Sport activity in patients with implantable defibrillator: Playing with death?

Regular physical exercise has the potential to lower cardiovascular risk and improve quality of life.¹ However, sports activity is associated with an increased risk of life-threatening ventricular arrhythmias in susceptible athletes with cardiovascular diseases.² Implantable cardioverter defibrillators (ICDs) may offer protection against sudden cardiac death (SCD) in at-risk athletes, but there is general concern that sports activity may influence the efficacy and safety of ICD therapy and increase rates of device and lead failure (Figure 1).³

First, neuroautonomic and metabolic changes associated with exertion, which induce high catecholamine levels, electrolyte imbalance, metabolic acidosis and alterations in cardiac loading, can lead to an increase of the defibrillation threshold (DFT) and induce arrhythmic storms whereby defibrillation may not be successful. Infusion of epinephrine at a dose mimicking adrenergic stimulation during mild to moderate exercise has been associated with a minimal increase of DFT and a decrease of first-shock efficacy in terminating ventricular fibrillation (VF) in ICD patients undergoing DFT testing.⁴ This finding is in agreement with the observation that DFT tends to be higher and first-shock efficacy lower in the morning, when the level of catecholamines is highest.⁵

Second, sinus tachycardia and other supraventricular tachyarrhythmias occurring during sports activity with a rate high enough to reach the VF or ventricular tachycardia (VT) detection zone may trigger inappropriate device discharges. Other causes of inappropriate ICD therapy include T-wave oversensing and device/lead failures (insulation failure, fracture or abrasions) as well as external electromagnetic interferences, all factors which may be favoured by sustained and intense physical exercise.

Third, physical trauma, whether caused by direct or indirect contact, may lead to device injury and malfunction. Athletes with ICDs have an increased risk of injuring their devices, especially when engaged in sports with significant body contact. The ICD system can be damaged, either directly as a result of blunt physical trauma, or indirectly because of repetitive bending or stretching of leads. As a consequence of electromechanical noise, the ICD device may deliver an inappropriate discharge which, in turn, may trigger a life-threatening ventricular tachyarrhythmia. Moreover, a damaged ICD may fail to deliver enough energy to terminate a malignant arrhythmia, for instance because of a lead break or a generator failure.

Fourth, ICD carriers are at risk of trauma due to syncope attributable to malignant ventricular arrhythmias. The latency of interrupting such tachyarrhythmias by the ICD may not prevent syncopal attacks from happening. Loss of consciousness can be hazardous in certain sports in which athletes may harm themselves, such as running, weight-lifting and gymnastics, or harm themselves as well as other competitors, such as canoeing and car, bicycle, or motorcycle racing.

For these reasons, patients with an ICD have been traditionally considered not eligible to engage in competitive sports activity, except for disciplines characterised by a low cardiovascular demand.³ However, despite these ample theoretical reasons to restrict athletes with ICDs from sports participation, there are conflicting viewpoints on the eligibility of ICD carriers to competition.⁶ Scientific evidence that sports are dangerous and that competition increases the health risks in patients/athletes with an ICD is lacking. Moreover, restricting or prohibiting competitive sports for certain patients may cause deep psychological, physical and financial consequences that outweigh the potential theoretical risk of harm. Indeed, in the general population of ICD carriers, low physical activity is associated with a higher risk of cardiac death.⁷

In the past decade, there have been new scientific data showing that ICD successfully prevents SCD during sports. The most compelling evidence on ICD efficacy and safety comes from a prospective, multinational registry which recruited 372 athletes with an ICD from the USA and Europe.⁸ Over a median follow-up of 31 months, although many ICD shocks occurred during and after sports participation, there were no arrhythmic deaths, resuscitated cardiac arrests or shock-related injuries. Of note, more individuals received either appropriate or inappropriate shocks during physical activity than during rest (16% vs. 6%). Predictors of appropriate shocks on VT/VF during sports included age of 20 or more years and underlying cardiovascular diseases such as arrhythmogenic right ventricular cardiomyopathy (ARVC) and idiopathic VF. Ventricular tachyarrhythmias requiring multiple high-energy shocks occurred during eight episodes (seven related to competition or other physical activity and one occurring at rest) in seven individuals, i.e. in 2% of the study population. Freedom from lead malfunction was 97% at 5 years and 90% at 10 years from ICD implant, which did not differ significantly from that in non-athletic ICD patients.

Figure 1.

Potential unfavourable effects of sports activity in athletes with an implantable cardioverter defibrillator (ICD). Sports in ICD carriers is associated with an increased risk of adrenergic-dependent ventricular tachyarrhythmias, inappropriate interventions, injury to the patient or damage of the lead/device. Sports activity may also promote the development of phenotypic expression and accelerate disease progression of the underlying cardiomyopathy. (A) Intracardiac electrogram showing an appropriate shock on fast ventricular tachycardia occurring during sports activity; (B) Athlete’s injury caused by loss of consciousness due to a syncopal tachyarrhythmia with a delayed ICD intervention. (C) Pathogenesis of sports-induced progression of arrhythmogenic right ventricular cardiomyopathy. Disruption of genetically defective intercellular junctions by mechanical stress (top left) leading to myocyte detachment and death with repair fibrofatty myocardial replacement (top right). Cardiac magnetic resonance imaging of intramyocardial scar (bottom left) and ECG recording of a scar-related ventricular tachycardia (bottom right). (D) Intracardiac electrogram showing an inappropriate shock on supraventricular tachycardia during sports activity (left). Intracardiac electrogram demonstrating bipolar ventricular channel oversensing caused by lead fracture in an athlete with inappropriate ICD shocks (right).

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More recently, the same authors confirmed these outcomes in the athletes enrolled in the same registry over a long-term follow-up (44 months).⁹ The pro-arrhythmic effect of sports activity accounted for the occurrence of appropriate shocks, respectively, in 11% of participants during exercise and in 6% at rest. An underlying ARVC was the only variable associated with exercise-induced ICD shock.

In this issue of the journal Heidbuckel et al.¹⁰ further reported on arrhythmic outcome and ICD performance in those intensive recreational athletes with ICDs who were enrolled in the European recreational arm of the registry, and compared the findings to those of the competitive athletes in the registry. Individuals engaged in recreational sports were middle-aged individuals practising endurance disciplines (such as running or cycling) for a mean of 4.5 hours per week; they received an ICD mostly for primary prevention of SCD in relation to a variety of underlying at-risk diseases. The vast majority of athletes were treated with beta-blockers. Although leisure-time athletes were older and more often affected with ARVC, they received exercise-related appropriate ICD interventions less often than their counterpart of competitive athletes. Moreover, although the proportion of athletes who received at least one appropriate intervention was similar in the two groups, competitive athletes more often experienced multiple shocks. Most importantly, no athletes died suddenly because of the inability of the device to terminate the arrhythmia. Overall, the study results indicate that recreational sports activity is associated with a lower incidence of ventricular tachyarrhythmias requiring termination by ICD discharge (three of 80 individuals) and, thus, should be considered safer than competitive sports activity.

Pooled together, data from the registry are very informative and provide a basis for more informed physician and patient decision-making in terms of sports participation for patients with an ICD. In line with these new data, the most recent American Heart Association/American College of Cardiology recommendations stated that competitive sports may be allowed in selected athletes with an ICD.¹¹ According to the data of the present study by Heidbuckel et al.,¹⁰ physicians and patients with an ICD may feel more assured that the practice of leisure-time physical activities of moderate intensity is reasonably safe.

It should be emphasised that the reasons for competitive sports restriction in young patients with a prophylactic ICD go beyond the increased risk of unsuccessful shock, inappropriate interventions, injury to the patient or damage of the device. Systematic and intense athletic training itself may increase the risk of SCD by accelerating the evolution of the underlying pathological condition and worsening the arrhythmogenic substrate, mostly in young patients who receive an ICD because of genetically determined and progressive heart muscle disorders. In patients with ARVC caused by genetically defective desmosomes, mechanical wall stress such as that occurring during intense physical exercise can accelerate the development of fibrofatty myocardial replacement through the disruption of cell-to-cell junctions and cell detachment leading to myocyte death.¹² Likewise, athletes with hypertrophic cardiomyopathy are exposed during physical activity to recurrent attacks of small vessel disease-related myocardial ischaemia, with cumulative myocardial damage and replacement fibrosis which increases the ventricular electrical instability.¹³

In conclusion, the results of this and previous studies show that ICD is an effective strategy for the prevention of SCD also in athletes. Sports activity increases the chance of experiencing a life-threatening ventricular arrhythmia, which in some cases requires multiple ICD shocks. Leisure-time sports activity of moderate intensity appears safer and is associated with a lower risk of device shocks than high intensity competitive sports. ICD carriers should not be entirely deprived of many benefits offered by regular exercise, but an individualised exercise prescription, which takes into account the specific patient’s risk profile, with particular reference to the underlying arrhythmogenic disease, is warranted. Device programming plays a key role in minimising inappropriate ICD discharges as several algorithms have been developed to discriminate supraventricular rhythms from VT based on the assessment of the variability of cycle length, slope of rate acceleration and QRS duration/morphology during tachycardia. Moreover, a significant lowering of inappropriate therapy rates can be obtained by increasing the VT/VF detection rate or by delaying ICD intervention.¹⁴ The availability of an automated external defibrillator in the athletic field should be considered as an additional ‘back-up’ measure to prevent SCD.¹⁵ Finally, the new subcutaneous ICD system appears as a promising therapeutic option aimed at avoiding the risk of sports-related transvenous lead damage.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: supported by the research grant BIRD (budget for integrated departmental research) 2016, University of Padova, Italy.

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