TTE

The purpose of this content is to introduce you, the critical care provider, to the basic and introductory techniques of bedside TTE. It should be noted that this is not an all inclusive TTE presentation, nor does it certify you to perform it. It is meant to be an awakening of your potential in delivering critical care, provide you insights into bedside echo and promote further study and skill enhancement. There are essentially four cardiac TTE views for bedside echo that are outlined here, starting with the apical 4 chamber view. This view has relevance to a wider patient population in anesthesia practice. While rescue TEE has shown to have benefit to intraoperative patients involved with cardiac problems or unresolved hemodynamic instability, TTE can rapidly provide valuable insight to the provider in clinical decisions. Information regarding the wall motion, gross valve anomalies, pericardial vs. pleural effusion are reliably obtained. These structures can be imaged and identified with relative ease by the critical care provider, but it's important that solid documentable scans should be performed and interpreted by those specifically trained in echocardiography.  These pericardial  views require a small footprint phased array probe with visual capabilities to image to about 10-20 cm. The traditional linear or curved probes are generally insufficient to create these views. There are a few different techniques described in literature such as the FATE protocol that stands for  Focussed Assessed Transthoracic Echo, part of the RUSH exam (rapid ultrasound for shock and hypotension). Specifically, the FATE exam has demonstrated useful information in 97% of critically ill patients. The particular protocol or algorithm used is not of importance. The impetus stems from quickly and effectively performing these series of ultrasound views to answer or rule out specific reasons for patients presentation. An example of this is specifically looking at systolic function of the left ventricle to assess for cardiogenic shock. Traditionally there are several views helpful in clinical TTE. These views help to assess discrete elements of cardiac function and having a focussed or primary question or goal in mind while performing the exam is recommended.. There are multiple other elements possible with these scans as well such as pressure calculations, however, for the acute care provider such as in anesthesia, these elements may be cumbersome and delay critical care interventions. The following sections will introduce you to the most prevalent TTE views worth knowing, and are associated with the FAST exam. They will describe the proper view, how to obtain it, and what it will be helpful in knowing.

A helpful hint for TTE scanning is to use small slow movements to correct your image. You'll find that body habitus, large inflated lungs and gross obesity will all work against you during the scan. Be patient, move slowly and optimize patient positioning and visual quality through the variety of settings on the machine. Practice on healthy specimens in optimal positions before challenging yourself in a critical scenario. 

And remember- your results MUST match the clinical scenario. You should not solely rely on echo, especially in your learning phases. 


Apical four chamber view: 

This is an extremely helpful view for all providers. Begin this scan by placing the probe into the region of the left anterior chest where the maximum cardiac vibrations or activity  can be felt with the non probe hand. This region is traditionally known as the point of maximal impulse (PMI). This is usually just inferior to the nipple in normal males. Ideally the patient should be positioned on their left side, but can be done supine. The probe should be placed with the indicator towards the patients left side. The goal of this view is to see all four chambers of the heart in long axis. This affords viewing of the atria and ventricles, mitral and tricuspid valves in long axis, and importantly a view of the pericardium both anterior and posteriorly. A helpful pearl of this technique is to position the probe slightly lateral to display the true long axis view of the ventricle. The valves in this display include the mitral and the tricuspid in long axis can be visualized with color doppler to asses for regurgitation by looking for a blue “back jet” in the opposite direction of the expected flow. The intraventricular septum is also seen and should not be more than about 2 cm in most adults. This view is helpful in determining ventricular ejection by simply viewing the ventricle at maximal dilation and contraction. View this in the internal lumen of the chamber in M or B mode. Aim the probe face towards the heart and let the available structures guide your way. 

Good for: 

  • Comparing the RV vs LV size (PE)
  • Mitral or tricuspid valve regurgitation 
  • Septal wall defects
  • Anterior and posterior regional wall abnormalities
 

Sub-costal four chamber view:

This scan is also very helpful for a global view of the heart and contractile motion. It begins by placing the probe in below the zyphoid and directing the ultrasound beam towards the heads with the indicator left shoulder. The liver, and to some extent the right lung will provide a border or acoustic window directing imaging towards the patients left side. Probe selection is more diverse in this view as probes with smaller footprints can more easily image in this tight space. Imaging between the inferior ribs can also be more easily accomplished with smaller probes. The disadvantage is a reduced image size, and thereby a reduction is nearby structures making some identification of key areas more difficult. As with the other scans presented in this work, the heart and pericardial space should be imaged in both long axis. The long axis view can produce a characteristic four chamber view that has a multitude of uses and value. In long axis view, an anechoic stripe surrounding any part of the heart can be significant for a pericardial effusion that could lead to tamponade. A closed right atrium in the presence of such a stripe can indicate this, so evaluating the heart for chamber motion is important during this scan. Some scenarios that this scan may prove valuable are patients with hemodynamic changes following PTCA, penetrating wounds to the chest, the patient who fails to show improvement or worsens following a decompression of a pericardial centesis, a decompensating patient following a difficult, non-ultrasound guided central line placement or patient showing hypotension following a chest procedure. These seem to have greater  relevance to the critical care provider.

Good for: Comparing the RV vs LV size (PE), mitral or tricuspid valve regurgitation , septal wall defects and anterior and posterior regional wall abnormalities- similar to the apical 4 chamber.


Sub-costal IVC view:  

This view is part of the FATE (focussed assessment transthoracic echocardiography) and RUSH (rapid ultrasound for shock and trauma) exam recently described as techniques to organize your exam for completeness. It begins by placing the probe in the sub zyphoid region as done with the sub costal view. Position the indicator towards the head with a slight rightward tilt. The goal of this view is to visualize the inferior vena cava in long or short axis as it transitions into the right atrium. The descending aorta can also be viewed from this position in long or short axis by tilting the probe leftward. This view may be helpful in determining aortal pathologies. This view, like the sub costal four chamber view is made possible via the acoustic window through the liver. The same limitation of bowel air will obstruct the view. The long axis view go the inferior vena cava will reveal its frequent collapse due to pressure changes caused by respiration. 

 Probe selection is more diverse in this view as probes with smaller footprints can more easily image in this tight space. Imaging between the inferior ribs can also be more easily accomplished with smaller probes. The disadvantage is a reduced image size, and thereby a reduction is nearby structures making some identification of key areas more difficult. The curved probe is also effective in this view as it enhances lateral or wider views. The IVC can be viewed in long or short axis, and the goal of the exam is to not only view it for anomalies, but to view its collapsibility. View the IVC as it enters the right atrium, and check collapsibility at the region around the hepatic vein (vessel going upward into the liver). The adjacent chart shows a relatively novel use of metrics from the IVC. While it’s been shown not to accurately predict fluid responsiveness, it does however show the relative CVP. Simply measure the IVC in short or long axis at it’s largest and smallest, then apply the numbers to this formula:

Max - Min / Max

(Max subtract Min divided by Max)

Apply the result to the chart to predict the CVP. 

The chart information is from “Recommendations for Chamber Quantification: A Report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group. PG 1458-9.

The image below shows the long axis IVC opening into the right atrium. Note that the M-mode vector is through the region near the opening. It has also bee described to be viewed between the hepatic vein, which is also helpful for viewing for dilation (see chart). Note the change in the black stripe at the bottom of the image. This represents the changes in the IVC over time. Here is the location viewed for collapsibility. 


Parasternal long axis view:

To perform this exam place the probe in the 3rd-4th intercostal space just lateral to the left sternal border. The probes direction  indicator should be directed towards the right shoulder. It is the only view that requires this right favored orientation. Maneuver the probe to reveal the image that should include septum, RVOT, left atrium and left ventricle in long axis, the aortic and mitral valve, descending thoracic aorta, and coronary sinus at the bottom of the image. The descending aorta in the deep portion of the image. This should be noted as fluid collections anterior (superficial) to the level of the descending aorta should be considered as pericardial in nature. Whereas fluid collection posterior (deep to) the descending aorta should be considered plural in nature. Good image criteria should include having the septum in a well defined horizontal plane, and the aortic and mitral valves should be easily seen. Generally the apex of the left ventricle is not seen in this image. This view is good for observing aortic stenosis and evaluation of regurgitation with application of the Doppler. Not a good choice for right ventricular structure or function evaluation. It's important that the depth setting is such that the area posterior to the heart can be seen. Failure to image the posterior space will prevent the provider from ruling in a pleural effusion. Its recommended that you orient yourself and organize the structures to be sure you recognize them. Good for:

LV and LA gross function, mitral, aortic valves. LVOT for calculation of stroke volume and cardiac output

Pleural vs pericardial fluid imaging

 

 


Parasternal short axis view: 

There are three distinct views described in this view, known as the ventricular view, the mid-papillary view and the mitral valve view. They are all obtained in close proximity of each other. Begin this exam by placing the probe as you would for the long axis view (3-4 intercostal space) and rotate the indicator to the patients leftshoulder (about 90 degrees). This view should include primarily the left ventricle and right ventricle in short axis. The right ventricle should appear crescent shaped, and the left ventricle should be thicker, and round. Moving the probe lateral mad medial slowly should allow for each of these views to be visualized. The first view is of the left ventricle in short axis. Papillary muscle may be visible but the goal of this view does not include the mitral valve. There are three levels traditionally sought from this probe position. This view affords visualization of the left ventricle contracting towards the center of the chamber. It allows for “eyeballing” the left ventricle and estimation of ejection fraction. Wall motion can also be seen here.  This view also shows contrast between the right and left ventricles. The right should always be only 2/3rds the size of the left ventricle. A large dilated right ventricle is suggestive of pathology, such as RV outflow obstruction like a pulmonary embolus. The view below shows a healthy ventricular view below the level of the papillary muscles. Note the the size and shape of the ventricles and thickness of the septum.

The mid papillary view seeks to evaluate the left ventricle in short axis and images the posterior medial and anterior lateral papillary muscle of the mitral valve . This short axis view should exhibit the classical circular view of the ventricle. Failure to produce this classic sign may indicate anatomic structural problems. The right ventricle should also been viewed in short axis as a crescent shape agin, normally less than 2/3rds the size of the left ventricle in comparison. This view allows for quick evaluation of ventricular wall motion helpful in a variety of scenarios. This view also allows for a quick view of the pericardial sac to rule in effusion or tamponade. Evaluation of the left ventricular wall motion, contractility, chamber size and circumferential intrusion are all useful from this view. Evaluation of the papillary muscles can show normal filling vs the “kissing papillary sign” indicative of low intra chamber volume. While a video presentations best, the image here nicely depicts the closeness of the papillary muscles, displayed as the two echogenic circles close to each other in the center of the chamber.

Good for:

  • Eval of volume status
  • Evaluation of the left ventricular 
  • wall motion, 
  • contractility 
  • chamber size and circumferential intrusion

Mitral Level View:

The mitral level view of the Parasternal short axis view images the mitral valve and can focusses on the anterior and posterior leaflets. It has been described as viewing a fishes mouth opening and closing. This view seeks to simply visualize the valves function. It can be helpful if mitral regurgitation is detected in a long axis. In that instance, simply rotate the probe 90 degrees from the long axis level. The rotation should be slow and deliberate, and include imagining the proper healthy view in your mind prior to the scan. A video presentation here is best to appreciate the valves motion, and similarity to the “fish mouth”. But note the valves closure in the image here. Note its proximity to the right ventricle as well, although this view is not particularly helpful in detecting right heart pathology. 

Typical PSAX view of the mitral valve