Patient Education and Consent
Appropriately used, external cardiac pacing is associated with few complications. Skin burns, pain, discomfort, and failure to capture are the main limitations of this method. Good pacing pad to skin attachment and close proximity of the pads to the heart are important factors in reducing the pacing threshold, which is the most important factor predicting discomfort and reliability of the captures. It is important to educate the patient about the procedure and especially about potential discomfort related to skin tingling and burning and associated skeletal muscle contractions. If time allows, obtain informed consent.
Equipment
Equipment used in transcutaneous cardiac pacing includes the following:
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Pacing unit
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Cardiac monitor
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Defibrillator (see the image below)
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Pacing electrodes (pads)
Although some pacing units provide only pacing, most defibrillators provide both cardiac pacing and rhythm monitoring. Those units can usually deliver a current as high as 200 mA for as long as 40 ms. The stimulus current is usually delivered in a rectangular waveform, which has been shown to be associated with lower excitation thresholds than other impulse shapes. [20]
The size of the electrode pads usually ranges from 8-15 cm, and the pacing electrodes can be applied by medical personnel. Chest pressure can be applied and cardiopulmonary resuscitation performed by pressing on the pads. To record a clear electrocardiographic rhythm, the recording electrode should be placed as far as possible from the pacing pads (see Positioning).
External pacemakers
Transcutaneous pacing with external pacemakers is indicated as a temporizing measure for treatment of symptomatic bradycardias, including sinus bradycardias and atrioventricular (AV) nodal blocks; it may also be used prophylactically in patients with these rhythms who are maintaining a stable blood pressure. External transcutaneous pacing has been used successfully for overdrive pacing of tachyarrhythmias; however, it is not considered beneficial in the treatment of asystole.
Modern external pacemakers use longer pulse durations and larger electrodes than the early models did. These modifications allow administration of higher currents with less patient discomfort. Studies have demonstrated that more than 90% of patients tolerate pacing for 15 or more minutes. Modern devices are capable of delivering up to 140-200 mA tolerably.
Patient Preparation
Anesthesia
Transcutaneous cardiac pacing may be associated with discomfort such as a burning sensation of the skin, skeletal muscle contractions, or both. Because of this, patients who are conscious and hemodynamically stable should be sedated with a drug, such as midazolam, before initiation of pacing (see Procedural Sedation).
The literature reports a wide range of sedation techniques and sedative agents. Combination sedation with benzodiazepines and narcotics appear to be in relatively broad use. [21]
Positioning
Before applying the pacing electrodes, wipe the patient’s skin with alcohol, and allow the area to dry. Without abrading the skin, carefully shave excessive body hair, which can elevate the pacing threshold and increase burning and discomfort.
Skin abrasions, the presence of a foreign body beneath the electrodes, sweating, and a high pacing threshold increase the patient’s pain and discomfort. Try to avoid abrading the skin when shaving excess hair, to remove a foreign body, to clean the skin, and to review and address the above-mentioned factors that may increase the pacing threshold.
The anterior electrode should have negative polarity and should be placed either over the cardiac apex or at the position of lead V3. If the positive electrode is placed anteriorly, the pacing threshold may increase significantly; this, in turn, increases the patient’s discomfort and may result in failure to capture.
The posterior electrode, which should be of positive polarity, should be placed inferior to the scapula or between the right or left scapula and the spine; it should not be placed over the scapula or the spine. Alternatively, the positive electrode can be placed anteriorly on the right upper part of the chest (see the image below). The latter configuration does not affect the pacing threshold. [15]
Transcutaneous Cardiac Pacing. The pacing electrode pads of an external pacing unit and locations in which each pad should be placed.
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Transcutaneous Cardiac Pacing. Normal action potential of myocyte and main ion channels that play major roles in different phases of action potential.
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Transcutaneous Cardiac Pacing. A defibrillator with pacing capability.
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Transcutaneous Cardiac Pacing. The pacing electrode pads of an external pacing unit and locations in which each pad should be placed.
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Transcutaneous Cardiac Pacing. A rhythm strip showing failure to capture in the first four pacing stimuli that did not produce any pulse. When capture occurred, each pacing artifact was followed by a QRS complex (albeit bizarrely shaped) and pulse.
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Transcutaneous Cardiac Pacing. Transcutaneous cardiac pacing in a patient with third-degree heart block. Video courtesy of Therese Canares, MD; Marleny Franco, MD; and Jonathan Valente, MD (Rhode Island Hospital, Brown University).
