Patrick Ockerse, MD
James Fair, MD
Echocardiography can be useful during CPR for multiple reasons. It can help identify reversible causes of cardiac arrest and evaluate for meaningful cardiac activity during pulse checks. Bedside transthoracic echocardiography (TTE) can be challenging to perform during CPR as there are significant difficulties unique to performing TTE during chest compressions. The current AHA guidelines recommend limiting interruptions in chest compressions, ideally decreasing pulse checks to less than 10 seconds.1 This is a narrow window in which to obtain adequate transthoracic imaging. Performing TTE during CPR is further complicated by competition for space on the patient’s chest during the resuscitation. External compressions, manually or by device, limit the parasternal views and the placement of defibrillator pads can hinder the apical view. Transesophageal echocardiography (TEE) during CPR is superior to TTE as it does not require access to the patient’s chest, allowing easier acquisition of images during both chest compressions and pulse checks. If available, TEE should be used to guide resuscitation during cardiac arrest.
Although use of bedside ultrasound is becoming more common in critical care and resuscitation, TEE remains unfamiliar to many providers. However, TEE can be learned with minimal training and is well within the scope of practice of emergency physicians and resuscitationists.2 The probe is inserted in a similar fashion to an oral-gastric tube and should ideally be placed during a pause in chest compressions to avoid potential oropharyngeal and esophageal injury. While the probe is in the esophagus, the airway must be secured with an endotracheal tube to allow for ventilation. With minimal manipulation, a mid-esophageal 4 chamber view can be obtained by simply placing the probe down to a depth of approximately 14cm where it sits behind the left atrium.3 This provides a continuous and unobstructed cardiac view through the heart similar to the more familiar TTE apical 4 chamber view.
With the TEE probe in position, pulse checks can be performed faster and more accurately. Continuous visualization of the heart can rapidly identify cardiac standstill versus significant cardiac activity and decrease pulse checks to only a few seconds. This will limit drops in coronary perfusion pressure associated with longer pauses in compressions.4 TEE also provides the potential for improved accuracy of pulse checks as standard palpation has been demonstrated to often be inaccurate.5,6 A lack of palpable pulse with organized cardiac activity is often referred to as “pseudo-pulseless electrical activity (PEA)”. Pseudo-PEA may be better managed as a profound state of shock and hypoperfusion rather than with compressions only as it is not a true electromechanical dissociation like PEA.7 TEE is best suited to distinguish pseudo-PEA from true PEA because of the continuous internal monitoring of cardiac activity it allows.
TEE can also identify shockable rhythms during compressions before they are visible on a monitor. Accuracy in rhythm analysis during CPR is poor in part due to the misidentification of fine ventricular fibrillation as asystole.8 One study evaluating 100 out-of-hospital cardiac arrests, surprisingly showed that 35% of patients initially classified as asystole on ECG actually had cardiac contractility identified by echocardiography.9 Shockable rhythms like ventricular fibrillation and ventricular tachycardia can be identified by TEE,3 sometimes during compressions, so defibrillation can occur earlier than at the next pulse and rhythm check. Furthermore, TEE provides continuous monitoring during defibrillation which can reveal the presence of organized cardiac activity immediately after a shock is delivered.
In addition to its ability to assess rhythm, TEE can potentially improve the quality of chest compressions during CPR. Hand placement using external landmarks can result in maximal compression over the aorta rather than the ventricles of the heart. TEE can uniquely identify where maximal compression is occurring and allow for appropriate adjustments to be made.
Like TTE, TEE can also identify reversible causes of cardiac arrest including myocardial infarction by wall motion abnormality, cardiac tamponade, hypovolemia or shock, and pulmonary embolism.10 TEE can also assist with ECMO initiation by confirming arterial and venous cannulation if pursuing extra-corporeal cardiopulmonary resuscitation.11
It is easy to imagine the benefits of having visualization of the heart during CPR, yet the 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care give only mild endorsement, stating “ultrasound may be considered as an adjunct to standard patient evaluation.”1 This is likely due to the inherent difficulties of performing TTE during CPR. However, the use of TEE nullifies these issues and should be pursued when available due to the significant benefits. There are limitations to using TEE with CPR including equipment cost and availability, as well as the need for training. However, as the cost of this technology continues to decrease, there will be fewer barriers to the use of TEE with cardiac resuscitation and more providers will discover the significant benefits for themselves.