Transthoracic echocardiographic evaluation of the heart and great vessels
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Transthoracic examination of the heart and great vessels is an essential skill that allows the anesthesiologist to evaluate cardiac function. In this article, we describe a pragmatic technique to obtain the essential views to evaluate normal or abnormal cardiac function and to appreciate great vessel anatomy and physiology.
The cardiac anatomy and function can be described using standard parasternal, apical, and subcostal views. These windows can also be used to assess the aorta, pulmonary artery, and vena cavae; however, other transthoracic and abdominal windows can be used to complete the evaluation of the great vessels.
The integration of the echocardiographic information particularly from the heart and great vessels with the case story, physical examination, laboratory data, and other relevant clinical information should become the way of the future, and this will benefit the patients under our care.
Évaluation échocardiographique transthoracique du cœur et des grands vaisseaux
L’examen transthoracique du cœur et des grands vaisseaux est une compétence essentielle qui permet à l’anesthésiologiste d’évaluer la fonction cardiaque. Dans cet article, nous décrivons une approche pragmatique pour l’obtention des vues essentielles permettant d’évaluer une fonction cardiaque normale ou anormale et d’apprécier l’anatomie et la physiologie des grands vaisseaux.
L’anatomie et la fonction cardiaque peuvent être décrites au moyen des vues parasternales, apicales et sous-costales. Ces fenêtres peuvent également servir à évaluer l’aorte, l’artère pulmonaire et la veine cave; cependant, d’autres vues transthoraciques et abdominales peuvent être utilisées pour compléter l’évaluation des grands vaisseaux.
L’intégration de l’information échocardiographique, concernant en particulier le cœur et les grands vaisseaux, dans l’histoire clinique, l’examen physique, les données de laboratoire et autres renseignements cliniques pertinents devraient devenir une voie d’avenir qui bénéficiera aux patients dont nous prenons soin.
Introduction and key questions
Preoperative assessment of the airway and anticipation of potential difficulties has become a standard skill that every anesthesiologist performs routinely. However, in our daily practice, the prevalence of patients with a difficult airway is significantly less than that of significant cardiovascular disease and hypoxemia. Consequently, one could imagine that eventually anesthesiologists will not limit their preoperative physical examination to a focus on the airway and will also consider the examination of the heart and great vessels, using bedside ultrasound as part of their routine, to anticipate and treat potential hemodynamic instability while providing standard anesthesia care. This concept has already been nicely illustrated in a study by Zhang et al. where 90 patients with an American Society of Anesthesiology (ASA) physical status I/II/III (27/36/27) were induced with etomidate.1 Significant hypotension occurred in 46.7% of patients. The authors found that the degree of collapsibility of the inferior vena cava (IVC) measured before induction using echocardiography was superior to commonly used demographic or hemodynamic variables in predicting hypotension. This is a simple illustration of how bedside ultrasound can be used in our daily practice and shows its potential role in the anticipation of intraoperative hemodynamic instability. In our opinion, this represents a major advantage and could be used to optimize the care of our patients as previously presented in the Journal.2,3
In this article, the authors, who are experienced bedside ultrasound instructors and use this technology in their daily practice, will share their experience in learning the technique, teaching it, and using it routinely before, during, and after anesthesia. We will limit our discussion to the heart and great vessels, using two-dimensional (2D) imaging as well as basic colour Doppler, to identify various abnormalities. Advanced diastology will not be covered. Those interested in a more detailed analysis of this topic are referred to other published articles.4,5
Throughout the text several technical tips and clinical pearls from the authors will be shared with the reader. We have also used simulator technology (CAE Vimedix simulator, with permission from CAE Healthcare) to facilitate comprehension of the anatomy. Some of the pitfalls of the 2D ultrasound examination will be covered. The extra-cardiac aspects will be examined in more detail in other articles within this special issue of the Journal.6
Anatomy of the heart and great vessels
Before performing an ultrasound examination of the heart and great vessels, it is essential to understand the anatomy. This requires an understanding of the relationship among the heart, great vessels, and surrounding organs. The heart itself is a very complex structure. A simple tip we use as instructors to explain anatomical relationships while scanning the heart from top to bottom or from left to the right with the ultrasound beam kept along the same orientation is the following:
The left ventricle has a bullet-shape aspect that can be sliced longitudinally or in a transverse fashion. It is subdivided in a basal region that includes the mitral valve, a mid-papillary region (or level), and an apical region (or level). Contraction of the left ventricle has three components based on the orientation of the myocardial fibre: radial and longitudinal shortening as well as a twisting motion. Conditions such as Takotsubo cardiomyopathy (or stress cardiomyopathy) will typically be associated with preserved basal left ventricular function and progressive myocardial dysfunction with typical apical akinesia.7 Myocardial ischemia resulting from left anterior descending ischemia can also be associated with apical akinesia or with anterior mid and basal hypokinesia with preserved inferior basal motion.
The left atrium is normally smaller in dimension than the left ventricle. The left atrial appendage is typically positioned in an anterolateral position. A dilated left atrium is typical of diastolic dysfunction provided there is no severe mitral or aortic valve disease. The left atrial dimension has been called the “glycosylated hemoglobin” of diastolic dysfunction because it will remain chronically dilated regardless of filling pressure.
The right ventricle has a complex crescent-shape structure with an inflow and outflow portion. The right ventricle has three walls: inferior, lateral, and anterior. These walls end at the infundibulum, which corresponds to the outflow part. The outflow is more trabeculated at its apex than the left ventricle and has thinner walls. The “pumping action” of the right ventricle is peristaltic, or a wringing effect, generated via a piston-like action mediated mostly by longitudinal shortening. Despite looking smaller on ultrasound images, the end-diastolic volume of the right ventricle is larger than that of the left.8 The right ventricle can easily alter its volume and shape depending on its pre- and afterload status.
The right atrium dimension is typically smaller than the right ventricle. It also has an appendage located anteriorly. Being a structure with lower pressures, it is easier to compress during global or regional tamponade.
A normal aortic valve has three cusps. From an echocardiographic viewpoint, the non-coronary cusp faces the interatrial septum (IAS), the right coronary cusp is most anterior where the right coronary artery originates, and the remaining left coronary cusp is where the left main coronary artery originates. The aortic valve is part of the aortic root complex, which includes the three sinuses of Valsalva, the sinotubular junction, and the ascending aorta.
The mitral valve is a complex structure with two leaflets, anterior and posterior, attached via the chordae tendineae to the anterolateral and posterior-median papillary muscles, respectively. The posterior-median papillary muscle is more commonly ruptured than the anterolateral in myocardial ischemia because the posterior-median papillary muscle is perfused only by the right coronary artery as opposed to the anterolateral papillary muscle, which typically has a dual blood supply from the left circumflex and left anterior descending artery.9 Although it appears smaller in various echocardiographic views, the posterior leaflet of the mitral valve generally contributes to a greater extent to the mitral valve annulus and is more susceptible to left ventricular dilatation. Annular dilatation could lead to posterior leaflet tenting and mitral regurgitation.
The pulmonary valve has three cusps, the right, left, and anterior. In venous air embolism, air will typically be located under the anterior leaflet in the patient in supine position. The tricuspid valve has three leaflets attached to papillary muscles via chordae tendineae.
The interventricular septum separates both ventricles. The IAS typically has a thinner portion called the fossa ovalis. In up to 20% of adult patients,10 communication between the two atria can occur through a patent foramen ovale. In right ventricular failure, this can be problematic and may lead to chronic right ventricular volume overload, right-to-left shunting with resultant hypoxemia, and paradoxical emboli.
The heart is typically surrounded by a dense membrane called the pericardium. There usually is a small anechoic space between the pericardium and myocardium, which is filled with pericardial fluid and is easier to see in dependent areas. It is important to realize that pericardial fat may have a similar appearance; however, it tends to have a non-homogeneous aspect and be present in a non-dependent location. Although a visible space is considered normal during systole (physiologic pericardial fluid), when this phenomenon is seen in diastole, the term pericardial effusion is used.
Other intracardiac structures
Venous drainage of the heart ends in the coronary sinus, which is typically smaller than 1 cm. Chronically increased right atrial pressure of any etiology can cause dilation of the coronary sinus. A dilated coronary sinus may occur in patients with a left-sided SVC or pulmonary hypertension or with congenital malformations where anomalous venous drainage exists.11,12
This may lead to an aberrant position of the central venous catheter. Two other structures are frequently found in the right atrium including the Thebesian valve, which can be present at the entrance of the coronary sinus, as well as both the Eustachian valve and Chiari network, which originate at the junction of the IVC and right atrium.13
Blood from both axillary veins, the jugular and subclavian veins, drains into the SVC. In addition, the right azygos vein typically drains into the SVC. The IVC becomes intrahepatic before draining into the right atrium. In a rostral position, the hepatic veins draining in the IVC can be seen. The portal veins will typically be seen in a more caudal and anterior position. In some cases, however, caudal hepatic veins can also be present and the echographer must rely on the fact that portal veins have thicker walls and that blood flow is opposite to the hepatic veins. Hepatic and portal veins are among the easiest structures to image because the liver is a very echogenic structure and Doppler analysis of the blood travelling in them can easily be performed. Information derived from hepatic veins has been shown to be very useful in the stratification of patients in shock.3,14 In a similar fashion, analysis of portal veins has been used to detect portal hypertension resulting from cirrhosis or elevated right atrial pressure.15,16
Finally, the pulmonary artery divides into left and right main arteries. The right portion goes under the aortic arch and divides in further ramifications. This infra-aortic position of the right pulmonary artery explains why ascending aortic aneurysm and aortic type A dissection can be associated with right ventricular dilatation since these pathologies can result in acute or chronic compression of the right pulmonary artery, which increases right ventricular afterload.
Echocardiographic examination of the heart
Acoustic windows and acoustic opportunities
It is important to realize that the same cardiac structure can be seen from different angles by using these different acoustic windows (SAX, LAX, A4C, A5C, A2C, and subxyphoid views). The heart can be thought of as a house; you can look inside the heart (the house) through windows that are in the front, on the side, or from the backyard. What you see will be different according to the point of view and there may be obstacles (walls) preventing you from seeing certain aspects. Nevertheless, it is still the same house. From a clinical point of view, the limitations of one acoustic window can usually be compensated by examining the heart and great vessels from a different perspective (a different acoustic window).
Important steps before beginning the examination
Positioning the patient: the patient should be as close as possible to the anesthesiologist echocardiographer or ultrasound examiner. Operating tables are generally designed to be as narrow as possible; however, this can become an issue in a recovery room or intensive care unit bed. In such situations, it is important to place the patient as close as possible to the examiner, also raising the height of the bed to make sure that the examiner’s back is straight and that the patient is at the level of the examiner’s elbow while performing an examination. Positioning the patient can also be used to optimize a specific acoustic window. For example, in the echo laboratory, the patient will be placed in a left lateral decubitus position with the left arm oriented upward while obtaining a long or short axis parasternal view. This position usually improves the quality of imaging from the parasternal view by bringing the heart closer to the thoracic wall and by opening the intercostal space in the left parasternal region.
Positioning the examiner: in the cardiac echo laboratory, cardiologists and technicians will typically be positioned to the left side of the patient. In the operating room and intensive care unit, the position of the examiner will be personalized and determined by the environment. In the perioperative or intensive care unit environment, there is great variability between patients and the ultrasound examiner must be flexible.
Positioning the ultrasound machine: the machine should be positioned on the same side of the patient as the examiner. The height of the machine keyboard should be adjusted so the examiner can stand upright.
Positioning the ultrasound probe: probe positioning varies according to the convention being used (“cardiology vs radiology convention”). In this article, the cardiology convention will be used and probe orientation will be described accordingly. This means that the marker on the probe will be oriented upward for sagittal, longitudinal, and coronal views. On the screen for these views, cephalad structures will appear on the right and caudal on the left. In the radiology convention, cephalad structures will appear on the left and caudal on the right. For the transverse or SAX view, the marker will be pointing on the patient’s left. On the screen for these views, right-sided structures will appear on the left of the screen and left-sided structures on the right of the screen. This is the same for both cardiology and radiology conventions. When performing a 2D examination, the structure being examined should be as close to the probe as possible and ideally placed at a 90° angle. This will maximize the ultrasound waves being reflected back to the probe and improve image quality.
A common mistake when obtaining images is moving the probe too quickly. When teaching point-of-care ultrasonography, we often use the metaphor that the probe should move at the same speed as a growing plant. It is very important to remember that the normal heart is the size of a closed fist and clinical information can easily be overlooked when moving too fast. Another common mistake is trying to chase an image or a specific view. While being examined, some patients are breathing heavily and this can cause the image to become black (the probe is over a bony structure such as a rib) or grey (the lung moves between the probe and the structure being examined). Sometimes the best approach is not to move and wait for the image to come back since patients have to alternate between inspiration and exhalation, which will cause the rib or the lung to stop obstructing the view. The focus should always be on the structure you are trying to examine (e.g., left heart structures) and it may be necessary to adapt your technique to the challenges that a specific patient represents.
The parasternal views
Parasternal LAX view (Fig. 7)
Left ventricle: in this view, the anteroseptal and the inferolateral walls of the left ventricle are visualized. In some patients, it may not be possible to see the left ventricle from the base all the way to its apex. Therefore, it may be necessary to perform a gentle sliding of the probe toward the apex to visualize the entire left ventricle.
Left atrium: in this position, the left atrium will be seen in the far right of the screen. This is the typical position where its dimension is measured. Nevertheless, it should be kept in mind that a single 2D measurement is not as precise at estimating the left atrial area when compared with the 3D measurement technique, which uses two orthogonal planes (typically the A4C view).
Right ventricle: the RVOT is seen as the structure closest to the ultrasound probe. The right ventricle can also be seen by tilting the probe on is long axis, thus directing the ultrasound beam to the patient’s right (Fig. 7 E-H). Initially the interventricular septum will be seen followed by the right ventricle, tricuspid valve, and right atrium.
Right atrium: the right atrium is not seen in the LAX view unless the beam is directed to the patient’s right. By performing this maneuver, in some patients it is possible to see both the IVC and the SVC entering the right atrium as well as the right atrium appendage. It is also an excellent view for the tricuspid valve.
Valves: the LAX offers a rapid evaluation of the aortic and mitral valve. Whenever evaluating cardiac valves, it is important to proceed in sequence by starting with a 2D evaluation followed by colour flow Doppler. Colour interrogation is useful to detect pathologies such as aortic or mitral regurgitation, abnormal mitral inflow velocity, and aortic outflow velocity. Nevertheless, 2D evaluation does provide important diagnostic information and can be essential for proper clinical management of a specific situation. For example, imagine identifying mitral regurgitation and increased aortic outflow velocity in a patient who is hemodynamically unstable. Nevertheless, upon 2D examination, you identify that the patient has a LVOT obstruction due to septal hypertrophy and that the mitral regurgitation is secondary to systolic anterior motion (SAM). This is an important diagnosis because it represents an absolute contraindication to the use of inotropes. Patients with SAM require a reduced heart rate, increased afterload, and adequate filling.21 The 2D information is likely to have completely changed your management of the situation. The tricuspid valve can be assessed in this view by tilting the beam to the patient’s right side.
Parasternal SAX view (Fig. 11)
Moving the ultrasound beam upward, a view of the RVOT can be obtained with the origin of the pulmonary valve. To optimize the view of the pulmonary artery bifurcation, further rotation to a transverse or 3 o’clock view can be used. This view is similar to the one obtained with computed tomography. Pulmonary emboli and saddle embolism can be seen from that view.
Apical four-chamber view (Fig. 14)
Bring the apex in the middle of the screen by sliding the probe laterally to medially.
Align the apex vertically with the interventricular septum by tilting the probe on its short axis.
- 3)Identify the optimal coronal view of the heart (Fig. 13). The optimal coronal axis of the heart is the one where the heart is cut from the middle of the apex to the middle of the left atrium close to the lower pulmonary veins. In some patients, the apical acoustic window will lead to a beam position above the true apex and in other patients it will be below. The beam may be turned too far clockwise or counter-clockwise. These inappropriate positions will lead to the inability to obtain an optimal combined apical and atrial view (Fig. 16). To ensure being in the proper coronary plane, the coronary sinus and aortic root can be used as landmarks. When the probe is tilted too anteriorly, the aortic root will appear and it signals the need to angulate downward to obtain the true coronal plane. Similarly, when the probe is tilted too posteriorly, the coronary sinus will come into view, which is a sign that the probe should be tilted upward. Clockwise or counter-clockwise rotation of the probe may be necessary to optimize visualization of the ventricles and obtain a true four-chamber view. When performing these rotation motions, the echographer should focus on the left ventricle first and then the right-sided structures.
In the A4C view, the IAS can also be evaluated. The position and mobility of the IAS are very useful in hemodynamic management because they represent the relationship between the right and the left atrial pressure.22,23 A fixed position or deviation of the IAS to the left typically indicates right-sided pathology such as right ventricular failure. Deviation of the IAS to the right indicates a left-sided pathology. In a study by Haji et al.,23 septal curvature of the IAS correlated with left-sided filling pressure. Further scanning steering the beam anteriorly to the aortic valve can reveal the right ventricular inflow, RVOT, pulmonary valve, artery, and bifurcation.
Apical two-chamber view (Fig. 18)
To obtain the A2C view, rotate the probe counter-clockwise (45-80°) from the A4C view. In this view, the left ventricular anterior wall is on the right side of the screen and the LV inferior wall is on the left. The mitral valve, left atrium, and part of the ascending aorta will be seen (Fig. 18 A-D). Beam tilting to the right on its long axis can give a nice view of the LVOT (Fig. 18 E-H). Furthermore, in some patients the A2C view can provide one of the most spectacular views of the right ventricle where its “crescent” shape can easily be appreciated (Fig. 18 I-L). The inflow and outflow tracts of the right ventricle can be seen simultaneously. Further counter-clockwise to the right is the bi-caval view.
The subcostal view (Fig. 19)
Position the patient on their back with slight elevation of the trunk and/or flexion at the hips.
Press firmly on the probe to push against the abdominal wall.
Tilt the probe upward on its long axis to orient the beam posteriorly toward the liver and find the IVC.
Follow the IVC up by tilting the probe downward on its long axis to the right atrium and align it with the left atrium and the IAS by tilting the probe on its short axis.
Then align both atria with the ventricles to get a coronal view (Fig. 19) of the heart. This is done by gently rotating the probe counter-clockwise (most of the time) or clockwise. This view is similar to the A4C but the heart is now examined by looking through the right atrium instead of the apex. With this approach, the left lobe of the liver is used as an acoustic window.
Bring the right atrium in the middle of the screen and then apply a counter-clockwise rotation on the probe. The IVC will be seen in a longitudinal or sagittal fashion.
The subcostal view is the most useful when examining a patient in the supine position because both cardiac function and the IVC can be evaluated from the same acoustic window. It is the closest view to the right atrium. It is also sometimes the only view you can get in an unstable patient during resuscitation or a patient in respiratory distress who cannot be turned on the left side.
Echocardiographic examinations of the great vessels
Aorta (Fig. 23)
Venae cavae (Fig. 25)
The main pulmonary artery and its bifurcation are most easily seen in the SAX view in a transverse view (Fig. 11). Similar to the aorta, suprasternal views can also be used to visualize the pulmonary artery which is to the patient’s left of (i.e., medial to) the aorta. From an SAX view, positioning the probe in a 0° orientation permits the identification of both the right and left pulmonary artery. In several patients, however, the medial portion of the lung will prevent adequate visualization of those structures. Apical and subcostal views can sometimes reveal the proximal portion of the pulmonary artery.
Qualitative vs quantitative evaluation
As a novice in bedside point-of-care ultrasound, one will mostly rely on qualitative evaluation of function and structure. In terms of cardiac function in the presence of hemodynamic instability, an anesthesiologist must decide if inotropes will be used. They are considered in severe left or right ventricular dysfunction. In mild to moderate dysfunction they can also be used; however in hyperdynamic hearts or in the presence of LVOT or RVOT obstruction inotropes are contraindicated. Such decisions are based mostly on pattern recognition rather than precise measurements. Nevertheless, as experience increases, a more quantitative approach can be used. This will be particularly useful in determining for example if a cavity is normal or dilated (i.e., ventricular or atrial). The reader is referred to guidelines for cardiac chamber quantification.26 Quantification of the severity of aortic stenosis is beyond the scope of the point-of-care evaluation. Nevertheless, recognition or suspicion of a valvular pathology, either stenosis or regurgitation, should prompt consultation for confirmation and assessment of severity by an expert colleague or an echocardiographist. Guidelines for the evaluation of valvular heart disease and prosthesis have been recently updated.27-29
Special applications of the examination of the heart and great vessels
In 2010, Labovitz published guidelines for the use of focused cardiac ultrasound in the emergent setting.30 The five indications for these guidelines are assessment of pericardial effusion, assessment of global cardiac function, indication of marked right and left ventricular assessment, intravascular volume assessment, and confirmation of transvenous pacing wire placement. In the operating room room, those conditions will present as hemodynamic instability, hypoxemia, or the combination of both. The approach to hemodynamic instability was described previously as a two-part series in the Journal in 2014.2,3 In terms of hypoxemia, the vast majority will be related to pulmonary pathologies, which will be discussed in the section on the lung and pleura. We previously proposed a simple approach to hypoxemia.31 Nevertheless, cardiac examination should always be performed in the presence of hypoxemia to rule out for instance myocardial dysfunction associated with pulmonary edema or because of septic shock with pneumonia. Myocardial dysfunction can occur in up to 50% of patients with septic shock,32 particularly right ventricular dysfunction.33 In the presence of normal lung examination, intracardiac shunt or massive pulmonary embolism should be ruled out.
Pitfalls of the 2D examination
There are several pitfalls of the 2D examination. Some of them have been highlighted with the use of 3D echocardiography in terms of misalignment in the measurement of cardiac structures or valvular evaluation. Other pitfalls are related to operator experience. For instance, hyperdynamic cardiac function associated with pulmonary edema can be the result of severe mitral regurgitation particularly in patients with SAM, as mentioned previously, which could be missed if colour Doppler evaluation is not performed. We often observe a strong focus on left ventricular function in novice users of ultrasound. For example, we have found that the hypertrophied left ventricle is often misinterpreted as a sign of hypovolemia and that the right ventricle is often neglected, resulting in excessive fluid administration followed by complications of fluid overload34 including right heart failure. It is therefore important not to treat an image but a patient while integrating all the clinical and imaging information, including assessment of both ventricles.
Among pitfalls of 2D examination are the recognition of 2D artefacts. Detailed description of those are beyond the scope of this manuscript but are important to acknowledge in using bedside 2D ultrasound.35 Finally, pitfalls could be generated by poor quality of images and lack or mistaken integration of the echographic findings with the clinical situation.
In summary, 2D echographic examination of the heart and great vessels is a clinical skill likely to be mastered by every anesthesiologist in the 21st century. These skills will be integrated into routine practice in the pre-, intra-, and postoperative period. Imaging the heart and great vessel structures will enhance the clinical examination of the patient by direct visualization. Nevertheless, clinical decisions should not be based on 2D images alone. The integration of the echocardiographic information with the case story, physical examination, laboratory data, and other relevant clinical information should become the way of the future and this will benefit the patients under our care.
Conflicts of interest
A.Y. Denault is an instructor for CAE Healthcare and on the Speakers Bureau for Edwards, Medtronic and Masimo; A.Y. Denault, S. Langevin, M.R. Lessard, J.F. Courval, and G. Desjardins give courses on ultrasound using CAE Healthcare simulators.
This submission was handled by Dr. Gregory L. Bryson, Deputy Editor-in-Chief, Canadian Journal of Anesthesia.
Supported by the Richard I. Kaufman Endowment Fund in Anesthesia and Critical Care.
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