Chapter 24

The treatment of individuals at high risk for sudden death has changed dramatically with the introduction of implantable cardioverter-defibrillator (ICD) technology. The superiority of the ICD device over antiarrhythmic therapy has been confirmed in randomized trials.1–3 Expanding clinical indications for the implantation of these devices arose with the publication of the MADIT (Multi-center Autonomic Defibrillator Implantation Trial) trial, the results of which have been validated by the MUSTT (Multicenter UnSustained Tachycardia Trial) trial. These studies demonstrated a survival benefit of ICDs in patients with nonsustained ventricular tachycardia.4,5 The number of ICD implants continues to increase. In 1999 alone, based on industry statistics, close to 50,000 ICDs were implanted in the United States.6

The Emergency Department will often be the contact point for these patients. This requires Emergency Physicians to be familiar with the problems that can be encountered by a patient with an ICD. This chapter deals with technical aspects of an ICD, basic interrogation of the device, and the general approach to a patient who presents to the Emergency Department with an implantable defibrillator.

ICD technology has progressed exponentially since its introduction by Mirowski and colleagues in the early 1980s.7 Early devices were true “shock boxes,” capable of detecting a tachycardia and delivering a shock without the ability to pace.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 24-1). 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

FIGURE 24-1

Abdominal placement of the ICD generator. Initial implants required a thoracotomy to position the epicardial patches needed for defibrillation as well as the screw-in sensing leads. The leads were tunneled abdominally to the ICD generator.

ICD implantation has evolved quite rapidly due to advancements in lead technology, generator technology, and the development of biphasic defibrillation waveforms which lowered the energy requirements necessary for successful defibrillation.10 The creation of a (bipolar) lead combining pacing and sensing capabilities with a high-voltage electrode coil allowed for nonthoracotomy system implants, which reduced surgical morbidity and mortality.11 The leads were now positioned transvenously via the subclavian vein and fixed to the inside of the right ventricle. However, the leads still had to be tunneled subcutaneously to the abdomen, as the generators remained fairly large. Technology has advanced the development of more compact generators. The smallest commercially available devices today are under 40 cm3 ...

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