Using Ultrasound for Cardiac Arrest
Editor’s note: This is the second in a three-part series examining prehospital applications for point-of-care ultrasound. Find the first part at www.emsworld.com/12286042. For a primer on using this technology in the field, see “It’s Time to Embrace Point-of-Care Ultrasound” from September 2016 at www.emsworld.com/12231975.
While EMS systems around the world are continuing the good fight to improve cardiac arrest outcomes, we need to admit we are handicapped by our current diagnostic arsenal. This is apparent in cases of pulseless electrical activity (PEA) more than any other. Current ACLS treatment guidelines for PEA boil down to “CPR and epinephrine, repeat until death.” Sure, there is the classic “treat reversible causes,” but how many of the classic “H’s and T’s” can we really reliably diagnose in the field? Not too many—most require either a thorough and accurate history and exam or EKG findings, which may not be possible during the arrest, or diagnostic tools typically unavailable in the field. This shotgun approach to cardiac arrest is undoubtedly leaving thousands of bodies in the streets. We can do better. The first step is adopting point-of-care ultrasound (POCUS).
Key views for use of ultrasound in cardiac arrest include the following:
Subxiphoid—The subxiphoid view is familiar to anyone with exposure to the FAST exam. This view looks from the upper abdomen, just below the costal arch, upward. Ideally all four chambers are visible, with the right heart at the top of the image. This view allows the operator to be well out of the way during CPR, though the view may be difficult to get in patients with large abdomens.
Parasternal long axis—The parasternal long axis view gives a great look at the left ventricle (LV) and atrium, as well as the mitral and aortic valves. Due to the angle of the slice the view produces, only a small sliver of the right ventricle (RV) is visible, making it less than ideal for estimating ventricle size ratios. It is possible to obtain this view while a LUCAS device is in use.
Apical four-chamber—The apical four-chamber view looks directly through the apex of the heart. All four chambers of the heart are visible and in their proper proportion, making it the view of choice when there is concern about the relative size of the RV. Though it may be more difficult than the other two, it is theoretically accessible with the LUCAS device deployed.
Now that we have an idea of what we’re looking at, let’s check out some of the pathologies encountered during cardiac arrest and how POCUS can improve their detection and treatment. (Tension pneumothorax was covered here.)
Volume status can be estimated by assessing the function of the left ventricle as well as the inferior vena cava (IVC). A healthy heart typically produces an ejection fraction (EF) of 55%–65%. Put simply, that means the left ventricle (LV) collapses 55%–65% during the systolic phase. The ejection fraction increases in a hypovolemic state as the heart struggles to circulate as much fluid as possible. Severely hypovolemic patients may have an EF approaching 100%, and the walls of the LV may appear to “kiss.” In addition the LV will appear smaller than usual due to the lower volume of fluid filling it.
The shape and behavior of the IVC, having little structure on its own, depends on fluid. Typically the IVC is easily seen and has some diameter variability during respiration due to pressure changes. As circulating volume reduces, the IVC diameter shrinks and the respiratory variability increases. While there is some controversy on the utility of IVC measurement to estimate volume status on its own, by combining it with LV assessment, it becomes a valuable tool to the prehospital provider.
Fluid buildup in the pericardium is referred to as a pericardial effusion. When the pressure within the pericardium grows to where hemodynamics are affected and the right ventricle (RV) begins to collapse, it becomes a pericardial tamponade. The textbook finding in pericardial tamponade is Beck’s triad: jugular vein distension (sensitivity of 54%), hypotension (sensitivity of 28%) and muffled heart tones (sensitivity of 22%). As with many physical exam findings we’re taught to look for during schooling, the true utility of Beck’s triad tends to be exaggerated. In the patient suffering from cardiac arrest secondary to pericardial tamponade, survival is questionable at best whether the cause is traumatic or medical, as no amount of CPR or epinephrine will be able to overcome the structural pathology of a nonfunctioning RV. Contrary to popular belief, this is not necessarily a rare condition. One study showed that of 51 patients presenting with PEA, five (9.8%) were suffering from tamponade.4
Fortunately POCUS makes the detection and treatment of pericardial effusion easy. Fluid around the heart will be seen as a distinct black collection, and in the case of tamponade, the RV will be distorted if it’s visible at all. In cases of severe tamponade, the heart can be seen swinging around like a pendulum within the pericardium—which is the cause of electrical alternans. Ultrasound can then be used to guide a needle directly to the largest point of fluid collection in the pericardium and drain it. As the needle is guided visually, any cardiac view can be used to perform pericardiocentesis, eliminating the need for the typical landmarks and subxiphoid approach.
Pulmonary embolism is responsible for more than 10% of arrests of noncardiac origin and is associated with a low survival rate.5 Just as with cardiac tamponade, CPR and epinephrine will do nothing for a massive clot in the pulmonary vasculature.
When you view the heart with ultrasound, the LV should be grossly larger than the RV. In the case of pulmonary embolism, the RV increases in size until it is as big or even larger than the LV. As the right heart attempts to pump blood to the lungs, blood is unable to effectively complete its journey due to the embolism. This causes blood to back up into the RV, which dilates like an overfilled balloon.
This is best seen in the apical four-chamber view, as this view allows visualization of the entire heart in proper proportion, and clues may be seen in the IVC as well. As the RV struggles to overcome the pressure in the pulmonary vasculature, the right atrium will overfill too, limiting incoming flow from the IVC. This causes the IVC to become distended, with little to no variation in diameter on respiration. If these findings weren’t enough on their own, an embolus may even be found floating in the RV.
While there are no readily available field treatments for pulmonary embolism, obtaining this information can help with transport decisions. This is a case where rapid transport to a hospital would be appropriate, as you know no field treatment will fix this patient. Better yet, the ability to reliably diagnose pulmonary embolism may lead to the adoption of better field treatments, such as tPA. A recent study administered a small dose of tPA to patients in cardiac arrest secondary to pulmonary embolism. No bleeding complications were noted, and 87% of these patients were alive two years later and had returned to their normal lifestyle with no disability.6 Though this was only one study and more investigation is needed, low-dose tPA shows enormous potential for this typically lethal condition.
In addition to pathology, POCUS can be used to verify rhythms. This may seem like a party trick—after all, asystole is asystole, right? In the age of POCUS, it may not be quite that simple. Multiple trials and case studies have discovered a new phenomenon: cardiac wall motion during apparent electrical asystole. This is such a new discovery that the publication of a recent study identifying this phenomenon was delayed, as reviewers did not believe the data could be correct.
Studies have revealed a 10%–35% occurrence of cardiac motion in asystole.4,7 It is not unreasonable to suspect many of our asystolic patients are not receiving indicated treatments, including defibrillation.
Point-of-care ultrasound represents the next frontier in improving prehospital care in many ways, but the treatment of cardiac arrest perhaps has the most to gain from its adoption. We are rapidly approaching the point where we are maximizing our existing resources and methods. To continue to improve, we must be open-minded and willing to examine new diagnostics and treatments so we can give our patients the care they deserve.
1. Argula RG, Negi SI, Banchs J, Yusuf SW. Role of a 12-lead electrocardiogram in the diagnosis of cardiac tamponade as diagnosed by transthoracic echocardiography in patients with malignant pericardial effusion. Clin Cardiol, 2015 Mar; 38(3): 139–44.
2. Tasci O, Hatipoglu ON, Cagli B, Ermis V. Sonography of the chest using linear-array versus sector transducers: Correlation with auscultation, chest radiography, and computed tomography. J Clin Ultrasound, 2016 Jul 8; 44(6): 383–9.
3. American Heart Association. 2015 Guidelines for CPR & ECC, https://eccguidelines.heart.org.
4. Breitkreutz R, Price S, Steiger HV, et al.; Emergency Ultrasound Working Group of the Johann Wolfgang Goethe-University Hospital, Frankfurt am Main. Focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients: a prospective trial. Resuscitation, 2010 Nov; 81(11): 1,527–33.
5. Hess EP, Campbell RL, White RD. Epidemiology, trends, and outcome of out-of-hospital cardiac arrest of non-cardiac origin. Resuscitation, 2007 Feb; 72(2): 200–6.
6. Sharifi M, Berger J, Beeston P, et al.; “PEAPETT” investigators. Pulseless electrical activity in pulmonary embolism treated with thrombolysis (from the “PEAPETT” study). Am J Emerg Med, 2016 Oct; 34(10): 1,963–7.
7. Gaspari R, Weekes A, Adhikari S, et al. Emergency department point-of-care ultrasound in out-of-hospital and in-ED cardiac arrest. Resuscitation, 2016 Dec; 109: 33–9.
Branden Miesemer, NRP, FP-C, is a flight paramedic in the Midwestern United States and an adjunct paramedicine instructor for several local colleges. He is an advocate for leveraging technology and social media to provide low-cost, cutting-edge medical education and training. Follow him online at EMSPOCUS.com, Facebook.com/emspocus and on Twitter at @emspocus.