Eur J Cardiothorac Surg 1998;14:S130-S133
© 1998 Elsevier Science NL
Utility of spiral CT in minimally invasive approach for aortic valve replacement 1
Rony Ammara,c,*,
Eyal Porata,c,
Dorit Schlag Eisenbergb,c,
Gideon Uretzkya,c
a Department of Cardiothoracic Surgery, Carmel Medical Center, 7 Michal Street, Haifa 34362, Israel
b Department of Radiology, Carmel Medical Center Haifa, Israel
c Rappaport Family Institute for Research in the Medical Sciences, Faculty of Medicine Technion-IIT, Haifa, Israel
* Corresponding author. Tel.: +972 4 8250256; fax: +972 4 8343554.
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Abstract
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Objective: Several surgical approaches exist for a minimally invasive replacement of the aortic valve. A great concern exists about the variable exposure of the aortic root. We suggest the use of spiral CT as a non-invasive method for accurate determination of aortic annulus position. Methods: Three patients scheduled for minimally invasive aortic valve replacement underwent chest spiral CT, (Select SP, Elscint, Haifa, Israel). Scanning was performed during breath holding using 5-mm thick slices, reconstructed every 2 mm (3 mm overlap), and a 1.5 pitch. Average scanning time was 30 s. No intravenous contrast media was used. Multiplannar and 3D images were reconstructed, using an Omnipro work station (Elscint LTD, Haifa, Israel). The position of the aortic valve annulus, in relation to the anterior chest wall was defined on these images. Results: In all patients, the length and location of the incision were determined by the preoperative measurements. The location of the aortic valve was found highly correlative to the preliminary study. There was no need to extend the length of the incision, or change the surgical approach. Conclusions: We find spiral CT scanning enables accurate pre-operative anatomical assessment. This assessment, provides the surgeon with the advantage of preliminary planning of the appropriate approach for minimally invasive aortic valve replacement.
Key Words: Minimally invasive • Aortic valve replacement • Mid-sternotomy • Parasternal incision • Spiral computed tomography (CT) • 3D reconstruction
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1. Introduction
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One of the most important aspects of minimally invasive aortic valve replacement is to determine the vertical position of the aortic annulus and the ascending aorta in relation to the surrounding bony structures. There is great concern about the variability in exposure of the aortic root. Transesophageal echocardiography (TEE) has been proposed as the only means to determine the position of the aortic annulus. However, this method seems to be inaccurate as it is unable to locate the bony structure surrounding the aortic annulus.
Our study defines the role of spiral computed tomography (CT) as an accurate, rapid and non-invasive method for surgical planning of aortic valve surgery via the minimally invasive approach.
As spiral CT scanning is performed very rapidly, the whole chest can be scanned in one breath-hold (30 s), allowing for true volume data acquisition [3, 6]. Since data obtained is true volumetric, retrospective transaxial reconstruction in different degrees of overlap, as well as optimal multi-planar 2D and 3D images can be performed. Surgical planning is an important application of advanced 3D imaging techniques.
In the present study, we used the excellent multi-planar information obtained by spiral CT to pre-plan the appropriate length and exact position of the minimally invasive incision in patients scheduled for aortic valve replacement
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2. Materials and methods
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Three patients were included in this preliminary study. Each patient underwent chest spiral CT (Select SP, Elscint, Halfa, Israel) using a slice thickness of 5 mm, and 1.5 pitch. The images were reconstructed every 2 mm (3 mm overlap). We used 120 KV, and 210 mAS per slice. Scanning was performed during breath-hold and completed within 30 s. Data was processed using an Omnipro work station and software (Elscint, Haifa, Israel).
Sagittal, coronal and 3D reformatted images were performed. The axial and reconstructed images, were filmed using bone and soft tissue windows. No intravenous contrast media was used. The aortic valve annulus was identified according to calcium deposits. Corresponding lines from the annulus to the anterior chest wall were drowned by the computer on the images using the above software.
The following data was obtained.
- 1. Location of the aortic valve and ascending aorta relative to the mid-sternal line, from a coronal image. The mid-sternal line is traced down from the center of the sternal notch (Fig. 1).
- 2. Vertical distance between aortic valve and sternal notch from coronal image (Fig. 1).
- 3. Depth of the aortic valve relative to the sternum from axial and sagittal images (Fig. 2).
- 4. The exact length of the sternal incision was determined from sagittal images, considering the natural angulation of the sternum (Fig. 2).
- 5. Simulation of mid- and para-sternal incision, exposing the aortic valve and ascending aorta. This was done by 3D reformation, and removal of part of the chest wall by the software (Fig. 3).
All three patients were operated through a minimal midline incision. The length of the incision and the level of the transverse sternal division were done according to anatomical landmarks, namely the location of the sternal notch.
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3. Results
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The preoperative measurements obtained from the CT studies are presented in Table 1
. In all three patients the length of the incision and the location of the transverse sternal division were performed according to the preoperative measurements. There was no need to extend the incision in any of the cases.
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4. Discussion
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Aortic valve operations have been traditionally performed via a median sternotomy with direct aortic and right atrial cannulations for cardiopulmonary bypass. A minimally invasive procedure for performing repair or replacement of the aortic valve has been developed, simplifying the technique and reducing surgical trauma [1]. The new procedures have been developed without jeopardizing surgical results.
This minimally invasive technique eliminates the need for a median sternotomy while providing excellent exposure of the aortic root and left ventricular outflow tract [4]. It provides beneficial results for the patient by reducing potential wound complications and offering better cosmetic results. Furthermore, earlier extubation and shorter hospital stay makes this procedure cost effective [2].
Spiral (helical) CT is the latest development in body imaging [5]. When it made its debut above 5 years ago, few people could have predicted the profound implications that such a rapid data acquisition technique would have. Spiral technology has not merely been an incremental improvement in CT imaging, it has revolutionized computerized tomography and opened up whole new applications, surgical planning being one of them. While diagnosis can often be made from planar slices, the performance of an accurate surgical procedure demand that the surgeon has a thorough understanding of the anatomy in three dimensions [7].
In this preliminary study, we used the excellent multi-planar information obtained by spiral CT to pre-plan the appropriate length and exact position of the minimally invasive incision in patients scheduled for aortic valve replacement. Good correlation was found between the preliminary assessment and the anatomical findings during surgery as regards to the exact location of the calcified aortic annulus in relation to the sternum. Nevertheless, this new technique needs further improvements and validation. In patients were the aortic annulus is not calcified, the use of intravenous contrast should be considered in order to facilitate the identification of the valve on CT images.
In further cases, an improved method to assure the site of the skin incision might be to determine the level of the aortic annulus by CT scanning, to mark the skin by a radioopaque marker, and to repeat the CT acquisition in order to trace the site and length of the incision on the skin.
We find that spiral CT and 3D reformatted images of the chest enable accurate preoperative planning of the appropriate location and exact length of the surgical incision concerning aortic valve surgery via the minimally invasive approach.
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Footnotes
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1 Presented at the World Congress on Minimally Invasive Cardiac Surgery, Paris, May 30–31, 1997. 
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References
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Abstract
1. Introduction
