (defibrillated).  Beta-blocker use was not associated with a decreased chance of receiving an appropriate shock.

Estimated lead survival (maintenance of good electrical connection of the device) was 97% at five years.  This is no different than lead survival rates reported previously in more typical patient populations.

This study does seem to show that athletes with potentially fatal cardiac conditions can continue to engage in sports participation with an ICD in place, and that the ICD will terminate a potentially-fatal arrhythmia when it occurs.  An association between activity and a higher risk of shock was verified, but there was no difference in the risk of shock delivery between patients in competition and patients participating in recreational exercise.  Importantly, the majority of athletes who did receive shocks chose to continue playing, indicating that participation was an important part of the subject’s perceived quality of life.

The authors emphasize the importance of exercise testing to rule out a high likelihood of exercise-induced arrhythmia or correctible coronary ischemia (blocked artery).  They also note that the subgroup of patients with ARVD (right ventricular dysplasia) might deteriorate more quickly with regular exercise and that this should be taken into account in patients with this condition, separate from a discussion of arrhythmia risk.   The authors also noted the high ejection fraction of the study population, commenting that the results of this study cannot be generalized to ICD patients with poor cardiac function.  Finally, there were few study participants in sports such as ice hockey or football where injury to leads might be more likely to occur.  For this reason, recommendations for participation in these sports should not necessarily be made on the basis of this study’s results.

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