Chapter 46: Automatic Implantable Cardioverter-Defibrillator Assessment

INTRODUCTION

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 have examined the prophylactic indication for ICD therapy in high-risk groups.^1-7 The ICD has become a more common therapeutic option for Brugada syndrome, prolonged QT syndrome, and cardiomyopathies.⁸

An ICD is often placed prophylactically to prevent sudden cardiac death from ventricular arrhythmias. An ICD follows an algorithm and applies a full-energy shock, a low-energy shock, or it can overdrive pace the heart. All ICDs have a pacemaker function that can be set. Some ICDs can transmit to remote monitors.

The Emergency Department is often the initial contact point for these patients. Emergency Physicians must be familiar with the problems that can be encountered by a patient with an ICD.^9-13 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.

TECHNICAL CONSIDERATIONS

The ICD has four main functions. It recognizes and records local atrial and ventricular electrogram signals. It then classifies the sensed signals to programmable heart rate zones. The ICD provides a shock to terminate ventricular tachycardia or ventricular fibrillation. It has a pacing capability for bradycardia and/or cardiac resynchronization therapy. Therapy to terminate the arrhythmia is initiated with a high-energy shock of up to 40 J when detection criteria are satisfied.

ICD technology has progressed exponentially since its introduction in the early 1980s.¹⁴ 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. The earliest systems required that the pulse generators be placed abdominally due to their large size (Figure 46-1). Defibrillation was delivered via two epicardial patches positioned anteriorly and posteriorly. A transvenous spring electrode in the superior vena cava was occasionally used with an epicardial patch. Sensing was achieved through separate epicardial screw-in electrodes. Initial lead placement required a sternotomy, lateral thoracotomy, or a subxiphoid approach, which made early implants quite cumbersome.¹⁵

The smaller size devices used now allow for superficial implantation of the pulse generator in the anterior chest wall (Figure 46-2). The current ICD systems are comprised of three main parts (Figure 46-3). The pulse generator is programmable and capable of analyzing ...