Transcutaneous Pacing: Part I
TCP In Transit: A case reviewing transcutaneous pacing, false electrical capture, and re-arrest.
Josh Kimbrell, NRP
@joshkimbre
Judah Kreinbrook, EMT-P
@JMedic2JDoc
This is the first installment of a blog series showing how transcutaneous pacing (TCP) can be difficult, and how you can improve your skills. We will be using redacted information from different cases where paramedics attempted TCP in the field. Details are edited and redacted to preserve patient anonymity.
In this case, paramedics were called to an elderly male's apartment, and after troubleshooting an inaccurate address from dispatch, they ultimately located a somewhat cluttered residence, which required nimble footing while gaining access to the patient. They found him to be morbidly obese. They felt a weak radial pulse and were unable to obtain an O2 saturation secondary to cold extremities. High-flow oxygen was provided. They elected to extricate first due to varying scene hazards of large items stacked precariously, as well as concern for pests.
The patient is re-assessed once secured in the ambulance. The crew starts with placing the patient on the monitor, and they notice a heart rate of 60. The crew identified this as Sinus Rhythm (Figure 1), but in retrospect it seems to be a Junctional Rhythm.
Figure 1. Junctional Rhythm, heart rate close to 50.
Suddenly, the patient has a bowel movement and becomes pulseless / apneic. The paramedics begin CPR. Intubation is attempted, but unsuccessful. A supraglottic airway (King) is placed and confirmed with both capnography and breath sounds. CPR is performed with manual compressions as no mechanical CPR device is available. Two paramedics are in the rear of the ambulance managing resuscitation (another crew had arrived and provided support with a driver).
During transport, the paramedic not dedicated to compressions is able to establish IV access in the patient's hand. After administering 1mg of epinephrine ROSC is noted with a bradycardic rhythm (Figure 2).
Figure 2. Junctional Rhythm, occasional PAC's, and artifact.
Concerned about the patient's hemodynamic status post-arrest, the crew elects to initiate TCP, and sets the initial current to 70mA, as demonstrated in Figure 3.
Figure 3. Pacer set to 70 bpm and 70mA.
There is false electrical capture obscured by artifact.
The crew mentions in the narrative that they felt a weak pulse, but just 45 seconds later they increase the current to 75mA, which yields more false capture obscured by artifact (Figure 4).
Figure 4. Current 75mA, false capture with artifact.
Sixty seconds later, the crew doubts the efficacy of intervention, again, and proceeds to increase the current to 85mA (Figure 5). Not only is false electrical capture difficult to discern amidst simultaneous artifact, but the artifact itself [08:19:39 -- 08:19:43] is interpreted as underlying native beats by the LP15, which halts any pacer voltage from being deployed. This is demonstrated (Figure 5) by the gap in arrows at the bottom of the strip, signifying that the demand pacemaker has recognized an underlying rhythm (in this case, artifact from a moving ambulance). The artifact fools the pacemaker into thinking the rhythm is native. Notice the triangle on different parts of the waveform, and the lack of arrows at the bottom of the strip.
Figure 5. Current 85mA.
The crew recognizes that this isn't working and stops TCP. They are unable to feel a pulse and resume CPR. This false electrical capture may have made cardiac arrest recognition difficult, and the re-arrest may have gone unrecognized for an unknown amount of time.
On ED arrival ROSC is achieved. The receiving staff suspects pulmonary embolism due to S1Q3T3 on the ECG and administers TPA. The patient did have massive pulmonary emboli, but he also had profound intraventricular and subarachnoid hemorrhages. The patient was ultimately discharged with a poor neurologic outcome.
Learning points:
TCP is primarily recommended for bradycardia that does not respond to atropine, or other agents. Escalating directly to TCP requires a certain technical acumen to ensure its efficacy. As this case shows, electrical capture isn't always possible at lower currents, especially with pads placed in a standard anterolateral "defibrillation" position.
The University of Maryland found that capture occurred in only 42-78% of patients, dependent on pad positioning (Moayedi et al, 2022). The anterior-posterior position, however, was 80% more likely to gain capture.
Importantly, they used maximum output on their Zoll TCP device (140mA) in relatively healthy patients. If higher currents are required in the EP lab, it may be necessary to increase currents in the prehospital setting, as well.
The patient had an obscured re-arrest because of false electrical capture. This is a serious issue which could lead to death and/or disability. It cannot be emphasized enough: You must be very skeptical of TCP. That is to say, if there is any doubt that you have achieved capture it is imperative to have a low threshold for abandoning the intervention.
TCP is not benign when done inappropriately. If the pacer current is not leading to myocardial contractility, then you are needlessly "frying" the patient with electricity.
Notice how the paramedic relied on manual pulse palpation. This is not only difficult in cardiac arrest, but the skeletal muscle contractions from TCP make this worse! A close analysis of the SpO2 Pleth waveform, capnography, and overall hemodynamic status, should be used in addition to validated femoral pulse palpation by multiple clinicians.
