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Pacemakers are common among Emergency Department patients. Patients may present due to symptoms referable to pacemaker malfunction or symptoms unrelated to the pacemaker, and its presence may modify the investigation and therapeutic approach. It is important for the Emergency Physician to understand the workings of a pacemaker, the problems that may be encountered, the etiologies of the problems, and the assessment of a patient with a pacemaker.
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There are numerous indications for the implantation of a cardiac pacemaker.1–8 However, a detailed discussion regarding the indications for permanent pacemaker insertion is beyond the scope of this chapter.1,6,7 The most common indication for permanent pacemaker placement is symptomatic bradycardia. Mortality rates can be decreased in these patients with pacing. A permanent pacemaker is inserted prophylactically when intrinsic cardiac rhythms can degenerate to higher-degree blocks or in patients who may develop symptoms in the near future even though the initial presentation was asymptomatic. An example would be the Mobitz type 2 second-degree atrioventricular (AV) block. In addressing the treatment modalities for cardiac rhythm disturbances, the decision to implant a pacemaker can be difficult and must be reached by a careful review of each patient on an individual basis.
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The pacemaker unit is implanted by a Cardiologist in the cardiac catheterization laboratory. The pacemaker unit consists of the pacemaker generator, the pacemaker wires (also known as electrodes or leads), and the terminal electrodes. The square or rectangular pacemaker generator is implanted subcutaneously in the left or right upper chest. It is responsible for the functioning of the unit and contains the battery that powers it. A reed switch in the pacemaker generator can be used to inactivate its sensing mechanism and cause it to perform in an asynchronous mode. The pacemaker wires are embedded in plastic catheters and attached to the pacemaker generator. The wires are inserted through the subclavian vein or, less commonly, through the cephalic vein and into the right side of the heart. The terminal electrodes are at the distal end of the pacing wires and are designated as unipolar or bipolar. The terminal electrodes are placed under fluoroscopic guidance in the right ventricle for single chamber pacing or the right atrium and right ventricle for dual chamber pacing. After insertion, the unit is programmed and tested.
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The North American Society for Pacing and Electrophysiology and the British Pacing and Electrophysiology Group have accepted a five-letter pacemaker code, which is also followed by the pacemaker industry (Table 34-1). The code is generic in nature. The character position is labeled in Roman numerals I through V. The first letter designates the chamber(s) in which pacing occurs. It can be designated as none (0), atrial (A), ventricular (V), or both atrial and ventricular (D or dual). The second letter designates which cardiac chamber(s) the pacemaker uses to sense intrinsic electrical cardiac activity. It can be designated as none (0), atrial (A), ...