18
Intraoperative and Interventional Echocardiography
LIMITATIONS AND TECHNICAL CONSIDERATIONS
CLINICAL UTILITY OF INTRAOPERATIVE TEE
CLINICAL UTILITY IN TRANSCATHETER AND HYBRID PROCEDURES
Atrial Septal Defect or Patent Foramen Ovale Closure
Transcatheter Aortic Valve Replacement
Transcatheter Mitral Valve Repair
The principles of diagnostic TEE and intraoperative TEE are identical in terms of image plane orientation, anatomic findings, and Doppler flow patterns (see Chapter 3). In addition, standard methods for the evaluation of ventricular systolic and diastolic function, valve dysfunction, congenital heart disease, and so on, as described in previous chapters, are also utilized for intraoperative TEE. Three-dimensional (3D) echocardiography is particularly important during monitoring of procedures, both in the operating room and in the interventional suite.
Time constraints may require a focused examination.
Altered loading conditions may affect the evaluation of valve and ventricular dysfunction.
Baseline and postintervention evaluations must have matched loading conditions.
Urgent decision making based on imaging information may be necessary.
Any limitations of the TEE information must be promptly recognized.
Clear communication between the echocardiographer and surgeon is essential.
This chapter provides an introduction to the basic principles and major clinical applications of intraoperative TEE. Echocardiographers who practice intraprocedural TEE should review training guidelines and refer to the additional books and articles included in the Suggested Reading at the end of this chapter (Table 18-1). In addition, other echocardiographic modalities may be used in the operating room (e.g., epicardial echocardiography) and in the interventional laboratory (e.g., intracardiac echocardiography) for procedural guidance (see Chapter 4).
TABLE 18-1
Recommendations for Training in Basic and Advanced Perioperative Echocardiography∗
∗This table shows the minimum number of procedures recommended to achieve and maintain competency.
Summarized from Mathew JP, Glas K, Troianos CA, et al: American Society of Echocardiography; Society of Cardiovascular Anesthesiologists. American Society of Echocardiography/Society of Cardiovascular Anesthesiologists recommendations and guidelines for continuous quality improvement in perioperative echocardiography. J Am Soc Echocardiogr 19(11):1303-1313, 2006. The specific cognitive and technical skills needed for competency are listed in that reference.
Basic Principles
The indications for intraprocedural TEE range from basic monitoring of cardiovascular function to evaluation of function after complex intracardiac surgical repairs (Table 18-2). In addition to traditional surgical approaches in the operating room with full cardiopulmonary bypass, TEE now also is utilized with alternate surgical and transcatheter approaches. The role of TEE has become more important as imaging replaces direct visualization of cardiac structure and function.
TABLE 18-2
Indications for Intraoperative or Intraprocedural TEE
Monitoring ventricular function
Before and after cardiopulmonary bypass in high-risk patients
During noncardiac surgery in high-risk patients
Cardiac surgical procedures
Mitral valve repair
Mechanism of regurgitation
Severity of regurgitation
Functional assessment after mitral valve repair
Complications after mitral valve repair
Prosthetic valve replacement
Evaluation after valve implantation
Detection of complications
Complex surgical valve procedures
Aortic valve resuspension and aortic root repair
Coronary artery reimplantation
Endocarditis
Valve involvement and dysfunction
Assessment after repair or valve replacement
Hypertrophic cardiomyopathy
Evaluation before and after myectomy
Aortic dissection repair
Congenital heart disease—before and after surgical repair
Transcatheter interventions
Transcatheter aortic valve replacement (TAVR)
Transcatheter mitral valve repair procedures
Balloon mitral valvotomy
Balloon mitral valvotomy
Transcatheter closure for paravalvular regurgitation
Atrial septal defect or patent foramen ovale closure
Septal ablation for hypertrophic cardiomyopathy
Placement of intracardiac devices
Cannula placement
Ventricular assist devices
Aortic cannulation (avoid atheroma)
Pericardial disease, including loculated effusion
General surgical complications
Intracardiac air
Preoperative Diagnosis
For elective surgical and transcatheter procedures, the diagnosis and surgical plan should be determined before the operative date (Fig. 18-1). Often, a diagnostic TEE is performed as part of surgical planning in addition to other diagnostic imaging studies, such as coronary angiography, cardiac magnetic resonance (CMR) imaging, or computed tomography (CT). This allows time to review and discuss the diagnostic data, resolve any apparent discrepancies, and obtain additional data, as needed. In addition, the surgical options can be reviewed and discussed with the patient.
Figure 18–1 Flow chart illustrating integration of intraoperative TEE into clinical decision making.
Provide additional information on valve repairability
Serve as a baseline comparison for the postprocedure study
Hemodynamics
Assessment of cardiac hemodynamics and ventricular function in the operating room is affected by:
Positive pressure mechanical ventilation
Myocardial “stunning” secondary to aortic cross-clamping
Effects of cardiopulmonary bypass
Typically, general anesthesia is provided by inhalational agents with supplemental opioids and muscle relaxants, all of which may alter preload and afterload. Many agents impair myocardial contractility, decrease systemic vascular resistance, or both. During weaning from cardiopulmonary bypass, vasodilators or vasopressors may be used to maintain a normal systemic vascular resistance, and inotropic agents may be used if ventricular systolic function is impaired. Positive pressure ventilation at baseline and after cardiopulmonary bypass may reduce systemic venous return because of the increase in intrathoracic pressure; this effect may be most pronounced when ventricular filling volumes are low. The combination of changes in preload, afterload, and contractility may result in variation in the severity of valve regurgitation (Fig. 18-2). Antegrade velocities and pressures gradients also will vary with volume flow rates.
Figure 18–2 Effect of loading conditions on mitral regurgitant severity.
Color Doppler flow imaging shows a vena contracta width (VC) of 0.7 cm when the systolic blood pressure (SBP) is 85 mm Hg compared to VC width of 1.1 cm at an SBP of 140 mm Hg on images taken a few minutes apart with no other intervention. (Courtesy Donald C. Oxorn, MD.)
Surgical Manipulation and Instrumentation
During an open cardiac surgical procedure, the effects of surgical manipulation are directly observable on the TEE images (Fig. 18-3). For example, if the left atrial (LA) appendage was inverted during a mitral valve repair procedure, the inverted appendage may appear as a “mass” in the LA that disappears when the appendage resumes its normal shape. Cannulas for cardiopulmonary bypass may be visualized to confirm correct positioning but also may result in shadowing and reverberations that limit the evaluation of cardiac function. Infusion of cardioplegia results in a contrast effect that may be visualized as increased echogenicity of the perfused myocardium. Intracardiac air related to the open surgical procedure has a characteristic bright appearance, which can be used to ensure that there is no intracardiac air at the end of the procedure (Fig. 18-4). Electronic interference from electrocautery creates an artifact on TEE images and disrupts the color Doppler signal.
Figure 18–3 External cardiac compression on intraoperative TEE.
Comparison of the normal baseline TEE four-chamber view (left) to the same view (right) when the surgeon’s hand is compressing the right heart (arrow). (Courtesy Donald C. Oxorn, MD.)
Time Constraints
Quantitative approaches that are simple and fast are preferred over more complex methods, when possible. For example, valve regurgitation may be quantitated by measurement of vena contracta width, rather than optimizing the proximal isovelocity signal or comparing volume flow rates across the regurgitant and a normal valve. LV ejection fraction most often is visually estimated, rather than tracing end-diastolic and end-systolic borders for a biplane ejection fraction calculation. Three-dimensional image acquisition with semiautomated border detection facilitates quantitative evaluation of LV function. The use of simultaneous imaging in two planes (Fig. 18-5) and the use of simultaneous two-dimensional (2D) imaging and color Doppler helps minimize the exam time while enabling the echocardiographer to acquire a complete image set. Once images are obtained, the echocardiographer also needs to be cognizant of any limitations in the data and communicate those issues to the surgeon. If the echocardiographic data are essential for decision making, adequate time for imaging without electronic artifacts needs to be provided.
Figure 18–5 3D TEE for LV volumes and ejection fraction.
Mid-esophageal views of the LV obtained using 3D imaging (top), with display of the four-chamber (4C) view (left) showing the inferior septum (S) and lateral (L) wall, and the two-chamber (2D) view (right) showing the inferior (I) and anterior (A) walls. Transducer frequency and depth have been adjusted to include the entire LV length and to optimize endocardial definition.
Echocardiographic Approach
The primary goal of an intraprocedural TEE is to address the specific clinical issue in that patient, so a focused examination is appropriate in many situations. However, a complete examination requires only a few minutes and is recommended whenever possible. The American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists recommend a standard series of 20 views (Fig. 18-6). Each view is recorded as a 2-second cine loop, so all these images can be recorded within 10 minutes by an experienced operator, even assuming an average of 30 seconds to obtain each view. Additional time is needed for the evaluation of abnormal findings, color and Doppler spectral recordings, and discussions between the anesthesiologist, surgeon, and cardiologist. Quantitation of LV systolic function using the biplane apical approach with 2D imaging or 3D LV volumes is recommended when time allows (Fig. 18-7).
Figure 18–6 Standard 20 TEE views.
A complete intraoperative examination that includes all of these views is recommended by the American Society of Echocardiography and the Society of Cardiovascular Anesthesiology. asc, ascending; AV, aortic valve; LAX, long axis; ME, mid-esophageal; SAX, short axis; TG, transgastric; UE, upper esophageal. (Modified from Shanewise JS, Cheung AT, Aronson S, et al: ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesth Analg 89[4]:870-884, 1999.)
Figure 18–7 3D LV volume calculations.
A four-beat full volume acquisition was used to calculate LV volumes and ejection fraction using semiautomated border detection. The wire frame end-diastolic and color coded end-systolic endocardial borders show marked hypokinesis of the anterior wall, with inferior apical dyskinesis.
Sequence
There are several possible sequences of image acquisition, all of which are appropriate as long as the needed diagnostic images are obtained. Some echocardiographers prefer to obtain all the views from each transducer position:
This approach minimizes the time needed for acquisition and is easy to remember.
In this sequence (see Fig. 18-5 and Table 18-3), starting in a mid-esophageal four-chamber view with depth adjusted to show the entire LV, the image plane is rotated toward the two-chamber and then long-axis view (see Figs. 3-3, 3-7, and 3-9). The “mitral commissural” view describes a two-chamber plane in which both the medial and lateral commissures are seen and may be identical to the standard two-chamber view at about 60° rotation. An additional “two-chamber” view at about 90° rotation provides visualization of additional segments of the mitral valve and the LA appendage. These views also allow sequential evaluation of regional wall motion in the four-chamber view (inferior septum and lateral wall), the two-chamber view (inferior wall and anterior wall), and the long-axis view (posterior wall and anterior septum).
From the long-axis view, depth is decreased to focus on the aortic and mitral valves. Then the transducer is moved superiorly in the esophagus to visualize the ascending aorta, first in long axis (see Fig. 3-10), followed by rotation of the image plane to a short-axis view of the ascending aorta, with the pulmonary artery seen in long axis. The probe is advanced to a short-axis view of the aortic valve (see Fig. 3-13) and then the tricuspid and pulmonic valves. Turning the probe to the right with further rotation of the image plane yields the bicaval view of the right atrium (RA) (see Fig. 3-12).
From the transgastric position, standard views include the short-axis views at the mid-LV and mitral valve levels, followed by rotation of the image plane to about 90° to show the two-chamber view (see Figs. 3-16 and 3-18). The probe is then turned rightward for a long-axis view, which includes the aorta, and an RV inflow view. From the deep transgastric position, an anteriorly angulated four-chamber view can be obtained in some patients. The descending thoracic aorta is examined in sequential short-axis views from the level of the diaphragm to the arch, as the probe is slowly withdrawn in the esophagus. These short-axis views are supplemented with long-axis views at 90° rotation when abnormalities are seen. The arch is seen from an upper esophageal position by turning the image plane rightward, with a short-axis view obtained by rotation of the image plane.
All four cardiac chambers (LV, RV, LA, RA)
All four valves (aortic, mitral, tricuspid, pulmonic)
Both great arteries (aorta, pulmonary artery)
Systemic and pulmonary venous return (IVC, SVC, four pulmonary veins)
Reporting and Image Storage
Intraprocedural TEE results are communicated directly to the surgeon at the time of data acquisition to facilitate prompt decision making. Intraprocedural TEE results should be available throughout the surgical procedure, verbally or in written format. In addition, a permanent written or electronic report that includes indications, a description of the procedure, and diagnostic findings should be included in the medical record. The report should indicate whether a comprehensive examination (most of the 20 recommended views) was recorded or whether it was a focused or limited examination to address a specific clinical issue. Intraprocedural TEE images and reports should be stored at each medical center in digital format with other echocardiographic images and reports to allow later review and comparison with subsequent studies.
Limitations and Technical Considerations
As with any echocardiographic study, intraprocedural 2D TEE images should be aligned in standard image planes corresponding to long-axis, short-axis, four-chamber, and two-chamber views, with scanning between standard image planes to ensure a comprehensive study. Three-dimensional views also are recorded in standard orientations (see Chapter 4). Internal anatomic landmarks are used to define correct image alignment. The rotation angles provided in tables only serve as a guide to the typical angle needed for a given view; the actual rotation angle varies from patient to patient. In addition, individual variability in the anatomic relationship between the esophagus and the heart results in variability in image plane orientation, so correct alignment of views is not always possible.
Doppler Interrogation Angle
A parallel alignment between the Doppler beam and blood flow of interest is not always possible on TEE imaging. The probe position is constrained by the anatomic relationship between the esophagus and the heart, so even with careful adjustment of transducer position and rotation of the image plane, the interrogation angle may still be nonparallel, with potential underestimation of flow velocities. Intercept angle has a limited impact on the diagnostic value of color Doppler, because the color Doppler flow image corresponds to the spatial pattern of the flow disturbance, even though exact velocities cannot be accurately measured. For spectral Doppler recordings, a near-parallel alignment is easily obtained by TEE for LV inflow across the mitral valve and for LA appendage and pulmonary vein flow (Fig. 18-8). From a high esophageal position, flow in the pulmonary artery also can be recorded at a near parallel intercept angle. However, alignment of the Doppler beam with the LV outflow tract and transaortic flow is problematic. On mid-esophageal views, parallel alignment is not possible. Sometimes better alignment can be obtained from a transgastric long-axis view or a deep transgastric anteriorly angulated four-chamber view. However, underestimation of velocity is likely and should be considered, particularly with TEE evaluation of aortic stenosis severity.
Figure 18–8 Pulmonary vein flow.
A pulsed Doppler sample volume is positioned about 1 cm into the left superior pulmonary vein (LSPV) to record normal systolic (S) and diastolic (D) pulmonary venous inflow into the LA and a slight reversal of flow with atrial contraction (a) in a patient in sinus rhythm.
Technical Issues in the Operating Room and Interventional Suite
During an intraoperative or intraprocedural TEE, the echocardiographer needs to be alert to interference or technical artifacts. Cannula, catheters, and other devices may cause acoustic shadows or reverberations, obscuring the structure or flow of interest (Fig. 18-9). Electronic interference from electrocautery or other procedures precludes diagnostic images or Doppler data (Fig. 18-10). If reverberations and shadowing cannot be avoided by repositioning the probe, alternate approaches, such as epicardial scanning with a sterile transducer, may need to be considered. Electronic devices should be paused when possible to allow recording of echocardiographic data without interference artifacts.
Figure 18–9 Shadowing and reverberations on TEE.
The long-axis TEE view in a patient with endocarditis of a mechanical aortic valve prosthesis shows shadows and reverberations originating from the posterior aspect of the prosthetic valve (yellow arrow) extending in alternating bands (between blue arrows) of dark (shadows) and white (reverberations) to obscure more distal structures, including the anterior aspect of the valve and the LV outflow tract.