1.1

Towards Precision Medicine was a statement published by The United States National Research Council in 2011, to encourage the medical community to strive towards providing patient-centered care . Precision medicine describes a modern approach to medical practice where care is specifically tailored to patients to improve outcomes. In the acute care setting, applying technology to the patient’s bedside has been transformational in ushering in an era of precision medicine. This is exemplified by the emerging role of resuscitative transesophageal echocardiography (rTEE) in the care of patients with critical hemodynamic instability.

Though the definition varies, rTEE is fundamentally the application of TEE to assist with the diagnosis and management of critically unstable patients. RTEE occurs during the resuscitation of patients with cardiovascular collapse, undifferentiated shock states or cardiac arrest. According to the Resuscitative TEE Project, a multidisciplinary working-group collaborating to promote rTEE advancements, rTEE entails using TEE as a point-of-care modality to facilitate decision making and guide hemodynamic management in critically ill patients ( link: https://www.resuscitativetee.com/aboutresustee ). Point-of-care technology is applied to answer specific and often binary clinical questions. RTEE can reliably assess for the presence or absence of various clinical entities which can precipitate hemodynamic collapse. There is observational data demonstrating that rTEE can identify the etiology of cardiac arrest and directly influences management during CPR . In a systematic review by Hussein et al., rTEE was able to identify a reversible cause for cardiac arrest in 41 % of patients with undifferentiated in-hospital and out-of-hospital cardiac arrest . RTEE’s role in cardiac arrest management extends beyond determining the cause. RTEE guides high quality CPR by identifying the area of maximal compression (AMC), discerns shockable rhythms from those not amenable to defibrillation, and facilitates safe central venous access.

The landmark technique represents the standard of care for locating the site for chest compressions during CPR. A myriad of studies have shown that this technique is imprecise and inadvertently centers compressions over the LVOT, aortic valve, or non-cardiac structures, including the lung, in a sizable cohort of patients. Consequently, the AMC has emerged as a novel concept in CPR of potential significance. Using the mid-esophageal long axis (MELAX) view, the AMC can be identified in real-time. Using rTEE, the location of compressions can be redirected to prevent iatrogenic mechanical obstruction during CPR . When rTEE is used to monitor the AMC during chest compressions, the likelihood of achieving ROSC and ICU survival increases .

Accurate rhythm detection during CPR is crucial but often challenging. Pseudo-PEA ( organized myocardial contraction without a palpable pulse, often misclassified as true PEA ) may be impossible to discern from PEA without ultrasound because central pulses may remain absent. RTEE can assist with identifying pseudo-PEA by visualizing coordinated myocardial activity. Furthermore, rTEE can discriminate between fine ventricular fibrillation and asystole which enables prompt defibrillation . By improving the accuracy of rhythm detection, rTEE enhances CPR quality. Therefore, rTEE is an invaluable tool in the armamentarium of physicians who care for patients with cardiac arrest.

In the peri-arrest setting, rTEE can be used to elucidate the etiology of hemodynamic collapse in patients with undifferentiated shock. RV failure can be identified by numerous qualitative echocardiographic signs including left-ward interventricular septal deviation, RV dilation, RA enlargement, gross RV systolic dysfunction, tricuspid regurgitation and LV underfilling. The mid-esophageal 4-chamber view (ME4C) can be used to screen for McConnell’s sign, which has a 94 % specificity for pulmonary embolism (PE) . PE may also be diagnosed if clot-in-transit is identified, which can be seen on the mid-esophageal (ME) bicaval or ME4C views. The trans -gastric short axis (TG-SAX) view can be used to identify regional wall motion abnormalities (RWMA) suggestive of ischemia-mediated myocardial dysfunction, while global LV systolic dysfunction can be appreciated in several views. A hyperdynamic LV seen in the MELAX or TG-SAX views may suggest hypovolemic shock, and systolic anterior motion (SAM) of the anterior mitral valve leaflet with mitral regurgitation (MR) and evidence of flow acceleration across the LVOT may suggest dynamic LVOT obstruction, an underappreciated cause of critical hemodynamic instability. In addition, the TG-SAX and MELAX views can detect pericardial effusion with or without cardiac tamponade.

1.2

While the utility of TTE during CPR has been demonstrated, there are drawbacks which limit its use in this context. Obtaining parasternal views necessitates pausing chest compressions or delays chest compression resumption. Not surprisingly, the use of TTE during CPR has been shown to cause an increase in chest compression interruptions . Considering high-quality CPR is associated with better neurological outcomes in cardiac arrest, and since minimizing delays in chest compressions is a pillar of high-quality CPR, one can infer that delaying compressions to use TTE may exacerbate neurological hypoxic-ischemic injury. The subxiphoid view is the only transthoracic window rendered available without interrupting chest compressions. However, this view is challenging to obtain and provides limited information in isolation. Additionally, subcutaneous emphysema from sternal fractures, positive pressure ventilation (PPV), defibrillation pads, automated chest compression devices, wound dressings and obesity all impose barriers to acquiring interpretable TTE views. Unlike TEE which can provide real-time imaging, TTE images obtained during CPR are static. Finally, ergonomic challenges associated with TTE use during CPR arise as the echocardiographer competes to occupy space at the patient’s bedside.

1.3

Ultrasound is being applied in innovative ways to enhance resuscitation protocols. Point-of-care ultrasound resuscitation protocols adapt as new evidence and technology emerges. The original protocols correspond to when TTE was the modality of choice in resuscitation. The FATE protocol (Focus-Assessed Transthoracic Echocardiography) used five basic TTE views to systematically assess patients with critically hemodynamic instability. The extended-FATE protocol added six advanced views to screen for a broader range of pathologies [15]. Numerous critical care ultrasound credentialing pathways offer unique scanning protocols. The Focused Ultrasound in Intensive Care (FUSIC) HD protocol offered by the Intensive Care Society (ICS) uses TTE to assess for LVOT obstruction, fluid-responsiveness and evidence of elevated pulmonary artery pressure .

Since rTEE utilization in critical care is increasing, several rTEE scanning protocols have been published to guide its implementation. The American College of Emergency Physicians (ACEP) published guidelines for the use of rTEE in cardiac arrest . The guidelines advocate for the use of a real-time scanning technique to identify rhythm changes and to screen for cardiac activity. The scanning protocol is simple and requires three views including ME4C, MELAX and TG-SAX. The Resuscitative TEE Project published a four-view scanning protocol including the ME4C, MELAX, TG-SAX and ME bicaval views. Using these views, a prodigious amount of clinical information is obtained. To begin, the ME4C, MELAX and TG-SAX views are obtained to assess for the presence of effusion or tamponade while chest compressions ensue. The MELAX view is used during CPR to identify the AMC and to rule out LVOT or aortic valve compression. At the pulse and rhythm check, the ME4C view helps with rhythm detection. These views are used to assess gross LV function, regional wall motion abnormalities, RV function, valvular competence, volume status and volume responsiveness. The ME bicaval view is used to facilitate central venous access. Finally, various views can demonstrate cardiac standstill which may lead to termination of CPR.

2.1

The scope of rTEE differs from that of the Adult Comprehensive TEE Exam. The latter, in accordance with the 2013 American Society of Echocardiography (ASE) Guidelines, requires 28 views and several quantitative measurements . While comprehensive TEE is an indispensable tool used in the perioperative management of cardiac surgical patients, it is less suitable for resuscitation. Patients with profound hemodynamic instability, undifferentiated shock states or cardiac arrest are moribund. Consequently, various rTEE protocols have been developed to enable systematic, qualitative and timely echocardiographic assessment to guide resuscitation ( Table 1 ).

The Focused TEE (fTEE) protocol is used for patients with critical hemodynamic instability in the acute care setting or undergoing non-cardiac surgery . To conduct the fTEE exam, eight basic TEE views are required, and scanning modalities are limited to 2-dimensional echocardiography and color doppler. The eight views were determined by an expert panel and deemed sufficient to identify common etiologies responsible for critical hemodynamic instability . These views include the ME4C, mid-esophageal two chamber (ME2C), MELAX, ME bicaval, mid-esophageal RV inflow-outflow, mid-esophageal ascending aorta long axis, mid-esophageal descending aorta short axis and TG-SAX.

Alternatively, a protocol referred to as the rTEE protocol has gained popularity in the cardiac arrest, peri-arrest and trauma settings. This protocol entails sequential view acquisition as dictated by the 3 + 2 scanning protocol. The ME4C, MELAX and TGSAX views are acquired to answer five cardinal resuscitation questions– is there organized cardiac activity, what is the gross left ventricular function, what is the gross right ventricular function, what is the volume status and is there a pericardial effusion. Subsequently, the ME bicaval and ME descending aortic SAX views are obtained. The former can provide information regarding venous line placement, while the latter can assess the aortic isthmus region for evidence of dissection in trauma and for arterial cannulation during extra-corporeal CPR (eCPR) institution.

2.2

Many of the limitations inherent to TTE use during CPR are circumvented by using rTEE in its place ( Table 2 ). RTEE obviates the need to access the patient’s precordium, which promotes high quality CPR by reducing delays or pauses in compressions. TEE views are superior in quality and can be acquired proficiently with minimal training ^,. Factors which reduce TTE view quality do not impair TEE views. TEE confers the added advantage of continuous, real-time visualization of the heart. This allows rapid recognition of re-arrest, return of spontaneous circulation (ROSC), rhythm detection, and ongoing surveillance for the AMC. Resuscitation is a dynamic process and continuous evaluation via TEE enables proactive decision management.

2.3

3.1

Resuscitative transesophageal echocardiography (rTEE) provides reliable, high-quality cardiac imaging during arrest, enabling prompt recognition of reversible causes such as tamponade, pulmonary embolism (PE), hypovolemia, and aortic dissection. Multiple studies and systematic reviews have shown that intra-arrest TEE can identify reversible etiologies in up to 41 % of cases ^,. Compared with transthoracic echocardiography (TTE), TEE is less affected by patient habitus, ventilation, or chest compressions, allowing continuous imaging throughout cardiopulmonary resuscitation (CPR) ^,. TEE’s posterior vantage point also improves detection of posterior pericardial effusions, RV strain, and thrombus in proximal pulmonary arteries .

3.2

TEE adds value beyond ECG by differentiating true asystole from fine ventricular fibrillation and distinguishing pseudo-PEA (organized contractility without palpable pulse) from true electromechanical dissociation. In some series, TEE reclassified rhythms initially thought to be asystole into fine VF requiring immediate defibrillation ^,. Similarly, pseudo-PEA can be identified, which is associated with higher rates of ROSC and may warrant escalation of vasopressor or procedural therapy, rather than termination of efforts .

3.3

TEE provides continuous visualization of cardiac motion, offering superior accuracy compared to manual or TTE-based pulse checks. Studies have shown that TEE reduces CPR interruptions, with pulse checks averaging ∼9 s with TEE vs. 19 s with TTE ^,. The absence of myocardial activity (cardiac standstill) on TEE strongly predicts poor outcomes, while the presence of organized contraction correlates with higher likelihood of ROSC and survival ^,. Furthermore, recent work highlights prognostic significance of left ventricular outflow tract (LVOT) patency during compressions: persistent LVOT closure during CPR correlates with failed resuscitation, whereas LVOT opening is associated with ROSC . Collectively, these findings underscore the multifaceted diagnostic and prognostic utility of resuscitative TEE during cardiac arrest, summarized in Table 3 . Building upon these diagnostic and prognostic applications, the algorithm for implementing resuscitative TEE during cardiac arrest is illustrated in Fig. 1 .

Table 3

Applications of resuscitative TEE in cardiac arrest.

Domain	TEE Findings	Clinical Impact
Reversible causes	Pericardial effusion/tamponade; RV dilation ± thrombus (PE); hypovolemia (small, hyperdynamic LV); aortic dissection	Immediate targeted interventions (pericardiocentesis, thrombolysis, fluids, surgical repair)
Rhythm classification	Fine VF vs asystole; pseudo-PEA vs true standstill	Avoid missed defibrillation; tailor management (escalate vs terminate efforts)
Prognostication	Presence vs absence of myocardial activity; LVOT patency during CPR	Presence of motion predicts ROSC; persistent standstill predicts futility; LVOT opening linked to successful resuscitation
Pulse check accuracy	Continuous real-time visualization of cardiac motion	Reduced CPR interruptions (TEE ∼9s vs TTE ∼19s); more accurate confirmation of ROSC
CPR quality feedback	Area of maximal compression (AMC), LVOT obstruction	Optimize hand position, ensure effective forward flow

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