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The introduction of implantable cardioverter-defibrillator (ICD) technology has revolutionized the fields of cardiology and electrophysiology. More than 100,000 such devices are implanted annually in the United States alone. ICDs allow life-threatening ventricular tachycardia and ventricular fibrillation to be safely controlled and benefit patients at risk for sudden cardiac death. Multiple studies (e.g., CABG patch, MADIT, MADIT II, MUSTT, DINAMIT, AMIOVIRT, COMPANION, SCD-HEFT) have examined the prophylactic indication for ICD therapy in high-risk groups.1–7 The ICD is becoming a more common therapeutic option for the young population with a diagnosis of Brugada syndrome, prolonged QT syndrome, and hereditary cardiomyopathies to name a few.
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The Emergency Department is often the initial contact point for these patients. Now more than ever Emergency Physicians must be familiar with the problems that can be encountered by a patient with an ICD. This chapter describes technical aspects, basic interrogation of the device, and a general approach to a patient who presents to the Emergency Department with an ICD.
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The ICD has four main functions. It recognizes and records local atrial and ventricular electrogram signals. It then classifies the sensed signals according to programmable heart rate zones. The ICD provides therapy (i.e., a shock) to terminate ventricular tachycardia or ventricular fibrillation. It has a pacing capability for bradycardia and/or cardiac resynchronization therapy. When detection criteria are satisfied, therapy to terminate the arrhythmia is initiated with high-energy shock of up to 40 Joules (J).
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ICD technology has progressed exponentially since its introduction by Mirowski and colleagues in the early 1980s.8 The ICD system is comprised of a pulse generator, a battery, and a lead system. The lead system is required for sensing, pacing, and the delivery of therapy. Earlier systems required that the pulse generators be placed abdominally due to their large size (Figure 35-1). Defibrillation was delivered via two epicardial patches positioned anteriorly and posteriorly. Occasionally, a transvenous spring electrode in the superior vena cava was utilized with an epicardial patch. Sensing was achieved through separate epicardial screw-in electrodes. Initial lead placement required either a sternotomy, lateral thoracotomy, or a subxiphoid approach, making early implants quite cumbersome.9
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The smaller size of the newer devices allows for superficial implantation of the pulse generator in the anterior chest wall, similar to a pacemaker (Figure 35-2). The current ICD systems are comprised of three main parts. The pulse generator is programmable and capable of analyzing and recording the patient's heart and rhythm. The ICD generator houses the batteries, high-voltage capacitors, and microprocessors necessary to process sensed intrinsic cardiac electrical activity. In essence, the generator ...