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This page is intended as a supplementary resource to the didactic knowledge found in a paramedic program. This will cover the basic anatomy and physiology of transcutaneous pacing as well as the differences between demand and non-demand pacing. This page is not intended to be a guide for treatment of a bradycardic patient as it will only speak briefly of other treatments including fluid administration and pharmacologic agents. This page will give basic guidelines and information on transcutaneous pacing without bias towards a single device or manufacturer. Always refer to local protocols when using a new or unfamiliar monitor/defibrillator. If you are on this page to learn the sequence of events to cardiovert, skip to How to Pace.
What is Transcutaneous Pacing?[edit | edit source]
[Paced Heart Rhythm EKG]
Transcutaneous pacing, or TCP, is the process of applying electrical current from an external device that manually depolarizes heart muscle to effect an increase in heart rate in a bradycardic patient. Transcutaneous pacing is different than transvenous (through the veins) pacing and an implanted pacemaker where electrodes directly contact the atrial or ventricular walls. With transcutaneous pacing (TCP), pads are placed on the patient in the conventional anterior-lateral position (Figure 1) or the anterior-posterior (Figure 2) position.
After the pads have been placed, the provider manually chooses both a rate in beats per minute (bpm) and current in milliamps (mA) that allows for capture, electrical and/or mechanical response to the pacing. With electrical capture, a pacer spike will be followed by an abnormally wide complex when viewing the rhythm on a monitor. This wide complex is indicative of ventricular depolarization. Mechanical capture refers to the finding that the patient’s pulse can be palpated at a rate similar to the visualized rate on the monitor.
When do we pace?[edit | edit source]
Pacing is at its heart the act of artificially increasing a patient’s heart rate utilizing electrical impulses to depolarize the myocardium and ideally create contractions. Because of this, pacing is generally reserved for patients with clinically significant and/or life-threatening bradycardias in the emergency environment. Patients who present with a bradycardia who are unstable (by AHA definitions: hypotensive, altered mental status, compliant of chest pain, or signs of poor perfusion) meet criteria for emergent TCP. Stable patients may also be paced via TCP, though several pharmacological methods should likely be attempted first, if not contraindicated, due to the discomfort that can be caused by pacing.
Mechanism of TCP[edit | edit source]
Although it has already been briefly discussed in the What is Transcutaneous Pacing? section of this page, the mechanism of TCP is the use of externally provided current to provoke cardiac contractions at a set rate. Remember back to the Physiology of the Heart and focus on how a cardiac contraction occurs at an electrical level. As the membrane potential reaches threshold, the cell undergoes a rapid depolarization that is able to be conducted (quickly in the conduction system or slowly in cell-to-cell conduction) throughout the heart. This wave of conduction can be viewed on an EKG as a distinct set of waves that each correspond to depolarization or repolarization of a certain area of the heart. In a healthy heart, this wave of depolarization will trigger a muscular contraction that will ultimately let the heart function as it should to provide perfusion to the body.
When we choose to provide transcutaneous pacing, we are essentially providing external electrical current that will depolarize the myocardium in a similar enough way to its natural ionic depolarization that a muscular contraction will happen. TCP is similar to cardioversion or defibrillation in the way that electricity is delivered to the patient’s heart but differs from both because TCP continues to provide organized shocks as opposed to the single shock of cardioversion or defibrillation. TCP is meant to be an ongoing treatment that, once begun, should not be stopped without good reason.
Demand vs. Non-demand pacing[edit | edit source]
A monitor has two different options available to it when providing pacing to a patient: demand and non-demand. These options are directly related to the monitor’s ability to view the patient’s underlying electrical rhythm. Both types of pacing are dependent on the set beats per minute on the monitor; higher BPM will lead to faster demand and non-demand pacing and vice-versa.
Demand Pacing[edit | edit source]
Demand pacing works by taking the set BPM and subtracting the patient’s intrinsic BPM to only provide pacing as needed. For example, if your patient has a heart rate of 40 bpm and you have set a rate of 80 bpm, the monitor will only pace the patient 40 times per minute to create an overall 80 bpm. Demand pacing requires the monitor be able to view the patient’s underlying cardiac rhythm, as this will allow it to compute how much pacing is actually required. Certain sets of defibrillation pads may allow your monitor to pace and view the rhythm simultaneously, if you do not have these special pads, the four leads must be placed for demand pacing to occur (because the monitor cannot read and shock simultaneously through normal pads). If your patient’s intrinsic rate is higher than the set pacing rate, the monitor will not provide pacing to the patient.
Non-demand pacing[edit | edit source]
Non-demand pacing is implemented by setting the paced rate on the monitor and increasing the current until you receive mechanical and electrical capture. While demand pacing augments the patient’s underlying electrical rate by pacing only when the patient’s heart has not spontaneously had an electrical impulse, non-demand pacing provides the set rate of electrical impulses regardless of the patient’s underlying rhythm. Unlike demand pacing, non-demand pacing does not require the monitor to have access to the patient’s electrical rhythm; for this reason, non-demand pacing may be initiated only with defibrillation pads without a 4 lead ECG. Because non-demand pacing does not allow for patient initiated electrical activity, it should be avoided unless the patient’s underlying rhythm is insufficient (i.e. large amount of non-perfusing PVCs).