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Chapter 33: Cardiac Pacing and Implanted Defibrillation

Swee Han Lim; Wee Siong Teo; Anantharaman Venkataraman

PURPOSE OF PROCEDURE

Cardiac pacing serves to maintain or restore myocardial depolarization and thus ensure adequate cardiac output. In the ED, pacing is performed therapeutically to correct an ongoing rhythm disturbance or in anticipation of the onset of a conduction problem with hemodynamic impact.1

Indications for emergency pacing are listed in Table 33-1.

TABLE 33-1Indications for Emergency Pacing
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TABLE 33-1 Indications for Emergency Pacing
Indication Comments
Symptomatic or hemodynamically unstable bradycardia/AV block

Symptoms include hypotension, change in mental status, angina, and pulmonary edema.

Pharmacologic therapy may be used to temporize while preparing to pace.
Severe sick sinus syndrome with prolonged asystole (generally >3 s) and syncope —
Ventricular standstill due to complete heart block or Mobitz type II AV block —
Torsade de pointes Overdrive pacing.
Recurrent monomorphic ventricular tachycardia

Overdrive pacing.

The technique is limited by:

Maximum pacing rate of the pacing device (usually 180 beats/min).

Potential of accelerating the ventricular tachycardia and inducing ventricular fibrillation.
Unstable supraventricular tachycardia Overdrive pacing should only be used after pharmacologic intervention and cardioversion have failed.

Abbreviation: AV = atrioventricular.

The indications for emergency cardiac pacing are found in chapter 18, "Cardiac Rhythm Disturbances."

GENERAL EQUIPMENT

All cardiac pacemakers deliver an electrical stimulus to the heart by electrodes that cause depolarization and subsequent cardiac contraction.2 The modern pacemaker only stimulates the heart chamber if it does not recognize (sense) intrinsic electrical activity from that chamber after a selected time interval. Impulses are delivered to either the atria or ventricles, or to both.

Components of a cardiac pacemaker include:

  • Pulse generator

  • Electronic circuitry for sensing and pacing

  • Lead system that connects the pulse generator to the electrode(s) and stimulates the myocardium

Relevant clinical details of these components are listed in Table 33-2.

TABLE 33-2Pacemaker Component Details
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TABLE 33-2 Pacemaker Component Details
Pacemaker Type Pulse Generator Location Electrode Location
Transcutaneous External

Skin of anterior chest wall and back or

Anterior chest wall below right clavicle and apex
Transvenous External Venous catheter with tip in right ventricle and/or right atrium
Transesophageal External Esophagus
Epicardial External or Internal

Epicardium

Electrodes are usually placed on heart's surface during surgery
Permanent Internal (subcutaneous in the prepectoral region) Venous or epicardial

TRANSCUTANEOUS PACING

Transcutaneous pacing is the emergency technique of choice because of its easy application. It uses externally applied electrodes to deliver an electric impulse directly across the intact chest wall to stimulate the myocardium. Transcutaneous pacers differ from standard pulse generators in several important ways. The pulse duration of the stimulating impulse is longer and the current output higher than in internal pacing. Muscle contraction (usually the chest ...

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