Temporary Pacing

CHAPTER 216 Temporary Pacing



William Ellert


For various reasons, primary care clinicians may need to perform temporary cardiac pacing. Several types of pacing are available, with the primary purpose being to maintain circulatory stability until either the situation resolves or a permanent pacemaker can be installed. This chapter covers external (transcutaneous) and internal (transvenous) emergency ventricular pacing. Transesophageal pacing, usually limited to atrial pacing, and transmyocardial transthoracic pacing are beyond the scope of this chapter.


The basic uses for temporary cardiac pacing are as a standby should the patient become symptomatic or complete heart block occur and as a way to increase heart rate during periods of symptomatic bradycardia. In addition, overdrive pacing may be used to terminate arrhythmias (e.g., sustained supraventricular or ventricular tachycardia); atrioventricular (AV) sequential pacing may be used to prevent arrhythmias. “Medicinal” pacing (e.g., atropine, isoproterenol) is also available, with advanced cardiac life support (ACLS) guidelines being helpful to guide its use. Overall, the indications for temporary pacing can be divided into therapeutic, prophylactic, and diagnostic categories. For the purposes of this chapter, only therapeutic and prophylactic pacing are covered.



External (Transcutaneous) Pacing


Most defibrillator/cardioversion units are now capable of performing external transcutaneous pacing. Modern transcutaneous pacing units represent a major improvement over the units first developed in the 1950s. Those units frequently inflicted severe chest and back muscle stimulation and discomfort, and they often left burns on the skin. At least one suicide was recorded of a pacer-dependent patient who removed the leads from one of the older units to “end the pain.” In the 1960s, transcutaneous pacing was largely replaced with the newly available transvenous pacing.


Subsequent discoveries rejuvenated transcutaneous pacing, especially since the 1980s. Researchers found that increasing the pulse duration from 2 to 20 milliseconds (msec) not only increased the safety of transcutaneous pacing (reduced the risk of ventricular fibrillation), but reduced the required current. Reduced current meant less pain and fewer burns. The development of electrodes with a larger surface area also decreased the pain and risk of tissue burn. Use of larger electrodes allows for a reduction in the current density, or the amount of current penetrating per square unit of skin. These developments have resulted in more frequent use of transcutaneous pacing, especially on a standby basis, and consequently decreased the use of transvenous pacing.


One of the shortfalls of external pacing, even with today’s somewhat sophisticated equipment, is the difficulty of achieving capture in about one fifth of patients. Reasons for difficult or ineffective external pacing include increased intrathoracic air (such as barrel chests or chronic obstructive pulmonary disease), a large pericardial effusion or tamponade, recent thoracic surgery, obesity, and the improper placement of electrodes. Increased output for capture may be required in these individuals. Another shortfall is that it is rare for patients not to complain of some pectoral muscle stimulation. Although most patients rate the discomfort as mild or moderate and easily tolerable, approximately one third of patients rate the pain as severe or intolerable. Therefore, analgesics, narcotics, or sedatives should be considered when using the external pacer, especially if the required mean current for capture is 50 milliamperes (mA) or more (a common threshold).


Because the high voltages required for external pacing produce significant muscle twitching, conventional electrocardiographic (ECG) monitors and recorders are useless. To provide decent tracings despite the large pacer spikes and their aftermath, routine ECG monitors must be equipped with an output adapter. Fortunately, most external pacer units come equipped with a monitor capable of filtering the spikes. Without an adequate ECG monitor, treatable ventricular fibrillation could be masked by the large pacing spikes, with disastrous results. This is one of the grave risks of transcutaneous pacing.



Indications



• Short-term pacing until transvenous pacing can be initiated or underlying conditions requiring pacing are corrected (e.g., drug overdose, hyperkalemia)

• When medical therapy is not immediately available, or when significant bradyarrhythmias have not responded to medical therapy (e.g., atropine, isoproterenol)

• Symptomatic patients (e.g., syncope, presyncope, dizziness, fatigue) with type I or type II second-degree AV block, third-degree or complete AV block, asystolic pauses exceeding 3 seconds, or an escape pacemaker rate less than 40 beats per minute (bpm); also for patients who become symptomatic because of a bifascicular block or sinus node dysfunction

• As a standby or prophylaxis in conscious patients with hemodynamically stable bradycardia

• As a standby or prophylaxis before surgery in patients with a preexisting cardiac conduction block (anesthesia can exacerbate the block); also before cardiac diagnostic studies

• As a standby or prophylaxis in conscious patients with an expected bradyarrhythmia or a new type II second-degree, third-degree, or complete AV heart block in the setting of ischemia or infarction (frequently seen with acute anterior or inferior wall myocardial infarctions or digoxin overdose)

note: Preliminary trial of pacing should be performed to ensure that capture is achievable and that pacing is tolerated by the patient.


• In children with primary bradycardia from congenital defects or after open-heart surgery

• To be considered when fluoroscopy (the preferred technique) is not available for transvenous pacer insertion


Contraindications


All of the contraindications are relative.


• Bradycardia in patient with significant hypothermia; as the core temperature drops, the ventricles become more irritable and prone to fibrillation that is resistant to defibrillation. In addition, bradycardia may be physiologic due to a decreased metabolic rate in these individuals.

• Bradycardia in children: usually due to hypoxia or hypoventilation, the best intervention is to provide an adequate airway as opposed to pacing (exceptions as mentioned in the Indications section).

• Overdrive pacing in tachyarrhythmias with rates greater than 180 bpm because that is the maximal rate of most external pacers.

• Bradyasystolic or asystolic arrest of more than 20 minutes’ duration because of the well-documented poor resuscitation rates.

• Patient is unable to cooperate or tolerate the procedure (in life-threatening situation, provide sedation).

• Lack of therapeutic benefit because of advanced disease or terminal illness.


Equipment



• Two 8-cm electrodes. These are usually round or rectangular and packaged in pairs. The negative electrode may also be labeled “front,” “apex,” or “anterior”; the positive electrode may be labeled “back” or “posterior.”

• Razor or scissors to remove body hair from the area of electrode placement.

• Pacing unit (contains pulse generator and monitor). The best units allow either fixed-rate or demand mode. Most allow a range from 30 to 180 bpm, with current output from 0 to 200 mA. Pulse durations vary from 20 to 40 msec and are not adjustable by the operator. To protect health care providers, some pacers shut off when an electrode falls off the chest.

note: Most defibrillator/cardioversion units contain a transcutaneous pacing unit as an integral part of the system.


• ECG leads capable of monitoring during transcutaneous pacing. If not purchased as part of the pacing or defibrillator/cardioversion system, an output adapter to a separate ECG monitor is required to “blank” or neutralize the large electrical spikes from the pacer.


Preprocedure Patient Preparation


If time allows, explain the purpose and benefits of the procedure as well as the risks of not performing the procedure to the patient or representative. The patient should know what to expect, the sensations he or she may experience (e.g., muscle contractions, a slight tingling, burning or shocking sensation), and that although this may be uncomfortable, the majority of patients tolerate it well. Explain what will be done to minimize the discomfort (e.g., analgesic, sedation). A signed consent is not required to perform this procedure; however, implied consent should be documented in the medical record (e.g., “the risks and benefits have been explained to the patient, who agrees with having the procedure”).


Any dirt or debris should be cleaned from the skin; however, avoid using any flammable liquids such as alcohol. Patients with significant body hair may need to be shaved (unconscious patients) or the hair clipped or trimmed (conscious) to ensure good skin–electrode contact. Shaving should be avoided, if possible, in the conscious patient because any nicks or lacerations can increase the discomfort and skin irritation during pacing.



Technique



1 Attach the exposed adhesive surfaces of two large electrode patches to the anterior and posterior chest walls (Fig. 216-1). The negative (anterior) electrode should be placed over the apex (at the point of maximal impulse) or the septum of the heart (the lead V3 position), and the positive (posterior) electrode directly behind the anterior electrode, to the left of the thoracic spine, between the spine and the left scapula. Alternatively, the positive electrode can be placed on the right upper chest with the negative electrode over the apex of the heart.

2 If time allows, prepare the patient with analgesia such as a narcotic or sedation with a benzodiazepine (especially helpful if the required mean current for capture is ≥50 mA).

3 Turn on the pacing unit. Set the heart rate (e.g., 80 bpm) to demand pacing. Set the current output and sensing thresholds at levels similar to those used for internal pacing; however, remember that larger outputs are necessary. Keep in mind that for demand pacing, external units often do not have sensing thresholds. The final current output setting is usually 1.25 times the initial capture threshold. Patients with conditions that cause difficult or ineffective pacing may require higher outputs for capture. At these higher outputs, the resultant muscle twitches may be so severe as to preclude external pacer use.

4 Apply the electrical stimulation to the electrodes. For conscious patients, slowly increase the output from the minimal setting, at 5- to 10-mA increments, until capture is achieved. Electrical capture is usually indicated by a widening of the QRS complex and especially by a broad T wave. The output required to obtain capture is defined as the pacing threshold. For asystolic or unconscious patients, begin at full output (200 mA) and decrease until capture is achieved, which defines the pacing threshold. The final current output should be set at the pacing threshold or 5 to 10 mA above it. When transcutaneous pacing is used as a standby technique, most clinicians document capture by initiating a brief period of pacing at a rate slightly higher than the patient’s intrinsic rate. The pacing output threshold is then recorded and the pacing unit is returned to standby mode.

5 When successful pacing is achieved, prophylactic intravenous access (central venous [CV] catheter) through the right internal jugular vein may be helpful in case an internal pacer is needed urgently. Because external pacers have up to a 20% failure rate, having CV access available minimizes the risk of having to obtain it during a “code” situation.

6 Monitor continuously for capture and potential complications (e.g., treatable ventricular fibrillation, burns). The only sure sign of electrical capture is the presence of a consistent ST segment and T wave after each pacer spike. Palpation of the carotid to confirm a pulse is not helpful because the muscle stimulation and contractions produced by the pacer simulate a carotid pulse.

image

Figure 216-1 External (transcutaneous) pacing. The anterior electrode is placed at the apex (A), which is to the left of the sternum over the point of maximal impulse, or over the septum (B), which is the V3 position. The posterior electrode is placed to the left of the spinal column on the back, directly behind the anterior electrode.


(Adapted from Dahlberg ST, Benotti JR: Temporary cardiac pacing. In Rippe JM, Irwin RS, Alpert JS, Fink MP [eds]: Intensive Care Medicine, 2nd ed. Boston, Little, Brown, 1991.)


note: The increased use of external pacers has surely reduced the number of prophylactic internal pacers placed. However, in nontransient situations, external pacing is always a temporary measure until an internal pacer (probably transvenous, as described in the next section) can be placed.



Internal (Transvenous) Pacing


Clinicians who may need to insert a transvenous pacemaker should be familiar with the equipment and its use before needing it in an emergent situation. There are usually two lights, a sense indicator light, which is illuminated when a cardiac impulse is sensed, and a pace indicator light, which is illuminated whenever a pacing stimulus is generated. There is also usually a button to test the battery to ensure adequate voltage to operate the pacemaker generator. Although newer models have digital displays and more sophisticated pacing options, they function basically the same as older models.



Indications



Therapeutic



• Symptomatic, hemodynamically compromising or life-threatening bradyarrhythmias unresponsive to pharmacologic therapy (e.g., systolic blood pressure <80 mm Hg, change in mental status, angina, pulmonary edema), including sick sinus syndrome

• Bradycardia with ventricular escape rhythm, unresponsive to pharmacologic therapy

note: For tachyarrhythmias of less than 150 bpm, neither immediate cardioversion nor an immediate pacer is necessary.



Prophylactic (in Setting of Acute Myocardial Infarction)



• Symptomatic sinus node dysfunction or Mobitz type I second-degree AV heart block that is not responsive to atropine therapy

• Second-degree Mobitz type II, third-degree, or complete AV heart block*

• Newly acquired bundle branch block with first-degree AV block

• Bilateral or alternating bundle branch blocks

• An old right bundle branch block with first-degree AV block and a new fascicular block


Contraindications


Contraindications include those listed in Chapter 211, Central Venous Catheter Insertion, and those listed previously for external pacing. Other contraindications include the following:


• A situation in which the bradycardia is well tolerated and the symptoms are intermittent, mild, or rare.*

• Bradycardia in patients with significant hypothermia; as the core temperature drops, the ventricles become more irritable and prone to fibrillation (especially if the pacing wire contacts the heart muscle) that is resistant to defibrillation. In addition, bradycardia may be physiologic because of a decreased metabolic rate in these individuals (relative contraindication).

• Digoxin toxicity and other drug ingestions that may increase the irritability of the myocardium (relative contraindication in life-threatening situation).

• Presence of a prosthetic tricuspid valve (relative contraindication in life-threatening situation).

• Depending on access site, planned neck or clavicle surgical procedures (relative contraindication, may affect choice of site).

• Distortion of local anatomy or landmarks; for insertion from subclavian, moderate to severe chest wall deformities that distort local anatomy (relative contraindication, may affect choice of site).

• Suspected injury to the superior vena cava (relative contraindication, may affect choice of site; e.g., superior vena cava syndrome, in which insertion from below the diaphragm is preferable).

• Bleeding diathesis, anticoagulation therapy, or concurrent thrombolysis or fibrinolysis (unless emergent pacing is required, and then antecubital venous cutdown access is preferred).

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Temporary Pacing

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