a b s t r a c t

Introduction: Cardiac arrest management primarily focuses on optimal chest compressions and early defibrilla- tion for shockable cardiac rhythms. Non-Shockable rhythms such as Pulseless electrical activity and asystole present challenges in management. Point-of-care ultrasound in cardiac arrest is promising. Objectives: This review provides a focused assessment of POCUS in cardiac arrest, with an overview of transtho- racic (TTE) and Transesophageal echocardiogram , uses in arrest, and literature support.

Discussion: Cardiac arrest can be distinguished between shockable and Non-shockable rhythms, with manage- ment varying based on the rhythm. POCUS provides a diagnostic and prognostic tool in the emergency depart- ment (ED), which may improve accuracy in clinical decision-making. Several protocols incorporate POCUS based on different cardiac views. TTE includes Parasternal long axis, Parasternal short axis, Apical 4-chamber, and subxiphoid views, which may be used in cardiac arrest for diagnosis of underlying cause and potential prog- nostication. TEE is conducted by inserting the probe into the esophagus of intubated patients, with several studies evaluating its use in cardiac arrest. It is associated with few adverse effects, while allowing continued compres- sions (and evaluation of those compressions) and not interrupting resuscitation efforts.

Conclusions: POCUS is a valuable diagnostic and prognostic tool in cardiac arrest, with recent literature supporting its Diagnostic ability. TTE can guide resuscitation efforts dependent on the rhythm, though TTE should not inter- rupt other resuscitation measures. TEE can be useful during arrest, but further studies based in the ED are needed.

Introduction

Cardiac arrest is an emergent condition requiring immediate man- agement that is frequently encountered by emergency physicians. Ad- vanced Cardiac Life Support (ACLS) and Basic Life Support (BLS) measures focus on optimal chest compressions and Early defibrillation for shockable cardiac rhythms [1-3]. The prevalence of pulseless electri- cal activity (PEA) and asystole present challenges in management. Rath- er than treating the underlying rhythm, such as in Ventricular tachycardia and ventricular fibrillation (VF), PEA and asystole management focuses on the underlying cause. Conditions such as

? All authors contributed to the development of this review. BL and AK completed the literature review and primary writing. SA and KM completed editing and gathered images for the review. All authors evaluated the final review before submission.

* Corresponding author.

E-mail addresses: [email protected] (B. Long), [email protected] (S. Alerhand).

Tension pneumothorax, hypoxemia, hypovolemia, cardiac tamponade, and pulmonary embolism (PE) may be treatable if appropriately diag- nosed, though treatment is often invasive [1,3-5]. Despite the potential to address the underlying cause, outcomes can be poor in non- shockable rhythms [6].

Point-of-care ultrasound provides physicians a diagnostic and prognostic tool, especially in cardiac arrest where physical exami- nation is not always accurate [7-9]. POCUS may increase accuracy and confidence in clinical decision making for several emergent conditions, including cardiac arrest, and this review focuses on POCUS for cardiac arrest [1-3,10-27]. Recent literature has evaluated the use of Cardiac PoCUS in shockable and Non-shockable rhythms during resuscitation [13-26]. It is feasible for trained providers to obtain cardiac POCUS im- ages during resuscitation while not interfering with resuscitation mea- sures, and a consensus statement from the American Society of Echocardiography and American College of Emergency Physicians states POCUS “has become a functional tool to expedite the diagnostic evalua- tion of the patient at the bedside and to initiate emergent treatment and

https://doi.org/10.1016/j.ajem.2017.12.031 0735-6757/

triage decisions by the emergency physician.” [27] Several protocols are in existence for POCUS use in different cardiac rhythms and cardiac ar- rest [12,27-29]. These protocols and images may predict prognostic out- come, guide resuscitation, and identify treatable causes of cardiac arrest.

Methods

This is a narrative review of cardiac POCUS for shockable and non- shockable rhythms, with discussion of its use in VF/VT, PEA, and asystole. Authors conducted a literature review of Pubmed, EBSCO, and Google Scholar for topics including ultrasound or POCUS in cardiac arrest, VF/VT, PEA, and asystole, with search date from 1980 to Decem- ber 2017. Search terms included “cardiac arrest”, “ventricular tachycar- dia”, “ventricular fibrillation”, “echocardiogram”, “echocardiography”, “ultrasound”, “point of care”, “POCUS”, “asystole”, “pulseless”, “pulseless electrical activity”, “shockable”, “non-shockable”, “prognosis”, “diagno- sis”, “transthoracic”, “transesophageal”. Authors included studies evalu- ating US in cardiac arrest for diagnosis, prognosis, and protocol description. Case reports, case controls, cohort studies, randomized clin- ical trials, and reviews were included. Authors decided on inclusion of studies through consensus.

Discussion

Before discussion of the literature concerning protocols and out- comes, this review will discuss the goals of POCUS, transducer selection, and view orientation. One described objective of POCUS in cardiac arrest is to identify potentially treatable causes such as pericardial effusion resulting in tamponade, hypovolemia, right heart strain seen in pulmo- nary embolism, Proximal aortic dissection, septal or free wall rupture, acute severe valvular dysfunction, and pneumothorax [1-3,14,15, 19-23,27]. POCUS also allows the ability to prognosticate through eval- uation of Cardiac activity during arrest (i.e. organized cardiac activity, VF, cardiac standstill) [20-23,27].

POCUS views for Transthoracic echocardiography

The transducer commonly used in Transthoracic echocardiography is the low-frequency phased array transducer [15,27,30-32]. Whether the probe marker is on the left or the right of the screen based on the selected machine setting, the most important consider- ation is that the visualized image on the screen be oriented properly. For instance, the left ventricle should lie on the left side of the screen for the parasternal long axis view and on the right side of the screen for the subxiphoid view. Primary cardiac views include parasternal long axis (PSLA) (Video 1), parasternal short axis (PSSA) (Video 2), api- cal 4-chamber (A4C) (Video 3), and subxiphoid (SX) (Video 4).

POCUS in cardiac arrest

Detection of cardiac output through palpation of central pulses and other measures is not necessarily reliable, with up to 45% of healthcare providers unable to accurately detect central pulse during arrest [7-9]. This can result in prolonged periods of no compressions or inappropri- ate cessation of resuscitation. Arterial line placement is a potential solu- tion, but this can be technically difficult during cardiac arrest, especially in settings with limited resources or few providers. POCUS can be used to identify cardiac motion and contractile activity during arrest, as well as diagnose treatable conditions (tamponade, myocardial infarction, pulmonary embolism, pneumothorax, and hypovolemia) [14,15,20,21, 30-34]. The remainder of this review will evaluate TTE and transesoph- ageal echocardiogram (TEE) in cardiac arrest.

Cardiac tamponade resulting from pericardial effusion is a deadly con- dition for which POCUS can provide the diagnosis given the appropriate clinical picture (Videos 5 and 6, Fig. 1). POCUS will reveal a pericardial ef- fusion with diastolic Right ventricular collapse best seen in the parasternal

long or subxiphoid view [27,30-35]. POCUS is highly accurate for diagno- sis of pericardial effusion, with sensitivity over 96% and specificity over 98% [17,27,28,35]. It provides a reliable means of diagnosis by demon- strating the pericardial effusion, right atrial systolic collapse (the earliest sign), and right ventricular diastolic collapse [27,30-34,36-38]. In the parasternal long axis view, collapse of the right ventricle with diastole has been likened to an “invisible little man bouncing on a trampoline.” POCUS also assists in pericardiocentesis, with success rates N 90% and de- creased risk of complications with its use [39,40].

Several pitfalls are present in diagnosing pericardial effusion with POCUS. Fluid is usually anechoic and circumferential, though it may demonstrate complex echotexture if containing fibrin, clot, or pus, and may be regional in location [27,41]. Pericardial effusions typically track anterior to the descending aorta on the PSLA view, while pleural effu- sions will not. Epicardial fat can be isoechoic and often has a stippled ap- pearance, similar in echotexture to subcutaneous fat, with bright echogenic lines within the epicardial fat. Mistaking epicardial fat or a pleural effusion for pericardial effusion may result in harm if the physi- cian attempts pericardiocentesis [37-41].

Hypovolemia can be a cause of cardiac arrest, most commonly PEA [4,15,27]. POCUS may demonstrate a small, underfilled left ventricle and right ventricle on subxiphoid and long axis views of the heart [15, 42-49]. The left ventricle may be hyperdynamic, with obliteration of the LV volume at end of systole. One pitfall to avoid is improper orienta- tion and angulation of the probe that will “foreshorten” the left ventri- cle. Doing so underestimates the largest diameter of the ventricle and overestimates the ventricle’s contractility. Additionally, literature is controversial to begin with regarding POCUS reliability for predicting fluid responsiveness by Inferior vena cava collapsibility [27, 42-55]. It is even less accurate with positive-pressure ventilation, lack of cardiac contractility, chest compressions, venous pooling, and other factors that may affect IVC size and collapsibility in unpredictable ways. Myocardial infarction is a significant cause of cardiac arrest, often due to acute dysrhythmia, ventricular dysfunction, or myocardial tissue rupture [15,27,55]. If the patient is in arrest despite visualization of some cardiac contractility, POCUS can evaluate for regional wall motion abnormalities and for complications such as free wall or papillary mus- cle rupture. regional wall motion abnormalities on POCUS are not defin- itive for diagnosis of coronary artery disease as the cause of cardiac arrest, though these findings may suggest implementing therapeutic in- terventions such as immediate revascularization [15,27,30-34]. That being said, wall abnormalities may be difficult to identify within 10 s and should not supersede typical resuscitation measures. One common pitfall is mistaking the papillary muscles themselves for the ventricular wall, which overestimates contractility. In addition, the ventricular wall thickness should be examined when evaluating for regional wall

Fig. 1. PSLA view of Pericardial tamponade. The arrows point to the diastolic collapse of the right ventricle often likened to an “invisible little man bouncing on a trampoline.”

abnormalities, because even dead myocardium that does not contract will be dragged along during contraction by a healthier neighboring wall. POCUS for rapid diagnosis of free wall rupture is important, as this may result in immediate tamponade. Other complications of MI in- cluding ventricular septal defect, Mitral regurgitation, Right ventricular infarction, or intracardiac thrombus can also be readily diagnosed by POCUS [15,27,30-34].

Pulmonary embolism (PE) that occludes significant pulmonary vas- culature may account for over 5% of cardiac arrests in the U.S., with PEA being the diagnostic rhythm in 63% and asystole in 32% of cases [5,27,56, 57]. Thrombolytic use in a patient in cardiac arrest due to PE may be life- saving, and rapid diagnosis is thus essential. The A4C view can demon- strate right ventricular dilatation (size equal to or greater than the left ventricle) or thrombus in the right heart. Paradoxical septal motion in systole is suggestive of right-sided pressure overload, whereas septal flattening only in diastole is more consistent with volume overload of the right heart. Right ventricular mid free wall akinesia with normal apical cardiac motion (known as McConnell’s sign) can assist with diagnosis and may demonstrate higher specificity than several other POCUS findings [5,17,27,57,58]. Moreover, the parasternal short axis view can identify a D-shaped LV during systole, and in the parasternal long axis view, the RV will appear larger than normal (Video 7) [27, 58]. In particular, thrombus in the RV is associated with worse outcomes [27,57,58].

Tension pneumothorax may present with cardiac arrest, and POCUS of the lungs will demonstrate absence of “Lung sliding” between the vis- ceral and parietal pleura, with a sensitivity over 92% and specificity over 99% (Videos 8 and 9) [59-62]. Other signs of tension pneumothorax, such as absent breath sounds and elevated jugular venous pressure, are difficult to accurately assess during resuscitation [59-62]. The trans- ducer most useful for this diagnosis is the high-frequency linear trans- ducer. The most common location to assess for lung sliding and absence of a Lung point includes the 4th-5th intercostal spaces along the midclavicular line. In a Supine patient, this area is assumed to con- tain the most superior aspect of the pleura, where the gravitationally dependent air is most likely to track [27,30-34].

The literature behind POCUS in cardiac arrest supports its ability as a diagnostic and prognostic tool [20-27,63,64]. Cardiac arrest due to pulseless electrical activity and asystole is associated with poor out- comes [6], and the decision to cease resuscitation can be difficult. Sever- al studies and meta-analyses have evaluated POCUS use for prognostication. A meta-analysis in 2012 by Blyth et al. included 568 pa- tients, finding a specificity of 80% to predict ROSC when spontaneous cardiac motion is present [63]. A meta-analysis released in 2017 by Tsou et al. included 15 studies and 1695 patients, finding a sensitivity of 95% and specificity of 80% to predict ROSC with cardiac motion pres- ent, and sensitivity 90% and specificity 78% to predict survival to hospi- tal admission [20]. If cardiac motion was absent, negative likelihood ratio was 0.06 for ROSC and 0.13 for Survival to hospital admission [20]. Interestingly, a recent study conducted at three academic medical centers demonstrated that when prompted with 20-second clips, there was significant variability in physician interpretation of whether the clip demonstrated cardiac standstill (a = 0.47, n = 127) [65]. This lack of agreement persisted across specialties, self-reported training levels, and self-reported ultrasonography expertise. However, most re- spondents in this study report “basic skill level” with POCUS, a potential weakness in generalizability to centers with experienced ultrasonogra- phers. The study was non-randomized, with a convenience sample of patients [65]. This differs from other literature evaluating physician agreement on cardiac standstill. Gaspari et al. reports higher rate of agreement on interpretation (0.63) [21]. These studies suggest POCUS possesses a role in cardiac arrest, though agreement on what constitutes cardiac standstill as a component for termination of resuscitation re- mains indeterminate (Videos 10 and 11). Reaching such a consensus on definition of cardiac standstill would assist research of POCUS in car-

diac arrest and perhaps standardize its use in these situations.

The REASON trial was a multicenter, non-randomized, prospective, protocol-driven observational study that evaluated the use of POCUS at the beginning and end of resuscitation. Primary outcome was survival to hospital admission, and secondary outcome was survival to hospital discharge and ROSC [21]. Patients were included if they suffered non- traumatic, out-of-hospital arrest or in-ED arrest with PEA or asystole, with 793 patients initially enrolled. Of these patients, 208 survived ini- tial resuscitation, 114 survived to hospital admission, and 13 survived to hospital discharge. One third of the 793 patients, or 263 patients, demonstrated cardiac activity on initial POCUS, with 54% of PEA patients having cardiac activity on initial POCUS. Of these patients, 134 achieved ROSC (51%), 76 survived to admission (28.9%), and 10 survived to dis- charge (3.8%). Five hundred thirty patients had no cardiac activity on initial POCUS, and 76 achieved ROSC (14.3%), 38 survived to admission (7.2%), and 3 survived to discharge (0.6%). Authors state cardiac activity on POCUS was associated with Survival to admission (OR 3.6) and sur- vival to discharge (OR 5.7), while no cardiac activity was associated with non-survival (0.6% survived to discharge). POCUS did identify peri- cardial effusion in 34 patients (the group undergoing pericardiocentesis demonstrated slightly improved survival at 15.4%, though no true con- trol group was present) and PE in 15 patients (6.7% survival) [21].

One approach for use of TTE in PEA or asystole was described in 2008, though this is a description of one example protocol, with no sta- tistical analysis [12]. The C.A.U.S.E. protocol evaluates potential etiolo- gies of arrest with a four-chamber view of the heart and anteromedial views of the lung and pleura at the second intercostal space at the midclavicular line bilaterally, following standard resuscitation measures including compressions, airway management, and placement of moni- tors and intravenous access [12]. In this protocol, the 2.5-5.0 phased array transducer is recommended to avoid the need for switching trans- ducers. The four-chamber view can be obtained in the subcostal, parasternal, or apical views and is the first recommended view. Authors recommend using the subcostal view to avoid interruption of chest compressions, with apical or parasternal views during Pulse checks. Pneumothorax can then be assessed for at the second intercostal space. Once monitors are connected to the patient, the cause of arrest can be divided into shockable and non-shockable rhythms, with shock- able rhythms treated with defibrillation and non-shockable rhythms undergoing further evaluation with POCUS based on the protocol. If car- diac and lung views are negative, then alternate causes of arrest should be considered [12]. This protocol was completed by experienced ultra- sonographers, and the reported study provides a description of the pro- tocol, with no reported statistical analysis [12].

Another algorithm utilizes ECG and POCUS to evaluate PEA cardiac arrest [66]. Step one is to determine QRS width, with delineation of narrow (b 120 ms) versus wide (N 120 ms). Narrow QRS complexes are typically associated with mechanical pathology such as right ven- tricular inflow or outflow obstruction, including cardiac tamponade, tension pneumothorax, mechanical hyperinflation, pulmonary embo- lism, or acute myocardial infarction with rupture. POCUS evaluation will assist in further differentiating these causes: a collapsed RV suggests inflow obstruction while a dilated RV suggests outflow ob- struction. wide QRS complexes are associated with sodium-channel blocker toxicity, Severe hyperkalemia, agonal rhythm, or acute myocar- dial infarction with pump failure. In these etiologies, POCUS will often display a hypokinetic or akinetic LV or true PEA. However, this requires further validation and is not for use in trauma [66].

POCUS in PEA is also useful in differentiating pseudo PEA from true PEA. In pseudo PEA, the pulse generated is weaker and unable to be pal- pated during a pulse check. In true PEA, there is complete electrome- chanical dissociation, meaning that electrical activation is unable to produce any muscle contraction. Pseudo PEA often has a reversible cause and if identified and corrected, patients have a better prognosis than true PEA from electromechanical dissociation [12,20-27,66].

The most experienced physician with POCUS should be the one who conducts the examination, and by no means should a transthoracic

POCUS assessment hamper other resuscitation efforts such as compres- sions or defibrillations. During pulse checks, POCUS should be limited to at most 10 s [1-3,15,20-22,27]. Two studies released in 2017 suggest POCUS in cardiac arrest is associated with delays in compressions [67, 68]. One study demonstrates a significant increase in time of pulse check in which POCUS was conducted [67]. In patients not undergoing POCUS during pulse check and Rhythm analysis, mean duration of pulse check was 13 s (95% CI, 12-15 s), whereas those undergoing POCUS demonstrated a mean duration of pulse check 21 s (95% CI, 18-24 s) [67]. The second prospective cohort study including 24 pa- tients suggests a median compression pause of 17 s with POCUS versus 11 s without, though US fellowship trained physicians trended towards shorter compression pauses by 4 s when compared to those not fellow- ship trained [68]. POCUS should only be used as an adjunct in the assess- ment and management of patients in cardiac arrest.

Transesophageal echocardiogram in cardiac arrest

TTE may demonstrate poor Image quality due to large body habitus or gastric insufflation of air, and images of the heart can be difficult to obtain simultaneously during compressions. TEE provides several bene- fits over TTE in that it can provide high-resolution images not affected by body habitus, subcutaneous air, or lung disease, as the transducer is placed into the esophagus near the heart [69-75]. TEE provides constant visualization of the heart during compressions and procedures such as cardioversion, as it remains in place throughout resuscitation. It provides live feedback on cardiac contractility and the Quality of chest compressions, while also assessing for whether the compressions them- selves are adequately located to avoid obstruction of the left ventricular outflow tract [69-75]. TEE also allows improved visualization of effu- sion, tamponade physiology, Cardiac rupture, pulmonary embolism, ventricular fibrillation, asystole, valvular pathology, thrombi, and cardi- ac masses. Limitations of TEE include increased cost, further training required to obtain images, need for gastric decompression (air present in the gastric area will obstruct images), and the presence of mechanical or prosthetic interference and shadowing (though these also interfere in TTE) [69-75]. Most patients undergoing TEE in the ED are intubated. In the setting of extraglottic device for respiratory support, TEE is not compatible.

TEE is performed by inserting the probe into the esophagus. Laryn-

goscopy is not required for placement, though if the patient is already intubated, the probe is easily directed into the esophagus. The controls and the handle allow the physician to manipulate the POCUS for an array of visual cardiac orientations. The maximal penetrating depth is 19-20 cm, with high frequency [69-75]. TEE is relatively safe. However, since the transducer is most commonly passed blindly, pharyngeal and esophageal laceration or hematoma can occur [74-79]. The most dan- gerous complication is esophageal perforation, with incidence 0.03% [74-77]. Potential contraindications include perforated viscus, esopha- gectomy, and Upper gastrointestinal bleeding [70-79].

Views include the mid-esophageal 4 chamber view, the midesophageal long-axis view, and the transgastric view (Video 12). The mid-esophageal 4 chamber view, similar to the TTE A4C view, is easily acquired by even inexperienced users, as it only involves probe insertion to the mid-esophageal level with 0 degrees of omniplane. This view is recommended during cardiac arrest. After introduction of the probe into the esophagus, the heart will come to view with all 4 chambers at 0-20? multiplane. This view provides evaluation of RV and LV function and size, as well as assessment of perfusing rhythm. The midesophageal long-axis view, similar to the TTE PSLA view, utilizes the same probe location as the mid-esophageal 4 chamber view, but with multiplane set to 110-160?. This view allows assessment of LV function and compression adequacy and location. The transgastric short axis view utilizes the multiplane set to 0?, followed by probe ad- vancement into the stomach and anteflexion of the probe. It is similar to TTE PSSA view.

Several studies have evaluated the use of TEE in cardiac arrest. A study in 1997 evaluated 48 patients (28 in-hospital and 20 out-of- hospital cardiac arrests), with 4 surviving to discharge [71]. TEE demon- strated a 93% sensitivity, 50% specificity, and 87% positive predictive value for diagnosing cause of arrest. Major therapeutic decisions were based on TEE findings in 31% of patients [71]. Blaivas et al. described 6 illustrative cases in which TEE was utilized after TTE, which improved management: a contracting heart with low ejection fraction when TTE suggested asystole, inadequate chest Compression quality, a thrombus in the right atrium/right ventricle, a PICC line inserted too deeply and striking the RA, aortic dissection (apparent asystole on TTE), and chron- ic RV dilation (versus an acute process suggested by TTE) [72]. Manage- ment was altered in these cases based on the specific diagnoses obtained from TEE. However, TEE was performed by one physician in all six cases, and it is unclear if Mortality benefit would be observed if TEE is applied to larger populations in cardiac arrest. The series was meant to illustrate the potential utility of TEE. A 2016 study evaluated 54 cases with TEE, performed by 12 different physicians [73]. All pa- tients in this study were intubated. TEE influenced diagnosis in 78% of cases and management in 67% of cases [73].

The American College of Emergency Physicians (ACEP) released a clinical policy on TEE in cardiac arrest in 2017 [74]. This policy provided information on qualifications and responsibilities of the TEE performer, individual TEE examination specifications, documentation, equipment specifications, and quality control [74]. The ACEP clinical policy recom- mends the following for competency standards: 1) minimum of 2-4h of TEE specific training or education, 2) performed at least 10 proctored TEE examinations in Live patients and Simulation models, and 3) com- pleted a standardized assessment by a credentialed TEE provider.

Conclusions

POCUS in cardiac arrest is an excellent adjunctive tool in the hands of experienced providers. Although there are no current studies showing improvement in mortality, echocardiography is useful for both diagnos- tic and prognostic purposes in cardiac arrest. As emergency physicians are already trained in POCUS, addition of more advanced echocardiogra- phy training is a useful supplement. Both TTE and TEE have their place in cardiac arrest. Using TTE, clinicians can evaluate for potentially Reversible causes of cardiac arrest. With insertion of the TEE probe in intubated patients, clinicians can more closely elucidate any reversible causes of arrest and evaluate the quality of chest compressions, while minimizing interruption of compressions. Further studies evaluating echocardiography as a tool in cardiac arrest are warranted. As technological capabilities advance, there will be introduction of echo- cardiography probes that are smaller, more versatile, and with greater capabilities than those currently available in the market. Trained physi- cians will be better able to use these technological advances to poten- tially improve patient care.

Supplementary data to this article can be found online at https://doi. org/10.1016/j.ajem.2017.12.031.

Conflicts of interest

None.

Acknowledgements

This manuscript did not utilize any grants, and it has not been pre- sented in abstract form. This clinical review has not been published, it is not under consideration for publication elsewhere, its publication is approved by all authors and tacitly or explicitly by the responsible au- thorities where the work was carried out, and that, if accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder. This review does not reflect the views or opinions of

the U.S. government, Department of Defense or its Components, U.S. Ar- my, U.S. Air Force, or SAUSHEC EM Residency Program.

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