Chapter 32. Transthoracic Cardiac Pacing

Transthoracic cardiac pacing is a historic technique of pacing the heart with an electrode introduced percutaneously into the ventricular cavity using a needle trocar introducer. There is sparse literature on transthoracic cardiac pacing, and the benefits and complications are not well defined. Before the advent of effective and efficient transcutaneous pacing, transthoracic pacing was a faster alternative to transvenous pacing in the patient with an acutely unstable dysrhythmia. Presently, the indications for transthoracic pacing are extremely rare. The technique of transthoracic pacing is included in this text as it is occasionally performed in situations where transcutaneous pacing is unavailable or ineffective.1–3

The history of electrical stimulation of the heart dates back to 1862 when Walsh discussed the possibility of causing the heart to contract through stimulation of the sympathetic nervous trunk by an induced current.4 By 1910, it was largely understood that the neuromuscular mechanism of the heart was electrically dependant. In 1932, Hyman used a needle electrode to carry stimulating current directly to heart muscle.5 Zoll accomplished the first successful clinical application of external cardiac pacing in 1952 by resuscitating two patients in asystole following bradycardia from a high-degree AV block.6 He concluded that external cardiac pacing was a safe and effective means of resuscitating ventricular standstill. Unfortunately, Zoll's devices caused significant chest pain, skeletal muscle spasm, superficial skin burns, and disrupted electrocardiographic patient monitoring.6 The quest for alternative pacing modalities continued with the refinement of the transesophageal technique, initially suggested by Zoll in 1952, and clinically demonstrated by Shafiroff and Linder in 1957.7 In 1958, Thevenet et al. reported the emergency use of a lumbar puncture needle introduced 5 mm into the myocardium, through which a conducting wire was introduced, to produce transthoracic cardiac pacing.8 In 1959, Furman and Robinson passed a transvenous wire catheter and successfully applied an electrical current to the endocardial surface of the right atrium.9 Transvenous pacing subsequently became the most widely accepted method of emergency cardiac pacing until the reemergence of Zoll with a modified external pacing system in 1981.10

The heart is the only muscle of the body that generates its own electrical impulses. The initial cardiac impulse starts in the right atrium of the heart at the sinoatrial (SA) node. The sympathetic and parasympathetic nervous system controls the rate of impulse generation at the SA node. Once the electrical stimulus is generated, it is conducted along the internal conduction pathways of the heart to the muscular atrial and ventricular walls. A delicate balance between electrolyte flux to create action potentials, myocardial integrity to allow impulses to become contractions, and an intact conduction system must be maintained. The blood supply to the conduction system of the heart originates from the right coronary artery. Arrhythmias and conduction delays are often the result of inadequate blood flow to the heart due to ventricular infarction and coronary artery occlusion.

Considering the proven efficiency and efficacy of transcutaneous pacing modalities, the indications for transthoracic pacing appear extremely limited. Preston estimated a 40% success rate in achieving pacing by the transthoracic route.11 Transcutaneous pacing success rates of greater than 80% have been routinely demonstrated.12

Transthoracic cardiac pacing is a simple procedure and can be accomplished rapidly. Transthoracic pacing should be reserved for clinical situations where there is no transcutaneous pacing available, or when transcutaneous pacing in the perimorbid patient has been unsuccessful and the placement of a transvenous pacer is thought to be too time consuming.13,14

Unstable bradydysrhythmia is the obvious indication for emergency cardiac pacing. Several case reports document successful transthoracic pacing intervention in two patients with asystolic arrest.1 Other studies document successful pacing out of asystole in patients with in situ pacemakers.15 A more recent and prospectively designed study of approximately 300 patients with witnessed or early asystole demonstrated no improved outcome with early transcutaneous pacing intervention by first response emergency medical personnel.16 It can be concluded that although emergency transthoracic cardiac pacing has a very low success rate in asystole, the procedure may be lifesaving in the rare case.

Transthoracic cardiac pacing would be most effective following cardiac arrest from primary cardiac disease.13 Transthoracic cardiac pacing may not be effective in cardiac arrest secondary to hypovolemia (e.g., trauma), severe electrolyte or acid–base abnormalities, sepsis, or drug intoxication. Transthoracic cardiac pacing may be lifesaving when bradycardia or asystole secondary to prolonged ischemia during hypovolemic shock persists despite correction of the underlying pathology.

The use of transthoracic cardiac pacing in unstable patients is more controversial. Transthoracic cardiac pacing may be considered in patients with unstable sinus bradycardia, junctional bradycardia, atrial fibrillation with high-degree atrioventricular (AV) block, and AV dissociation with inadequate ventricular response, producing pulmonary edema, seizures, ventricular fibrillation, or ventricular tachycardia.13

Transthoracic cardiac pacing should not be performed in stable, awake patients. It is also contraindicated if the patient has a dysrhythmia that could be quickly and easily corrected by medication, cardioversion, or electrical defibrillation.

Transthoracic cardiac pacing may be ineffective in pulseless electrical activity and ventricular fibrillation. In ventricular fibrillation, the heart becomes insensitive to pacemaker activity, and in pulseless electrical activity, any mode of pacing is ineffective.20–23 Bellet et al. demonstrated that a pacemaker was ineffective in patients with prolonged cardiac arrest.15 Patients with cardiac arrest for more than 5 to 10 minutes could not be resuscitated with the use of cardiac pacing; but patients who had pacemakers placed within 2 to 4 minutes after cardiac standstill were successfully resuscitated. Hence, as shown in many studies, transthoracic cardiac pacing may be ineffective if used as a last alternative, as any technique of pacing would be.

• Povidone iodine or chlorhexidine solution
• Transthoracic cardiac pacing wires/kit
• Pacemaker generator
• 10 mL syringe
• Water-soluble lubricant
• Sterile gauze 4 × 4 squares
• Sterile drapes
• Sterile gloves and gown
• Face mask
• Cap

The widely used instrumentation for transthoracic cardiac pacing is a sterile, one-time-use, prepackaged kit. One example is the Elecath 11-KTM 1 kit (Figure 32-1). The apparatus consists of a 37 cm bipolar J-shaped pacing wire, a 6 inch 18 gauge blunt-end steel cannula with a pointed inner trocar, and a plastic electrical connector that accepts the pacing wire and can be attached to a battery-powered external pacemaker generator. The cannula and trocar function as a catheter-over-the-needle.

Explain to the patient the risks and benefits of the procedure if they are awake and alert. A signed consent is not required and time is often lacking to obtain a signature. Document in the medical record that the patient was informed of the risks and benefits of the procedure. Place the patient supine. Clean the chest and subxiphoid area of any dirt and debris. Apply povidone iodine or chlorhexidine solution to the chest and subxiphoid area. Allow it to dry if time permits. Apply sterile drapes to delineate a sterile field.

Cardiopulmonary resuscitation (CPR) can be continued during most of the procedure but should be stopped while the intracardiac needle is being inserted to avoid possible damage to the lung or myocardium. Full ventilation of the lungs is recommended during subxiphoid cannula placement to depress the diaphragm and thus minimize the risk of injury to the liver and stomach. Insert a nasogastric tube to decompress the stomach prior to performing the procedure.

The Emergency Physician should prepare themselves and the equipment. Put on a cap, mask, sterile gloves, and sterile gown. Open the transthoracic cardiac pacing kit onto a sterile field. Lubricate the trocar liberally and insert it securely into the steel cannula.

Quickly identify the anatomic landmarks necessary to perform this procedure and determine the approach to be used. The cannula-over-the-trocar can be inserted through the left fifth intercostal space either parasternally, 4 cm lateral to the midsternal line, or 6 cm lateral to the midsternal line (Figure 32-2A). The tip of the cannula-over-the-trocar should be aimed toward the second costal cartilage. Alternatively, the cannula-over-the-trocar can be inserted through the left xiphocostal junction and aimed toward the right shoulder, left shoulder, or sternal notch (Figure 32-2B).

If bedside ultrasound is available, the parasternal approach through the fifth intercostal space may be the technique of choice. Without ultrasound, the simplest and quickest approach is to insert the trocar at the left xiphocostal junction and aimed toward the sternal notch. This technique is described below.

Briefly stop CPR. Insert the cannula-over-the-trocar from the left xiphocostal region at a 30° to 40° angle to the skin and directed toward the sternal notch. Advance the cannula-over-the-trocar approximately three-fourths of its length. Hold and stabilize the cannula and withdraw the trocar. Attach a 10 mL syringe to the cannula. Apply negative pressure to the syringe. If the cannula is within the ventricle, the aspiration of blood into the syringe confirms proper positioning. If blood is not aspirated, withdraw the cannula and restart the procedure. Ideally, confirm placement with bedside ultrasound.

Insert the transcutaneous pacing wire. Advance the plastic sheath over the pacing wire until it straightens out and covers the J-shaped end of the pacing wire. Insert the plastic sheath into the cannula hub. Advance the pacing wire through the cannula and into the ventricle. Stop advancing the pacing wire when 4 to 5 cm remains outside the cannula. No resistance should be felt while the pacing wire is being advanced. If resistance is felt, the cannula is not within the ventricle. Remove the cannula and pacing wire as a unit and restart the procedure. When it is inside the ventricle, the pacing wire will reform its J shape. Hold the pacing wire securely. Withdraw the cannula over the pacing wire. Do not release the hold on the proximal end of the pacing wire outside the patient's thorax, so as to prevent it from slipping inside the thorax.

Insert the proximal end of the pacing wire into the plastic connector. Secure it with the screws in the body of the connector. Connect the positive and negative terminals of the plastic connector to the pacemaker generator. Turn on the pacemaker generator. Set the pacing rate at 70 to 90 beats per minute in an asynchronous mode. Set the current output to the maximum milliampere rate on the pacemaker generator. After myocardial capture of the electrical stimulus is demonstrated (i.e., each pacer spike followed by a QRS complex on the cardiac monitor), lower the current output until 1:1 pacing is lost. Gradually increase the current output to attain stimulation threshold when 1:1 capture is regained. The optimal current output is two to three times the stimulation threshold. Change the mode of the pacemaker to a demand pacemaker with a backup rate of 60 to 70 beats per minute. A complete description of the functioning of the pacemaker generator is reviewed in Chapter 34.

Pacer spikes should be seen on the electrocardiogram (ECG) tracing on the cardiac monitor. If not, check the contact between the pacer wire and electrical connector. Check the batteries in the pacemaker energy source. Pacer spikes not followed by myocardial capture usually indicate inadequate positioning of the pacing electrode. Gently manipulate the transthoracic pacemaker wire to change its position.

The positioning of the pacing wire should be verified by a chest X-ray. Obtain a 12-lead ECG to document capture and to verify the positioning of the pacing wire based on the QRS configuration in the ECG. A left bundle-branch-block configuration will be demonstrated on the ECG if the pacing wire is in the right ventricle. If the pacing wire is in the right atrium or left ventricle, it will still pace the myocardium but the ECG will have a different QRS configuration. If the patient is in AV block, an atrially positioned pacing wire will be ineffective.

If the patient survives, secure the pacing wire to the skin with 3-0 nylon suture. A transvenous or permanent pacemaker should be inserted as soon as possible. Consult a Cardiologist immediately and admit the patient to an intensive care unit.

Analysis of the complications of transthoracic cardiac pacing is greatly limited by the paucity of short-term survivors and the absence of radiographic or pathologic evaluation of nonsurvivors. Complications include laceration of the right atrium, ventricles, coronary arteries, great vessels, vena cava, stomach, liver, and lung. Hemopericardium is a ubiquitous finding in some autopsy studies, and cardiac tamponade has been reported.17,18 Pneumothorax has been reported and is a particular concern in persons receiving positive-pressure ventilation.19

The technique of transthoracic cardiac pacing has been clinically feasible for more than 50 years, but there is extremely limited literature supporting its regular use. The technique of transthoracic cardiac pacing is simple, can be performed in less than a minute, but carries a high risk for multiple significant complications. There is no clear understanding of the effect of transthoracic cardiac pacing on the outcome of cardiac arrest and the complications associated with the procedure. Most of the available information comes from animal studies, retrospective analysis, and anecdotal data.

Transthoracic cardiac pacing may be useful in the setting of cardiac arrest with asystole or a pulseless idioventricular rhythm. It may be performed if a transcutaneous cardiac pacing system is not available or not effective. In unstable patients with drug-resistant bradycardia producing cardiovascular collapse or lethal escape rhythms whose clinical condition does not warrant a delay to insert a transvenous pacing catheter, transthoracic cardiac pacing can be initiated promptly. Bedside ultrasound may be useful in guiding and confirming appropriate placement of the transthoracic pacing device.