Ultrasound-Guided Pacing


In 2005 the American Heart Association removed pacing asystole from the cardiac arrest algorithm. This action was a result of multiple studies (1,2) showing no benefit. These studies are full of limitations such as:

  • Mechanical capture not recorded or confirmed

  • Significant delays in initiation

  • Including all-comer asystolic patients

The difference between pacing bradycardia versus asystole becomes blurrier as the heart rate decreases. For example, consider these three scenarios:


You have a patient with a heart rate of 40, blood pressure 70/39, and unresponsive. Are you ok with pacing?


You have a patient with a heart rate of 30, blood pressure 68/34, and unresponsive. Are you ok with pacing?


You have a patient with a heart rate of 20, blood pressure 60/31, and unresponsive. Are you ok with pacing?


I have asked several people this question, in that order, and found typically everyone says yes to #1, most say yes to #2, and number three is where the discussion occurs. Regardless of whether the patient is in asystole or profoundly bradycardic, pacing is putting induced beats within an asystolic period. So why do we feel ok doing this during bradycardia versus asystole?


I believe it is because native heart beats give us hope that the issue is nodal versus mechanical.


When discussing this with Sam Ireland, he brought up an interesting perspective postulating a difference between patients who deteriorate to asystole versus patients bradying down to asystole. I think this makes a lot of sense in regard to ATP availability and the events leading to profound bradycardia/asystole.


My brain is not on-board with pacing asystole (yet), even in the patient that bradys down to asystole (as opposed to deteriorating from a shockable rhythm to asystole). I do however think there is a subset of patients who present with a bradycardic and pulseless rhythm, that would benefit from ultrasound-guided pacing instead of CPR. The only way you can tease out cardiac motion in the patient with a pulseless bradycardic rhythm is with ultrasound.


What is ultrasound-guided pacing?

Traditionally transcutaneous pacing involves a paramedic placing pads anterior/posterior (preferred), and turning up the milliamps until electrical capture is obtained. Electrical capture is obtained when a pacing spike is followed by a wide complex. The clinician will then try to palpate a pulse to confirm mechanical capture. Because the contractions of the pectoral muscles can tug on the muscles of the neck as well, AHA recommends palpating a femoral pulse versus a carotid (3) to avoid thinking you feel a pulse (false mechanical capture). Not only are events of false capture common, but there are even situations in which the paramedic swears they feel a pulse and observes the patient becoming more alert, and they never had mechanical capture (check out this post by my buddy Tom Bouthillet)


I believe most of us are using SPO2 pleth wave to confirm mechanical capture versus the subjectivity of palpating a pulse, but even patients with a pulse can have poor pleth wave readings. I believe ultrasound-guided pacing is ideal and should become mainstream. I typically find I can get a parasternal long view on ultrasound with the pads placed as illustrated below. However, there are other views if your pad sweet spot is obstructing where you wanna put the probe.


This is what I think the process would look like:

How do I know if contractions are adequate?

It is important to not just look for "weak organized twitching" of the heart. Our goal is contractions that appear as if they should correlate with a pulse. So how do we know if contractions are adequate based on ultrasound? Right after the LV ejects blood, a condition is met in which the pressure in the left atrium is higher than the pressure in the LV. The degree of this pressure differentiation can be estimated by looking at the mitral valve in relation to the septum.

This can be eye-balled (very common) or actually measured using something called E-Point septal separation. To obtain this measurement you drop a motion detector line over the distal end of the mitral valve while in a parasternal long view. You then will record the motion across a time axis. You then can pause it and measure how close the mitral valve gets to the septum as illustrated below. Note that the mitral valve will open twice during diastole. The first time it opens is because of a pressure gradient directly following systole, and the second time is atrial kick.

You will see a pulse on ultrasound before you feel one by palpation (4,5). This may be the difference between treating a patient like they are in cardiac arrest (asynchronous chest compressions) versus profound shock (volume, pressors, inotropes).


This is nothing profound and is definitely not a new concept in emergency medicine. It is however a new concept for paramedics and another feather in the cap of prehospital ultrasound. This weekend I will be releasing a podcast with Dr. Leon Eydelman on the utilization of ultrasound-guided pacing. Stay tuned!

Peer Review: Brian King

Another thought provking blog by Tyler, where he chalks up another use for point of care ultrasound in the prehospital field. This is a great example of where POCUS can be useful in really any environment where a patient is being transcutaneously paced. I know I have been in the situation a number of times where I have been pacing a patient or attempting to pace a patient or thought I was pacing a patient when I have palpated a carotid pulse and assumed that I had successfully obtained mechanical capture. I think we have all been in a similar situation. This is a excellent example of where POCUS can really confirm that mechanical capture is present and we are questioning if we felt the patients pulse or our own.


I will also add that Tyler brings up a excellent point about utilizing the pulse ox pleth to confirm mechanical capture. While he thinks that most utilize this method, I don’t believe this to be the case and had caused me to develop a itch that I feel needs to be scratched in the form of a blog on this topic.




References:

(1) Cummins RO, Graves JR, Larsen MP, Hallstrom AP, Hearne TR, Ciliberti J, Nicola RM, Horan S. Out-of-hospital transcutaneous pacing by emergency medical technicians in patients with asystolic cardiac arrest. N Engl J Med. 1993 May 13;328(19):1377-82. doi: 10.1056/NEJM199305133281903. PMID: 8474514.


(2) Armon C. Transcutaneous pacing in patients with asystolic cardiac arrest. N Engl J Med. 1993 Oct 21;329(17):1277. doi: 10.1056/NEJM199310213291716. PMID: 8413401.


(3) Doukky, R., Bargout, R., Kelly, R. F., & Calvin, J. E. (2003). Using transcutaneous cardiac pacing to best advantage: How to ensure successful capture and avoid complications. The Journal of critical illness, 18(5), 219–225.


(4) Ochoa FG et al. Competence of Health Professionals to Check the Carotid Pulse. Resuscitation 1998. PMID: 9715777


(5) Zengin S et al. Comparison of Manual Pulse Palpation, Cardiac Ultrasonography and Doppler Ultrasonography to Check the Pulse in Cardiopulmonary Arrest Patients. Resus 2018. PMID: 30253230


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