Feeling down about the lack of excitement in the 2015 ILCOR/AHA/ERC guidelines? We’re here for you. Let’s take a look at how we can go beyond the guidelines and into the future of cardiac arrest management.
PEA is something of an oddity. In any other recognized rhythm, we (basically) know what’s going on with the heart, both electrically and mechanically, at least qualitatively. With PEA, we’re presented with something of a catchall, with a treatment plan of “throw some stuff at it and see if it sticks.”
In the current AHA ACLS algorithms, PEA is grouped with asystole as nonshockable rhythms. Perhaps this makes sense for the lay rescuer, as the prescribed treatment for sudden cardiac arrest is simply CPR and defibrillation if indicated.
This is not necessarily a bad thing. Algorithms are for novices (this is in no way a pejorative term) who do not perform a particular skill or treat a certain condition on a regular basis. They are made to do the most good for the most patients. The simplicity offered here reduces stress and cognitive challenges in these inexperienced providers. Yes, there are patients who will not be helped, and some may even be harmed, but at least in theory, the majority of cardiac arrest patients will benefit from this algorithm. However, despite the designation of “Advanced Cardiovascular Life Support,” there is very little that is advanced about it.
Paramedics are often regarded as experts in cardiac arrest. You’d be hard pressed to identify any other group of healthcare providers who collectively see and manage as many sudden cardiac arrest cases as we do. Despite this, the only tip for PEA arrest that ACLS affords us is:
During each 2-minute period of CPR the provider should recall the H’s and T’s to identify factors that may have caused the arrest or may be complicating the resuscitative effort
Then we are presented with the following ten possible and treatable causes of the arrest:
While I can appreciate the chart’s concise yet fairly exhaustive nature, we’re typically trapped in a macabre guessing game with rare exception. Is there a tool that can help us in differentiating what exactly is going on in this population?
Well…yeah. This post would be a ridiculous waste of time if there wasn’t one. And you’d be reading this elsewhere if the answer was anything but point of care ultrasound.
Let’s go back to the basics of PEA. When it comes to how to approach it, the first question we should ask is, “what is the heart doing?” We know that the electrical system is firing, otherwise we’d be looking at electrical asystole. What we need to know is what the heart is doing (or not doing), mechanically speaking.
Is the heart moving?
If we can reliably answer that question at the initial presentation of PEA, we’re suddenly playing a whole new game and taking our practice to the next level.
Through that single question, PEA can be differentiated into two categories: true PEA (also known as electro-mechanical dissociation, or EMD) and pseudo-PEA. With true PEA, the electrical system is working, but that’s about it. The myocardium is not contracting, and obviously there is no pulse. At the risk of oversimplification, picture this as a really fancy looking asystole for now. In pseudo-PEA, the electrical system is operational and the myocardium is contracting (at least to an extent), but there is no palpable pulse. What’s the difference between profound shock and pseudo-PEA? Not a whole lot.
Given this, perhaps the patient deserves something a bit sweeter than the standard cocktail of compressions and enough epinephrine to explode an elephant’s heart.
“But ultrasound is haaaaard! Can’t I just load and go??”
No, it’s not. And no, you can’t. Stop whining and I’ll prove it. Let’s play a little game. If you’ve never interpreted a cardiac ultrasound before, you can play. If you have, grab a colleague or student that hasn’t. Make it interesting and put something at stake– money, corporeal punishment, whatever. Be creative. Is your victim ready? Okay, here we go:
Which heart is beating?
If you answered B, congratulations! You just interpreted an echocardiogram! You’re basically a doctor now (no you’re not, calm down, Ace). Even if that’s the only question you can answer by looking at the image on the screen, you’re already miles ahead of the pack.
But is this actually feasible in the real world? A trial published in 2010 in Resuscitation sought to answer that question.
Focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients: A prospective trial (FEEL)1
FEEL collected data from four German EMS agencies, representing both rural and suburban systems. Crew configuration for the trial consisted of paramedics and emergency physicians who underwent an eight-hour standardized training program (four hours of theory, four hours of hands-on practice)2. Between August 2002 and December 2007, 230 non-trauma patients were enrolled in the study, 204 of which were in a peri-arrest shock state (103) or full cardiac arrest (100; 97 of which had no palpable central pulses on EMS arrival). The remaining balance consisted of patients where ultrasound was used for abdominal studies or vascular access. The primary outcome measured was survival to admission (NOT survival to discharge).
In 96% of cases (and 100% of CPR cases), diagnostic quality images were obtained. As interesting as the applications of POCUS in shock are, we’ll keep the focus on cardiac arrest for today.
“We already have a cardiac monitor, why are we bothering with this crap?”
Here’s where it gets good. After POCUS imaging was completed on those presenting with PEA (with an enforced CPR interruption of less than 10 seconds), 75% showed cardiac wall motion, placing them into the category of pseudo-PEA. The remainder (25% for those who haven’t hit the therapeutic level of caffeine yet today) showed cardiac standstill, indicating true PEA.
For those unfortunate souls presenting with true PEA, their POCUS adventure is all but over. The victims of pseudo-PEA are those who truly have the potential to benefit from advanced diagnostics. In this data set, the pseudo-PEA group demonstrated the following:
Impaired LV function – 59%
Pericardial tamponade* – 9.8%
Significant RV dilation – 7.8%
Hypovolemia – 3.9%
*Diagnosed by combination criteria of pericardial effusion on exam and CPR
With this data available to providers, some of the “H’s & T’s” can actually be confirmed and treated. While pericardiocentesis has fallen out of favor in the prehospital critical care arena in recent years, a much better case can be made for the procedure when tamponade can be confirmed and when the actual procedure can be done under ultrasound guidance.
Impaired LV function may be precipitated by myocardial infarction. While obviously there is little we can do in the field about this, such a finding has the potential to influence transport decisions. With the advent of mechanical CPR and more catheterization labs beginning to perform PCI on certain populations of field VF arrests, the eligibility criteria for intraarest PCI could foreseeably be altered to account for these potentially salvageable cases that we are currently missing.
RV dilation is highly suggestive for pulmonary embolism, especially in cardiac arrest. Suspicion for PE can be increased by other findings on echocardiography as well. This may open the doors for an increased occurrence of emergency thrombolysis, whether thrombolytics are administered in the field by the agencies that carry them, or the decision to emergently transport to a capable facility is made.
Beyond guiding treatment modalities, POCUS has enormous potential in prognostication for PEA. Pseudo-PEA had a 55% survival to admission, while true PEA had a dismal 8%. As the termination of futile resuscitative efforts in the field has become an accepted standard, this is valuable data to consider when making that final decision.
Another interesting and surprising finding of FEEL was in patients presenting in asystole. A whopping 35% of asystole cases (with ECG interpretation by experienced providers) showed coordinated cardiac wall motion on echocardiography. While this may offer little help in terms of particular treatments administered, just as in PEA, it has interesting repercussions on prognostication. As expected, “asystole” with wall motion showed a far higher survival to admission (24%), as opposed to true asystole with cardiac standstill (11%). When both the PEA and asystole groups are pooled together, patients with cardiac wall motion showed a 34% survival to admission, compared to 6% in those with cardiac standstill.
As delicious as the Kool-Aid is, there are some pretty big limitations to this study that need to be considered before chugging away. For most of us, 100 cardiac arrests is a lot. Scientifically, this isn’t exactly the deepest data pool around. Secondly, a lot of arguments can be made regarding the primary outcome measured. While ROSC was once the king of cardiac arrest outcomes, we’ve come to realize that it’s a fairly useless number and that neurologically intact survival to hospital discharge is what truly matters to our patients. Personally, I wouldn’t give “survival to admission” much more weight than “patients achieving ROSC.” On a similar note, there was no randomization. While there is definitely some interesting data presented on the contrast of survivability in asystole and PEA based on the presence or absence of cardiac wall motion, there is no data to compare to. That is, there is nothing to show that the use of ultrasound actually had any effect on mortality. Granted, it makes a lot of intuitive sense that being able to identify and treat a specific pathology would decrease morbidity and mortality; however, definitive proof is needed for decision makers to take notice and invest the time and effort needed to establish an effective prehospital POCUS program. Lastly, this trial used physicians to conduct and interpret the echocardiograms. There are other papers showing that paramedics can rapidly learn to perform quality ultrasound imaging, though it would have been a bit more convenient for our purposes if paramedics were utilized in this particular study.
Despite these shortcomings, there is a lot of good conceptual information here. While a closer look at the subject is needed, especially at the paramedic level, the potential for intraarest echocardiography is evident. In this era of integrated cardiac arrest care, which emphasizes starting treatment at the citizen level and moves as many advanced beneficial treatments toward the front of the chain of survival as possible, expect the subject of POCUS to quickly come into the spotlight as the future of prehospital care.
- Breitkreutz R, Price S, Steiger H V., et al. Focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients: A prospective trial. Resuscitation. 2010;81(11):1527-1533. doi:10.1016/j.resuscitation.2010.07.013.
- Breitkreutz R, Uddin S, Steiger H, et al. Focused echocardiography entry level: new concept of a 1-day training course. Minerva Anestesiol. 2009;75(5):285-292. http://www.ncbi.nlm.nih.gov/pubmed/19412146. Accessed October 24, 2015.