Surgery for Acute Aortic Transection

Abstract

Traumatic transection of the thoracic aorta is a lethal condition that results in ininietliate death approximately 8S% of the time.' Injury results from rapid deceleration secondary to a fall from a height or high-speed motor vehicle accident. Profound intraluminal hypertension, with pressures in excess of 2,500 mm Hg, are needed to generate a traumatic rupture2 in an area where the aorta is relatively fixed in position. Greater than 90% of the injuries arise in the descending thoracic aorta at the level of the ligamentum arteriosum. An additional 5% of patients will sustain an aortic transection in the ascending aorta, just above the sinotubular junction, whereas the remaining 5% of patients sustain one in the distal descending thoracic aorta or aortic arch.< Patients surviving the initial insult are found to have a partial thickness tear of the aorta or a full thickness tear with the hematoma being contained by intact parietal pleura. The need for urgent intervention is highlighted by the fact that 46% of patients will expire in the 2 weeks after the injury. Nearly 98% of patients will not survive beyond 1 month. The small percentage of patients who evade initial detection are still at high risk for death. Approximately 20% of patients will rupture a traumatic pseudoaneurysm within 5 years of d e t e ~ t i o n . ~ The mere presence of the injury should be an indication for repair. The only exception to this is if the patient has other, life-threatening injuries that require immediate attention. These patients should be managed with aggressive beta-blockade and afterload reduction in an effort to decrease dP/dt and minimize intralumiiial wall tension.' However, this is a calculated risk and repair should be undertaken as soon as the patient is able to tolerate the procedure. The radiographic detection of a traumatic transection is a rapidly evolving field. Angiography remains the gold standard for confirming the presence of an aortic transection with an accuracy of nearly 10070. Angiograms also provide precise anatomic detail that allow for more careful planning of operative intervention. This test remains the diagnostic tool of choice in our practice. Three less invasive modalities, computed tomographic (CT) scanning, transesophageal echocardiography (TEE), and magnetic resonance imaging (MRI), have also been applied to this tenuous patient population. CT has gained popularity because it is noninvasive and wiclely available. It is often used in the trauma patient to evaluate intracranial or intraabdoniinal injury. The addition of il chest wan does not greatly increase the amount of time spent in the radiology suite and the appeal of a single diagnostic procedure before surgical intervention cannot be discounted. To date, however, the accuracy of CT scans are only 90% in the best and most experienced hands and only when strict interpretation criteria are applietL6 Reliahle interpretation must become more standardized hefore widespread application in the setting of acute aortic transection can be advocated. Aortic imaging using TEE has proven its use as a highly accurate method of diagnosing aortic dissection.' In limited reports, the accuracy has been shown to exceed that of CT scans in traumatic transections.' It is an attractive method because of its ready availability in both the emergency department and the operating rooms. However, interpretation can be obscured by the tracheal air column behind the distal aortic arch. Hypertension associated with the procedure may also precipitate rupture. Further experience with TEE may ultimately make it the modality of choice in this setting. MRI, although highly accurate, cannot be advocated for diagnosis of acute transections at the present time. Radiological interpretation is highly variable as is the quality of the machines. More importantly, it is time consuming and patients cannot be adequately evaluated and monitored while the procedure is being performed. The preferred method of surgical repair has been a hotly debated issue for decades. The simplest method remains the clamp and sew technique. Advantages include the elimination of anticoagulation ancl an operative field free of the tubing and cannulae needed with an extracorporeal circuit or shunt. Advocates of this method have consistently shown low rates of paraplegia when the cross-clamp time can be kept to 30 minutes or less.y Some of the earliest repairs in the literature were performed using an extracorporeal circuit. ' Since then many methods have been advocated for repair of traumatic transections. These include partial left-heart bypass with and without heparin, femoral-femoral cardiopulmonary bypass with full dose heparin and passive shunts into the descending thoracic aorta from both the ascending aorta and the left ventricular apex. In 1992, a large meta-analysis reviewed over 1,700 cases of acute traumatic aortic transection repaired with a variety of the aforementioned techniques. This analysis suggests improved neurological outcome with the use of distal