AORTIC DISSECTION - ANATOMIC TYPES AND SURGICAL APPROACHES

Our classification system of acute dissection of the aorta is based on the site of the main intimal tear: Type A: on the ascending aorta; ty pe B: on the transverse aortic arch; type C: on the descending aorta. The extension of the dissecting process is classified as ''antegrade'' or ''retrograde''. Acute dissection involving the ascending aorta is an absolute surgical urgency. Any delay in referring the patient to a proper surgical institution or to the operating room increases the ris k of death. Fifty per cent of patients, indeed, either untreated or me dically supported, die within 48 hours after the onset of symptoms. Su rgical therapy is mainly aimed at preventing the patient from dying fr om intrapericardial rupture of the aorta or from acute massive aortic regurgitation. In type A, it is necessary to replace the ascending aor ta with a bloodtight Dacron prosthesis after resecting the entry site, if possible. Downstream, joining the two dissected cylinders by two r unning sutures and the aid of GRF glue, seals the false lumen. Upstrea m, the reconstruction of the aortic root and the resuspension of the a ortic valve, also by means of running sutures and GRF glue, suppress t he aortic valve insufficiency in 90% patients. However, in case of pre -existing annulo-aortic ectasia, the ascending aorta must be replaced by a composite tube according to the Bentail technique. The use of GRF glue since the beginning of 1977, has dramatically improved the immed iate and long-term results, accounting for a hospital mortality rate o f 10%, in patients less than 65 years old. In type B, resecting the en try site requires that the transverse arch be partially or totally rep laced. It is, therefore, mandatory to protect the Central Nervous Syst em. In our experience this is best achieved by perfusing the carotid a rteries with cold blood (6-degrees-C) during circulatory arrest at mod erate core hypothermia (28-degrees-C). With this technique of ''Cerebr oplegia'', the hospital mortality rate has been lowered to 28%, higher , though, than in patients undergoing isolated replacement of the asce nding aorta. In type C, only the dissections demonstrating symptoms of major complications (rupture or deleterious ischemia) require urgent surgical treatment. In the remaining cases, medical treatment, based o n permanent and accurate control of the patient's blood pressure, lead to a good long-term survival rate. Close survey at regular intervals, by means of CT scan or MNR is mandatory to detect any aneurysmal evol ution, which may require surgery. In those cases, our technique is bas ed on anatomic replacement of the dilated aortic portion (generally, t horaco-abdominal) with the aid of cardio-pulmonary bypass and profound hypothermia, in order to protect the spinal cord during the time of a ortic cross-clamping. In addition all patients undergo arteriographic assessment of the spinal chord vascularization prior to surgery.