Cardiac Rhythm Management Devices (Part I)

PACEMAKER1 and internal cardioverter–defibrillator (ICD) devices have undergone remarkable evolution since the first implantation of an asynchronous singlechamber pacemaker in 1958 and of an ICD in 1980. Today, more than 500,000 patients in the United States have pacemakers, and up to 115,000 new devices are implanted each year. The number of ICDs implanted each year has steadily increased, reaching 50,000 new implants worldwide in 1999. Contemporary singleand dual-chamber pacemakers are sophisticated devices, with multiple programmable features, including recently introduced programmable lead configuration and automatic mode-switching. Many devices use adaptive-rate pacing to modify the pacing rate for changing metabolic needs. First-generation ICDs were short-lived. A formal thoracotomy was required for epicardial lead placement. Today, ICDs are multiprogrammable, are longer-lived, have transvenous leads, and may incorporate all capabilities of contemporary pacemakers. Furthermore, ICDs have multiple tachycardia detection zones, with programmable detection criteria and tiered therapy (i.e., antitachycardia pacing ATP, followed by shocks if needed) for each. ICDs also store dysrhythmia event records and treatment results. Finally, clinical experience with an internal atrial cardioverter (atrioverter) has been reported. In this first installment of a two-part communication, we discuss indications for implanted pacemakers or ICDs, provide an overview of how devices are selected, and describe the basics of device design and function. Only brief mention is made of temporary pacing indications and technology. In the second installment, we discuss the potential for device malfunction in the hospital environments, perioperative management for patients with implanted devices, and care of patients during device implantation or system revision.