Correspondence

Inappropriate ICD Shocks Caused by External Electrical Noise

N Engl J Med 2009; 360:1363-1364March 26, 2009

Article

To the Editor:

Because of the growing number of patients worldwide who are receiving implantable cardioverter–defibrillators (ICDs)1 and the increasing number of indications for their use, physicians and patients need thorough safety guidelines about potential environmental hazards associated with these devices. Patients should be told of the potential risks not only so that they can make an informed decision about whether to accept the device, but also so that they can take the necessary precautions to prevent the occurrence of inappropriate shocks. Since proarrhythmia due to inappropriate shocks is well known and is potentially lethal,2 it is important to minimize the risk of its occurrence.

We recently cared for a patient who, after receiving an ICD for a ventricular tachycardia, was readmitted shortly after hospital discharge because of two shocks delivered while the patient was showering. Analysis of the shock episodes raised suspicion that electrical noise had caused an inappropriate ICD discharge. At our request, an electrician visited the patient's house and found that the shocks were caused by a current leak between the showerhead and bathroom drain, which was attributable to improper wiring.

Current leaks are common and can have many different causes, such as defective grounding.1,2 When current leaks are as small as in the above case (i.e., 3.5 to 4.0 mA), they can be unobservable unless they are specifically sought out or they cause interference with medical devices. Most ICDs are programmed to detect ventricular fibrillation at a cycle length of less than approximately 300 msec. Thus, when a current leak runs through a person with an ICD, it can be interpreted as ventricular fibrillation on the ventricular channel because of electrical activity that is consistent with an alternating current of 50 to 60 Hz.

Inappropriate ICD shocks due to a current leak are not common, but we suspect that they may be underdiagnosed. Shocks due to abnormal ICD sensing should be investigated carefully for potential environmental causes. Safety guidelines for ICDs should address these risks in order to prevent potentially harmful incidents.

Anna Margrethe Thøgersen, M.D.
Søren Pihlkjær Hjortshøj, M.D.
Aalborg Hospital, 9100 Aalborg, Denmark

Kristian Eskesen, M.D.
Gentofte Hospital, 2900 Hellerup, Denmark

Dr. Hjortshøj reports receiving lecture fees from St. Jude Medical Denmark. No other potential conflict of interest relevant to this letter was reported.

2 References

1. 1

   Maisel WH, Moynahan M, Zuckerman BD, et al. Pacemaker and ICD generator malfunctions: analysis of Food and Drug Administration annual reports. JAMA 2006;295:1901-1906
   CrossRef | Web of Science | Medline

2. 2

   Dimitri H, John B, Young GD, Sanders P. Fatal outcome from inappropriate defibrillation. Europace 2007;9:1059-1060
   CrossRef | Web of Science | Medline