WHEN AND WHY TO USE TRANSCUTANEOUS PACING IN ADULT CARDIAC CARE

Transcutaneous cardiac pacing (TCP) is a critical, non-invasive method for temporarily overriding a patient’s intrinsic cardiac rhythm when it is inappropriately slow or absent, posing a significant threat to hemodynamic stability. It involves delivering electrical impulses through the skin to stimulate myocardial contraction, thereby increasing heart rate and improving cardiac output. This technique is invaluable in emergent situations such as complete heart block, symptomatic bradycardia unresponsive to medication, or as a bridge to transvenous pacing or definitive therapy. While conceptually straightforward, effective and safe TCP requires a thorough understanding of its indications, contraindications, equipment, and a systematic approach to its application.

Indications for Transcutaneous Pacing

The primary indication for TCP is symptomatic bradycardia. This typically presents with a heart rate too slow to maintain adequate blood pressure, perfusion to vital organs, and oxygenation. Symptoms may include hypotension, altered mental status (confusion, lethargy, decreased consciousness), chest pain, shortness of breath, cool and clammy skin, and decreased urine output. Specific cardiac rhythms that may warrant TCP include:

• Symptomatic Sinus Bradycardia: When the sinus node generates impulses too slowly to sustain adequate cardiac output.
• Symptomatic Junctional Rhythms: When the heart’s natural pacemaker activity originating from the atrioventricular (AV) junction is too slow.
• Symptomatic AV Block:
  • Second-degree AV block, Mobitz II: This type of block has an unpredictable block in the His-Purkinje system, making it prone to progressing to complete heart block.
  • Third-degree (complete) AV block: In this condition, there is a complete dissociation between atrial and ventricular activity, leading to a slow, often unreliable escape rhythm. Pacing is crucial to ensure ventricular depolarization.
• Asystole: While TCP is not a primary treatment for asystole, it can be utilized as a temporizing measure while preparing for other interventions or confirming asystole.
• Cardiopulmonary Arrest (CPA) due to Bradycardia: In the context of cardiopulmonary arrest, if a pulse check reveals bradycardia, TCP should be initiated concurrently with chest compressions and other resuscitation measures.
• Electromechanical Dissociation (EMD): When there is electrical activity on the ECG but no palpable pulse. TCP may be considered to ensure mechanical contraction.

It is crucial to differentiate between symptomatic and asymptomatic bradycardia. Asymptomatic bradycardia, especially with a stable blood pressure and normal mental status, may not require immediate pacing and can be managed with pharmacological agents first.

Contraindications for Transcutaneous Pacing

While TCP is a versatile tool, certain situations limit its effectiveness or pose risks:

• Refractory Ventricular Arrhythmia: TCP is not effective in pacing the ventricles during ventricular fibrillation or pulseless ventricular tachycardia, as these are typically rapid, disorganized rhythms. Defibrillation is the primary intervention.
• Severe Hypothermia: In profound hypothermia, myocardial cells become less responsive to electrical stimulation, rendering TCP less effective. Rewarming is the priority.
• Presence of a Permanent Pacemaker: If the patient already has a functioning permanent pacemaker, TCP can potentially interfere with its function or trigger inappropriate pacing. However, in a life-threatening emergency where the permanent pacemaker is failing and the patient is unstable, TCP might still be considered as a temporary measure. Careful assessment and consideration of the risks versus benefits are essential.
• Short QT Interval: A very short QT interval can increase the risk of torsades de pointes polymorphous ventricular tachycardia during pacing.
• Asystole: As previously mentioned, TCP is generally ineffective in asystole because there are no myocardial cells to stimulate. However, it may be applied in a desperate attempt while confirming asystole or preparing for other interventions.

Equipment Required for Transcutaneous Pacing

The essential equipment for TCP includes:

1. Transcutaneous Pacing Defibrillator/Pacemaker Unit: This is the core device. Modern defibrillator units often have integrated TCP capabilities. It should have a display screen for ECG monitoring, rate control, output adjustment, and sensing parameters.
2. Pacing Electrodes: Specifically designed for transcutaneous pacing, these are large, self-adhesive electrodes that ensure good electrical contact with the skin and distribute the electrical current over a wide area to minimize skin irritation and discomfort. Typically, two electrodes are used, placed strategically on the chest.
3. ECG Leads and Monitor: Standard ECG leads are necessary to visualize the patient’s underlying rhythm and to confirm capture.
4. Monitoring Equipment: Continuous monitoring of blood pressure, oxygen saturation (SpO2), and capnography (if available) is vital to assess the effectiveness of pacing and the patient’s hemodynamic status.
5. Medications: Emergency medications for bradycardia, such as atropine, epinephrine, and dopamine, should be readily available, as TCP may be used in conjunction with or after pharmacological attempts.
6. IV Access: Secure intravenous access is essential for administering medications.
7. Personal Protective Equipment (PPE): Gloves, gowns, and eye protection are standard for patient care.

Step-by-Step Guide to Performing Transcutaneous Pacing

Step 1: Assess the Patient and Recognize the Need for Pacing

• Primary Survey (ABCDE): Begin with a rapid assessment of the patient’s Airway, Breathing, Circulation, Disability (neurological status), and Exposure.
• Identify Signs of Hemodynamic Instability: Look for hypotension, altered mental status, chest pain, signs of poor perfusion (cool, clammy skin, delayed capillary refill), and shortness of breath.
• Obtain an ECG: A 12-lead ECG is crucial to identify the underlying rhythm, assess the heart rate, and determine the presence and type of any bradycardia or heart block.
• Evaluate Symptoms in Relation to Heart Rate: Correlate the patient’s symptoms with their heart rate. A heart rate that is too slow to maintain adequate perfusion and is causing the observed signs and symptoms is the primary indication for pacing.

Step 2: Prepare the Equipment and Patient

• Gather Equipment: Ensure all necessary equipment (pacing unit, electrodes, ECG leads, monitoring devices) is readily available and functional.
• Explain the Procedure to the Patient (if conscious and able to understand): Inform the patient that a temporary pacing device will be used to help their heart beat faster. Explain that they may feel a “tapping” or “thumping” sensation with each paced beat.
• Ensure Privacy and Dignity: Expose the patient’s chest adequately for electrode placement while maintaining privacy.
• Clean and Dry the Skin: Ensure the skin area where the electrodes will be placed is clean and dry. Remove any lotion, sweat, or debris to ensure good adhesion and electrical conductivity.

Step 3: Apply the Pacing Electrodes

• Electrode Placement: The correct placement of pacing electrodes is critical for effective pacing and sensing. The standard adult placement is as follows:
  • Anterior-Posterior Placement (Recommended):
    • One electrode is placed over the anterior chest in the anterior axillary line, just below the left clavicle (or in the V1-V2 precordial leads position).
    • The second electrode is placed over the posterior chest, directly behind the heart, on the left infrascapular region. This “sandwich” effect improves current delivery through the myocardium.
  • Anterior-Lateral Placement (Alternative if posterior access is limited):
    • One electrode is placed in the anterior chest, in the antero-lateral position (e.g., below the left clavicle, lateral or inferior to the sternum).
    • The second electrode is placed on the left lateral chest, in the anterior axillary line at the level of the cardiac apex.
• Ensure Good Adhesion: Press firmly on the electrodes to ensure they are well-adhered to the skin. This is crucial to prevent dislodgement and to ensure optimal electrical contact.

Step 4: Connect the Pacing Unit and Initiate Pacing

• Connect the ECG Leads: Attach the standard ECG leads to the patient and connect them to the pacing unit’s monitor. Choose a lead that provides a clear view of the patient’s rhythm for monitoring.
• Connect the Pacing Cables: Connect the pacing electrodes to the pacing unit according to the manufacturer’s instructions.
• Establish Baseline ECG Monitoring: Observe the patient’s intrinsic rhythm on the monitor.
• Set Pacing Mode: Most modern devices offer different pacing modes. For transcutaneous pacing, asynchronous pacing (e.g., VOO mode) is often initiated first, especially in unstable situations or when sensing is a concern. In VOO mode, the pacemaker delivers a stimulus at a set rate regardless of the patient’s intrinsic rhythm or electrical activity.
• Set Desired Pacing Rate: Set the pacing rate to a level that is expected to provide adequate cardiac output, usually between 60-80 beats per minute (bpm) for adults. However, this can be adjusted based on the patient’s clinical condition and response.
• Initiate Pacing at Minimum Output: Begin pacing at the lowest possible electrical output (milliamperes, mA) that consistently produces ventricular depolarization (a paced QRS complex) and, ideally, a palpable pulse. This minimizes patient discomfort and potential skin irritation.

Step 5: Assess for Capture

• Electrical Capture: Observe the ECG monitor. Look for a wide QRS complex following each pacing stimulus, indicating that the stimulus has successfully depolarized the ventricles. The paced QRS complex will typically be wider and have a different morphology than the patient’s intrinsic QRS complexes.
• Mechanical Capture: Simultaneously, assess for a palpable pulse distal to the pacing site (e.g., radial or femoral pulse) with each paced QRS complex. This confirms that the electrical depolarization is resulting in a mechanical contraction and effective cardiac output.
• Assess Hemodynamic Response: Monitor the patient’s blood pressure. An increase in blood pressure indicates improved cardiac output. Also, observe for improvement in mental status, skin perfusion, and oxygen saturation.
• Increase Output if Necessary: If electrical capture is observed but mechanical capture or a palpable pulse is absent, or if hemodynamic parameters do not improve, gradually increase the milliamperes (mA) output of the pacemaker in small increments (e.g., 5-10 mA) until mechanical capture and a palpable pulse are consistently achieved.

Step 6: Optimize Pacing and Sensing

• Sensing (Demand Pacing): Once capture is established, consider switching to a demand pacing mode (e.g., VVI or VVIR). In demand pacing, the pacemaker senses the patient’s intrinsic electrical activity and only delivers a pacing stimulus if the heart rate falls below the set rate. This allows the patient’s intrinsic rhythm to take over when present, conserving battery and minimizing unnecessary pacing.
  • Set Pacing Sensitivity (mV): Adjust the sensitivity setting to ensure the pacemaker accurately “sees” the patient’s intrinsic QRS complexes and inhibits pacing appropriately. The sensitivity is typically set to a value slightly lower than the amplitude of the patient’s intrinsic QRS complexes. If the sensitivity is set too low (less negative), the pacemaker may not sense the intrinsic R waves and pace unnecessarily. If set too high (more negative), it may fail to sense the R waves, leading to “R-wave oversensing” and failure to pace when needed.
• Troubleshooting Oversensing/Undersensing:
  • Undersensing: If the pacemaker fails to detect the patient’s intrinsic rhythm and delivers pacing spikes inappropriately, increase the sensitivity (make it less negative). Also, check electrode placement and ensure adequate contact.
  • Oversensing: If the pacemaker fails to pace when it should, or if it paces inappropriately, reduce the sensitivity (make it more negative). Also, consider movement artifacts, chest wall muscle activity, or T-wave sensing as potential causes. Repositioning electrodes or using a different ECG lead for monitoring might help.
• Fine-tune Rate and Output: Adjust the pacing rate and output to achieve optimal hemodynamic stability with minimal patient discomfort.

Step 7: Continuous Monitoring and Reassessment

• Monitor Vital Signs: Continuously monitor blood pressure, heart rate, respiratory rate, SpO2, and mental status.
• Assess for Complications: Be vigilant for potential complications of TCP, including:
  • Discomfort and Pain: TCP can be uncomfortable and even painful, especially at higher outputs. Adequate analgesia and sedation should be administered if necessary and the patient’s clinical condition allows.
  • Skin Irritation/Burns: Prolonged pacing or high outputs can cause skin irritation or burns under the electrodes. Regularly inspect the skin and reposition electrodes if necessary.
  • Muscle Fasciculations: Electrical stimulation can cause involuntary muscle contractions.
  • Arrhythmias: In rare cases, TCP can induce arrhythmias.
• Reassess Underlying Cause: Continue to investigate and treat the underlying cause of the bradycardia. TCP is a temporizing measure.
• Prepare for Definitive Therapy: TCP is a bridge to definitive therapy, which may include transvenous pacing, implantation of a temporary transvenous pacemaker, or treatment of the underlying reversible cause of the bradycardia.

Step 8: Weaning from Transcutaneous Pacing

• Gradual Reduction: Once the patient is hemodynamically stable and the underlying cause of the bradycardia is addressed, weaning from TCP can be considered.
• Reduce Rate: Gradually decrease the pacing rate while closely monitoring for signs of instability.
• Turn Off Pacing: If the patient maintains adequate heart rate and stability, the pacing can be turned off.
• Continue Monitoring: Closely monitor the patient for several minutes after turning off the pacemaker to ensure their intrinsic rhythm remains adequate.

Important Considerations and Nuances

• Patient Comfort: Transcutaneous pacing can be uncomfortable. Judicious use of analgesia and sedation is often necessary to improve patient tolerance and compliance, especially when pacing continuously. Titrate these medications carefully to avoid over-sedation and respiratory depression.
• Electrode Placement Accuracy: The efficacy of TCP is highly dependent on correct electrode placement. If pacing is ineffective, the first step is to re-verify electrode position.
• Skin Integrity: Regular inspection of the skin under the electrodes is vital. If irritation or burns are developing, reposition electrodes or consider alternative pacing methods.
• Sensing vs. Pacing: Differentiating between electrical capture and mechanical capture is paramount. A paced electrical complex without a palpable pulse indicates a problem.
• Pacemaker vs. Defibrillator: Ensure the device being used is capable of pacing. Many modern defibrillators have integrated TCP functionality.
• Teamwork and Communication: Effective TCP requires clear communication and collaboration among the healthcare team members.

In conclusion, transcutaneous cardiac pacing is a life-saving intervention for symptomatic bradycardia in adults. By following a systematic approach that includes proper patient assessment, equipment preparation, electrode placement, stepwise initiation, and continuous reassessment, healthcare providers can effectively utilize TCP to stabilize patients and bridge them to more definitive treatments when necessary. A thorough understanding of its indications, contraindications, and the technical steps involved is essential for optimal patient outcomes.

References

• American Heart Association. (2020). Advanced Cardiovascular Life Support Provider Manual.
• Tintinalli, J. E., Ma, O. J., Yealy, D. M., Meckler, G. D., Stapczynski, J. S., Cline, D. M., & Thomas, S. H. (2020). Tintinalli’s Emergency Medicine: A Comprehensive Study Guide (9th ed.). McGraw-Hill.
• UpToDate. (n.d.). Transcutaneous cardiac pacing. Retrieved from https://www.uptodate.com/contents/transcutaneous-cardiac-pacing (Subscription may be required)
• Grauer, K., & Cooper, A. (2017). The ECG Made Easy (4th ed.). Churchill Livingstone.
• National Emergency Nursing Association. (2021). EKG interpretation competency guide. (Note: Specific publication details may vary, refer to current NENA resources).