Resus: Resuscitative TEE: Background and Evidence
Introduction
Point of care ultrasound (POCUS) is a core tool in the emergency department and is useful in rapidly evaluating critical patients. The use of transthoracic echocardiography (TTE) in cardiac arrests has been shown to be useful in clarifying patient prognosis, identifying reversible pathology, and guiding ongoing resuscitation efforts (1). However, there are challenges associated with TTE that limit its utility and can even lead to suboptimal resuscitation. Limitations of TTE in resuscitation include potential difficulty in acquiring views in the limited time frame of pulse checks as well as challenges associated with obtaining adequate sonographic windows through the chest wall (2). Transesophageal echocardiography (TEE) does not have these constraints, allowing for faster acquisition of images during pulse checks and better visualization of relevant cardiovascular anatomy. As such, it has been increasingly used to overcome some of these limitations and provide additional information to support resuscitation.
Methods
Comprehensive TEE is an advanced imaging modality in cardiology. It involves the capturing of 28 individual views and is outside of the scope of emergency medicine or critical care (3). However, it has been shown that non-cardiologists can be successfully taught to acquire four useful TEE views within the course of a single-day training session (4). This focused TTE exam for critical care includes the mid-esophageal 4 chamber, mid-esophageal long axis, trans-gastric short axis, and bicaval views. Each corresponds to rough TTE view equivalents and can be used to answer specific clinical questions relevant to the resuscitation effort (Table 1). This focused exam, when conducted by trained practitioners, has been shown to have sensitivity, specificity, and accuracy in determining the primary diagnosis in critically ill patients. (5).
Table 1. TEE views with their analogous TTE views and specific clinical applications (1)
Benefits of resuscitative TEE
The primary benefits of intra-arrest TEE over TTE include a reduction in pauses during pulse checks in CPR, ability to monitor the heart in real-time during compressions to improve CPR quality, and increased ability to identify underlying pathology responsible for the arrest. Each is benefit is explored below.
Reducing time required for pulse checks - The strongest evidence in support of the preferential usage of TEE over TTE in resuscitation is the demonstrated difference in time required for pulse checks in CPR. The American Heart Association (AHA) recommends that pauses in compressions last less than 10 seconds for the maintenance of high-quality CPR (6). TTE evaluation during pulse checks has been associated with longer time off the chest and reduced chest compression fractions. A prospective cohort study out of the University of Maryland in 2017 monitoring 123 pulse checks in 23 patients reported a mean duration of checks with POCUS TTE to be 21.0s (95% CI 18-24s), compared with 13.0s (95% CI 12-15s) when conducted without TTE (7). Another prospective cohort study out of Highland Hospital and UCSF in 2018 documented 110 pulse checks in 24 patients and yielded similar results, reporting the median duration of pulse check to be 6.4 seconds (95% CI 2.1-10.8s) longer with POCUS than without (8). A 2019 prospective cohort study out of University of Utah compared TTE directly to TEE, monitoring 139 pulse checks across 25 cardiac arrest patients at an academic tertiary care facility. Checks with TEE were shown to take significantly less time (mean pause of 9 seconds (95% CI 8-14 seconds) compared to 19 seconds (95% CI 16-22 seconds) with TTE. (9.). This makes sense, as adequate TEE views can be acquired without ceasing compressions, meaning ultrasonic evaluation should not contribute to time off the chest.
Ensuring the effectiveness of CPR - Another unique advantage of using TEE is that it allows for real-time visualization of the heart during CPR, allowing for determination of the area of maximal compression (AMC) and appropriate adjustment as needed. For maximum effectiveness, the AMC should be directly over the left ventricle of the heart. However, anatomical variation and the imprecision of administering compressions over the lower part of the sternum leaves significant room for suboptimal mechanics. This was borne out in a 2009 prospective study of 34 patients with nontraumatic cardiac arrest conducted out of Yonsei University Wonju, which found the AMC was over the aorta in 59% of patients receiving compressions and over the left ventricular outflow tract (LVOT) in another 41% of patients. All patients were found to have significant narrowing of the LVOT with each compression (10). While further study of the effect on hemodynamics and patient outcomes is needed, the ability to observe and modify the positioning of compressions during resuscitation offers a possibility to provide higher-quality CPR with TEE monitoring.
Drawbacks to TEE
The primary drawbacks to resuscitative TEE are increased training requirements over TTE and the potential for complications that arise with a more invasive procedure.
Training - While training and skilled oversight are not available in many centers, focused education such as the program described by Arntfield et al. lowers the barrier to access (4).
Complications - TEE is more invasive and therefore more prone to complications than TTE, but it is generally considered a safe procedure. Complication rates for diagnostic and intraoperative TEE are low, with reports ranging from 0.8%-2.8%. (11). It is noted, however, that there is not published data on complication rates specifically for intra-arrest TEE, and differences in operators and circumstances may affect this.
Conclusions
While significant research including larger multicenter studies, outcome analysis, and specific complication rates is still needed, there is encouraging evidence for possible benefit from the regular use of resuscitative TEE in cardiac arrest. Given the relatively low barrier to training practitioners to proficiency and the low complication rate, academic centers should continue to expand their capabilities with this modality to better understand its potential use.
AUTHORED BY: CHRIS SCHLECHTER, MS4 CWRU SOM
FACULTY EDITING BY: COLIN MCCLOSKEY, MD
References
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