Transcutaneous Pacing

Introduction1

• Paul Zoll first applied clinically effective temporary cardiac pacing in 1952, using two hypodermic needles to the chest to apply a pulsating current.
• Technological developments since then have led to endocardial, epicardial, and gastroesophageal approaches, as well as the refinement of external pacing.
• All approaches involve providing rate support via electrodes driven by an external pulse generator, which can be easily discontinued once the underlying cause is addressed.

Indications¹

Contraindications

• If the underlying pathology causing the bradyarrhythmia is not considered to be transient.
• Severe hypothermia is the cause of bradycardia.
• Skin issues (i.e., burns, open wounds) at sites of pad attachment.
  • Adjust the pad placement position.
• Relatively contraindicated in prolonged asystole (>20 mins) due to poor resuscitative outcomes in these patients.

Advantages of Transcutaneous Pacing

• Widely available in most crash carts, along with defibrillator units
• Easy to perform and requires minimal training
• It can be initiated almost instantly without the setup and insertion time required by invasive techniques.
• Carries less risk and is more cost-effective

Approaches to Temporary Pacing^1-3

External (Transcutaneous) Pacing

• Modern transthoracic pacemakers function strictly in demand mode, with a maximum output around 150 milliamperes (mA).
• Skin at pacing patches should be thoroughly cleaned and allowed to dry.
  • Consider trimming hair for better pad-skin contact.
• Most modern-day defibrillators have transcutaneous pacing capacity.
  • Prophylactic pad placement with defibrillation function in cardiac surgery is a frequent practice given the high risk of perioperative tachyarrhythmias.
    • Common indications include redo sternotomies, low ejection fraction, preexisting bradycardia or atrioventricular block, and dilated cardiomyopathies.
• Pad placement should be standardized to one pad placed below the right clavicle, just to the right of the upper sternal border, and the other with its center in the left midaxillary line, below the armpit⁴ (Figure 3).
  • If this position is not possible, placing a pad on the left side of the chest, between midline and the nipple, and another posteriorly, just below the left scapula, is considered good practice.⁴
  • In female patients, it is recommended to place the anterior pad to the left of the lower sternum, avoiding breast tissue whenever possible.⁴

• Transcutaneous pacing should be considered only in emergencies or for rescue treatment until recovery or until a more reliable transvenous pacer is placed.

Settings

• Pacing units will allow for adjustable pacing rate (beats per minute (bpm)) and ventricular output (mA), intended to trigger ventricular depolarization.
• Unlike more permanent pacing devices, the sensing threshold of intrinsic ventricular electrical activity is not adjustable.
• Pacing threshold is the minimum amount of output required to capture a ventricular depolarization or until patient discomfort is considered intolerable.
  • In conscious patients, output should start low and slowly increase until the threshold is reached.
  • In emergencies, output is started high (to assure capture) and then dropped until the threshold is reached.
  • The set output should be 5-10 mA above this pacing threshold.
  • It might be increased in patients with pericardial effusions, emphysema, or positive pressure ventilation (due to increased chest cavity impedance).

Assessment of Successful Pacing³

• Successful electrical capture is confirmed by inspecting the ECG tracing on the monitor.
• Widened QRS (ventricular depolarization), followed by a distinct ST segment and broad T wave
• The set pacing rate should match the manual pulse check and monitor heart rate.
  • Consider a 12-lead ECG to document appropriate capture

Complications3

• Failure to capture
  • Capture should be evaluated periodically since the pacing threshold can change.
  • Suboptimal electrode placement is the most common cause.
    • Confirm correct chest placement of electrodes (anterior vs posterior).
    • Pads should be placed away from bony structures.
  • Poor skin-electrode contact from sweat, debris, and hair. It can also present as increased pacing thresholds.
• Increased chest impedance.
  • Due to fluids (i.e., effusions) or intrathoracic air (i.e., pneumothorax, positive pressure ventilation, recent thoracic surgery)
• Myocardial ischemia or metabolic derangements can also cause increased pacing thresholds.
• Pain or discomfort is a limiting factor, particularly if higher outputs are required.
  • Consider analgesia or anxiolytics
• Other
  • Hiccups due to diaphragmatic stimulation
  • Skin burns from prolonged transcutaneous pacing
  • If atrial rhythm is preserved, AV dissociation can occur if pacer is on purely demand mode.