A cardiac pacemaker (PM) is an electronic device that provides electrical stimuli for myocardial contraction when indicated. Current PM devices are used to treat bradyarrhythmias, tachyarrhythmias, and resynchronization, and, in some cases, are combined with implantable defibrillators. The first permanent cardiac PM was implanted in a human in 1958. Technological advances have since revolutionized the function of the PM and expanded therapeutic indications. The device has evolved from simple, single-chamber, fixed-rate PMs to multichamber, rate-responsive units with the capability of pacing, cardioversion, and defibrillation.
A cardiac pacing system consists of a pulse generator (battery), pulse-sensing elements, timing, and output circuitry lead(s) for signal transmission. The pulse generator is placed subcutaneous or submuscular in the chest wall. Pacing energy is delivered from a pulse generator to a single chamber (atrium or ventricle), dual chambers (atrium and ventricle), or multiple chambers (in biventricular pacing) using either unipolar or bipolar leads. Bipolar leads have been most commonly used due to the decreased susceptibility to electromagnetic interference (EMI). Cardiac pacing can be achieved in several ways, transcutaneous (by the application of external pacing pads), esophageal, transvenous (insertion of a pacing lead via central venous access), and intracardiac via implantation of endocardial or epicardial leads.
Symptomatic bradycardia is an indication for a PM. The most common reason for symptomatic bradycardia is sinus node dysfunction due to degeneration of the conduction system. Pacemakers can be temporary or permanently implanted devices (Table 8-1). Temporary cardiac pacing can serve as therapy for transient bradyarryhthmias or as a bridge for permanent generator placement. The Class I indications (i.e., the benefit greatly outweighs the risk, and the treatment should be administered) for temporary pacing include:
Sinus node dysfunction
Acquired atrioventricular block in adults
Chronic bifascicular block
After acute myocardial infarction
Hypersensitive carotid sinus syndrome and neurocardiogenic syncope
After cardiac transplantation
Pacing to prevent tachycardia
Patients with congenital heart disease
Table 8-1Permanent Pacemaker Indications |Favorite Table|Download (.pdf) Table 8-1 Permanent Pacemaker Indications
|Symptomatic diseases of impulse formation (sinus node disease) |
|Symptomatic diseases of impulse conduction (disease of the atrioventricular node) |
|Long QT syndrome |
|Hypertrophic obstructive cardiomyopathy (HOCM) |
|Dilated cardiomyopathy (D-CMP) |
The PM code of the North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG) or Generic Pacemaker NBG Code describes the pacing behavior (Table 8-2). There are five positions. In any of the positions, O indicates that pacing, sensing, or a function is not present.
The first position indicates the chamber(s) paced: A (atrium), V (ventricle), or D (dual chamber, both A and V).
The second position refers to the chamber where the PM senses native cardiac electrical activity: A, V, or D.
The third position indicates the response to the ...