TCP is the use of electrical stimulation through pacing pads that are positioned on a patient ’s torso to stimulate the contraction of the heart. TCP is also called temporary external pacing or noninvasive pacing.
TCP requires attaching two pacing electrodes to the skin surface of the patient ’s outer chest wall.
Although TCP is a type of electrical therapy, the current delivered is considerably less than that used for cardioversion or defibrillation. The stimulating current selected for TCP is measured in Fig. 6.8 Third-degree AV block with ST segment depression and inverted T waves. (From Aehlert B: ECG study cards, St. Louis, 2004, Mosby.)
TABLE 6.11 Characteristics of Third-Degree Atrioventricular Block
Regularity Ventricular regular; atrial regular; no relationship between the atrial and ventricular rhythms (ie, AV dissociation is present)
Rate The ventricular rate is determined by the origin of the escape pacemaker; the atrial rate is greater than (and independent of) the ventricular rate
P waves Normal in size and shape; some P waves are not followed by a QRS complex
PR interval None: the atria and the ventricles beat independently of each other, thus there is no true PR interval
QRS duration Narrow or wide, depending on the location of the escape pacemaker and the condition of the intraventricular conduction system
AV, atrioventricular
176 CHAPTER 6 Bradycardias
milliamperes (mA). The power delivered during each pacing impulse is less than 1 ⁄ 1000 of that delivered during defibrillation (Bessman, 2013). The range of output current of a transcutaneous pacemaker varies depending on the manufacturer. Because TCP is painful in conscious patients, sedation, analgesia, or both may be needed to minimize the patient ’s discomfort associated with this procedure.
Indications [Objective 3]
TCP is indicated for symptomatic bradycardias unresponsive to atropine therapy or when atropine is not immediately available or indicated. It may also be used as a bridge until transvenous pacing can be accomplished or until the cause of the bradycardia is reversed (as in cases of drug overdose or hyper-kalemia). Some clinicians prophylactically apply pacing electrodes to all critically ill patients with bradycardia to facilitate immediate TCP should decompensation occur (Bessman, 2013). Whether or not TCP is effective, the patient should be prepared for transvenous pacing and expert consultation sought.
Fig. 6.9 Bradycardia algorithm. (American Heart Association bradycardia algorithm. Reprinted with permission. 2015 Amer-ican Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care—Part 7: Adult Advanced Cardiovascular Life Support. ECC guidelines.heart.org. ©2015 American Heart Association, Inc.)
Procedure [Objective 3]
Take appropriate standard precautions, and verify that the procedure is indicated. Place the patient on oxygen, if indicated. Assess the patient ’s vital signs and establish IV access. Because continuous mon-itoring of the patient ’s ECG is essential throughout the procedure, apply ECG electrodes. Position the ECG electrodes as far away as possible from where the pacing pads will be applied to minimize distortion of the ECG signal by the pacing current (Boehm, 2007; Del Monte, 2006). Identify the rhythm on the cardiac monitor. Record a rhythm strip and verify the presence of a paceable rhythm.
To improve electrode adherence and maximize the delivery of energy through the chest wall, prepare the skin on the patient ’s chest (and back if the anterior – posterior pad position will be used) by washing with a nonemollient soap and water (Spotts, 2011). When preparing the skin, avoid the use of flammable liquids (eg, alcohol, benzoin) because of the increased potential for burns (Spotts, 2011). Remove any transdermal medication patches that may be present and wipe away any residue.
Apply adhesive pacing pads to the patient according to the manufacturer ’s recommendations (Fig. 6.10). Do not place the pads over open cuts, sores, drains, dressings, or over an implanted pace-maker or defibrillator. Avoid placing the pacing pads over bone (eg, sternum, spine, scapula) because this increases the level of energy needed to achieve capture, increases patient discomfort, and increases the possibility of noncapture (Spotts, 2011). When using the anterior – posterior position for pad placement, the anterior electrode is placed between the xiphoid process and the left nipple, which corresponds with the V 2 to V 3 ECG electrode position (Boehm, 2007; Del Monte, 2006). Ensure that the upper
edge of the electrode is below the nipple. If the patient is female, place the electrode beneath the breast and against the chest wall (Bessman, 2013). The posterior electrode is placed beneath the left scapula and lateral to the spine at the level of the heart. Some clinicians recommend placing the posterior pad first to prevent buckling of the anterior electrode when rolling the patient to the side (Boehm, 2007). When using the anterolateral position for pad placement, which is also called the sternum – apex position, the lateral (ie, apex) pad is placed lateral to the left nipple in the left midaxillary line, which corresponds with the V 6ECG electrodeposition. The anterior electrode is placed to the rightof the sternum and belowthe clavicle. Do not reverse placement of the pacing pads; doing so can result in the need for more current to achieve capture, which can result in increased patient discomfort (Del Monte, 2006).
Next, connect the pacing cable to the pacemaker and to the adhesive pads on the patient. Turn the power to the pacemaker on. Set the pacing rate to the desired number of paced pulses per minute (ppm) (Fig. 6.11). Generally, a rate that is between 60 and 90 pulses/min will maintain an adequate blood pres-sure and cerebral perfusion in an adult (Del Monte, 2006).
After the rate has been regulated, start the pacemaker (Fig. 6.12). Slowly increase the stimulating current (ie, output or mA) until pacer spikes are visible before each QRS complex (ie, capture). This control is usually labeled “Current,” “Pacer output,” or “mA.” Electrical capture occurs when a pacing stimulus leads to ventricular depolarization and is achieved in many patients between 50 and 100 mA (Del Monte, 2006). Although the amount of current necessary to achieve capture varies among individ-uals, it does not appear to correlate with body surface area or patient weight ( Boehm, 2007; Del Monte, 2006). Electrical capture usually is seen in the form of a wide QRS and a broad T wave on the ECG (Fig. 6.13). The captured QRS complex may be deflected in a positive or negative direction ( Del
Fig. 6.10 Apply adhesive pacing pads to the patient according to the manufacturer’s recommendations. (From Roberts and Hedges ’ clinical procedures in emergency medicine, ed 6, Philadelphia, 2014, Saunders.)
Fig. 6.11 Turn the pacemaker on and set the pacing rate to the desired number of ppm. (From Roberts and Hedges ’ clinical procedures in emergency medicine, ed 6, Philadel-phia, 2014, Saunders.)
178 CHAPTER 6 Bradycardias
Monte, 2006). For some patients, electrical capture is less obvious; it may only be indicated as a change in the shape of the QRS.
ACLS Pearl
During TCP, the muscle twitching that occurs with skeletal muscle contraction is not an indicator of electrical or mechanical capture ( Boehm, 2007 ).
Assess mechanical capture. Mechanical capture refers to contraction of the myocardium and occurs when pacing produces a response that can be measured, such as a palpable pulse. Other signs of increased
cardiac output resulting from mechanical capture include an improved level of responsiveness, a rise in blood pressure, and improved oxygen saturation and skin color (Boehm, 2007; Del Monte, 2006).
To minimize confusion between the presence of an actual pulse and skeletal muscle contractions caused by the pacemaker, assess mechanical capture by assessing the patient ’s femoral pulse, right brachial pulse, or right radial pulse. If available, bedside ultrasound may be useful in determining mechanical capture (Bessman, 2013). After capture is achieved, continue pacing at an output level slightly higher than the threshold of initial electrical capture.
Assess the patient ’s level of responsiveness, oxygen saturation, blood pressure, and other vital signs.
Closely monitor the patient, and assess the skin under the pacing electrodes for irritation after the first 30 minutes of pacing and periodically thereafter (Boehm, 2007). Documentation should include the following (Boehm, 2007; Del Monte, 2006):
• The date and time pacing was initiated (including baseline and pacing rhythm strips)
• The current required to obtain capture
• The pacing rate selected
• The patient ’s response with capture (ie, mental status, blood pressure, oxygen saturation)
• Medications administered during the procedure
• The date, time, and reason pacing was terminated, if applicable
Limitations
The main limitation of TCP is patient discomfort. The discomfort is proportional to the intensity of skeletal muscle contraction and the direct electrical stimulation of cutaneous nerves (Box 6.2). Patients have described the sensations associated with skeletal muscle contractions as tapping, twitching, or thud-ding (Boehm, 2007; Del Monte, 2006). Sensations associated with cutaneous nerve stimulation have been described as tingling, stinging, pinching, or burning (Boehm, 2007; Del Monte, 2006). When using the anterior – posterior position for pacing pad placement, discomfort may be reduced in some patients by moving the anterior electrode from its V 2 to V 3 position more laterally to a V 6 position, rec-ognizing that pacing will be temporarily discontinued during the period in which the pacing pad is moved (Boehm, 2007; Del Monte, 2006).
Another possible limitation of TCP is the use of incompatible pacing electrodes. For example, TCP electrodes used in the out-of-hospital setting may be incompatible with those used in the emergency Fig. 6.12 After the rate has been regulated, start the
pace-maker and slowly increase the current output until electrical capture is achieved. (From Roberts and Hedges ’ clinical pro- cedures in emergency medicine, ed 6, Philadelphia, 2014, Saunders.)
Fig. 6.13 After electrical capture is achieved, assess for mechanical capture by palpating for a pulse. (From Roberts and Hedges ’ clinical procedures in emergency medicine, ed 6, Philadelphia, 2014, Saunders.)
department. Similarly, TCP electrodes/connectors used in the emergency department may be incompat-ible with those used in other areas of the hospital (Bessman, 2013).
Capture may be difficult to achieve or it may be inconsistent for some patients. Increased stimulating current may be required for patients with increased chest wall muscle mass, chronic obstructive pulmo-nary disease, pleural effusions, dilated cardiomyopathy, hypoxia, or metabolic acidosis because of the extremely high current thresholds required.
Possible Complications [Objective 3]
Possible complications of TCP include the following:
• Coughing
• Skin burns
• Interference with sensing from patient agitation or muscle contractions
• Discomfort as a result of the electrical stimulation of the skin and muscles
• Failure to recognize that the pacemaker is not capturing
• Tissue damage, including third-degree burns, with improper or prolonged TCP
• When pacing is prolonged, pacing threshold changes, thereby leading to capture failure
BOX 6.2 Patient Responses to Current with Transcutaneous Pacing*
OUTPUT (mA) RESPONSE
20 Prickly sensation on skin
30 Slight thump on chest
40 Definite thump on chest
50 Coughing
60 Diaphragm pacing and coughing
70 Coughing and knock on chest
80 More uncomfortable than 70 mA
90 Strong, painful knock on chest
100 Leaves bed because of pain
*Responses with Zoll transcutaneous pacemaker.
From Flynn, JB: Introduction to critical care skills. St. Louis, 1993, Mosby-Year Book.
180 CHAPTER 6 Bradycardias