Transcutaneous pacing (TCP) is a non-invasive, temporary intervention used to manage symptomatic bradycardia, a dangerously slow heart rhythm. This procedure involves delivering external electrical impulses through large electrode pads on the chest wall to stimulate the heart muscle and achieve a faster, more effective heart rate. TCP serves as a bridge therapy to stabilize a patient while waiting for a more definitive treatment, such as rate-increasing medications or the insertion of a permanent or transvenous pacemaker. The goal is to quickly restore adequate blood flow and oxygen delivery to the body’s organs.
Identifying the Need for Transcutaneous Pacing
The decision to initiate transcutaneous pacing is based on two concurrent factors: the presence of bradyarrhythmia and the resulting signs of poor perfusion, which is why it is called “symptomatic” bradycardia. Bradycardia is generally defined as a heart rate below 60 beats per minute, but pacing is needed when this slow rate causes symptoms because the heart is not pumping enough blood to meet the body’s metabolic demands.
Signs of poor perfusion can include hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, or acute heart failure. According to Advanced Cardiovascular Life Support (ACLS) protocols, if a patient with bradycardia is displaying these unstable symptoms, pacing must be initiated immediately if the initial dose of atropine is ineffective. In cases of severe instability, pacing may be started without delay, even before administering atropine.
TCP is often required for specific types of heart blocks, such as a second-degree Atrioventricular (AV) block Type II or a third-degree (complete) AV block, where atropine is often ineffective. TCP is not recommended for asystole or for patients with severe hypothermia, as pacing is relatively contraindicated in these situations.
Pre-Procedure Setup and Pad Placement
Before activating the pacer, careful preparation of both the equipment and the patient is necessary to maximize the success of the procedure. The pacing unit, typically a monitor/defibrillator device, must be connected to the patient with both the standard ECG monitoring leads and the large pacing electrode pads. The skin underneath the pacing pads must be clean and dry to ensure good electrical contact and minimize impedance.
Any excessive chest hair should be quickly clipped or shaved, and any transdermal medication patches, jewelry, or implanted devices should be removed from the path between the two pads. Since transcutaneous pacing can cause significant skeletal muscle contraction and be painful for the conscious patient, gathering supplies for sedation and analgesia is a necessary step before pacing begins. Pain medication such as fentanyl and a sedative like midazolam or ketamine are often prepared to ensure patient comfort.
The most effective method for pad placement is the anterior-posterior configuration, which is preferred because it effectively “sandwiches” the heart between the two electrodes. This arrangement minimizes transthoracic electrical impedance, meaning less current is needed to achieve capture. The anterior (negative) pad is placed to the left of the sternum, while the posterior (positive) pad is placed on the patient’s back, ideally to the left of the spine, directly behind the anterior pad.
Setting the Pacer Rate and Output
After the pads are securely placed, the monitor must be switched into the “Pace” mode to begin the technical setup. The first setting is the desired heart rate, which is the rate at which the machine will deliver electrical pulses. A typical starting rate for transcutaneous pacing is between 60 and 80 beats per minute, which is adequate for maintaining perfusion.
Next, the electrical output, measured in milliamperes (mA), must be set to represent the strength of the electrical pulse delivered. The output is initially set low (e.g., 0 or 10 mA) and then slowly increased until the patient’s heart responds to the electrical stimulus. This process determines the Capture Threshold: the minimum amount of current required to consistently depolarize the heart muscle and initiate a heartbeat.
Once the capture threshold is identified, the final electrical output is set 10 to 20 mA above this threshold to establish a safety margin. This margin ensures that minor changes in skin impedance or patient movement do not result in a sudden loss of pacing. Most modern devices operate in a “Demand Mode,” meaning the pacer only delivers a pulse if the patient’s intrinsic heart rate falls below the set rate.
Assessing Mechanical and Electrical Capture
Verifying the effectiveness of transcutaneous pacing requires confirming both electrical and mechanical capture. Electrical capture is confirmed by observing the cardiac monitor for a distinct, wide QRS complex that immediately follows each pacing spike. The pacing spike is the vertical line on the electrocardiogram (ECG) that represents the delivery of the electrical impulse, confirming the electrical stimulus successfully depolarized the ventricles.
Mechanical capture verifies that the electrical activity is producing an actual heartbeat and circulating blood. This is confirmed by palpating a pulse that is synchronized with the set pacer rate. Due to the muscle twitching caused by the electrical current, it is more reliable to check for a central pulse, such as the femoral or carotid pulse, rather than a peripheral pulse.
The patient’s clinical status is monitored closely, including checking their blood pressure, as this directly indicates whether the pacing is improving cardiac output. If the blood pressure remains low despite successful capture, the pacing rate may need to be adjusted higher, or a rate-increasing medication may be required. If capture is lost, troubleshooting involves checking pad adherence, ensuring all cables are securely connected, and increasing the current output to re-establish the capture threshold.