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a Epworth Hospital, Richmond, Victoria, 3121 Australia
b Royal Melbourne Hospital, Suite 27, Private Medical Centre, Parkville, Melbourne, Victoria, 3050 Australia
(Email: brianbuxton{at}ozemail.com.au).
The use of three dimensional multi-detector computed tomographic angiography (MDCTA) in assessing patients requiring reoperative cardiothoracic surgery has brought diagnostic information to a new level. The results of reoperative cardiac surgery have been improving despite the increased comorbidities of these patients prior to the introduction of MDCTA. New strategies have evolved such as non-sternotomy approaches, for example, mini-anterior and lateral thoracotomy. Conventional median re-sternotomy has been simplified by creating a mini-tunnel confined to the immediate posterior aspect of the sternum with improved protection of the right ventricle and mediastinal structures. Pharmacologic decompression and peripheral cannulation, either by the axillary or transfemoral routes, and deep hypothermic cardiac arrest minimize trauma to retrosternal coronary artery bypass grafts, the right ventricle, and the aorta, thus minimizing blood loss. Development of new anesthetic, myocardial protection strategies together with improved management of postoperative comorbidities have further contributed to narrowing the mortality gap between primary and reoperations [1]. Introduction of three-dimensional imaging of important mediastinal structures provides new information that may further improve the level of safety and comfort for the reoperative surgeon.
An MDCTA provides detailed information about graft patency and disease with a diagnostic accuracy approaching selective angiography [2, 3]. Recognition and avoiding SV disease minimizes distal atheroembolism. Defining the interrelationship of the bypass grafts and the native vessels assists the surgeon in protecting grafts and locating target arteries. An additional benefit has been the serendipitous findings of unsuspected pulmonary and mediastinal masses. Previously undiagnosed intrathoracic lesions have been found in about 10% of elderly patients undergoing reoperative coronary artery bypass surgery.
New iterations of MDCTA with submillimeter definition improve diagnostic accuracy minimizing motion, calcification, and stent artifacts. Incorporation of functional measurements may alter future practice [4]. Although the striking MDCTA images are of great assistance to the surgeon, complications from additional radiation exposure and introduction of iodine containing dye subject the patients to potential complications of radiation therapy and renal failure. The use of MDCTA is not applicable to patients with an emergent presentation as this may delay surgery. A strategy of routine MDCTA prior to a reoperation therefore requires balancing the risks and benefits. In the situation where urgent re-do surgery is required, it may be sufficient to perform a non-contrast MDCTA, which, while not giving precise information about bypass grafts, does at least demonstrate the position of the aorta and innominate vein in relation to the back of the sternum, which may be sufficient, depending on the procedure that was previously performed.
The authors [5] have demonstrated a low mortality and morbidity after being forewarned of the proximity of bypass grafts and aorta to the posterior aspects of the sternum, thus enabling alternative strategies to be implemented in high-risk patients. Such information is particularly useful in a referral practice where the details of bypass graft anatomy from the primary surgery are not known. Inadequate mobilization of the internal thoracic artery, excessive length, adherence to the sternum, and crossover grafts less than 1 cm behind the sternum make it prone to injury. Coronary artery disease and dilatation of the right ventricle as a result of mitral valve disease represent a high-risk subgroup. The absence of appropriate control data (level C) evidence confirms that no strong recommendations can be made on scientific grounds. The early observational data and benefits to the surgeon suggest that MDCTA will find an important place in the management of most patients presenting for elective reoperative cardiac surgery.
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