Ann Thorac Surg 2006;82:2254-2259
© 2006 The Society of Thoracic Surgeons
New Technology
Epicardial Real-Time Three-Dimensional Echocardiography in Cardiac Surgery: A Preliminary Experience
Stefano De Castro, MDa,*,
Valeria Salandin, MDb,
Elena Cavarretta, MDa,c,
Loris Salvador, MDb,
Carlo Valfré, MDb,
Stefano Caselli, MDa,
Sara Di Michele, MDa,
Francesco Faletra, MDd,
Natesa G. Pandian, MDe
a Cardiovascular and Respiratory Sciences, University of Rome "La Sapienza," Rome, Italy
b Regional Treviso Hospital, Treviso, Italy
c Sant’Andrea Hospital, University of Rome "La Sapienza," Rome, Italy
d Cardiocentro Ticino, Lugano, Switzerland
e New England Medical Center, Tufts University, Boston, Massachusetts
Accepted for publication April 28, 2006.
* Address correspondence to Dr De Castro, Department of Cardiovascular and Respiratory Sciences, University of Rome "La Sapienza," Viale del Policlinico 155, Rome 00161, Italy (Email: stefano.decastro{at}uniroma1.it).
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Abstract
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PURPOSE: Intraoperative two-dimensional transesophageal echocardiography (2DTEE) is a widely accepted method to guide cardiac valve surgery. The aim of our study was to evaluate the feasibility, effectiveness, and incremental value of intraoperative epicardial real-time three-dimensional echocardiography (RT3DE).
DESCRIPTION: Thirty consecutive patients (18 aortic and 12 mitral valve diseases) underwent intraoperative 2DTEE and RT3DE before and after cardiopulmonary bypass. Five observers compared independently 2DTEE to live and full volume images and to the surgical view, to assess the incremental value of RT3DE in depicting the different anatomic structures.
EVALUATION: Epicardial RT3DE was feasible in all patients. Qualitative evaluation determined RT3DE superiority in depicting aortic cusp morphologic lesions; left ventricular outflow tract spatial relationships with mitral apparatus and aortic root; and both anterior and posterior mitral leaflet scallops, particularly posterior commissure.
CONCLUSIONS: In our study, epicardial RT3DE has been demonstrated to improve morphologic definition of anatomic valvular lesions and their relationship with cardiac adjacent structures. It may be a valid substitute when the 2DTEE approach is contraindicated, or it could have a complementary role, coupled with 2DTEE, to give additional information for surgical planning.
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Introduction
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Echocardiography has become an indispensable, widespread tool to assess cardiac morphology and function. It has also entered the operating room where, since the 1970s, intraoperative (including transesophageal, epicardial, and epiaortic) echocardiography has demonstrated its unique value in cardiac surgery patients’ management [1, 2]. Because the heart is a three-dimensional (3D) structure, two-dimensional (2D) echocardiography is limited in providing an adequate picture of all possible heart views, and leaves to the operator a mental reconstruction of 3D images. In the recent past, 3D transesophageal echocardiography has demonstrated its feasibility and accuracy in the management of patients mainly undergoing mitral valve [3, 4] and other valvular repair [5, 6]. Unfortunately, even though useful, this technique is time consuming and requires a long off-line elaboration, which does not offer available information immediately, thus not always leading to satisfactory results. Today, with the introduction of a new transthoracic probe able to detect a 3D dataset of intracardiac anatomic views, 3D echocardiographic images can be visualized in real time.
We sought to evaluate the feasibility, effectiveness, and incremental value of intraoperative epicardial real-time 3D echocardiography (RT3DE) in the cardiac surgery scenario, in comparison with 2D transesophageal echocardiography (2DTEE).
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Technology
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Patients
Thirty consecutive patients scheduled for cardiac valvular surgery, between January 10 and February 28, 2005, were enrolled. An informed consent for intraoperative echocardiography and the approval of the hospital’s Institutional Board was obtained. As routinely performed at our institution, all patients underwent a detailed 2D transthoracic preoperative examination, including color flow and spectral Doppler to confirm the need for cardiac surgery.
Image Acquisition and Planes
Two-dimensional TEE was performed by an experienced cardiologist or cardiac anesthesiologist with a multiplane probe using a Philips iE33 ultrasound machine (Philips, Andover, Massachusetts) after anesthesia induction and before other preparative procedures. For mitral valve apparatus, standard midesophageal views at about 0, 60, and 150 degrees, and transgastric view at 90 degrees [1] were examined. For the aortic root, the short axis longitudinal midesophageal and the 90-degree transgastric views were carried out [1].
Epicardial RT3DE was performed by a trained cardiac surgeon, under guidance of a cardiologist or cardiac anesthesiologist after completion of median sternotomy and pericardiotomy, before cardiopulmonary bypass. Pericardial space was filled by a warm saline solution and the matrix array X4 probe (iE33; Philips), inserted into a sterile sheath filled at its extremity with ultrasonic gel, was positioned on surface of the saline solution. The matrix probe was positioned over the aortic or mitral valve in both short-axis and long-axis orientation, as well over the ventricle at the level of papillary muscles and over the ascending aorta and arch, according to the epicardial intraoperative views previously described by Eltzschig and colleagues [7].
The new X4 Matrix Array probe consists of almost 2,400 piezoelectric crystals all activated at the same time, which allows volumetric rather than planar acquisition. Two image modalities were recorded: live 3D and full volume.
Live 3D imaging allows visualization of a pyramid with an angle of 58 degrees azimuth and 29 degrees elevation. This could be useful when a specific region of interest is selected and displayed on line. To obtain a data set large enough to cover the heart comprehensively, the full volume acquisition, composed of four sequential parallel fanlike electrocardiographic gated scans, was performed. A pyramidal 3D dataset of 90 degrees by 90 degrees is obtained, at a frame rate of 20 to 25 Hz, in which all the cardiac structures are encompassed. It takes approximately 5 minutes to extract different images, cutting the volume in as many planes as you need. The 3D images were digitally stored in the machine and exported on digital video disks for a further off-line analysis with dedicated software (Q-Lab Advanced; Philips).
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Technique
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Two-Dimensional and Three-Dimensional Qualitative Analysis
For comparative analysis, the description of the aortic and mitral valve anatomy reported by the surgeons was recorded.
Regarding the aortic valve, number, morphology, prolapse, and calcifications of the leaflets were considered. For the mitral valve, according to Carpentier’s subset [8], six scallops were identified: lateral (P1), middle (P2), and median (P3) for the posterior leaflet; and three corresponding scallops for the anterior leaflet (A1, A2, A3).
Surgical Procedures and Visualization of Affected Valves
After the exposure of the valve involved, surgeons were invited to describe the valve; a report of anatomic surgical findings and of the explanted valves was recorded. After the intervention, five observers experienced in echocardiographic techniques (two cardiologists, one anesthesiologist, and two surgeons) were invited to judge independently 2DTEE and RT3DE image quality. The two surgeons were also asked to judge the echocardiographic image resemblance to the anatomy. We here consider "definition" as "resolution," namely, the capability of an imaging method to distinguish two structures in close proximity to each other. The best "definitions" and best "resemblances to anatomy" scored 10, the lowest 0.
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Clinical Experience
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Indications for cardiac surgery were 18 aortic valve and 12 mitral valve pathologies. Among the aortic defects, 10 were pure aortic stenosis, 2 mixed stenosis and regurgitation, 4 lone regurgitation, and 2 aortic dissections with regurgitation. In 6 patients, coexisting ascending aortic aneurysms was detected. Among the mitral group, 9 patients had a degenerative disease, 1 had ischemic, and 2 had rheumatic calcified mitral stenosis.
Feasibility and Qualitative Evaluation of RT3DE
Epicardial RT3DE was feasible in all examined patients. The quality of 3D reconstruction was graded as good in 90%, fair in 5%, and poor in 5% of the patients. In Table 1, qualitative evaluation of echocardiographic images is shown as median and range (minimum–maximum) of scores credited to every image by the observers. A patent superiority of epicardial RT3DE in comparison to 2DTEE was achieved in visualizing the papillary muscles (Fig 1), the left ventricular outflow tract and its spatial relationships with the mitral valve, and some components of the mitral valve apparatus, like the mitral artificial cordhae, the whole extension of mitral ring, and the fibrous trigone.
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Fig 1. Papillary muscles in end diastole, attached to trabeculae carnae rather than to the left ventricular wall.
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Two-Dimensional TEE and Epicardial RT3DE Versus Surgical Findings
The correlation among 2DTEE, RT3DE, and surgical findings are reported in Table 2. With respect to 2DTEE, RT3DE was able to detect some new findings in aortic valve and ascending aorta morphology (Fig 2), coaptation defect, fenestrations, perforations of the cusps and location of the intimal tear (Fig 3). For the mitral valve, there was a small difference in prolapsing scallops number found by 2DTEE and epicardial RT3DE. Only two new findings were recognized in A3 (Figs 4 and 5)
and P3 scallops, in proximity of the posterior commissure, usually not well visualized by 2DTEE. Two sites of calcifications, 1 fenestration and 1 perforation of aortic leaflets, were missed with both echocardiographic techniques compared with surgical findings.
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Table 2. Correlation Among 2DTEE, RT3DE, and Surgical Findings Regarding Aortic Valve and Ascending Aorta Pathologies, and Mitral Valve Prolapsing Scallops
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Fig 3. Aortic root dissection: intimal flap, tear, and their relationship with the aortic valve and noncoronary Valsalva sinus.
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Fig 4. Anterior prolapsing scallop (A3) of the mitral valve close to the posteromedial commissure. Surgical view from above (left atriotomy).
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Fig 5. Spatial relationship between mitral prolapsing scallop, left atrium, and left ventricle. Longitudinal view from above.
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Comment
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Our preliminary data demonstrated that epicardial RT3DE is feasible in a cardiac surgery setting and may have an incremental value in improving anatomic definition of cardiac valvular lesions.
Previous and recent studies showed that 2D epicardial echocardiography may be considered an examination complementary to the intraoperative TEE. In many cases, large section of the ascending aorta are not visible on TEE, and epiaortic scanning has proven to be superior to TEE and aortic palpation in determining the extent of the plaque in the ascending aorta [9] and in acute aortic dissection.
However, in the last 20 years, 2DTEE has been the most effective tool to improve diagnosis of valvular pathologies in the operating room, to suggest the best surgical plan for repair, and to assess the quality of the intervention [2].
In addition to effectiveness, 2DTEE has the advantage of not interfering with surgical field and not lengthening the intervention time. Nowadays, technology does not allow real-time 3D acquisition with TEE probe because of the lack of a proper probe holding 2,400 crystals in a small volume. Waiting for this progress in technology in the near future, the 3D epicardial approach can be considered, for now, as a source of improvement in quantity and quality of information obtained with 2DTEE. Again, 3D epicardial examination could be a better approach than the actual sequential 3DTEE images. In Table 3
are listed advantages and disadvantages of 3DTEE versus epicardial RT3DE. The main drawbacks of epicardial RT3DE are the necessity to interfere with the surgical field, which results in a modest lengthening of time, and the nearness of the probe to the studied structure that sometimes makes it difficult to visualize the closest region. This is the reason why, in terms of feasibility, we obtained a poor quality of images in 10% of our patients.
An important limitation of RT3DE is the application of color flow, especially for the accurate flow-volume calculation of regurgitant jets. Turbulent flow, flow velocities above the Nyquist limit, the need to acquire more than seven alternate cardiac cycles, the frame rate of 20 Hz, and sometimes arrhythmia influence the quality of 3D color Doppler. The result is that, to date, epicardial RT3DE has not demonstrated any superiority compared with 2DTEE in changing surgical planning.
On the other hand, epicardial RT3DE is not inferior to 2DTEE in detecting valvular alterations, and it is in some cases more effective. This is the case in the identification of tears and intimal flaps in ascending aorta and aortic arch. Regarding mitral valve apparatus, epicardial RT3DE has not demonstrated a significant superiority in locating prolapsing leaflets, as shown in Table 2, whereas the entire mitral native or prosthetic ring and the fibrous trigone, usually not depicted with the 2DTEE, are clearly visualized by epicardial RT3DE. The RT3DE approach provides a unique picture of the left ventricular outflow tract and its relationships with mitral valve apparatus through the possibility to cut the volume of acquisition in an infinite number of planes, and provides a better resolution in showing papillary muscles and ventricular mass.
Regarding papillary muscles, all conventional anatomic descriptions depict them as having a broad-based connection with left ventricular wall. However, a recent study has shown that papillary muscles are attached to the trabeculae carnae, rather than directly to the wall’s solid portion [10]. In our study, we confirmed such a peculiar aspect, as we found the same architecture in all our patients (Fig 5). This aspect is dynamic and can be appreciated only in diastole. It has been missed in the anatomical description because anatomical specimens usually are in a strong contractile state. Even during surgery, the papillary muscles base is often hidden from a direct view. Current imaging techniques, with the exception of the new multislice computed tomography, generally do not have a spatial resolution high enough to resolve submillimeter distances. With epicardial RT3DE, such a limitation can be overcome. Because of its peculiar crystal arrangement, the matrix transducer has the same resolution in all three axes, improving image quality.
The choice of surgical observation as the gold standard to judge echocardiographic images can be criticized because the surgeon observes the heart motionless; but this is true for both 2DTEE and RT3DE approaches and does not influence the comparison between the two methods.
We are strongly convinced that 3D imaging requires quite a different practice with respect to 2D imaging, because we are used to translating the cardiac structure, observed in two dimensions, in a 3D mental representation, not as in the reality. In fact, the most enthusiastic judges of the quality of 3D images were surgeons.
In conclusion, epicardial RT3DE has been demonstrated to be a truly useful complementary tool to assess valvular and aortic lesions in the operating room, and a fully valid substitute when TEE examinations should be contraindicated, until an RT3DE transesophageal probe is provided by technologic progress.
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Disclosures and Freedom of Investigation
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The ultrasonography machine was provided on loan by Philips Medical System (Andover, Massachusetts) to perform the study without further financial support. The authors had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report.
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Footnotes
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Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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References
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- Iglesias I, Bainbridge D, Murkin J. Intraoperative echocardiography: support for decision making in cardiac surgery Semin Cardiothorac Vasc Anesth 2004;8:25-35.[Abstract/Free Full Text]
- De Castro S, Salandin V, Cartoni D, et al. Qualitative and quantitative evaluation of mitral valve morphology by intraoperative volume-rendered three-dimensional echocardiography J Heart Valve Dis 2002;11:173-180.[Medline]
- Fabricius AM, Walther T, Falk V, Mohr FW. Three-dimensional echocardiography for planning of mitral valve surgery: current applicability? Ann Thorac Surg 2004;78:575-578.[Abstract/Free Full Text]
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- Rosenhek R, Binder T, Maurer G. Intraoperative transesophageal echocardiography in valve replacement surgery Echocardiography 2002;19:701-707.[Medline]
- Eltzschig HK, Kallmeyer IJ, Mihaljevic T, et al. A practical approach to a comprehensive epicardial and epiaortic echocardiographic examination J Cardiothorac Vasc Anesth 2003;17:422-429.[Medline]
- Carpentier A. Cardiac valve surgery—the "French Correction." J Thorac Cardiovasc Surg 1983;86:323-337.[Medline]
- Sylivris S, Calafiore P, Matalanis G, et al. The intraoperative assessment of ascending aortic atheroma: epiaortic imaging is superior to both transesophageal echocardiography and direct palpation J Cardiothorac Vasc Anesth 1997;11:704-707.[Medline]
- Axel L. Papillary muscles do not attach directly to the solid heart wall Circulation 2004;129;:5145-5148.
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Abstract
Introduction
