Inappropriate Implantable Cardioverter-Defibrillator (ICD) Shock in an Adolescent Secondary to Alternating Current in an Ungrounded Swimming Pool: An Important Potential Source of Electromagnetic Interference in Young People with ICDs

DOI: 10.19102/icrm.2014.050807

¹MINH B. NGUYEN, MD, ¹ROBERT H. PASS, MD and ²SCOTT R. CERESNAK, MD

¹The Pediatric Arrhythmia Service, Pediatric Heart Center, The Children’s Hospital at Montefiore, Albert Einstein College of Medicine, Bronx, NY, USA

²Lucille Packard Children’s Hospital, Stanford University, Palo Alto, CA, USA

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ABSTRACT. Though implantable cardioverter-defibrillators (ICDs) have greatly improved in reliability, ICDs may inappropriately shock patients as a result of many environmental causes. We present the case of a 16-year-old boy with an ICD who received an inappropriate shock from an unusual cause, an alternating current from an ungrounded pool.

KEYWORDS. adolescent, arrhythmia, defibrillators, electrophysiology, implantable, pediatrics.

The authors report no conflicts of interest for the published content.
Manuscript received April 4, 2014, final version accepted June 18, 2014.

Address correspondence to: Minh B. Nguyen, 3415 Bainbridge Avenue, Rosenthal Pavilion, R1, Bronx, NY 10467.
E-mail: minh.b.nguyen@med.einstein.yu.edu

Case report

The patient was a 16-year-old boy with a prior history of ventricular fibrillation (VF) arrest, dilated cardiomyopathy, and complete heart block with a dual-chamber implantable cardioverter-defibrillator (ICD) who was otherwise in good health. The day prior to presentation, he was playing in a pool at camp with many other children when all the children felt a sudden electrical “shock.” A few moments later, the patient felt his own ICD deliver a shock. He was asymptomatic before and after the time of the ICD discharge. He left the pool and was noted to be alert and stable. A remote transtelephonic transmission was performed and demonstrated 60 Hz artifact on both the atrial and ventricular leads with ventricular oversensing and an inappropriate shock for presumed VF (Figure 1). Sinus rhythm was noted immediately post shock with resolution of the 60 Hz artifact.

The patient was seen for evaluation and ICD interrogation the following day. The patient’s ICD was a Medtronic Protecta XT DR D314DRG (Medtronic Inc, Parsippany-Troy Hills, NJ, USA), and his leads were a Medtronic Capsure Fix Novus in the right atrium and a Medtronic Sprint Quattro in the right ventricular apex. The device had been programmed for VF detection for 18/24 beats at a ventricular rate greater than 200 bpm. The sensitivity on the ventricular lead was programmed at 0.3 mV. Testing of both atrial and ventricular leads revealed no significant lead abnormalities, with stable lead impedances, sensing, and pacing thresholds (ventricular lead pacing impedance was 361 ohm and defibrillation impedance was 59 ohm). The electrical sensation noted by the other children in the pool, the revelation that the pool was not appropriately grounded, and the artifact caused by 60 Hz electrical interference on both the atrial and the ventricular leads suggest the trigger for inappropriate ICD shock was electromagnetic interference (EMI) from the ungrounded swimming pool.

Discussion

We present the unique cause of an inappropriate shock from an ICD caused by EMI in an ungrounded swimming pool. Though ICDs are used to provide life-saving therapy in patients who are at risk of having life-threatening ventricular arrhythmias, inappropriate shocks can cause significant physical and psychological harm in children.¹

EMI can be interpreted by ICDs as ventricular fibrillation because the interval of an alternating current is often 50–60 Hz (50 cycles per second or a cardiac cycle length of 20 ms), which is far shorter than the interval threshold programmed in most ICDs to identify ventricular fibrillation. In our patient, the alternating current running through the pool was interpreted by his pacemaker as ventricular fibrillation at a cycle length of 120 ms (heart rate of 500 bpm) (Figure 1). After fulfilling the programmed criteria for ventricular fibrillation (18 out of 24 cycles), the ICD readied the charge for defibrillation therapy, and a shock of 35 J was administered (Figure 1).

Inappropriate shocks are commonly caused by non-ventricular tachyarrhythmias (such as supraventricular tachycardia), lead malfunction or fracture, and ventricular oversensing.^2,3 Inappropriate shocks have been reported to occur in up to 25% of children and young adults with ICDs due to multiple causes.⁴ EMI is a well-known cause of inappropriate activity in both ICDs and pacemakers, and has been demonstrated to lead to oversensing in pacemakers and ICDs.^5,6 In the adult population, documented reports on ventricular oversensing secondary to EMI were found to be due to a variety of causes. There have been reports of inappropriate shocks in adults due to cleaning a lamp, electronic muscle stimulation treatment for lower back pain, microwave therapy for pain relief, power tools, and swimming pools.^5,6 This case illustrates the importance of appropriate pool grounding for children with pacemakers and ICDs.

Fortunately, advances in ICD technology and innovation have decreased the amount of ventricular oversensing due to EMI, lead malfunction, and supraventricular tachycardias. However, inappropriate shocks are still a problem in children with ICDs.^2,4,7 Families of children with pacemakers and ICDs need to be aware of this potential swimming pool hazard and the potential for inappropriate ICD shock from an improperly grounded swimming pool.

Conclusion

ICD and pacemaker therapies have been increasingly utilized in the pediatric population for children with heart rhythm disorders. EMI is a known cause of inappropriate shock in patients with ICDs. In this case, we have demonstrated an inappropriate shock from an ungrounded camp swimming pool. It is important for pediatricians and pediatric cardiologists to be aware of this additional pool safety hazard for children with pacemakers and ICDs.

References

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