The Pre-brief
Since the beginning of the COVID-19 pandemic, we’ve seen a tremendous uptick in the number of thromboembolic emergencies. It’s such an incredible prothrombotic disease, which has allowed me to hone in and practice my right heart echo skills, especially in our cardiac arrests. In this post, I wanted to talk about RV assessment during the management of cardiac arrest.
The Challenge of RV Size
Signs of a potential pulmonary embolism on a non-arresting heart include dilated RV, McConnell’s sign, bowing of the interventricular septum, and hypokinesis of the RV free-wall. But when it comes to intra-arrest management, RV size has become quite a mystery. The conventional theory would lead you to believe that in the arresting heart, a dilated RV means potential PE or cor pulmonale, just like in the non-arresting heart. However, some thought that the RV size might be a manifestation of pulmonary embolism, or it may just be normal arresting physiology of the heart.
After doing an extensive literature review, it’s quite surprising that there is such a lack of research on this topic. Nevertheless,, some data is coming from porcine models that may help us understand this mystery.
What is CASA?
First, let’s look at the CASA (Cardiac Arrest Sonographic Assessment) exam, the popular intra-arrest TTE exam that helps minimize interruptions of chest compressions, and its principal purpose is to evaluate for potentially reversible causes of cardiac arrest. The exam is a three-step protocol that looks for:
- Pericardial effusion
- Right heart strain
- Cardiac activity
We will focus on the right heart strain for this discussion. The cardiac probe is placed in the subxiphoid position just before a chest compressions pause during the rhythm/pulse check.1 Essentially, the right heart assessment looks for RV dilation and bowing of the interventricular septum, which may indicate a PE, making up 4.0-7.6 percent of cardiac arrests. The REASON Trial looked at using ultrasound to assess patients presenting in PEA. It showed that a subset of patients (15/793) evaluated for PEA had RV strain suspected to be a PE and were given thrombolytics had a survival rate of 6.7% vs. 3.8% for other participants in the trial. So logically, if there is a patient suspected of having a PE and in arrest, there should be a consideration of using thrombolytics. 2
What is the Evidence?
But back to the question: does having a dilated right ventricle intra-arrest indicate a PE? There are a few studies that looked at porcine hearts intra-arrest. In two studies by Aagaard et al., they found that when they induced cardiac arrest on juvenile pigs through hypoxia, arrhythmia, or pulmonary embolism, all had dilated right ventricles. However, the pulmonary embolism pigs had a slightly larger dilation of 7-9mm. Physicians trained in basic focused echo could not identify the subtle changes less than 10mm, leading to a conclusion that echo assessment of a pig heart during arrest from various etiologies is not helpful. The authors’ findings indicate that right ventricle dilation may be inherent to cardiac arrest rather than being associated with specific arrest causes.3,4
What about human studies? I could only find one that looked at this question precisely. Comess et al. published a prospective observational study of consecutive patients (n=36) who were admitted with (n=20) or unexpectedly developed (n=16) sudden cardiac arrest of unknown cause were studied with transesophageal echocardiography during CPR. They found that in one sample of 25 patients with PEA, 14 had a significantly enlarged RV. Still, PE could only be confirmed in nine cases by either direct visualization with TEE or autopsy.2
The Debrief
So, what to do with this information? Am I reaching for the tPA when I see right heart strain intra-arrest? Ultrasound is merely a tool. When deciding if right heart strain patterns should lead you to consider using intra-arrest tPA, there needs to be a reasonably convincing pretest probability of a pulmonary embolism rather than relying on the ultrasound findings alone. A history of cancer, smoking, known thrombotic disease, pregnancy, recent surgery, inactivity/immobility, obesity, >60 years old, and now COVID is all risk factors for PE. A dilated RV during intra-arrest echo may be just an inherent part of cardiac physiology. Until we have more studies that look at this topic, RV dilation during cardiac arrest should be taken with a grain of salt.
References
- Gardner KF, Clattenburg EJ, Wroe P, Singh A, Mantuani D, Nagdev A. The Cardiac Arrest Sonographic Assessment (CASA) exam – A standardized approach to the use of ultrasound in PEA. Am J Emerg Med. 2018 Apr;36(4):729-731. doi: 10.1016/j.ajem.2017.08.052. Epub 2017 Aug 26. PMID: 28851499.
- Comess KA, DeRook FA, Russell ML, Tognazzi-Evans TA, Beach KW. The incidence of pulmonary embolism in unexplained sudden cardiac arrest with pulseless electrical activity. Am J Med. 2000 Oct 1;109(5):351-6. doi: 10.1016/s0002-9343(00)00511-8. PMID: 11020390.
- Aagaard R, Granfeldt A, Bøtker MT, Mygind-Klausen T, Kirkegaard H, Løfgren B. The Right Ventricle Is Dilated During Resuscitation From Cardiac Arrest Caused by Hypovolemia: A Porcine Ultrasound Study. Crit Care Med. 2017 Sep;45(9):e963-e970. doi: 10.1097/CCM.0000000000002464. PMID: 28430698.
- Aagaard R, Caap P, Hansson NC, Bøtker MT, Granfeldt A, Løfgren B. Detection of Pulmonary Embolism During Cardiac Arrest-Ultrasonographic Findings Should Be Interpreted With Caution. Crit Care Med. 2017 Jul;45(7):e695-e702. doi: 10.1097/CCM.0000000000002334. PMID: 28403120.
- Butts, Christine MD The Speed of Sound, Emergency Medicine News: June 2019 – Volume 41 – Issue 6 – p 30 doi: 10.1097/01.EEM.0000559983.36855.5f
