Chapter 31. Transcutaneous Cardiac Pacing

First documented as a technique in 1872, transcutaneous cardiac pacing (TCP) was successfully demonstrated in two patients with underlying cardiac disease and symptomatic bradycardia by Paul Zoll in 1952.1 Studies involving open-chest and transvenous pacing, as well as open-chest cardiac massage, were occurring simultaneously by other groups. Zoll recognized the clinical difficulty of these approaches for the treatment of “ventricular standstill” in an emergent setting.1,2 Zoll and colleagues performed animal experiments using electrodes placed in various positions prior to the use of subcutaneous needle electrodes at points “in a line transversing the ventricles” as described in the initial case report.1 In 1956, they described the use of their procedure during eight surgical cases in which cardiac arrest occurred, with five patients successfully surviving to discharge.2 At this time, cardiac monitoring during surgery was not routinely performed, thus the underlying rhythm being paced was not specifically determined in all reported cases.

Further work related to TCP seems to have lapsed until the 1980s, when several groups studied the technique for treatment of symptomatic bradycardias, asystolic cardiac arrest, and bradyasystolic cardiac arrest both in-hospital and in the Emergency Department. The results of these investigations were summarized by Hedges et al.3 They concluded that TCP is as successful as transvenous cardiac pacing in obtaining electrical and mechanical capture in bradyasystolic arrests. TCP was easier to initiate than transvenous cardiac pacing. However, TCP did not improve the overall survival rates for these patients.3

TCP was recommended for cardiac emergencies by the International Liaison Committee on Resuscitation (ILCOR) guidelines beginning in 1980, and is currently recommended for treatment of symptomatic bradycardias, especially when the conduction block is at or below the His-Purkinje level.4,5 TCP is no longer indicated for the treatment of asystolic cardiac arrest as there are no improvements in the rate of hospital admission or survival to hospital discharge in this setting.5–7

With current technology and equipment, TCP offers several advantages when compared to the placement of a transvenous cardiac pacemaker in the Emergency Department. The procedure requires minimal training and can be performed quickly. TCP is a noninvasive procedure and is not associated with the major complications of placing a transvenous cardiac pacemaker. This includes inadvertent arterial puncture, hemorrhage, pneumothorax, or cardiac tamponade from cardiac rupture. TCP is an ideal early and temporary intervention for patients requiring stabilizing cardiac pacing support until more invasive procedures can be arranged in the proper clinical setting.

In the normal heart, electrical impulses originating in the sinoatrial (SA) node create an action potential that is conducted along the intrinsic cardiac nerve pathways to the atrioventricular (AV) node and disseminated through the His-Purkinje system. This action potential stimulates electrolyte flux, myocardial muscle depolarization, and subsequent cardiac muscle contraction. Electrical propagation and myocardial contraction occur separately in the atria and ventricles, with the atria contracting slightly ahead of the ventricles during ventricular diastole. This timing delay assists in filling the ventricles prior to their next ventricular systolic phase. The intrinsic heart rate is controlled by a balance of input from the sympathetic nervous system acting directly on the cardiac muscle and the parasympathetic nervous system acting most prominently at the SA and AV nodes.

The intrinsic heart rate can be disrupted due to a wide variety of disease processes. The usual blood supply for the SA node is from an early branch of the right coronary artery. Coronary artery disease can disrupt blood flow and oxygen supply to the myocardium, creating areas of cardiac ischemia that affects the conduction system, the impulse production, or conduction at the SA and AV nodes. Cardiac ischemia can result in action potential conduction delays and heart blocks, with resultant symptoms in the patient of bradycardia and hypotension. Electrolyte disturbances (e.g., hyperkalemia), structural heart disease, drug toxicity (e.g., calcium channel blockers and β-blockers), systemic toxins (e.g., cyanide), or systemic hypothermia are other causes of intrinsic conduction delays and heart blocks that can be considered in the differential diagnosis.

TCP delivers an extrinsic electrical impulse that overrides the intrinsic cardiac action potential. Initial pulse durations used were short at 1 to 2 milliseconds (ms). They have now been extended to 20 to 40 ms to decrease the threshold current or the current needed for cardiac muscle stimulation. The longer pulse duration also decreases patient comfort, as it is the degree of skeletal muscle contraction generated by the TCP pulse that determines patient discomfort.8 Most TCP devices can generate up to 200 milliamps (mA) of current, while mean pacing currents needed to obtain capture have been shown to range from 40 to 100 mA.8–11

Transcutaneous cardiac pacing is technically the fastest and easiest method of emergency cardiac pacing. It is a temporary intervention prior to implementation of transvenous cardiac pacing or placement of a permanent cardiac pacemaker for primary cardiac dysfunction or until the underlying etiology of the bradycardia can be reversed. It is indicated for patients with symptomatic bradycardia from any etiology in whom pharmacologic interventions such as atropine have been unsuccessful. It can be effectively applied in the prehospital setting by EMS personnel, in a clinic, in the Emergency Department, or in the hospital. In patients with bradyarrhythmias that are expected to be transient (e.g., digoxin toxicity or AV block in the setting of an inferior wall myocardial infarction), TCP is quick, simple, and not associated with the morbidity or mortality of transvenous cardiac pacing.

It is indicated in patients with AV conduction blocks and sinus node dysfunction. It should be performed in symptomatic patients (e.g., syncope, presyncope, dizziness, fatigue, etc.) with complete or third-degree AV block, asystolic pauses exceeding 3 seconds, or an escape pacemaker rate less than 40 beats per minute. Patients with type I or type II second-degree AV block who are symptomatic should be transcutaneously paced. Symptomatic bifascicular block is also an indication for temporary TCP. Patients with sinus node dysfunction are candidates for pacing. Sinus node dysfunction includes sinus pause with symptoms of cerebral hypoperfusion (e.g., syncope, presyncope, and dizziness), chronic sinus node dysfunction with or without symptoms but with escape rates of less than 40 beats per minute, or symptomatic sinus bradycardia.

TCP electrodes should be placed on patients in anticipation of potential clinical deterioration and bradyarrhythmias in the appropriate setting.10 For example, a patient with a β-blocker overdose may present with a slow or normal heart rate but are otherwise asymptomatic. In this clinical scenario, hemodynamic deterioration is possible. Preparation for TCP (i.e., electrodes applied and connected to a generator unit, unit in standby mode, etc.) can be easily accomplished while further efforts related to the diagnosis and treatment are undertaken. If the patient develops bradyarrhythmias, the transcutaneous pacer can be immediately activated without the delays associated with obtaining the equipment and setting up the system.

TCP can also be used for overdrive cardiac pacing in event of a supraventricular or ventricular tachydysrhythmia such as ventricular tachycardia, torsade de pointes, or paroxysmal supraventricular tachycardia in the patient who is clinically stable.12–15 A major limitation to overdrive cardiac pacing would be the maximum rate that the pulse generating unit can achieve. The technique requires pacing the patient at a rate of 20 to 60 beats per minute faster than the tachydysrhythmia.14 Patients do not usually tolerate transcutaneous overdrive pacing due to the accompanying chest wall contractions and discomfort. The transvenous or transthoracic routes are preferred for overdrive pacing of the myocardium.

There are no absolute contraindications to TCP. Hypothermia has been considered a relative contraindication to TCP. The associated bradycardia seen during hypothermia is thought to be a result of direct myocardial depression and decreased metabolic rate.16,17 Concerns related to ventricular irritability, dysrhythmias, and resistance to defibrillation have led to the idea that electrical manipulation of the hypothermic myocardium should be avoided.18 There are, however, case reports of successful TCP use during rewarming for severe hypothermia.19 TCP is also relatively contraindicated for prolonged bradyasystolic cardiac arrest due to the overall poor resuscitation rates and outcomes of these patients.6,7,10 TCP is no longer indicated for the treatment of asystolic cardiac arrest as there are no improvements in the rates of hospital admission or survival to hospital discharge in this setting.10

• Pulse generator and monitor unit
• Pacing cable attached to the monitor
• Pacemaker patches or electrodes:
  • 6 × 7 cm2 for infants and young children
  • 13 × 15 cm2 for older children and adult
• ECG patches or electrodes (if pacemaker patches and unit do not monitor patient)
• ECG cable attached to cardiac monitor (if pacemaker patches and unit do not monitor the patient)
• Intravenous access supplies
• Sedative and analgesic medications
• Povidone iodine or chlorhexidine solution
• Skin razor

Most commercially available cardiac defibrillators used in the Emergency Department are a combination cardioverter, defibrillator, and cardiac pacer with an associated ECG monitor. (Figure 31-1) The unit is usually available on all code carts in the Emergency Department and throughout the hospital. The Emergency Physician should become familiar with their specific institutional equipment prior to an emergent situation requiring its use.

The pacing patches are either round or rectangular, and come packaged as pairs with illustrations to demonstrate proper placement of the electrode (Figure 31-2). The negative electrode will be labeled “front” or “apex.” The positive electrode may be labeled “back” or “posterior.” Most modern TCP electrodes are disposable, single patient use, and multipurpose. The one electrode can be used to perform cardioversion, defibrillation, ECG monitoring, and TCP. Some older units may not have this flexibility and require separate ECG leads.

If time allows, discuss the procedure with the patient and/or their representative. This should include the reason for performing the procedure, the risks of the procedure including pain-related issues and how pain will be addressed, and the benefits of the procedure including expected symptom improvement. There is a small risk of developing a ventricular tachydysrhythmia during TCP.20 A written and signed consent documenting this conversation is always preferred. However, it is not required in an emergent situation. Documentation of the conversation in the medical record should be adequate in an emergent situation. Preparation for transvenous cardiac pacing (Chapter 33) can be simultaneously undertaken in the event that TCP is unsuccessful.

The patient's skin should be relatively clean and free of debris. Warm, soapy water can be used as a cleansing agent. Avoid potentially flammable cleansing solvents such as alcohol-based solutions. The skin should be dry. Trim the patients back and chest hair if the patient is hirsute and the pacing patches are poorly adherent. Trimming is preferred to shaving to avoid skin disruption or abrasions that may cause increased pain, skin irritation, and bacteremia during the procedure. If shaving is required, and pacing is not emergently required, first apply povidone iodine or chlorhexidine to the area and allow it to dry. This will decontaminate the skin prior to shaving.

Administer sedative and analgesic medications to manage the discomfort related to the chest wall skeletal muscle contractions associated with TCP.20 Pain levels associated with TCP were found to be moderate to moderately severe (mean of 3.2 on a five-point scale) in 30 healthy volunteers.11 One volunteer quit the study due to the severity of the pain.

Pad Placement

Two pacing electrodes must be applied to the thorax (Figure 31-2). Place the front, anterior, or negative labelled electrode on the anterior chest wall, and centered over the apex of the heart (Figure 31-3A) or over the V3 lead position (Figure 31-3B). In females, the anterior electrode should be positioned by lifting the breast and placing it under the fold of the breast and against the chest wall. Place the back, posterior, or positive labelled electrode directly behind the anterior electrode and to the left of the thoracic spine, between the spine and the scapula (Figure 31-3C). Avoid trapping air or debris under the pad during placement. As an alternative, the positive electrode may be placed on the right upper chest and the negative electrode over the apex of the heart (Figure 31-4).

Pacing

Once the pacing electrodes are positioned, connect the cable from the electrodes to the pacer/monitor unit. Turn the output current (mA) dial as low as possible (Figure 31-5). Set the pacing rate between 80 and 90 beats per minute. Select the pacer function of the pacer/monitor unit. Turn the unit on. Gradually increase the current output by 5 to 10 mA at a time until capture is achieved (Figure 31-6). Note the mA output value that is required to initiate TCP. This is known as the threshold current. Increase the output current approximately 10%, or 5 to 10 mA, above the threshold current. Maintain the output current at this level.

In the near-arrest or unconscious patient, start with the output current set at maximum. Turn the unit on. Dial the output current down until capture is lost. This is the threshold current. Raise the output to restore capture. Increase the output current approximately 10%, or 5 to 10 mA, above the threshold current. Maintain the output current at this level.

Some pacer/monitor units can operate in a “standby mode.” This mode can be used for patients who are at risk of developing symptomatic bradycardia, but who are currently clinically stable. Set the unit to “pacing mode.” Attach the pacer electrodes to the patient and the unit. Initiate a brief period of TCP at a rate slightly faster than the patient's intrinsic rate to determine the threshold current and if capture is possible. Turn the unit off. Set a reduced rate on the pacer dial. This rate should be below the patient's current heart rate but also be the minimal heart rate acceptable to the Emergency Physician for the patient. Switch the unit to “standby mode” and turn it on. If the patient's heart rate falls below the value set on the unit, the pacer function will automatically engage.

Overdrive Pacing

When performing overdrive TCP, full cardiac resuscitation equipment should be available and ready at the bedside, as rhythm acceleration and subsequent hemodynamic instability are possible. The pacer electrodes and pacing unit setup remain the same to perform overdrive TCP for a tachydysrhythmia. Administer sedative and analgesic medications as required. Set the current output at 120 mA, as this current generally will exceed the threshold value for most patients. Turn on the unit and initiate asynchronous cardiac pacing at a rate of 20 to 60 beats per minute higher than the intrinsic rate of the tachydysrhythmia.14 Once capture is achieved, decrease the current output to just above the threshold current. Slowly lower the pacing rate to decrease the patient's heart rate to the desired level. TCP for overdrive pacing may not be possible due to the upper heart rate limit of the available pacing unit.

Pacing Pediatric Patients

There is limited data available on the use of TCP in the pediatric population. The indications for the procedure, however, are the same as those in adults. The technique used to accomplish TCP is the same as in an adult. TCP is often more effective in children because their smaller chest wall results in a lower transthoracic resistance to the pacing current.

There are, however, special considerations when performing TCP in the pediatric population. TCP was undertaken in newborns with complete AV node block.21 This small case series of two patients, as well as others, documented significant thermal injury to the underlying skin.21,22 This was most likely related to the newborn's thin and fragile skin. Increased monitoring of the skin surrounding the electrodes is mandatory in children, especially in cases of prolonged TCP. Pediatric-sized transcutaneous pacing electrodes are available and should be used to limit surface contact. One study comparing the use of adult versus two specially sized pediatric electrodes for TCP demonstrated a lower mean current output with the smaller pads (63 mA vs. 51 to 53 mA).23 Appropriately sized electrodes are available for children under 15 kg (33 lbs) and should be used.

Only one study has documented the outcomes of TCP in pediatric out-of-hospital cardiac arrest.24 In six drowning victims and three sudden infant death syndrome patients who received TCP by EMS providers, only two patients achieved electrical and mechanical capture, both with an initial rhythm of asystole. In total, seven patients presented with asystole and two patients presented with ventricular fibrillation. Only one patient, with an initial rhythm of asystole, survived to hospital discharge but was severely neurologically impaired and died 6 months later. Further study in this area is warranted.

The Emergency Physician must assess the patient for both electrical capture and associated mechanical capture when considering whether or not the procedure was successful. Successful capture is usually characterized by a wide QRS complex, since it is ventricular in origin, and a broad T wave. It is easy to mistake the wide, slurred afterpotential following an external pacing spike for electrical capture. Electrical capture is best judged by the presence of a consistent ST segment and T wave after each generated pacer spike (Figure 31-6C). Paced beats below the patient's intrinsic cardiac rate may not produce an associated QRS complex (Figure 31-6B), and electrical capture is not achieved. In this situation, the pacing rate must be increased to achieve capture. Table 31-1 discusses common causes of failure to capture and suggested solutions.

Once electrical capture is achieved, mechanical capture must be ensured by either a palpable pulse rate or arterial catheter blood pressure monitoring. The patient will have a pulse rate that is exactly equal to that of the paced rhythm on the cardiac monitor if mechanical capture is achieved. Assess the pulse using palpation of the carotid or femoral artery to avoid confusion with skeletal muscle contractions generated by the pacing current. If the palpated pulse rate is less than that of the paced rate, mechanical capture has not been achieved. Increase the threshold current. Mechanical capture is also achieved when the invasive arterial blood pressure line demonstrates a pulse rate that is exactly equal to that of the paced rhythm on the cardiac monitor.

Threshold current values will vary depending on the clinical situation. Transcutaneous pacing thresholds tend to be lowest in healthy individuals or in patients with minimal hemodynamic compromise. In these settings, the threshold is usually in the range of 40 to 80 mA.10,28 Most patients are paced using a current in the range of 20 to 140 mA.10 No clear correlation has been established between the pacing threshold and patient age, weight, body size, chest diameter, or etiology of heart disease.10,29,30 However, thresholds are usually elevated following thoracic surgery or in patients with COPD, a pneumothorax, a pericardial effusion, heavy thoracic chest wall musculature, and after positive-pressure ventilation.10

Success rates in achieving ventricular capture vary widely depending on the setting where TCP is being used. Success rates appear to be highest when TCP is used prophylactically or early (within 5 minutes of bradycardic arrest). In these settings, success rates may exceed 90%.10 Zoll et al. reported a 78% success rate in diverse clinical situations.10 The time to the initiation of TCP largely determines the success rate. With prolonged pacing, there can be changes in pacing threshold leading to capture failure. Failure to capture may be encountered due to a variety of reasons.

Ultrasound has been used as a method to confirm electrical and mechanical capture.25,31,32 Use ultrasound to determine the ventricular contraction rate. The patient will have a heart rate that is exactly equal to that of the set paced rate if mechanical capture is achieved. This eliminates the artifact seen on the ECG monitor from chest wall muscle contractions. Refer to Chapter 29 for the complete details of cardiac ultrasonography.

The most important assessment in the aftercare period is to ensure continuous electrical and mechanical capture. This should be accomplished by frequent checks of the cardiac monitor, palpation of a pulse, and measurement of a blood pressure. This is more easily established using an arterial line. Threshold current values can change with prolonged TCP. The system can be somewhat tenuous in practical use, so frequent checks are advisable. Insert a transvenous cardiac pacer in the Emergency Department or make arrangements with a Cardiologist to place one in the catheterization lab if the patient requires prolonged TCP.

Patient comfort must be continuously re-assessed. Pain can be due to chest wall muscle contractions or other causes (Table 31-2). Do not assume that pain is from chest wall muscle contractions until other etiologies are ruled out. Repeated doses of sedative and/or analgesics may be required to ease the discomfort of chest wall muscle contractions. Periodically assess the skin under the electrodes for burns or damage. Reposition the electrodes if skin erythema or any sign of a burn is present. This is especially important in patients who are young children, unconscious, or have altered mental status as they cannot complain of pain.

There are few major complications related to this procedure. One of the most important complications to consider is the failure to recognize underlying rhythm changes in the patient or loss of electrical or mechanical capture once the procedure is completed. A rhythm change to ventricular fibrillation is easy to miss and can be ascribed to pacing artifacts and chest wall muscle contraction. These complications are mitigated by close patient and monitor surveillance during TCP. Tachydysrhythmias related to TCP have been documented, but the overall risk for this complication is considered small.14 Myocardial damage from TCP has been examined in animals and humans without significant findings.2,26,27 Thermal injury to the skin from the electrodes is a known complication, especially in situations of prolonged TCP, but can be minimized with careful observation and electrode adjustments. Pain is the most commonly reported complication (Table 31-2) and needs to be continually addressed. The most common etiology of the pain is from chest wall muscle contractions.

TCP is a temporary method of cardiac pacing in patients with severe symptomatic bradyarrhythmias due to high-grade AV blocks, sinus node dysfunction, bradyasystolic cardiac arrest, or rarely for overdrive pacing to suppress ventricular and supraventricular tachyarrhythmias. It is comparatively easy to perform and requires minimal training. Once capture is achieved, the current output should be set at a level slightly higher (5-10 mA) than the pacing threshold. Successful TCP can be established in 80% to 90% of patients. Discomfort and pain due to muscle contraction are the most common side effects. Most patients will require sedation and/or analgesics to tolerate TCP for a significant length of time.