Although the concept of 3-dimensional (3D) echocardiography was first introduced in the early 1970s, its utility in the perioperative environment has only recently been recognized. Three-dimensional reconstruction echocardiography using conventional 2-dimensional (2D)-phased array multiplane probes has been commercially available for >15 years. However, its practical use in the operating room environment can be challenging, because optimal images worthy of interpretation require respiratory and electrocardiogram gating, lengthy acquisition periods, and significant expertise to obtain and edit full volume datasets. Alternatively, more recently introduced real-time 3D echocardiography using miniaturized matrix arrays permits the acquisition of true live displays of pyramidal volumes, as well as hybrid reconstructed full volumes.1–6
Perioperative 3D transesophageal echocardiography (TEE) has emerged as an important imaging technique for enhancing the diagnostic confidence of conventional echocardiography, and potentially facilitating surgical planning, especially in patients with functional or degenerative mitral valve (MV) disease.7–9 Intraoperative 3D TEE can potentially provide a more efficient comprehensive examination of the MV in the intraoperative environment, where timely, effective, and clinically relevant decision making is critical. Although a comprehensive 2D TEE examination of the entire MV apparatus requires acquisition of 6 imaging windows using several probe manipulations, including advancement of the TEE probe through 3 esophageal depths, an infinite number of flexion maneuvers and 150 degrees of multiplane rotation,10,11 the acquisition of a single pyramidal 3D volume that includes the entire MV apparatus can be obtained and displayed in real time with a 3D TEE matrix array probe from a single imaging window.1–4 Furthermore, these full-volume 3D sets can be rotated, cropped, and displayed from any perspective. Consequently, the intraoperative echocardiographer can appreciate MV anatomy more efficiently with significantly less dependency on scanning, geometric assumptions, or pattern recognition.1–4 Three-dimensional TEE may also permit more effective communication with cardiac surgeons and interventionalists, and lead to more accurate diagnoses.12–15 The functional geometry of the MV apparatus can be displayed in a variety of en face views using different rotational angles,16 thereby providing unique views that are more familiar to cardiac surgeons and interventional cardiologists, which may facilitate a better understanding of abnormal anatomy and associated pathology. Finally, accurately identifying the specific location and severity of mitral regurgitation (MR) jets, especially immediately following MV repair or replacement, can also facilitate decision making regarding the need for urgent further intervention.17
In this issue of Anesthesia & Analgesia, Hien et al.18 report that intraoperative 3D TEE was superior to 2D TEE for delineating MV pathology in 62 consecutive patients with MR scheduled for elective MV repair. All patients in this study underwent comprehensive intraoperative 2D and 3D TEE examinations of the MV (IE33; x7-2t Matrix array; Philips Healthcare, Inc., Andover, MA). The 2D TEE examination was performed according to published guidelines using only midesophageal views10,11 and was supplemented by color flow Doppler imaging. Following the 2D TEE examination, the MV image was first optimized in the “x-plane” view using 2 simultaneously displayed 2D live orthogonal views. Subsequently, a 3D TEE MV image was acquired using “zoom” mode, which provides an enlarged 3D pyramidal volume. Contrary to the 2D TEE examination, 3D TEE color flow Doppler was not used. The intraoperative TEE findings were compared against direct visual inspection of the MV by the operating cardiac surgeon during cardiopulmonary bypass, who provided diagnoses of ruptured chordae, leaflet prolapse, clefts, and grades of MR using a saline test. Offline, 2D and 3D images were presented independently and in random order to 2 expert interpreters who were blinded to the images of the other modality and the preoperative or intraoperative findings. Of note, no color Doppler TEE images were available to the offline interpreters nor were color flow 3D volumes acquired. However, extensive manipulation of the 3D MV images was performed using the “multiplanar reconstruction” mode, a proprietary, yet commercially available software tool that enables the creation of an infinite number of 2D transectional planes from a 3D TEE pyramidal volume data set, to facilitate diagnosis of complex MV anatomy and geometrical relationships. Surgical inspection identified 52 cases of MR due to MV prolapse. Real-time 3D TEE correlated stronger with the surgical findings than 2D TEE for detection and localization of MV prolapse (P < 0.001) and chordal rupture (P < 0.001).
The fundamental findings of Hien et al. contribute to an expanding body of literature that suggests a consistent advantage of intraoperative 3D TEE compared with 2D TEE for diagnosing complex, degenerative MV disease12–14,19 (Table 1). The utility of 3D TEE for locating prolapsing segments and identifying less commonly observed clefts and commissural pathology may enable more effective surgical planning, since some of these findings are often subtle and difficult to appreciate in the unloaded heart during cardiopulmonary bypass. Despite the apparent similarity in the findings reported in these studies that compare intraoperative 3D TEE with 2D TEE during MV surgery, it is important to appreciate differences and limitations in methodology, including the variability in experience and the number of echocardiographers responsible for acquiring images and interpreting the data, whether data can be further “interrogated” (when in the native full-volume set) or not (when saved in DICOM format) as well as the number of surgeons evaluating the MV anatomy. In addition, bias is inevitably introduced when the 2D TEE examination precedes a subsequent, “focused” 3D TEE examination. Details pertaining to the extent of using preprocessing techniques and parameters for determining the ideal balance between frame rate (temporal resolution), line density (spatial resolution), and 3D pyramidal volume size are often not well delineated in the methods, while the lack of standardization for defining ideal postprocessing (gain and compression), display and cropping techniques, and variability in the use of miscellaneous proprietary or commercially available tools (i.e., Q-labs: Philips Healthcare Inc; Tomtec, Inc, Hamden, CT) for quantitative analysis can make it difficult to compare findings from different studies. Furthermore, the absence of color flow Doppler in some studies may limit the ability to interpret and determine the comparative practical value of the results. Although determining the presence, location, and severity of prolapse may be useful in guiding the surgical approach, it is the severity of MR defined by color flow Doppler techniques that is most correlated with short-term and long-term repair durability and morbidity. Finally, the use of direct surgical inspection for validating the accuracy of MV pathology poses an ironic limitation. While seemingly an obvious “gold standard,” surgical inspection is universally performed during cardiopulmonary bypass on the flaccid and retracted heart using saline to “load” the ventricle, a technique that is hardly capable of simulating the dynamic nature of the complex mitral apparatus that can actually be clearly visualized and analyzed with 3D TEE.
It is important to realize that over the years a great emphasis on the role of cardiac ultrasound during MV surgery has been focused on its use within the practice of echocardiography, which is primarily defined by the technical and cognitive skills needed to perform a comprehensive examination, and to a great extent is focused to the acquisition and display of views for the purpose of enabling diagnoses of mitral apparatus anatomy, functional geometry, and pathophysiology. However, a physician with advanced training in perioperative echocardiography, independent of his or her medical subspecialty (i.e., cardiology or anesthesiology), should ideally assume the role of an echocardiologist whose responsibilities are not only limited to image acquisition, display and diagnoses, but also more importantly involve the integration of these data into the practice of medicine, with the specific intention of facilitating clinical decision making. Interestingly, the majority of currently published studies investigating the utility of 3D TEE during MV surgery do not actually evaluate the practical value of intraoperative 3D TEE and its impact on surgical and clinical decision making or on morbidity and mortality, and therefore do not prospectively assess the role of the perioperative physician as an echocardiologist. In fact, there are actually few studies that have pursued and proven this important association even for 2D TEE, perhaps because this important diagnostic tool and monitor of cardiac performance has become universally accepted as a standard of care during MV surgery, thus making it difficult or impossible to randomize patients or to totally blind anesthesiologists and surgeons to intraoperative echocardiography data.
Despite these apparently intimidating limitations with which one may be confronted when designing and performing studies involving intraoperative real-time 3D echocardiography, or when merely trying to interpret the clinical significance of the results, this technology is actually only in its relatively early stages of development. Today, intraoperative 3D TEE may, in fact, be defined more by its utility to obtain “pretty pictures” rather than its undisputedly proven favorable impact on surgical decision making and clinical outcomes. However, although it is unlikely that 2D echocardiography for the perioperative assessment of MV disease will become obsolete in the near future, the continued exponential growth in the technological development of more sophisticated and miniaturized ultrasound transducers, along with the introduction of improvements in image acquisition, processing speed, real-time volume rendering with superimposed color flow Doppler at practical frame rates, and the creation of semiautomated quantitative analysis tools20 will almost certainly guarantee that intraoperative 3D TEE is here to stay. This technology remains promising in its utility for improving the efficiency, accuracy, and communication of important diagnoses related to cardiovascular disease, and may even permit the construction of individualized prosthetics and the creation of virtual surgical platforms. However, further research using standardized protocols for obtaining imaging windows and incorporating the available techniques for qualitative and quantitative analysis of complex MV disease will have to be performed to identify the practical and clinically useful value of intraoperative 3D TEE. In the meantime, echocardiologists should become facile with both 3D and 2D echocardiography and should consider them as valuable complimentary techniques to be used for the performance of a comprehensive intraoperative echocardiographic examination in patients undergoing complex MV surgery.
Name: Nikolaos J. Skubas, MD, FASE.
Contribution: This author helped write the manuscript.
Attestation: Nikolaos J. Skubas approved the final manuscript.
Conflicts of Interest: The author has no conflicts of interest to declare.
Name: Stanton K. Shernan, MD, FAHA, FASE.
Contribution: This author helped write the manuscript.
Attestation: Stanton K. Shernan approved the final manuscript.
Conflicts of Interest:www.e-echocardiography; Philips Healthcare, Inc.
This manuscript was handled by: Martin J. London, MD.
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