Subcutaneous Implantable Cardioverter Defibrillator for Treating Life-threatening Ventricular Tachyarrhythmia

Proprietary names: Cameron Health S-ICD, EmblemTM Subcutaneous Implantable Defibrillator (S-ICD) System; S-ICD™ System; SQ-RX® Pulse Generator, Model 1010; Emblem S-ICD, Model A209; Q-TRAK® Subcutaneous Electrode, Model 3010 and 3401; Q-TECH™ Programmer, Model 2020 and 3200, Q-Guide™ Electrode Insertion Tool, Model 4010 and 4711; S-ICD System Magnet, Model 4520.

Generic names: Subcutaneous implantable cardioverter defibrillator; subcutaneous implantable cardiac defibrillator; subcutaneous defibrillator.

Ventricular tachyarrhythmia (VTA) is a heterogeneous class of abnormal cardiac rhythms originating in ventricular tissue.1,2 The most common types of VTA are ventricular tachycardia and ventricular fibrillation.2-4 Ventricular tachycardia is a heart rhythm faster than 100 beats per minute with 3 or more consecutive irregular beats at that heart rate, and ventricular fibrillation is the disorganized quivering of the ventricles.1,4 Both ventricular tachycardia and ventricular fibrillation result in failure of the heart to pump sufficient blood to the body and may lead to sudden cardiac death.1

VTA usually occurs with underlying heart disease, but it also affects individuals with structurally uncompromised hearts.1 The most common causes of VTA are coronary artery disease, myocardial infarction, and acute myocardial ischemia.1,5 Risk factors for developing VTA are similar to those of coronary artery disease and include a family history of arrhythmias, male sex, blood lipid abnormalities, hypertension, physical inactivity, obesity, cigarette smoking, excessive alcohol intake, diabetes, and poor diet.6

Symptoms of VTA, including both ventricular tachycardia and ventricular fibrillation, include:1

Clinicians usually diagnose VTA by taking a detailed medical history and performing a physical evaluation.5 Diagnostic tests include ventricular function assessment using a 12-lead electrocardiogram (ECG), laboratory tests for cardiac enzyme (i.e., troponin, creatine kinase) levels, and echocardiograms to reveal structural heart disease.4,5

Initial management of VTA depends on the patient's symptoms and hemodynamic state at the time of presentation.3 Stable patients with mild ventricular dysfunction are hospitalized, and pharmacologic agents (i.e., beta blockers, class I and class III antiarrhythmic medication, calcium channel blockers) are administered to restore regular heart rhythm.5 If pharmacologic agents are insufficient or hemodynamics are unstable, clinicians administer synchronized cardioversion (therapeutic electric shocks delivered during the R phase of the cardiac cycle).1,5 In patients without a pulse, clinicians administer unsynchronized electric current (defibrillation) to restore blood circulation.1

After diagnosis, clinicians attempt to identify underlying reversible conditions that may trigger VTA and prescribe corrective measures that may decrease or eliminate the arrhythmia.1,5 Preventive radiofrequency catheter ablation is an option, especially in younger patients, for correcting VTA, although success rates vary based on the type of VTA and the extent of underlying structural heart disease.3 The American College of Cardiology, the American Heart Association, and the European Society of Cardiology recommend implantable cardioverter defibrillators (ICDs) for both primary and secondary prevention in patients at risk of sudden cardiac death.1,4,5,7,8 Pharmacologic agents are frequently administered in conjunction with ICDs to reduce the frequency of ICD therapy delivered.1 In patients who are poor candidates for ICD and/or radiofrequency ablation, clinicians prescribe antiarrhythmic medications to manage VTA...