Introduction to Perioperative Echocardiography

Perioperative echocardiography has become an essential tool in the anesthetic management of the cardiac surgical patient. Moreover, echocardiographic skills and knowledge can be applied to patients irrespective of the nature of surgical procedure. Consequently, this text begins with a discussion about transesophageal echocardiography (TEE) and other echocardiographic modalities. Because in recent years cardiac anesthesia has increasingly been associated with the use of TEE, this introduction will also serve to present the TEE examination of the normal patient with normal heart structures. Throughout this book, TEE will be employed to illustrate various cardiac pathologies and the anesthetic manipulations required to manage patients with a variety of cardiac conditions. In fact, TEE imagery will be integrated into the discussion and explanations of anesthetic management much in the way that echographic images are employed in routine anesthetic practice. Although it is not the authors' intention to write a definitive text of perioperative echocardiography, it is hoped that the reader will become sufficiently familiar with this valuable tool to appreciate how echocardiographic imagery can be mated with clinical knowledge and clinical experience to effectively manage the cardiac surgery patient or any patient perioperatively.

Perioperatively, TEE has been employed to help anesthesiologists, surgeons, and cardiologists answer questions related to the structure and function of the heart. TEE assists in a number of ways including:

1. Identify the source of hemodynamic instability: TEE can detect areas of myocardial ischemia, poor ventricular function, and inadequate volume load secondary to pericardial tamponade or hypovolemia.

2. Determine hemodynamic parameters: TEE can be used to determine stroke volume (SV) and cardiac output (CO) and can also be used to assess pulmonary arterial and intraventricular pressures.

3. Examine and confirm structural diagnoses: TEE perioperatively can detect new pathology perhaps missed on previous examinations including: patent foramen ovale, atheromatous aorta, or undiagnosed valvular heart disease. More likely, however, perioperative TEE will confirm the patient's previous cardiac diagnoses.

4. Guide and confirm adequacy of surgical interventions: TEE is essential in determining the adequacy of valvular repair/replacement and in detecting any unexpected surgical complications.

5. Postoperative hemodynamic instability: Echocardiography will readily determine causes of postoperative hemodynamic instability secondary to pericardial tamponade, left, right or biventricular failure, pulmonary embolism, aortic dissection, and other catastrophic perioperative events.

Throughout this text, echocardiography will be integrally linked to perioperative anesthetic management and its use in each of the ways described above illustrated.

TEE was introduced in the operating rooms in the mid to late 1980s. By the mid 1990s it had increasingly become a "routine" part of perioperative management.1 The National Board of Echocardiography (NBE) was subsequently established to credential and "certify" individuals in perioperative TEE. TEE is the echocardiographic modality most commonly associated with cardiac anesthesiologists. Anesthesiologists have subsequently expanded the use of TEE in the noncardiac surgical suites and in the intensive care unit (ICU) (Figures Intro–1, Intro–2 and Video Intro–1).

Transthoracic echocardiography (TTE) is more commonly associated with cardiology evaluations and is less frequently employed perioperatively. TTE is noninvasive; however, the surgical field and drapes preclude its use as a monitor during cardiac surgical procedures. Although TTE could be employed perioperatively in some surgical procedures, its use is awkward in the surgical suite and thus rarely used there. On the other hand, anesthesiologists and intensivists in the ICU and in preoperative evaluation frequently employ TTE.2 ICU physicians can readily perform a TTE examination in order to answer basic questions related to hemodynamic instability. A limited TTE examination can determine if the pumping function of the heart is adequate or not or if the heart is adequately volume loaded. Such information can be invaluable in quickly determining the etiology of a patient's perioperative hypotensive episode. Noninvasive TTE can answer questions, which otherwise would require invasive hemodynamic pressure monitoring with a pulmonary artery catheter.

Epiaortic ultrasound (EAU) (Video Intro–2) and epicardiac ultrasound (Figures Intro–3 and Intro–4) are used as perioperative adjuncts to TEE but also can be used when TEE is contraindicated. EAU is useful because the ascending aorta is not completely imaged by TEE. Interposition of the airway between the TEE probe in the esophagus and the aorta prevents visualization of the distal ascending aorta and proximal aortic arch. Since aortic atherosclerosis is associated with embolic stroke during cardiac surgery,3,4 EAU may serve to identify areas of the aorta not amenable for surgical manipulation and thus reduce the incidence of perioperative embolic stroke.

Intraoperative three-dimensional echocardiography performed in real time has lately become popular (Video Intro–3). Although studies have not as of yet demonstrated specific outcome benefits for 3-D images perioperatively,5,6,7 3-D echocardiography is likely to continue to be the subject of extensive study. Three-dimensional echocardiography may better quantify intraventricular volumes and provide additional information regarding complex valvular structures such as the mitral valve apparatus.

Studies are continually underway to demonstrate the use of perioperative TEE to improve or to positively influence surgical outcomes. However, TEE is not mandated for the management of routine coronary artery bypass grafting. Nonetheless, the so-called "routine" patient is somewhat of a rara avis in today's cardiac surgery operating room. As such, perioperative TEE has found its way into routine cardiac anesthesia practice to assist in the assessment and management of patients undergoing the entire spectrum of cardiac surgical procedures from "simple" coronary artery bypass graft surgery up to heart transplantation. Perioperative TEE can be used to:

• Assess hemodynamic instability
• Guide valvular repair
• Guide congenital heart disease repair
• Assess resections of myocardial tissue during hypertrophic obstructive cardiomyopathy surgery or ventricular aneurysmectomy
• Detect atrial and ventricular septal defects
• Diagnose pericardial tamponade
• Detect myocardial ischemia
• Monitor responses to inotropic therapy
• Evaluate aortic diseases such as aortic atherosclerosis and aortic dissections
• Determine correct placement of ventricular assist device cannulae
• Confirm correct placement of an intra-aortic balloon pump
• Provide perioperative hemodynamic measurements in place of a pulmonary artery catheter

In other words, there are many things that perioperative TEE provides to the anesthesiologist and surgeon to aid in patient management. Moreover, TEE can be used in the noncardiac surgery patient to answer basic questions regarding hemodynamic instability.

TEE is contraindicated in patients with overt esophageal pathology. Esophageal cancer, esophageal strictures, and other esophageal problems should be considered absolute contraindications to TEE. TEE is relatively contraindicated in patients with previous mediastinal irradiation. The risks and benefits of TEE probe placement should also be considered in patients with gastric pathology such as ulcers and hiatal hernias. Perforation of the esophagus can be a life-threatening complication associated with TEE use. During preoperative assessment, the anesthesiologist contemplating use of TEE should elicit a history of any esophageal pathology or swallowing difficulties. Risks associated with the use of TEE include endotracheal tube dislodgement, dental injury, esophageal abrasions, and esophageal perforation. As with most things in anesthesiology, it is never wise to apply force in order to place the TEE probe. The TEE probe should pass easily and be freely manipulated. Should a resistance be encountered it is best to forgo TEE examination. Although the information is far less complete, the handheld EAU probe can be used by the surgeon to provide intermittent epicardial and epiaortic echo imagery from the surgical field.

TEE generates heat that could in theory produce a thermal injury. When not being used, the TEE should be placed on standby. TEE machines will generally shut down when the probe reaches a preset elevated temperature.

Finally, it is important to note that correct interpretation of TEE images takes much time, practice, and rigorous credentialing. Simply put, TEE cannot be learned in a day—but, some basic TEE imagery can be mastered and some essential diagnoses made with relatively little training.

Echocardiography relies upon the principles of ultrasound. Ultrasound is sound at a frequency greater than normal hearing. In TEE, a piezoelectrode in the esophageal probe transducer converts electrical energy delivered to the probe into ultrasound waves. Typical ultrasound waves used in echocardiography range in frequency from 2 to 10 MHz. The higher the ultrasound frequency, the greater the resolution of the image. The lower the frequency the greater the depth of ultrasound penetration. The ultrasound image is created because blood and tissue have different acoustic impedance. That is, when sound travels through several media of the same acoustic impedance it travels without difficulty. However, when the ultrasound travels though media of different acoustic impedance, the sound wave is affected by its interaction with the various tissues resulting in reflection, refraction, and scattering of the sound wave. The reflected sound wave (the echo) interacts with the transducer, which records the time delay between the transmitted and the reflected wave. Knowing the time delay and the speed of the ultrasound wave through the tissues, the location of various cardiac structures can be displayed with accuracy and therefore images can be constructed. Obviously, this is a very rudimentary explanation and there are myriad of echocardiography texts available which describe the physics of ultrasound in great detail producing much agony for the clinician reader as well as those preparing for advanced or basic certification in TEE from the NBE.

Echocardiography also makes use of the Doppler effect. The Doppler effect is the result of the apparent change in frequency of sound waves when the source of the wave and the observer of the wave are in relative motion. Observer and source moving toward one another result in the sound wave being compressed, whereas the source and the observer moving apart from one another result in the sound wave being elongated. For example, the blood in the heart is in motion either away from the transducer in the esophagus or toward it. As they travel, red blood cells reflect ultrasound resulting in a change of the frequency emitted by the transducer based on the direction of flow. When blood flows toward the transducer (ie, blood ejected out from the left ventricle into the ascending aorta), the reflected signal will be compressed resulting in a signal with a higher frequency. When blood flows away from the transducer (blood flowing in diastole through the mitral valve from the left atrium to the left ventricle), the frequency of the reflected signal received by the transducer is going to be lower than the original frequency transmitted by the transducer. The change in the transmitted frequency is known as the Doppler frequency shift. Using the Doppler equation, the velocity of the blood flow could be calculated from the Doppler frequency shift.

Doppler equation:

V = (FR − FT/cos θ)(1540 m/s/2FT)

where:

• V = blood velocity
• FT = transmitted Doppler frequency
• FR = received Doppler frequency
• 1540 m/s = speed of sound in tissue
• cos θ = cosine of the angle of incidence between the Doppler beam and the blood flow
• cos 90° = 0 cos 0° = 1

Therefore, velocity determinations are best made when there is no angulation between the Doppler beam and the flow of blood. The velocity of blood cannot be determined when the Doppler beam is perpendicular to the blood flow.

As shall be seen in later chapters, alterations of both the direction of blood flow in the heart and the velocity of that flow are used by echocardiographers to discern defects in cardiac structure and function. The echo machine has the ability to determine and display a range of velocities of blood flow in the heart using either continuous wave (CW) or pulsed wave (PW Doppler). When using CW Doppler the echo machine sends a sound wave from one ultrasound emitting crystal and receives the returned signal using a second crystal. In PW Doppler the machine uses the same ultrasound emitting crystal to send and receive the sound wave. Consequently, PW Doppler is limited to measure slower blood velocities in the heart since the single emitter has to wait for the reflected echo before sending another burst of ultrasound. The rate at which the transducer emits ultrasound bursts is known as the pulse repetition frequency. When PW Doppler measures faster velocities than it is capable to, the apparent direction of flow becomes confused and the machine interprets this fast flow as going in a direction opposite to that in which it is actually flowing. This phenomenon is called "aliasing" and is very useful in perioperative TEE as shall be seen. The maximal frequency that can be measured by the PW Doppler is the Nyquist limit and is equal to one-half of the pulse repetition frequency.

CW Doppler uses two crystals: one to send a signal and the other to receive the reflected signal. CW Doppler is therefore useful to determine both the direction of flow and the velocity of blood flow at higher velocities. Normal blood flow velocity in the heart is less than 1 m/s. In areas of cardiac pathology (ie, valvular stenosis or regurgitation), flow velocity can become greatly increased confusing PW Doppler measurements. In this instance CW Doppler can be used to measure the velocity of rapid blood flow.

Lastly, color flow Doppler (CFD) (Video Intro–4) can create a visual picture of the blood flow by color coding the Doppler velocities, therefore enabling an estimation of the direction and velocity of blood flow in the heart. It is a form of PW Doppler in which more commonly flow toward the transducer is depicted arbitrarily as red and flow away from the transducer is blue with various color hues assigned to turbulent, high velocity blood flow. Because it uses PW Doppler for velocity measurements, CFD is subject to aliasing. At velocities higher than the Nyquist limit, although the blood flow is directed toward the transducer (ie, red) it will be displayed as flow directed away from the transducer (ie, blue).

The American Society of Echocardiography (ASE) and the Society of Cardiovascular Anesthesiologists (SCA) in 1999 published guidelines for the performance of a perioperative TEE examination (Figures Intro–5 and Intro–6). Subsequently, guidelines have been published regarding conduct of perioperative epiaortic and epicardiac ultrasound examination.

The cardiac anesthesiologist usually places the TEE probe after induction of general anesthesia and placement of the endotracheal tube. General anesthesia is not necessary per se for a TEE examination as cardiologists routinely perform this procedure with sedation and topicalization of the oropharynx. At times anesthesiologists may be called upon to provide sedation for the TEE examination performed by the cardiologist.

The probe is introduced into the esophagus and advanced until the heart and great vessels are visualized. Generally, the four-chamber view is identified and from this point the examination commences.

The TEE machine can be rather overwhelming when first encountered. There are many, many controls that are described in great detail in the technical manuals. For the purposes of this introduction the key settings and controls are those that help provide the best view of the structures of interest. For example, the frequency of the probe can be adjusted to provide for higher resolution or greater depth. Recall, a higher frequency provides better resolution while a lower frequency penetrates further. The depth knob helps to center the image in the center of the screen. The gain control augments the signal returning to the transducer. Too much gain and the image is unclear and too bright. Too little gain and the image is too dark. Usually the cardiac structures appear as grayish white structures and the blood appears dark.

The probe has a number of dials which mechanically turn the probe from left to right and from anterior to posterior (Figure Intro–7). The probe also has a locking feature which locks the probe in a certain position. Manipulating the probe when locked in a certain position may cause patient injury. The TEE probes also have a button, which rotates the ultrasound beam through 180 degrees permitting a multiplane examination. TEE provides a two-dimensional image of a three-dimension structure (the heart). The angle of the imaging multiplane can be set from 0 to 180 degrees. Depending upon the position of the probe and the orientation of the ultrasound beam, the two-dimensional image will change, permitting different views of the three-dimensional structure of the heart (Figure Intro–8). With time and practice, anesthesiologists can readily obtain the 20 views, which constitute the standard echocardiography examination as recommended by the guidelines established by the ASE and SCA. Each of these views has their own nomenclature depending if they are originated from the midesophageal (ME), upper esophageal (UE), transgastric (TG), or deep transgastric (deep TG) positions.

TEE is a very sensitive monitor of myocardial ischemia and function. The left ventricle has been divided into 17 segments, which can be visualized in different views. These segments are supplied by the various coronary arteries (Figure Intro–9). Using echo imagery it is possible to determine if the segment's wall motion isnormal, hypokinetic, akinetic, or dyskinetic. Segmental wall motion should be judged based on the percentage of myocardial thickening in systole and inward endocardial border excursion in systole. Akinetic wall motion means that the myocardium does not contract and thicken during systole. Dyskinetic wall motion means that the wall does not contract during systole but rather movesoutwardly. A normally contracting LV is easy to identify (Video Intro–5). Likewise, the LV of the patient with severe heart failure is not easily missed (Video Intro–6). On the other hand areas with segmental wall motion abnormalities can be somewhat subtler (Video Intro–7).

The right ventricle (RV) is a much thinner structure than the LV. It does not have the same descriptive system to identify wall motion abnormalities as does the LV. Nonetheless, the normal RV is contractile, in the shape of a crescent hugging the LV when seen in a transgastric view (Video Intro–8). When the RV becomes dysfunctional it becomes more dilated and rounded (Video Intro–9).

The valves of the heart are visualized in multiple views during the routine examination.

The aortic valve normally consists of three leaflets. The left coronary artery can often be seen as it takes off from above the left coronary cusp (Video Intro–10). The two-leaflet mitral valve is likewise seen in many different images (Figure Intro–10). The mitral valve has two leaflets, anterior and posterior. The sections of these leaflets have their own descriptive code in order to help identify areas of the valve, which might be in need of surgical repair and facilitate communication amongcardiologists, anesthesiologists and surgeons.

The tricuspid valve is readily examined by TEE (Video Intro–11). The pulmonic valve is the farthest valve from the esophagus and is not as easily visualized.

The routine TEE examination also includes a thorough examination of the aorta. Examination of the aorta can identify areas of intimal thickening or calcification that could create arterial emboli if manipulated during surgery. Use of TEE and EAU can help guide surgeons away from areas of calcification or atherosclerosis in order to minimize the incidence of emboli8 (Video Intro–12).

The interatrial septum is examined (Video Intro–13) to rule out the presence of a patent foramen ovale (PFO). In the presence of a PFO, right-heart pressures higher than left-heart pressures may result in shunting of the blood across the PFO from right to left leading to a reduction in arterial saturation. Emboli could also cross from the right to the left side of the heart with potentially injurious results if thrown in the systemic circulation. Roughly, 20% of the population may have a PFO.

Real time three-dimensional echocardiography5 is now becoming increasingly employed as the probes and technology become more available to practitioners. At present there are no guidelines regarding performance of a three-dimensional examination. Recall that routine TEE provides a two-dimensional image of a three-dimensional structure—the heart. The echo beam is oriented through180 degrees creating images of the heart in various two-dimensional orientations. Three-dimensional echocardiography may provide better imaging for volume analysis of the heart as well as additional information regarding valvular structure and function.4 Time will determine the role of 3-D TEE in the routine management of patients.

The PA catheter has long been used as an aid in the clinical management of patients at risk for or experiencing hemodynamic instability. Using measures of cardiac output (CO), pulmonary capillary occlusion pressure (PCOP), and central venous pressure (CVP), anesthesiologists and intensivists have attempted to discern why patients are hemodynamically unstable. Many of these questions can be answered visually following TEE placement. A noncontractile heart is readily obvious even to the most inexperienced observer. Likewise, a contractile but underfilled heart is easily identified (Video Intro–14). Often perioperatively, these visual determinations will be all the information that the anesthesiologist wants or needs to initiate appropriate treatment.

However, should the anesthesiologist desire more quantitative assessments echocardiography can be used. The various TEE machines have incorporated within their software the abilities to make any number of calculations to determine cardiac output, valve areas, and pressure gradients. These will be illustrated during the course of the text as they apply to different cardiac conditions. Most of these measurements depend upon either the continuity equation for flow or volume or the Bernoulli equation.

The continuity equation is based upon the conservation of mass. In other words, as blood flows through the heart its mass is conserved, the volume of blood that flows through one point (eg, left ventricular outflow tract) is the same with the volume of blood that flows through another point (eg, aortic valve) in the absence of shunts (eg, ventricular septal defect). The flow of water down a river is often used to illustrate this principle. When the river is wide, the water flows leisurely; however, when it narrows—watch out for the rapids (Figure Intro–11). The heart is no different. When blood flows through areas of pathology, the flow is often accelerated allowing the calculation of the narrowing area by using the continuity of flow or volume equation.

Recall, Doppler allows the measurement of all of the velocities of blood flow depending upon whether flow is directed toward (+) or away (−) from the TEE probe in the esophagus. When Doppler is applied to blood flow the Doppler beam needs to be as parallel with the blood flow as possible to provide for an accurate measurement.

For example, when the PW Doppler sampling gate is placed in the left ventricular outflow track (LVOT), the machine measures the velocities in cm/s passing through that point in the LVOT (Figure Intro–12). The LVOT shape can be approximated with a cylinder and the cross-sectional area of the LVOT to a circle. Therefore, the cross-sectional area of the LVOT can be calculated by knowing the diameter of the LVOT. Using TEE the LVOT diameter can be measured (Figure Intro–13).

Recall, the continuity principle—whatever volume of blood goes into the heart must leave the heart. The TEE machine has provided the velocity of blood flowing through the LVOT and it has likewise provided a measure of the area of the LVOT based upon its diameter. What is not yet known is the volume of blood that is moving in the heart with each beat. Fortunately, the machine provides a Doppler measurement by which the stroke volume (SV) can be determined for each beat of the heart (Figure Intro–14). Not all blood flows at the same speed as it passes through the LVOT, so there are numerous velocities captured on the PW Doppler as a collection of velocities displayed as a spectral envelope. By tracing this wave, the machine can mathematically integrate the velocities and generate the time-velocity integral (TVI), which represents a measurement of the distance that the blood has traveled in the LVOT during any particular heartbeat. This distance is commonly known as stroke distance.

Area × Length = Volume

Area = (LVOT diameter)2 × 0.785 (the number comes from the formula for area of a circle [π × D2/2] where D = diameter of the circle)

Length = the measurement of the trace from the Doppler spectral envelope known as the time-velocity integral (TVI)

Therefore,

SV = (LVOT diameter)2 × 0.785 × LVOT TVI

Cardiac output (CO) = SV × Heart rate (HR)

Consequently, TEE can provide a measurement of cardiac output.

Since flow through any part of the heart must be the same on each beat based upon the continuity equation (assuming there are no shunts or regurgitant lesions), it is possible to compare the calculation of this volume at different points in the heart.

For example, Area 1 × TVI 1 must equal Area 2 × TVI 2. Generally, Area 1, TVI 1, and TVI 2 can be measured and used to calculate Area 2. These calculations will be demonstrated in detail when discussing valvular heart disease.

The other function of the PA catheter routinely used by anesthesiologists is to determine intracardiac pressures. Physicians have used these pressures to estimate the volume loading conditions of the heart. The relationship between volume and pressure in the heart is determined by compliance. Healthy hearts tend to be more compliant and as such can accommodate volume with relatively minimal increases in pressure. Unhealthy hearts tend to be less compliant and consequently small increases in volume can cause great increases in intracardiac pressures. The PA catheter has been used to identify poor compliance by estimates of pulmonary artery pressures, PCOP, and CVP. When performing a TEE examination, the pressure gradients between two chambers can be estimated by using the Bernoulli equation.

The simplified Bernoulli equation states:

Pressure gradient = 4 × V2 where V is the maximal velocity in m/s measured. The gradient is always directed from areas of high pressure to areas of low pressure. Gradients can be used to estimate pressures previously determined from the PA catheter.

Left Atrial Pressure (Lap)

It is well known that PCOP estimates the left atrial pressure.

The gradient between the left ventricle (LV) and the left atrium (LA) can be determined as follows. The left ventricle generates pressure during systole. Assuming there is no aortic valve disease, the systolic blood pressure is equal with the LV systolic pressure. If the patient has mitral regurgitation, flow occurs during systole not only from the LV into the ascending aorta but also from the LV into the LA. The maximal velocity of the flow from the LV into the LA can be measured by employing Doppler and the pressure gradient between the two chambers can be calculated using the Bernoulli equation:

Pressure gradient = 4 × Vmax2

Pressure gradient = LV systolic pressure − Left atrial pressure

Left atrial pressure = LV systolic pressure − 4 × Vmax2

Similar calculations can be done for various pressure measurements in the other chambers of the heart.

Pulmonary Artery Pressures

Routinely, cardiologists estimate systolic pulmonary pressures in the presence of tricuspid regurgitation (TR) by using the same principle. In the absenceof pulmonic valve disease the pressure in the right ventricle during systole is equal with the pulmonary artery systolic pressure. Assuming that the right atrial pressure (ie, CVP) is known, one can estimate the pulmonary artery systolic pressure using the same algorithm as above, by measuring the velocity of the tricuspid regurgitant jet.

4 × V2 = RV systolic pressure − Right atrial pressure (CVP)

• RV systolic pressure = PA systolic pressure
• PA systolic pressure = 4V2 (TR) + CVP

Left Ventricular End-Diastolic Pressure (LVEDP)

Likewise, LVEDP can be estimated in the presence of aortic insufficiency using the patient's diastolic blood pressure (DBP) and the Doppler velocity at end diastole of the aortic insufficiency jet.

LVEDP = DBP − 4V2(AI)

Practically, these calculations are not routinely done in the cardiac operating room as they are often time-consuming and PA catheters continue to be placed perioperatively often to assist in ICU management where TEE might not be as available as in the operating room (Figure Intro–15).

Learning Cardiac Anesthesia and TEE

How to proceed: Echocardiography can be distracting to the trainee in cardiac anesthesia; however, its mastery is essential for the practice of cardiac anesthesia and it has great utility in patients undergoing noncardiac surgery in situations of hemodynamic instability. It is not the intention of the authors to present a detailed review or text of perioperative echocardiography—there are countless such works available. Rather, as cardiac anesthesia principles are introduced, TEE imagery and techniques will be employed much as in current practice where TEE informs and influences anesthesia decision making throughout the conduct of cardiac anesthesia.

To start, it is important to review the standard images of the heart. Figure Intro–6 labels the standard views of the heart obtained during TEE examination.

Once having appreciated the structures that can be seen based upon the schematic from Figure Intro–6, the image and Video atlas (Figures A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, and A18, Videos A1, A2, A3, A4, A5, A6,A7, A8, A9, A10, A11, A12, A13, A14, A16, A17) will further provide orientation as to how the three-dimensional heart can be visualized by two-dimensional TEE.