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New Technology

Three-Dimensional Printing Creates Models for Surgical Planning of Aortic Valve Replacement After Previous Coronary Bypass Grafting

^a Department of Cardiac Surgery, Ludwig-Maximilian University, Munich, Germany
^c Department of Clinical Radiology, Ludwig-Maximilian University, Munich, Germany
^b Institute of Micro Technology and Medical Device Technology, Technical University Munich, Garching, Germany

Accepted for publication December 11, 2007.

^_* Address correspondence to Dr Sodian, Department of Cardiac Surgery, Ludwig-Maximilians-University, Marchioninistr. 15, Munich, 81377, Germany (Email: ralf.sodian{at}med.uni-muenchen.de).

	Abstract

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Purpose: Resternotomy for aortic valve replacement in patients with previous coronary artery bypass grafting and an internal mammary artery graft may be a surgical problem. Thus, we are exploring the effect of using rapid prototyping techniques for surgical planning and intraoperative orientation during aortic valve replacement after previous coronary artery bypass grafting (CABG).

Description: As a proof of concept, we studied a patient who had undergone CABG 5 years earlier. At that time the patient received a left internal mammary artery graft to the left anterior descending artery and a venous graft to the right coronary artery. Now the patient required aortic valve replacement due to symptomatic aortic valve stenosis. The left internal mammary artery bypass and the right coronary artery bypass were patent and showed good flow in the angiography. The patient was examined by 128-slice computed tomography. The image data were visualized and reconstructed. Afterwards, a replica showing the anatomic structures was fabricated using a rapid prototyping machine.

Evaluation: Using data derived from 128-slice computed tomography angiography linked to proprietary software, we were able to create three-dimensional reconstructions of the vascular anatomy after the previous CABG. The models were sterilized and taken to the operating theatre for orientation during the surgical procedure.

Conclusions: Stereolithographic replicas are helpful for choosing treatment strategies in surgical planning and for intraoperative orientation during reoperations of patients with previous CABG.

	Introduction

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In an aging population, more and more patients who have undergone previous coronary artery bypass grafting (CABG) are presenting with significant aortic stenosis [1]. Reoperation for aortic valve replacement (AVR) in these patients may be complicated because the actual anatomic structure is sometimes unpredictable. Repeat sternotomy carries the risk of dissection of patent vein or internal mammary grafts and aortotomy because of previously placed bypass grafts [2], and the reported mortality rate is still high [3, 4]. It is therefore important to establish high-quality preoperative data for optimal surgical planning and intraoperative orientation to minimize operative mortality and morbidity.

	Technology

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We have developed a new technique to fabricate a life-like model of the anatomic structures of patients with previous CABG using stereolithography, a rapid prototyping technique. Stereolithography is a new technology originally used in engineering and industry to generate prototype models. By transferring this method to medicine, it is possible to fabricate three-dimensional replicas of anatomic structures from the computed tomography (CT) or magnetic resonance imaging (MRI) data of patients.

	Technique

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In our current experiment, we used stereolithographic models derived from standard CT data to create accurate and realistic models of the cardiac and vascular anatomy for preoperative assessment and intraoperative orientation. As a proof of concept, we report an 81-year-old woman who had undergone a CABG operation 5 years before and had patent left internal mammary artery and right coronary artery (RCA) bypasses. Now the patient presented with symptomatic aortic valve stenosis that necessitated AVR. In this situation, solid replicas are helpful for preoperative and intraoperative orientation to minimize operative complications and perioperative death.

	Clinical Experience

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This patient had typical symptomatic aortic valve stenosis, including dyspnea, New York Heart Association (NYHA) functional class III to IV, left ventricular ejection fraction of 0.43, aortic valve regurgitation class II, and aortic valve stenosis (maximal pressure gradient across the aortic valve = 100 mm Hg; aortic valve area, 0.7 cm²). She had patent left anterior descending and RCA bypasses after a CABG operation 5 years earlier. The diagnosis was established by ultrasound imaging, cardiac catheterization, and CT (Figs 1A and B) as part of the normal clinical evaluation process. As indicated by the symptoms and the diagnostic findings, the patient required surgical treatment, and we decided to replace the aortic valve. The study was approved by the Institutional Ethics Committee, and patient consent was waived.

View larger version (80K): [in this window] [in a new window]   Fig 1. (A) A computed tomography scan of the patient with a patent left anterior descending artery and right coronary artery bypass (RCA) close to the sternum (arrows). (B) Three-dimensional segmentation of computed tomography data of the patient after previous coronary artery bypass grafting.

These data, which were in 0.1- to 2-mm slices, were entered into the stereolithography machine (ZCorp, Burlington, MA), and a lumen replica of the heart and the vascular anatomy was created. In this device, the model was produced by ink-jet printing technology using a three-dimensional printer. Using data derived from routinely performed CT linked to the rapid prototype stereolithography equipment, we were able to fabricate a replica of the cardiovascular anatomy, including the bypass grafts and sternum (Figs 2A and B).

View larger version (109K): [in this window] [in a new window]   Fig 2. (A) Stereolithographic model of patent left anterior descending bypass graft (yellow, arrow) behind the sternum as seen from the left side. (B) Stereolithographic model of patent right coronary artery bypass grafts (red) behind the sternum as seen from the right side.

	Comment

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Stereolithography has been shown to be a useful tool in maxillofacial surgery, reconstructive surgery, orthopedics, and in pediatric cardiac operations [5–8]. By using this technology, surgical templates or customized implants can be tested on the models, or anatomic structures can be reconstructed before the operation. These three-dimensional, life-like models might also be helpful for perioperative planning of surgical procedures in a wide variety of clinical situations.

Replacing the aortic valve in patients with previous CABG has an increased risk of perioperative morbidity, especially while reopening the sternum. Odell and colleagues [1] studied 145 patients who received AVR after previous CABG. Of these, 143 patients underwent redo sternotomy, and reentry problems occurred in 23 (16%). Two patients (1%) had cardiac arrest during anesthesia, and 21 (15%) sustained damage during dissection or, on reopening, to previously inserted grafts in 13 (9%), the innominate vein in 3 (2%), the right atrium in 2 (1%), and the pulmonary artery, aorta and right ventricle, in 1 patient each.

The surgical planning and intraoperative orientation in these patients is often difficult and associated with major limitations, particularly in patients with multiple bypass grafts. In such cases, it is often not easy to clearly identify the exact anatomic location. To overcome these shortcomings, our group applied rapid prototyping techniques to fabricate models of adult cardiovascular pathology.

Currently, there is little experience in using the rapid prototyping technology of stereolithography in adult cardiac surgery. Our experiment with its use for AVR after previous CABG demonstrates that with currently available CT technology, accurate three-dimensional models of the anatomy of live patients requiring reoperation for AVR after prior CABG can be fabricated.

These models allow the surgeon to better understand patient-specific three-dimensional anatomy. Moreover, being able to hold a model in one's hand and examine it from different sides allows the surgeon and the interventionist to develop the optimal surgical approach and to anticipate problems that may arise. The dimensions and distances can be easily identified, and interventions or surgical procedures can be planned preoperatively. All these are advantages compared with images created directly from the CT software.

The experiment we performed is a proof of concept and shows that it is possible to fabricate stereolithographic models from a routine preoperative CT scan for patients with complex and unpredictable anatomy owing to a previous CABG operation. It was not expected that use of the models would change the basic surgical plan or that the operation could not have been performed otherwise, but being able to know the exact position of the critical structures and to anticipate difficulties may reduce the perioperative risk to a minimum.

This technique is currently not established or being evaluated in adult cardiovascular surgery, but learning from other specialties, stereolithography is useful to aid comprehension of anatomic conditions and complex features and to prepare a surgical plan [9, 10]. One difficulty of the technique is the selection of correct segmentation values. This requires a multidisciplinary approach with surgeons and computer specialists cooperating to achieve perfect segmentation that yields a perfect, anatomically correct model.

In conclusion, the method described is feasible for patients with prior CABG requiring AVR. The system provides theoretic and practical advantages for surgeons and interventionists treating complex pathology in adult cardiac surgery. Future studies that include more patients and provide more data are expected to show that the use of preoperative models decreases peri-operative morbidity and mortality.

	Disclosures and Freedom of Investigation

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The stereolithographic models were purchased by the Institute of Micro Technology and Medical Device Technology (Technical University Munich). The authors have performed a free and independent development and evaluation of this new technology. The authors have no financial relationship with companies producing stereolithographic models.

	Acknowledgments

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We would like to thank Anne Gale, ELS, of the Deutsches Herzzentrum Berlin for editorial assistance in the preparation of the manuscript.

	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.

	References

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1. Odell JA, Mullany CJ, Schaff HV, Orszulak TA, Daly RC, Morris JJ. Aortic valve replacement after previous coronary artery bypass grafting Ann Thorac Surg 1996;62:1424-1430.[Abstract/Free Full Text]
2. Hoff SJ, Merrill WH, Stewart JR, Bender Jr HW. Safety of remote aortic valve replacement after prior coronary artery bypass grafting Ann Thorac Surg 1996;61:1689-1691discussion 1691–2.[Abstract/Free Full Text]
3. Fighali SF, Avendaño A, Elayda MA, et al. Early and late mortality of patients undergoing aortic valve replacement after previous coronary artery bypass graft surgery Circulation 1995;92(suppl 2):163-168.[Abstract/Free Full Text]
4. Collins Jr JJ, Aranki SF. Management of mild aortic stenosis during coronary artery bypass graft surgery J Cardiac Surg 1994;9:145-147.[Medline]
5. Winder J, Bibb R. Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery J Oral Maxillofac Surg 2005;63:1006-1015.[Medline]
6. Wong J, Fang C, Chung J, Huang JS, Lee JW. Comparison of 2 methods of making surgical models for correction of facial asymmetry J Oral Maxillofac Surg 2005;63:200-208.[Medline]
7. Fukui N, Ueno T, Fukuda A, Nakamura K. The use of stereolithography for an unusual patellofemoral disorder Clin Orthop Relat Res 2003:169-174.
8. Poukens J, Haex J, Riediger D. The use of rapid prototyping in the preoperative planning of distraction osteogenesis of the cranio-maxillofacial skeleton Comput Aided Surg 2003;8:146-154.[Medline]
9. Ngan EM, Rebeyka IM, Ross DB, et al. The rapid prototyping of anatomic models in pulmonary atresia J Thorac Cardiovasc Surg 2006;132:264-269.[Abstract/Free Full Text]
10. Sodian R, Weber S, Markert M, et al. Stereolitographic models for surgical planning in congenital heart surgery Ann Thorac Surg 2007;83:1854-1857.[Abstract/Free Full Text]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ralf Sodian Calin Vicol Bruno Reichart Christoph Schmitz Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sodian, R. Articles by Schmitz, C. Search for Related Content PubMed PubMed Citation Articles by Sodian, R. Articles by Schmitz, C. Related Collections Cardiac - other Related Article