Recommendations for Transesophageal Echocardiographic Screening in Transcatheter Aortic Valve Replacement: Insights for the Cardiothoracic Anesthesiologist

Abstract

In a recent Journal of the American Society of Echocardiography issue, Hahn et al. introduce a focus topic on “Recommended Standards for the Performance of Transesophageal Echocardiographic Screening for Structural Heart Intervention.”1 This manuscript, pertaining to pre-procedural workup, received endorsement from numerous prominent cardiology societies. However, although one cardiothoracic anesthesiologist contributed as an author, our subspecialty was overall a minority voice in this collaborative effort. This may be because cardiothoracic anesthesiologists do not frequently acquire outpatient images or report study results for these patients. Yet, as cardiothoracic anesthesiologists increasingly gain ground as perioperative echocardiographers and develop clinical expertise, especially with transesophageal echocardiography (TEE), we firmly believe these recommendations are highly relevant to us. Of all structural heart interventions, this is perhaps most true for transcatheter aortic valve replacement (TAVR). The global burden of aortic stenosis (AS) continues to increase dramatically as the aging population is expected to triple, from 137 million in 2017 to 425 million in 2050 for those over 80 years-old.2 TAVR has been recently shown to provide a safe alternative to surgical aortic valve replacement (SAVR) with comparable short- and long-term outcomes in low, intermediate, and high risk patients3-6 and TAVR volume has grown exponentially, exceeding numbers of isolated SAVR.7 Despite not regularly having our “hands on the probe” in the screening clinic, cardiothoracic anesthesiologists are tasked with interpreting the workup at Heart Team meetings in order to help determine the appropriateness of intervention. We are also called upon to re-assess suitability of TAVR during the periprocedural echocardiogram, and when warranted, given the power to revise the procedural plan. As valued members of the Heart Team and experienced structural imagers, our role in the structural heart arena is more important than ever. Accordingly, in this editorial we will review the recently published guidelines from the American Society of Echocardiography on TEE screening in structural heart interventions1, with a focus on pre-procedural imaging for TAVR. It is important to recognize that the screening guidelines by Hahn et al. for TAVR may have limited utility for pre-procedural evaluation as they only report recommendations for TEE. The majority of TAVR patients will not undergo this imaging test and instead undergo the less invasive transthoracic echocardiography (TTE) to confirm the severity of AS. Once the diagnosis is made, multidetector computed tomography (MDCT) has become the “gold standard” for evaluation of the aortic root and aortic annulus for device sizing and femoral vasculature for access.8 Two-dimensional (2D) TEE is associated with an increased incidence of patient-prosthesis mismatch and post-procedure paravalvular regurgitation.3 2D TEE also tends to underestimate the aortic annulus in patients with a smaller annulus and overestimate in patients with a larger annulus, while three-dimensional (3D) TEE tends to be more accurate for annular sizing.9 A recent meta-analysis and systematic review found that 3D TEE annular measurements had strong correlation with MDCT, and 3D TEE was able to predict paravalvular regurgitation with similar accuracy to MDCT10. There remain several advantages to pre-procedural screening TEE over MDCT, including evaluation of other valvular structures, diastolic function, and right ventricular systolic pressures. In TAVR, moderate or severe post-procedure mitral regurgitation is associated with higher early and 1-year mortality,11-13 and thus a pre-procedure assessment is necessary to determine baseline risk. Significant tricuspid regurgitation can be associated with right ventricular dysfunction and pulmonary hypertension; even mild pulmonary hypertension is associated with higher mortality after TAVR.14 Patients with AS routinely have a significant degree of left ventricular hypertrophy, which can be associated with diastolic dysfunction, and in the long-term, pulmonary hypertension due to left-sided heart disease. The degree of pulmonary hypertension may influence the choice of anesthetic (monitored anesthesia care versus general anesthesia) as well as vasopressor support during the procedure. Assessment of systolic function is also necessary, as patients with a depressed ejection fraction may need mechanical circulatory support during transcatheter valve implantation. In addition, assessment of left ventricular stroke volume is necessary to identify patients with low flow, low gradient AS, which may be associated with worse outcomes after TAVR.15 Finally, TEE may provide valuable information about presence or absence of calcifications in the left ventricular outflow tract (LVOT); moderate or severe LVOT calcification is associated with increased risk of annular rupture, especially with balloon-expandable valves.16 TEE evaluation of the LVOT may therefore change choice of device or suggest avoidance of pre- and post-deployment balloon dilation, and if calcifications are present in the aortic root, may change operative strategy completely (e.g. from a TAVR to a SAVR). A 2017 expert consensus decision pathway from the American College of Cardiology stated that TEE was “somewhat invasive” in the frail TAVR population and is “not recommended for routine pre-TAVR valve sizing.”17 However, TAVR is increasingly being performed in younger patients with fewer comorbidities, and thus performance of TEE under sedation may not confer substantial additional risk. While MDCT is less invasive, TEE can provide evaluation of other cardiac structures as well as accurate aortic annular and root measurements for patients who may have contraindications to MDCT (e.g., severe renal dysfunction) or when MDCT is unable to determine annular size for device selection (e.g. measurements fall in between two sizes). In cases where MDCT assessment is inadequate, TEE placed immediately pre-intervention can supplement evaluation, as well as provide the most current assessment of systolic, diastolic, and valvular function. Therefore, MDCT and 3D TEE can and should be used in a complementary fashion. Preprocedural TEE imaging should be focused on identifying the mechanism of valvular dysfunction, severity of disease, as well as appropriate anatomy for device selection.1 Comprehensive 2D and 3D images should be obtained, with a focus on 3D optimization of images for evaluation of the aortic valve structures. This manuscript provides some simple yet effective pearls in this regard: mid-esophageal (ME) short-axis (SAX) images (40-60°) from both the aortic side and ventricular should be used to identify unfavorable aortic pathology.1 Not emphasized were the ME long-axis (LAX) views (110-140°), which are required to evaluate leaflet and subaortic pathology as well as the basal ventricular septum. While real-time imaging (live 3D) can provide rapid visualization of the aortic valve, multi-beat imaging should be used whenever possible to improve both spatial and temporal resolution. The authors’ recommendations demonstrate their high level of expertise in 3D imaging. They provide excellent guidance concerning the limitations of various 3D techniques including how dropout, blurring, blooming, railroad shape, and reverberations and shadowing impacts our assessment of the native or artificial valve and catheters and wires during the intervention.1 The manuscript cautions against measurement directly on the 3D image due to parallax error, and instead suggests that when precise measurements are needed (e.g. aortic annular dimensions), multi-beat spliced images should not be used as undetectable splice artifacts may affect the measurement.1 The authors of this document are experienced interventional echocardiographers well-versed in aortic annular sizing by TEE, which was commonly performed before MDCT became the gold standard. This section should be carefully read and practiced in the cardiac operating room as there are fewer opportunities to master this skill in the structural heart setting. Accurate measurements of the aortic annulus are critical: oversizing can lead to frame distortion or catastrophes such as annular rupture while undersizing can lead to significant paravalvular regurgitation or even valve embolization18-20. Hahn et al. recommend a zoomed-in ME LAX view of the aortic valve with the LVOT aligned with the aortic root. The paper provides a great image on 3D multiplanar quantification describing where the annulus should be drawn (during mid-systole, defined by a line bisecting the valve between the noncoronary and left coronary cusps posteriorly and right coronary cusp anteriorly).1 This measurement should still be performed manually as the document cautions that newer automatic programs have yet to be validated. The LVOT diameter is key for the calculation of aortic valve area and stroke volume, and should be measured at the annulus for the greatest accuracy, from the right coronary cusp hinge anteriorly to the posterior aortic root at the base of the interleaflet trigone.1 Coronary artery obstruction is a known risk of TAVR, and typically occurs from displacement of the calcified coronary cusps towards the ostia of the coronary arteries21. A length of ≤ 10 mm from the aortic annulus to the coronary ostia is associated with a higher risk of coronary artery obstruction after TAVR.22 The distance from the annulus to the coronary ostia as well as the length of the aortic valve cusps should be measured from 2D reconstructed images from a 3D zoomed volume. Most cardiothoracic anesthesiologists are comfortable with the assessment of AS severity as determined by calculation of pressure gradients and aortic valve area via Doppler echocardiography, which is reviewed in this document. However, the recommendations regarding aortic regurgitation (AR) quantification may be new. While we are comfortable imaging and assessing AR pressure half-time, velocity-time integral, and jet density in the deep transgastric 5 chamber views, these guidelines suggest proximal isovelocity surface area (PISA) as an integral assessment of severity of AS. While PISA is not a new concept, the use of PISA for AR may be relatively new and should be reviewed in detail. With increasing TAVR volumes across the globe, cardiothoracic anesthesiologists may be increasingly expected to participate in pre-procedural evaluation of patients as part of the Heart Team. Consequently, it is imperative to have an expert understanding of aortic valve and root anatomy and measurement. Even if the cardiothoracic anesthesiologist is not involved in procedural decision-making, it is important to understand pre-procedural imaging and prepare for the potential complications after TAVR, including risk of paravalvular regurgitation, permanent pacemaker implantation, coronary artery obstruction, and device embolization. The guidelines provided by Hahn et al., while comprehensive, do fail to address a few pertinent areas of aortic valve assessment. There is increasing debate whether implantable valve size should be determined by perimeter; as the aortic valve becomes increasingly stenotic, it becomes more oval, and area reduces disproportionately to perimeter, leading to potential underestimation of the true annular dimensions and undersizing23. The guidelines do not provide detailed recommendations for measurement of membranous septum length, which is an important determinant of the risk of complete heart block and need for permanent pacemaker. Finally, Hahn et al. make no mention of the advantage that screening TEE can provide over MDCT in the precise localization of calcium deposits in the aortic annulus, cusps, LVOT, and root, which can be a risk factor for post-intervention paravalvular leak.24 Accurate aortic annular and root measurements are critical to appropriate device selection in TAVR. Pre-interventional imaging is key to procedural success. Both MDCT and 3D TEE have been shown to be accurate in measuring the aortic annulus and can be used in a complementary fashion. The cardiothoracic anesthesiologist may be increasingly involved in pre-procedural planning given the growth of the TAVR procedure. Pre-procedural TEE imaging should focus on optimization of 3D images, with intimate knowledge and acquisition of annular and root dimensions along with evaluation of biventricular systolic and diastolic function and mitral and tricuspid pathology. 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JACC Cardiovasc Interv 2(9):821-827, 200921. Ribeiro HB, Nombela-Franco L, Urena M, et al: Coronary Obstruction Following Transcatheter Aortic Valve Implantation: A Systematic Review. JACC Cardiovasc Interv 6(5):452-461, 201322. Corrigan FE, 3rd, Gleason PT, Condado JF, et al: Imaging for Predicting, Detecting, and Managing Complications After Transcatheter Aortic Valve Replacement. JACC Cardiovasc Imaging 12(5):904-920, 201923. Bleakley C, Monaghan MJ: The Pivotal Role of Imaging in TAVR Procedures. Curr Cardiol Rep 20(2):9, 201824. Bhushan S, Huang X, Li Y, et al: Paravalvular Leak After Transcatheter Aortic Valve Implantation Its Incidence, Diagnosis, Clinical Implications, Prevention, Management, and Future Perspectives: A Review Article. Curr Probl Cardiol 47(10):100957, 2022 E. Methangkool receives consultant fees from Edwards LifeSciences and author royalties from UpToDate, Inc. L. Rong is funded by NIH grant K23HL153836. None of these financial interests are relevant to the subject matter of the manuscript.