Interact CardioVasc Thorac Surg 2009;9:119-123. doi:10.1510/icvts.2008.189506
© 2009 European Association of Cardio-Thoracic Surgery
Best evidence topic - Cardiac general |
Does preoperative computed tomography reduce the risks associated with re-do cardiac surgery?
Nouman U. Khan* and
Nizar Yonan
Department of Cardiothoracic Surgery, University Hospital of South Manchester NHS Foundation Trust, Southmoor Road, Manchester, M23 9LT, UK
Received 29 July 2008;
received in revised form 2 February 2009;
accepted 25 February 2009
*Corresponding author: Tel.: +44 161 291 2092; Fax: +44 161 291 2091.
E-mail address: n_u_khan{at}hotmail.com (N.U. Khan).
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Abstract
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A best evidence topic was written according to the structured protocol. The question addressed was whether preoperative computed tomography (CT) scan reduces the risk associated with re-do cardiac surgery. A Medline search revealed 412 papers, of which seven were deemed relevant to the topic. We conclude that preoperative CT angiography using ECG-gated multi-detector scan enables excellent anatomical details of heart, aorta and previous grafts, and highlights high-risk cases due to adherent grafts or ventricle or aortic atherosclerosis. This allows for better risk stratification and change of surgical strategy to reduce the potential risk in patients coming for re-do cardiac surgery. According to published reports, high-risk CT-scan findings in these patients caused clinicians to cancel surgery in up to 13% of cases, while preventive surgical strategies including non-midline approach, peripheral vascular exposure or establishing cardiopulmonary bypass prior to re-sternotomy have been reported in over two-thirds of patients with significant reduction in the operative risk. The risk of damage to vital structures, including previous grafts, heart or larger vessels is generally reported fewer than 10%, with evidence of significantly lower incidence of intra-operative injuries in patients who had prior CT-scans compared to those who did not. Hence, adequate preoperative imaging using ECG-gated multi-slice CT is essential for optimum planning of re-do cardiac surgery.
Key Words: Re-do cardiac surgery; Re-sternotomy; CT-scan
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1. Introduction
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A best evidence topic was constructed according to a structured protocol. This is fully described in the ICVTS [1].
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2. Clinical scenario
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You are about to see a 74-year-old man who has been referred for re-do coronary artery bypass grafting. His first-time coronary artery surgery was performed over 10 years ago, with left internal mammary artery (LIMA) anastomosed to left anterior descending artery, a saphenous vein graft to the circumflex and another vein graft to the posterior descending branch of the right coronary artery. He has angina on exertion, and also has evidence of peripheral vascular disease. The coronary angiogram revealed a patent LIMA but the two vein grafts are occluded. There are suitable target vessels for surgical revascularization. However, you are concerned about the position of the patent LIMA graft, and want to know the risk of injury to LIMA during re-sternotomy. You also want to know if the aorta has significant atherosclerosis. You wonder if performing a multi-slice CT-scan will help to define the mediastinal anatomy, including route and adhesion of the LIMA graft, ventricle and the aortic atherosclerosis.
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3. Three-part question
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In (patients undergoing repeat sternotomy) does (a CT-scan) reduce the chances of (serious complications on resternotomy)?
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4. Search strategy
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Medline search 1950 – January 2009 was performed using OVID interface.
(Re-do cardiac surgery OR re-do coronary artery bypass grafting OR re-do CABG OR re-do off-pump CABG OR re-do valve surgery OR re-do aortic valve surgery OR re-do mitral valve surgery OR resternotomy OR repeat cardiac surgery OR re-operative heart surgery OR repeat CABG OR repeat coronary artery bypass grafting OR repeat valve surgery.mp).
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5. Search outcome
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Four hundred and twelve papers were found from Medline using the current search strategy. Seven were considered relevant and are documented in Table 1.
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6. Comments
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Recent decades have seen a steady increase in the number of cases referred for re-do cardiac surgery, which are associated with increased risk of morbidity and mortality compared to the first-time operations [2, 3]. Apart from older age and comorbidities, the presence of adhesions from previous surgery provides technical challenges for the surgeon, particularly to achieve safe re-entry, to prevent injury to previous grafts or adherent structures, and to obtain satisfactory myocardial preservation [4, 5]. One study showed the risk of catastrophic haemorrhage during sternal re-entry at approximately 1%, with an associated mortality of 21% [6]. Most studies have reported a higher risk (between 3–7%) of perioperative myocardial infarction (MI) in re-do cardiac operations [3, 7]. In a review of 655 patients undergoing re-do coronary artery bypass grafting (CABG) at Cleveland clinic, the prevalence of injury to patent LIMA graft was 5.3%, resulting in perioperative MI in 40% of these patients, and a higher mortality (8.6%) [8]. A recent study from the same centre looking at 1847 re-operations described the incidence of injury to previous grafts in 2.5%, injury to the heart in 2%, and injury to great vessels in 1.5% of patients. Approximately two-thirds of the injuries occurred during sternal re-entry and early dissection, resulting in significantly increased risk of death (12% vs. 4% in those with no intra-operative injuries, P<0.0001). Ellman et al. have reported 9.1% incidence of re-entry injuries; nearly half of them to the previous grafts. However, they found no difference in mortality between injured vs. non-injured group [9]. Some other centres have also reported an equal early mortality between first-time and re-do cardiac operations [10, 11].
To reduce the risk of repeat cardiac operations, meticulous surgical planning for entry, cannulation and myocardial preservation is pivotal [12]. Using alternate surgical strategies, D'Ancona et al. reported perioperative MI in 3.9% and a mortality of just under 5% in patients undergoing re-do coronary artery bypass grafting [7]. The crux of surgical planning is an accurate demonstration of mediastinal anatomy through preoperative imaging. The introduction of multi-slice CT-scan using ECG-gated technology and reconstruction techniques has allowed for high spatial and temporal resolution of the mediastinal anatomy [12, 13]. It has therefore gained popularity amongst cardiac surgeons allowing for better risk stratification, alteration of operative strategy and avoidance of potentially catastrophic injuries [14–16]. Reports from various centres reveal that CT-scan findings caused clinicians to cancel surgery in 4–13% of patients, while surgical approach is altered in up to 80% of cases with high-risk CT findings [14, 15]. The significance of chest imaging is highlighted in the report by Roselli et al. who mentioned that incomplete imaging was the prime cause of lapse in preventive strategy leading to inadvertent intra-operative injuries [17].
Despite preoperative CT imaging, intra-operative recognition of vital structures is often difficult. To overcome this issue, surgeons in Munich have reported the use of stereolithography, a rapid prototype technique to create a three-dimensional model of patient's anatomy using CT-scan data. This helped to clearly understand the relationship between various mediastinal structures, and prevent intra-operative injury [18].
Apart from topographical information, multislice CT-scan also demonstrates other vascular pathologies, such as aortic atherosclerosis and aneurysms [13]. Aortic atherosclerosis is recognized as the single most important determinant of postoperative stroke [19]. Based on the CT findings, surgeons can employ alternate strategies, including no-touch technique, axillary artery cannulation or avoidance of CPB with significant reduction in the risk of stroke [7, 20, 21].
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7. Clinical bottom line
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Re-do cardiac surgery is associated with an increased risk of morbidity and mortality, mostly related to the intra-operative injuries [17]. CT angiography provides optimum demonstration of mediastinal anatomy in patients coming for re-do cardiac surgery, however, its real advantage on circumventing procedure-related risks are debated. The available evidence shows that high-risk CT-scan findings led to cancellation of surgery in 4–13% of cases, whilst alternate surgical strategies were adopted in up to 80% of cases with significant reduction in the risk of re-entry injuries and mortality [14, 15, 22]. One study looking at intra-operative adverse events in 1847 re-do cardiac surgical patients revealed that most of the lapses in preventive strategy were due to incomplete preoperative imaging [17]. Hence, CT-scan forms an important tool for risk stratification in these patients.
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Abstract
1. Introduction