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Chapter 33: Cardiac Pacing and Implanted Defibrillation

Swee Han Lim; Wee Siong Teo; Venkataraman Anantharaman

PURPOSE OF PROCEDURE

Cardiac pacing serves to maintain or restore myocardial depolarization and thus ensure adequate cardiac output. In the ED, pacing corrects rhythm disturbances or starts in anticipation of a conduction problem with hemodynamic impact.1

Indications for emergency pacing are provided 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 —
Torsades 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 be used only after pharmacologic intervention and cardioversion have failed.

Abbreviation: AV = atrioventricular.

GENERAL EQUIPMENT

Cardiac pacemakers deliver an electrical stimulus to the heart through electrodes, causing depolarization and subsequent cardiac contraction.2 The modern implanted pacemaker only stimulates the heart chamber if it does not recognize (sense) intrinsic electrical activity from that chamber after a selected time interval. Impulses go to the atria, ventricles, or 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 provided 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 an emergency technique frequently chosen in patients presenting with hemodynamically significant bradycardia because of its easy application. It uses externally (chest wall) applied electrodes to deliver an electric impulse to stimulate the myocardium. Transcutaneous pacers differ from standard pulse generators: The pulse duration of the externally stimulating impulse is longer and the current output higher than in internal pacing. Muscle contraction (usually the chest wall or diaphragm) is notable during external pacing, especially at high outputs, and may be painful. The muscle twitching makes palpation of the radial, carotid, or femoral pulse difficult. Finally, cardiac ...

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