The Subcutaneous Implantable Cardioverter Defibrillator

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The subcutaneous implantable cardioverter defibrillator (S-ICD) is a subcutaneous alternative to conventional transvenous ICD (TV-ICD) systems, which have previously been shown to treat life-threatening ventricular tachyarrhythmias in cardiac disease patients. A review of the literature reveals that S-ICDs have similar shock efficacy rates for both induced and spontaneous ventricular tachyarrhythmias when compared with TV-ICDs. Furthermore, S-ICDs seem to have a higher specificity for withholding therapy when supraventricular tachycardia is present compared with TV-ICDs. The advantages of the S-ICD system are numerous: fewer vascular complications including thrombosis and hemothorax, avoidance of fluoroscopy, and an easier means of lead replacement. These advantages make the S-ICD system most suitable for younger patients who may require replacements in later life, those with abnormal venous anatomy, and individuals prone to infection and/or central vein thrombosis. However, S-ICDs are not without their complications and are associated with a higher incidence of inappropriate shocks secondary to T wave oversensing. S-ICDs also lack antitachycardia pacing, making them a suboptimal device in patients with recurrent monomorphic ventricular tachycardia who would otherwise benefit from the antitachycardia pacing offered in TV-ICDs. Lastly, the limited number of long-term randomized, head-to-head studies involving direct comparison with TV-ICDs poses a challenge in the implementation of the S-ICD.

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