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Inappropriate defibrillator shocks and mortality
  1. Reginald Liew
  1. Correspondence to Dr Reginald Liew, Duke-NUS Graduate Medical School, Singapore, Gleneagles Hospital, #03-37C, 6A Napier Road, Singapore 258500, Singapore; reginald.liew{at}duke-nus.edu.sg

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Despite the established survival benefits of implantable cardioverter defibrillators (ICD) in patients with ischaemic cardiomyopathy and other forms of cardiomyopathies, a major limitation of this technology remains the delivery of inappropriate shocks for reasons other than life-threatening ventricular tachycardia or ventricular fibrillation. Inappropriate ICD shocks may occur as the result of atrial arrhythmias with rapid ventricular conduction, abnormal sensing (such as T-wave oversensing) or lead artefact/ICD malfunction. Such events have been estimated to occur in approximately 10–15% of patients with ICD, and result in significant morbidity and distress to the patient.1 ,2 An important objective for both physicians looking after patients with ICD and manufacturers of the technology is to decrease the burden of inappropriate ICD shocks and improve the quality of life of patients with ICD. When an ICD discharges a shock to the myocardium, whether for an appropriate or inappropriate reason, there is likely to be a small degree of myocardial damage, as evidenced by a transient rise in serum troponin.3 ,4 It is presently unclear whether the increased mortality observed in ICD patients who experience shocks from their device is due to the detrimental effects of ICD shocks per se or due to the increased shocks being a marker of the higher-risk patient.1 ,5 A related question is whether inappropriate ICD shocks are also associated with an increased mortality. In a substudy of the primary prevention Multicenter Automatic Defibrillator Implantation Trial (MADIT) II study, analysis of stored ICD electrograms from subjects who received an ICD shock (83 out of 719 patients or 11.5%) revealed that inappropriate shock episodes accounted for 184 of the 590 total shock episodes (31.2%). Furthermore, patients who experienced inappropriate shocks had greater all-cause mortality during follow-up.6 Follow-up data from another primary prevention ICD trial involving the …

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