A 54-year-old male patient underwent off-pump coronary artery bypass surgery. Given severely compromised left ventricular (LV) performance with LV distension and chordal tethering of the mitral leaflet, high-dose inotropic therapy and intraaortic balloon pump (IABP) counterpulsation were initiated before his arrival in the operating room. Through anesthetic induction, mean arterial blood pressure 70 to 75 mm Hg and heart rate 90 to 100 beats/min were maintained.
Intraoperative 2-dimensional (2D) transesophageal echocardiography (TEE; iE33™, Philips Healthcare, Bothell, WA) revealed hypokinesia in the basal and apical inferolateral LV segments with an LV ejection fraction of 40% to 50%. The IABP tip was located approximately 10 to 12 cm distal to the opening of the left subclavian artery in the descending aorta. Orthogonal (short and long axis) 2D images were obtained to delineate the descending aorta around the IABP by advancing/withdrawing the 3-dimensional (3D) matrix array TEE probe (X7-2t™, Philips Healthcare). “X-plane” 2D images revealed diffuse thickening of the intimal layer with 2 small (<3 mm) protruding atheromatous plaques on the posterolateral walls of the descending aorta (Fig. 1A; Supplemental Digital Content 1, Supplemental Video 1, http://links.lww.com/AA/B319), corresponding to a “mild-grade” atheroma (Table 1).1
Real-time 3D, zoomed imaging of the same region of interest (ROI) revealed larger (>5 mm) atheromatous plaques with irregular surfaces (Fig. 1, B and C; Supplemental Digital Content 2, Supplemental Video 2, http://links.lww.com/AA/B320). Additional 3D “en face” (3D zoom) imaging, in which the ROI was rotated and adjusted to focus on the posterolateral aortic wall, revealed additional larger (>5 mm) plaques that were mobile and had irregular surfaces (Fig. 2, A and B; Supplemental Digital Content 3, Supplemental Video 3, http://links.lww.com/AA/B321). Additional multiplanar images with 3 different axes, which were rendered by the use of installed software (3DQ in QLab™, Philips, Baltimore, MD), confirmed the size of the larger plaques (Fig. 2, C and D), corresponding to “severe and complex grade” on the atheroma grading system (Table 1).
These plaques were felt to have potential to liberate emboli by the repetitive IABP inflation/deflation with possible mobilization into the cerebral circulation. An epiaortic 2D scan of the ascending aorta was performed and revealed small intimal thickenings in the anterior aspect of the sinotubular junction. Considering the relative thromboembolic risks of the descending aortic plaques, on-pump beating coronary artery bypass graft surgery with partial cardiopulmonary bypass (CPB) support through an ascending aortic cannula was performed, instead of the planned off-pump coronary artery bypass procedure with IABP support.
During cardiac displacement for anastomosis of the distal bypass grafts to the left anterior descending, the obtuse marginal, and the posterior descending arteries, CPB flow ranging from 1.5 to 2.0 L/min was applied with intermittent cardiac pacing. The IABP was then removed without further use during weaning from CPB, and, instead, high-dose inotropic support with milrinone, dobutamine, and phenylephrine was used until the immediate postoperative period. The patient was discharged 6 days after surgery without any thromboembolic complications.
An atherosclerotic plaque (atheroma) is a vascular deposit of calcium and fatty materials.2 Atheromas in the ascending or arch segment of the aorta are associated with a greater prevalence of stroke and embolic complications than in the descending aorta, because direct aortic cannulation, cross-clamping for CPB, and turbulent flow from the cannula can mobilize embolic debris out of atheromas located in these segments and into the cerebral circulation during cardiac surgery.3 Therefore, echocardiographic grading scales have been developed to evaluate atheromas in the ascending and arch segments of the aorta and to identify their risks to the patient. Atheromas that are large (>5 mm), mobile, or ulcerated, which are located in the ascending aorta, carry the greatest risk of stroke and embolic complications.1 In contrast, atheromas in the descending aorta have been regarded as having a lower risk of stroke. However, the repetitive inflation/deflation of an IABP and counterpulsation in the descending aorta may increase the risk of stroke attributable to atheromas in this area.3 Therefore, echocardiographic evaluation for atheromas in the descending aorta may be necessary when weighing the risk-benefit ratio of the use of an IABP in coronary artery bypass graft surgery patients. Early imaging data for the surgeon can be helpful to facilitate treatment strategies, based on the local surgical preferences, as in this case.
Intraoperative 2D TEE imaging is useful for detecting aortic atheromas and to making detailed evaluations during cardiac surgery,4,5 despite its inability to delineate the distal portion of the ascending aorta. However, 2D TEE requires frequent modification of the probe position and use of multiplane angles to detect and evaluate atheromas located at different levels of the aorta. X-plane imaging with the use of a 3D matrix array (or similar orthogonal imaging systems used by different ultrasound vendors), which produces instantaneous orthogonal images, can reduce the need to frequently change the multiplane angle.
As in this case, addition of a single real-time 3D zoom en face image to the conventional 2D echocardiographic evaluation may assist in intraoperative decision-making when using an IABP. The greater volumetric coverage and intuitive en face images produced by 3D TEE render it easier to quickly delineate multiple atheromas distributed over a broad aortic area and their mobility and surface contour (Fig. 2, A and B). Weissler-Snir et al. also included the surface contour (irregularity) for evaluating the complexity of the descending aortic atheroma, in addition to the conventional variables, such as thickness, ulceration, and mobility, and demonstrated a significantly greater complexity in thickness and irregularity with 3D TEE than with 2D TEE.6
Applying built-in 3D grids (dot-to-dot distance of 2 mm) also facilitates approximate measurement of plaque size at a glance (Fig. 2C). Multiplanar cut images, which were rendered out of 3D en face volume images, enabled detailed evaluation of plaque size without foreshortening (Fig. 2D). Piazzese et al.7 demonstrated that 3D TEE with semiautomated software enhanced both feasibility and accuracy for echocardiographic evaluation of the thickness, volume, and number of the descending aortic plaques.
However, 3D delineation of the esophageal aspect of the descending aortic wall is limited, because 3D (pyramid shaped) volume image sector corresponding to this aortic area is narrow and thin and close to the TEE probe. Unfortunately, increasing the angle of 3D image sector (to 60° at most) usually does not overcome this limitation and can paradoxically reduce temporal and spatial resolution. Therefore, not only appropriately selecting line density (i.e., resolution/speed balance) but also optimizing the size and location of the ROI of the 3D-zoom image is important when conducting a detailed evaluation. 3D full-volume imaging is one way to delineate a relatively wide aortic area without compromising image resolution, despite the possible association with electrocardiographic-gated stitching artifacts. However, 3D TEE cannot evaluate plaque composition including calcification, despite its superiority in plaque localization, quantification, and evaluation of surface contour. Reducing gain to evaluate plaque composition can reduce the plaque’s size and surface irregularity in the TEE image,7 as in the present case (Fig. 3). Without adopting a “gold-standard” imaging modality, determining the appropriate level of gain and compression for avoiding overestimation or underestimation of the plaques’ size and tortuosity is challenging. If the same atheroma is clearly noted in both 2D and 3D images, adjusting gain and compression to match their sizes may be beneficial.
Clinician’s Key Teaching Points
By Nikolaos J. Skubas, MD, and Martin J. London, MD
- An atherosclerotic plaque or atheroma is composed of calcium and fatty material. Surgically induced injury to the ascending aorta at the sites of aortic cannulation, cross-clamping, or anastomoses as well as possible “sand-blasting” effects by the aortic cannula on atheroma in the aortic arch can mobilize atherosclerotic debris, resulting in perioperative stroke or other embolic events (e.g., kidney, splanchnic). Atheromas in the descending aorta are considered lower risk, because they are less likely to be impacted by surgical interventions. However, they may be affected by placement of an intraaortic balloon pump (IABP).
- The risk for stroke or embolism is greater in thicker (>5 mm), protruding, or ulcerated surface atheromas. By using 2-dimensional (D) transesophageal echocardiography (TEE) in a transverse orientation, the entire thoracic aorta can be scanned for atheromas, except for a “blind spot” in the distal ascending and proximal aortic arch (because of interposition of the air-filled trachea). For thorough detection, the TEE probe should be advanced and withdrawn from the diaphragm to the aortic arch using simultaneous orthogonal imaging.
- In this case, an adult male patient with depressed left ventricular function that required inotropic and IABP support was scheduled to undergo off-pump coronary bypass. After induction of anesthesia, the descending aorta distal to the IABP tip was scanned for atheroma by the use of both simultaneous orthogonal 2D TEE and 3D TEE imaging. 2D TEE revealed small (<3 mm) atheromas. In contrast, 3D TEE in “full-volume” mode allowed the interrogation of a larger aortic area and revealed multiple, protruding, large atheromas, which were considered an embolic risk with the use of IABP counterpulsation. Thus, coronary revascularization was performed on-pump after a negative epiaortic scan of the ascending aorta.
- The morphology of atheromas is easier to clarify with 3D TEE. In some 3D TEE systems, superimposition of a linear grid allows a quick estimation of their size. However, the aortic wall proximal to the TEE probe may not be scanned by the apex of the 3D pyramidal sector and thus also should be imaged with 2D TEE.
Name: Won-Kyoung Kwon, MD, PhD.
Contribution: This author helped conduct the study and write the manuscript.
Attestation: Won-Kyoung Kwon approved the final manuscript.
Name: Nazri Mohamed, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Nazri Mohamed approved the final manuscript.
Name: Ga-Yon Yu, MD.
Contribution: This author helped conduct the study.
Attestation: Ga-Yon Yu approved the final manuscript.
Name: Rina Kim, BS.
Contribution: This author helped conduct the study and write the manuscript.
Attestation: Rina Kim approved the final manuscript.
Name: Tae-Yop Kim, MD, PhD.
Contribution: This author helped analyze the data, design the study, and conduct the study.
Attestation: Tae-Yop Kim approved the final manuscript.
This manuscript was handled by: Martin London, MD.
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