The heart’s electrical system is governed by the sinoatrial (SA) node, which acts as the body’s natural pacemaker. This electrical signal coordinates the contraction of the heart chambers to pump blood efficiently. A normal resting heart rate for an adult generally falls between 60 and 100 beats per minute. When this system is disrupted, the heart rate can become too slow (bradycardia), severely compromising circulation. A slow heart rate may lead to symptoms like lightheadedness, fatigue, or fainting, and in severe cases, shock or cardiac arrest. Maintaining a proper heart rhythm is an immediate necessity in these emergency situations.
What Transcutaneous Pacing Is
Transcutaneous Pacing (TCP) is a temporary, non-invasive intervention used to electrically stimulate the heart from outside the body. This technique uses large electrode pads placed on the patient’s skin, which are connected to an external pacing device. TCP is employed as an emergency measure to stabilize a patient experiencing a dangerously slow heart rhythm. It acts as a bridge, maintaining a functional heart rate until a more definitive treatment, such as the insertion of a transvenous pacemaker or a permanent device, can be arranged.
How Electrical Pacing Works
The TCP device generates an electrical current delivered across the chest wall, aiming for “capture” of the heart muscle. Capture means the electrical impulse is strong enough to override the heart’s native rhythm and initiate a ventricular contraction. Current intensity is measured in milliamperes (mA); operators start low and slowly increase the mA until electrical capture is confirmed on the electrocardiogram (ECG). This confirmation is typically seen as a wide QRS complex immediately following the pacer spike on the monitor.
Once electrical capture is achieved, a small safety margin of current, usually an additional 10% or 5 to 10 mA above the threshold, is set to ensure pacing is maintained. The required current, known as the pacing threshold, often ranges from 50 to 100 mA in adjustable devices. Factors like chest wall thickness or conditions such as emphysema can increase transthoracic impedance, requiring a higher current output. The pacing rate is also adjustable, commonly set initially around 80 beats per minute (BPM), and is increased if the patient remains unstable.
Conditions Requiring Temporary Pacing
The primary indication for transcutaneous pacing is severe symptomatic bradycardia—an abnormally slow heart rate causing signs of instability. These signs include hypotension, altered mental status, chest pain, or other indications of shock due to inadequate blood perfusion. The heart rate is typically below 50 or 60 BPM and is often unresponsive to initial drug treatments like atropine.
Specific rhythm disturbances that frequently necessitate TCP include high-degree atrioventricular (AV) blocks, such as Second-degree Type II and Third-degree (complete) heart block. In these blockages, electrical signals fail to consistently reach the lower chambers, leading to a dangerously slow or unreliable heart rate. Temporary pacing is also used in cases of profound sinus bradycardia or transient conditions, like digoxin toxicity or an AV block associated with an acute inferior wall myocardial infarction.
The Pacing Procedure and Patient Experience
The procedure involves placing large adhesive electrode pads onto the patient’s torso, preferably using an anterior-posterior configuration to minimize electrical impedance. A common placement is one pad on the front of the chest near the sternum, and the other on the back below the left shoulder blade. Before application, the skin must be prepared, which may involve clipping excessive hair to ensure a secure connection and reduce the pacing threshold.
The delivery of the electrical impulse often causes discomfort for the conscious patient due to the stimulation of chest wall muscles and cutaneous nerves. Patients may experience strong, involuntary muscle contractions and a painful sensation in the chest area. For this reason, adequate analgesia and sedation are frequently administered to make the procedure tolerable until a more permanent pacing solution is achieved. Continuous monitoring is performed throughout the process, including regular ECG assessment to confirm electrical capture and checking a central pulse (such as the femoral pulse) to ensure effective mechanical contractions and adequate blood pressure.