Intraoperative Echocardiography

The use of transesophageal echocardiography (TEE) in the operating room has evolved from a simple tool to look at ventricular wall motion to a powerful diagnostic modality for examining every facet of cardiac and noncardiac surgery. Its use has improved the quality of perioperative care. Intraoperative assessments of valvular function, chamber size, masses, and great vessels are covered in other chapters of this textbook.

The milieu of the operating room is unique and not always conducive to obtaining TEE images of high quality. Image quality can be improved by dimming the lights in the room as much as possible to avoid the necessity for overgaining, completing the important parts of the study before the surgical incision is made, and setting the loop cycle to a time-based rather than a beat-based mode to prevent premature looping when electrocautery is used. The TEE probe is placed under general anesthesia, making understanding of the difficulties of probe insertion and manipulation especially important.

Echocardiography

Procedural and Technical Experience

General standards and training requirements are necessary to ensure competency and the quality of echocardiography in any institution. Trainees perform and interpret studies under supervision from certified faculty and must meet certain criteria for their own certification.

Echocardiography is a growing field in terms of technology and its use for assessing diseases and confirming diagnoses. There is opportunity for lifelong learning and continued mastering of skills. The American Society of Echocardiography, Society of Cardiovascular Anesthesiologists, Canadian Cardiovascular Society, and European Society of Cardiology require continuing medical education (CME) and a minimum number of yearly TEE studies for maintenance of certification. Competency and certification are maintained by governing bodies, and a minimum number of procedures ensures adequate familiarity with the techniques. Proficiency in TEE includes the ability to perform the examination safely, manipulate the probe in a variety of domains, adjust controls to optimize images, recognize abnormalities in cardiac structures or function, perform qualitative and quantitative analysis, and accurately report findings.

Risks and Contraindications

Risks and contraindication for TEE are listed in Table 9.1 . TEE is contraindicated for patients with esophageal disease (e.g., esophageal stricture), tumor, active upper gastrointestinal (GI) bleeding, and perforated viscous. The risks associated with TEE are rare but can cause serious morbidity and mortality. Each case should be evaluated based on a risk-benefit analysis, with special attention to the absolute and relative contraindications to TEE.

TABLE 9.1

Relative and Absolute Contraindications to TEE.

Data from Hahn RT, Abraham T, Adams MS, et al. Guidelines for performing a comprehensive transesophageal echocardiographic examination: recommendations from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. J Am Soc Echocardiogr . 2013;26:921–964; Reeves ST, Glas KE, Eltzschig H, et al. Guidelines for performing a comprehensive epicardial echocardiography examination: recommendations of the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. J Am Soc Echocardiogr . 2007;20):427–437; Flachskampf FA, Badano L, Daniel WG, et al. Recommendations for transoesophageal echocardiography: update 2010. Eur J Echocardiogr . 2010;11:557–576.

Absolute Contraindications ^a	Relative Contraindications
Previous esophagectomy or esophagogastrectomy Active upper GI bleed Esophageal Stricture Tumor Injury Diverticulum	Esophageal varices Active esophagitis or peptic ulcer disease Restricted neck mobility Barrett esophagus Recent upper GI bleed History of GI surgery Dysphagia Vocal cord paralysis or injury Coagulopathy Severe thrombocytopenia Symptomatic hiatal hernia

GI , Gastrointestinal.

a There is debate among experts about what constitutes absolute contraindications; risks and benefits must be weighed for each patient.

Evaluation of Intraoperative Ventricular Function

LV Diastolic Function

In patients with impaired diastolic function, left ventricular (LV) filling in the period after separation from cardiopulmonary bypass is especially tenuous. Diastolic function is often further reduced, and depending on the degree, it may portend an increased incidence of adverse myocardial events. In addition to the standard parameters of mitral inflow and pulmonary venous flow velocities, newer techniques may be used to better define problems with ventricular filling. ^,

Tissue Doppler imaging (TDI) of the mitral annulus has been proposed as a descriptor of LV relaxation that is less affected by changes in loading conditions and ventricular function than more traditional Doppler parameters. Because the E′ velocity relates directly to LV relaxation, this parameter has been used to correct for LV relaxation and render the E wave of mitral inflow more accurate in the estimation of LV filling pressure (E/e′ ratio). This approach has been validated using transthoracic echocardiography (TTE) and also with TEE in the non-operative ICU setting; however, results obtained with TEE in patients undergoing cardiac surgery have not been replicated. Kumar et al., using filling pressures derived from pulmonary artery (PA) catheters as the standard, showed that TDI of the lateral mitral annulus was unable to accurately predict LV filling pressures. Many conditions other than left atrial (LA) pressure that influence the E/E′ ratio are present in the intraoperative population, limiting the usefulness of this parameter. ^,

Color M-mode flow propagation velocity is another less load-dependent measure of diastolic function and is attractive in that it examines simultaneous pulsed-wave (PW) Doppler measurements throughout the LV cavity. Djaiani et al. showed that in patients undergoing coronary artery bypass grafting (CABG), a value less than 50 cm/s identifies abnormal diastolic function. Color M-mode has shown dependability as a simple method to quickly and reliably evaluate LV diastolic function. The numerous parameters available and their lack of validity in the intraoperative setting limit the usefulness of diastolic dysfunction evaluation after cardiac surgery. ^,

Systolic Function

LV Systolic Function

The American Society of Echocardiography’s guidelines and standards committee published recommendations for chamber quantification by TTE and TEE. The normal ranges for dimension and volume are comparable for the two techniques. ^,

Several investigators have examined the intraoperative relationship between end-diastolic area or end-systolic area measured at the transgastric mid-papillary level and cardiac volume status. Cheung et al. performed an elegant study examining the effect of graded hypovolemia produced by autologous blood collection on hemodynamic- and TEE-derived indices of LV preload in patients undergoing coronary artery bypass surgery. Patients with valvular insufficiency, rhythms other than sinus, or overt congestive heart failure were excluded. End-diastolic area, end-systolic area, pulmonary capillary wedge pressure, and measures of end-diastolic and end-systolic wall stress decreased linearly as blood volume was reduced by 0% to 15% in all patients; however, in patients with impaired LV function, only the TEE-derived indices maintained linearity. As the study authors acknowledged, estimation of ventricular volume in patients with asymmetric ventricular dysfunction can be problematic because hypokinetic or akinetic areas may not be represented in the area of the two-dimensional (2D) cut.

The presence of a small end-diastolic area or end-systolic area does not always reflect decreased intravascular volume. Small LV volumes can be seen with restrictions to filling (e.g., pericardial disease) or decreased right-sided heart function ( Fig. 9.1 ), such as with a right ventricular (RV) infarction or a large pulmonary embolus. Other causes of a small LV volume include increased inotropy or redistribution of blood out of the thoracic cavity.

Fig. 9.1, Decreased LV end-systolic volume.

LV Volumes

The accepted approach for volume measurement is the biplane method of disks (i.e., Simpson’s rule). Studies using multiplane probes have shown that volumetric data obtained by 2D TTE and 2D TEE show minor or no differences.

3D TTE has proved to be a useful tool in the measurement of LV volumes, and normal ranges of values have been published. ^, Notwithstanding the fact that 3D echocardiography-derived volumes tend to be underestimated compared with cardiac magnetic resonance (CMR) imaging, the data obtained are significantly closer to those of CMR than 2D, and they are more robust when tested for intraobserver and interobserver variability and for test-retest reproducibility. Compared with magnetic resonance imaging (MRI), echocardiography slightly underestimates (by 4%) volumes and ejection fractions (EFs) and is less sensitive for detection of wall motion abnormalities.

The use of real-time 3D TEE in the operating room has increased dramatically, particularly for mitral valve assessment and periprocedural monitoring. Meris et al. compared intraoperative 2D and 3D TEE measurements of ventricular volumes and EFs. The 2D data were obtained using automated border detection, followed by manual tracing in the 2- and 4-chamber views and application of the Simpson rule. The 3D data were acquired in full-volume mode and subsequently analyzed with the use of Philips Q-lab 3D-Advanced quantification software (Philips Medical Systems, Boston, MA).

The results are shown in Table 9.2 . The EF was the same using both modalities. Ventricular volumes were greater in the 3D group, but although the difference was statistically significant, it did not lead to any differences in LV classification as normal, mildly to moderately dilated, or severely dilated. Data acquisition times were similar, but analysis of the data took longer in the 3D group and was predicated on a stable rhythm, a necessity for multiple beat acquisition.

TABLE 9.2

3D and 2D TEE Indexed Volumes and Function for a Study Population ( N = 152) and Its Subgroups.

From Meris A, Santambrogio L, Casso G. Intraoperative three-dimensional versus two-dimensional echocardiography for left ventricular assessment. Anesth Analg . 2014;118:711–720.

Parameter	3D TEE	2D TEE	P Value	Median Pairwise Difference (99% CI)
EF (%)	55 ± 14	55 ± 14	0.227	−0.4 (−1.2 to 0.3)
iEDV (mL/m ² )	54 ± 21	51 ± 21	<0.001	3.3 (2.5 to 4.2)
iESV (mL/m ² )	26 ± 18	24 ± 17	<0.001	1.4 (1.0 to 2.0)
3D and 2D iEDV (mL/m ² ) ^a
*Systolic Function*
Normal (62%)	47 ± 16	43 ± 15	<0.001	3.2 (2.3 to 4.4)
Mildly abnormal (16%)	53 ± 14	51 ± 12	0.794	3.6 (−3.8 to 5.8)
Moderately abnormal (14%)	71 ± 23	67 ± 23	0.001	3.3 (1.6 to 6.2)
Severely abnormal (8%)	89 ± 23	85 ± 24	0.023	3.9 (0.7 to 6.9)
*Ventricular Volume*
Normal (86%)	48 ± 12	45 ± 12	<0.001	3.5 (2.4 to 4.2)
Dilated (14%)	101 ± 19	96 ± 17	0.002	3.2 (1.2 to 5.6)

CI , Confidence interval; EF , ejection fraction; iEDV , indexed end-diastolic volume; iESV , indexed end-systolic volume; TEE , transesophageal echocardiography.

a Subgroups of patients are reported as a percentage (in parentheses) of the whole population ( N = 152).

Conclusions

Assessment of preload with intraoperative TEE is in most cases a semiquantitative estimate based on visual inspection of end-diastolic area and end-systolic area and supported by an array of Doppler indices. The use of 2D TEE to quantitate ventricular volumes is feasible, but the use of 3D TEE is limited by beat acquisition difficulties and long analysis times. Confounding conditions, such as RV failure, vasodilation, or the administration of inotropic agents, must be considered.

Global Systolic Function

Cardiac Output

Doppler TEE has the potential for use in the intraoperative setting for the continuous measurement of cardiac output. These methods are based on the concept that the cross-sectional area of a conduit in the cardiovascular system multiplied by the Doppler-derived time–velocity integral yields the stroke volume through that conduit. When the result is multiplied by heart rate, the product is cardiac output.

Several important assumptions are inherent in this approach. Valid area formulas must be applicable to the anatomic site being analyzed. The velocity profile across the valve must be flat and devoid of skew. ^, Whichever anatomic area is chosen, the ability to consistently obtain the image and to interrogate parallel to flow is mandatory.

Cardiac output can also be calculated from 2D or 3D volumetric measurements by subtracting the systolic volume from the diastolic volume and multiplying by the heart rate to obtain cardiac output. This process is more time-consuming than Doppler-derived data, less accurate in the setting of mitral regurgitation or arrhythmia, and seldom used in the operating room.

LV Outflow Tract

Use of Doppler technique in regard to the left ventricular outflow tract (LVOT) has been extensively studied and found to be extremely accurate when applied to a group of patients before and after cardiopulmonary bypass. With the probe in the stomach, turned leftward, in the flexed position, and at low imaging frequency, the aortic valve and LVOT can usually be imaged between 0 and 140 degrees ( Fig. 9.2 ). Imaging from the stomach allows parallel pulsed-Doppler interrogation of the LVOT; its diameter can be obtained from the stomach or from the mid-esophageal long-axis view. Calculations of the cross-sectional area and cardiac output follow the standard formula (see Fig. 9.2 ). To avoid contamination of the Doppler signal by the region of flow acceleration adjacent to the aortic valve orifice, the sample volume must be placed precisely in the LVOT. In the setting of outflow tract obstruction, the validity of the measurement may be compromised.

Lodato et al. measured LVOT area using 2D and 3D TTE with color Doppler in the assessment of stroke volume and compared the values with thermodilution-acquired stroke volumes. Although they correlated well, there was less bias with 3D measurements, which was attributed by the study authors to 3D’s independence from geometric assumptions. Similar findings with TTE were observed by Shahgaldi et al., who found that stroke volume measurements using a 3D planimetered LVOT area ( Fig. 9.3 ) were more accurate than traditional 2D measurements and the biplane method of disks (i.e., Simpson’s rule), although CMR remains the true gold standard for measurement of LV volumes.

Fig. 9.3, Multiplanar reconstruction of the LV outflow tract (LVOT) .

Montealegre-Gallegos et al. compared cardiac output measurements made with 2D and 3D TEE. They posited that the assumption of a circular LVOT could introduce error because of its actual ellipsoid shape. Using 3D TEE and multiplanar reconstruction, they substituted a planimetered measurement of the LVOT area. Although the 2D and 3D measurements were highly correlated, the 2D method was on average 10% lower. The main limitation was that there was no comparison with a gold standard.

Pulmonary Artery

With the probe at 0 degrees and retroflexed, the main PA and pulmonic valve can be imaged at the base of the heart. In a study by Gorcsan et al. using PW and continuous-wave (CW) methods and with the PA diameter measured just distal to the pulmonic valve, intraoperative cardiac output was calculated. Interobserver variability was low in all studies, and correlation with thermodilution cardiac output was strong. Alternatively, the main PA may be imaged at 60 to 90 degrees using the aortic arch as a window ( Fig. 9.4 ).

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