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Pacemakers

Description

The artificial cardiac pacemaker is an electronic device used to pace the heart when the normal conduction pathway is damaged. The basic pacing circuit consists of a power source (battery- powered pulse generator), one or more conducting leads (pacing leads), and the myocardium. The electrical signal (stimulus) travels from the pacemaker, through the leads, to the wall of the myocardium. The myocardium is “captured” and stimulated to contract.

Demand pacemakers, which are the most common, have the ability to sense the heart’s electrical activity and fire only when the heart rate (HR) drops below a preset rate. Demand pacemakers have two distinct features: (1) a sensing device that inhibits the pacemaker when the HR is adequate and (2) a pacing device that triggers the pacemaker when no QRS complexes occur within a preset time.

Permanent pacemakers are implanted entirely within the patient’s body. The power source is implanted subcutaneously, usually over the pectoral muscle on the patient’s nondominant side. It is attached to pacer leads, which are threaded transvenously (through a vein) to the right atrium and one or both ventricles. Indications for insertion of a permanent pacemaker are listed in Table 99.

Table 99

Indications for Permanent Pacemakers

■ Acquired AV block

■ Second-degree AV block

■ Third-degree AV block

■ Atrial fibrillation with a slow ventricular response

■ Bundle branch block

■ Cardiomyopathy

■ Hypertrophic

■ Heart failure

■ SA node dysfunction

■ Tachydysrhythmias (e.g., ventricular tachycardia)

AV, Atrioventricular; SA, sinoatrial.

A temporary pacemaker is one that has the power source outside the body. There are three types of temporary pacemakers: transvenous, epicardial, and transcutaneous. Table 100 lists common reasons for temporary pacing.

■ A transvenous pacemaker consists of a lead or leads that are threaded transvenously to the right atrium and/or right ventricle and attached to the external power source.

■ In epicardial pacemakers, atrial and ventricular pacing leads are attached to the epicardium during heart surgery. The leads are passed through the chest wall and attached to the external power source.

■ A transcutaneous pacemaker is used to provide adequate heart rate and rhythm to the patient in an emergency situation. This type of pacemaker involves the use of external electrode pads that are connected to the external power source.

Table 100

Indications for Temporary Pacemakers *

■ Maintenance of adequate HR and rhythm during special circumstances such as surgery and postoperative recovery, during cardiac catheterization or coronary angioplasty, during drug therapy that may cause bradycardia, and before implantation of a permanent pacemaker

■ As prophylaxis after open heart surgery

■ Acute anterior MI with second- or third-degree AV block or bundle branch block

■ Acute inferior MI with symptomatic bradycardia and AV block

■ Electrophysiologic studies to evaluate patient with bradydysrhythmias and tachydysrhythmias

AV, Atrioventricular.

*List is not all-inclusive.

Patient monitoring

Patients with temporary or permanent pacemakers are monitored by ECG to evaluate the status of the pacemaker. Pacemaker malfunction primarily involves a failure to sense or a failure to capture.

■ Failure to sense occurs when the pacemaker fails to recognize spontaneous atrial or ventricular activity and fires inappropriately. Failure to sense is caused by pacer lead fracture (breakage), battery failure, sensing set too high, or electrode displacement.

■ Failure to capture occurs when the electrical charge to the myocardium is insufficient to produce atrial or ventricular contraction. This can result in serious bradycardia or asystole. Failure to capture may be caused by pacer lead fracture, battery failure, electrode displacement, electrical charge set too low, or fibrosis at the electrode tip.

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Tags: Clinical Companion to Medical-Surgical Nursing

Oct 26, 2016 | Posted by admin in NURSING | Comments Off

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