Retrograde cerebral perfusion provides negligible flow through brain capillaries in the pig.

OBJECTIVES: Although retrograde cerebral perfusion is being used clinically during aortic arch surgery, whether retrograde flow perfuses the brain effectively is still uncertain. METHODS: Fourteen pigs were cooled to 20 degrees C with cardiopulmonary bypass and perfused retrogradely via the superior vena cava for 30 minutes: 7 underwent standard retrograde cerebral perfusion and 7 underwent retrograde perfusion with occlusion of the inferior vena cava. Antegrade and retrograde cerebral blood flow were calculated by quantitating fluorescent microspheres trapped in brain tissue after the animals were put to death; microspheres returning to the aortic arch, the inferior vena cava, and the descending aorta were also analyzed during retrograde cerebral perfusion. RESULTS: Antegrade cerebral blood flow was 16 +/- 7.7 mL. min(-1). 100 g(-1) before retrograde cerebral perfusion and 22 +/- 6.3 mL. min(-1). 100 g(-1) before perfusion with caval occlusion (P =.14). During retrograde perfusion, calculations based on the number of microspheres trapped in the brain showed negligible flows (0.02 +/- 0.02 mL. min(-1). 100 g(-1) with retrograde cerebral perfusion and 0.04 +/- 0.02 mL. min(-1). 100 g(-1) with perfusion with caval occlusion; P =.09): only 0.01% and 0.02% of superior vena caval inflow, respectively. Less than 13% of retrograde superior vena caval inflow blood returned to the aortic arch with either technique. During retrograde cerebral perfusion, more than 90% of superior vena caval input was shunted to the inferior vena cava and was then recirculated, as indicated by rapid development of an equilibrium in microspheres between the superior and inferior venae cavae. With retrograde perfusion and inferior vena caval occlusion, less than 12% of inflow returned to the descending aorta and only 0.01% of microspheres. CONCLUSIONS: The paucity of microspheres trapped within the brain indicates that retrograde cerebral perfusion, either alone or combined with inferior vena caval occlusion, does not provide sufficient cerebral capillary perfusion to confer any metabolic benefit. The slightly improved outcome previously reported with retrograde cerebral perfusion during prolonged circulatory arrest in this model may be a consequence of enhanced cooling resulting from perfusion of nonbrain capillaries and from venoarterial and venovenous shunting.

Favorable outcome after composite valve-graft replacement in patients older than 65 years.

BACKGROUND: Concomitant surgical replacement of the aortic valve and ascending aorta is an ideal treatment for aortic root aneurysms, but there may be hesitation in its use in older patients, despite their known increased risk of rupture. This study was conducted to examine our results in 84 patients older than 65 years undergoing elective aortic root resection with composite valve-graft replacement. METHODS: Eighty-four patients older than 65 years were operated on between June 1987 and August 1998. Median age was 74 years (range, 66 to 89 years), and 57 patients were men. Seventeen patients were undergoing reoperation. Aortic insufficiency was present in 70 patients. Forty-seven patients received a conduit using a bioprosthesis, whereas in 37 a mechanical valved conduit (St. Jude) was used. The ascending aorta alone was replaced in 23 patients; 50 had hemi-arch replacement, and in 11 the entire aortic arch was replaced. RESULTS: Hospital mortality was 8.3% (7 of 84). Sixteen late deaths (19%) were noted during a median follow-up of 3.2 years (range, 0 to 10 years). Only one late death was aorta-related. The incidence of thrombotic or hemorrhagic complications was 2.1/100 patient-years, with equal frequency for both mechanical and bioprosthetic valves. CONCLUSIONS: We conclude that composite valve-graft replacement in elderly patients results in a low operative mortality, yields excellent long-term survival, and averts fatal aneurysm rupture in this high-risk population.

Neurologic outcome after ascending aorta-aortic arch operations: effect of brain protection technique in high-risk patients.

OBJECTIVE: We sought to assess the optimal strategy for avoiding neurologic injury after aortic operations requiring hypothermic circulatory arrest. METHODS: All 717 patients who survived ascending aorta-aortic arch operations through a median sternotomy since 1986 were examined for factors influencing stroke. Temporary neurologic dysfunction was assessed in all patients who survived the operation without stroke since 1993. Multivariate analyses were carried out to determine independent risk factors for neurologic injury. RESULTS: Independent risk factors for stroke were as follows: age greater than 60 years (P <.001; odds ratio, 4.5); emergency operation (P =.02; odds ratio, 2.2); new preoperative neurologic symptoms (P =.05; odds ratio, 2.9); presence of clot or atheroma (P <.001; odds ratio, 4.4); mitral valve replacement or other concomitant procedures (P =.055; odds ratio, = 3.7); and total cerebral protection time, defined as the sum of hypothermic circulatory arrest and any retrograde or antegrade cerebral perfusion (P =.001; odds ratio, 1.02/min). In 453 patients surviving operations without stroke after 1993, independent risk factors for temporary neurologic dysfunction included age (P <.001; odds ratio, 1.06/y), dissection (P =.001; odds ratio, 2.2), need for coronary artery bypass grafting (P =.006; odds ratio, 2.1) or other procedures (P =.023; odds ratio, 3.4), and total cerebral protection time (P <.001; odds ratio, 1.02/min). When all patients with total cerebral protection times between 40 and 80 minutes were examined, the method of cerebral protection did not influence the occurrence of stroke, but antegrade cerebral perfusion resulted in a significant reduction in incidence on temporary neurologic dysfunction (P =.05; odds ratio, 0.3). CONCLUSIONS: The occurrence of stroke is principally determined by patient- and disease-related factors, but use of antegrade cerebral perfusion can significantly reduce the occurrence of temporary neurologic dysfunction.

A comparison of complete blood replacement with varying hematocrit levels on neurological recovery in a porcine model of profound hypothermic (<5 degrees C) circulatory arrest.

Profound hypothermia (<5 degrees C) may afford better neurological protection after circulatory arrest; however, there are theoretical concerns related to microcirculatory sludging of blood components at these ultra-low temperatures. We hypothesized that at temperatures <5 degrees C, complete blood replacement results in superior neurological outcome. Twelve Yorkshire pigs (30 kg) underwent thoracotomy, cardiopulmonary bypass (CPB), and were randomly assigned to one of three target hematocrits during circulatory arrest: 0%, 5%, 15%. Hextend (6% hetastarch in a balanced electrolyte vehicle) was used for the CPB prime and as an exchange fluid. Animals were cooled to a temperature <5 degrees C, underwent 1-h circulatory arrest, and were warmed to 35 degrees C with administration of blood to increase the hematocrit to >25% before separation from CPB. The primary outcome, peak postoperative neurobehavioral score, was compared between groups. The 0% group (mean +/- SD) had significantly (P: < 0.02) better neurobehavioral scores than the 5% and 15% groups (6.0 +/- 2.9 vs 1.3 +/- 1.0 and 1.5 +/- 0.6) respectively. Other variables (e.g., intracranial pressure) were similar between groups. In a porcine model of profound hypothermia (<5 degrees C) and circulatory arrest, complete blood replacement resulted in superior neurological outcome. This finding suggests that at ultralow temperatures, the presence of some blood component (e.g., erythrocytes, leukocytes) may be deleterious.

Results of immediate surgical treatment of all acute type A dissections.

BACKGROUND: Surgery for acute type A aortic dissection is associated with a high mortality rate and incidence of postoperative complications. This study was designed to explore perioperative risk factors for death in patients with acute type A aortic dissection. METHODS AND RESULTS: One hundred twenty-four consecutive patients with acute type A aortic dissection between 1984 and 1998 were reviewed. All underwent operation with resection of the intimal tear and open distal anastomosis: 107 patients had surgery within 24 hours and 17 patients had surgery within 72 hours of symptom onset. Median age was 62 years (23 to 89); 89 were men. Forty-three patients had ascending aortic replacement only, 72 had hemiarch repair, in 2 the entire arch was replaced, and in 7 replacement included the proximal descending aorta. The aortic valve was replaced in 54 patients, resuspended in 52, and untouched in 18. Hospital mortality rate was 15.3% (19 of 124): of these, 3 patients died during surgery, 4 had fatal rupture of the distal aorta before discharge, and 2 died of malperfusion-related complications. Multivariate analysis revealed age >60, hemodynamic compromise, and absence of hypertension as preoperative indicators of hospital death (P:<0.05); the presence of new neurological symptoms was a significant preoperative risk factor in univariate analysis. Ominous intraoperative factors included contained hematoma and a comparatively low esophageal temperature but not cerebral ischemic time (mean 32 minutes). The site of the intimal tear did not influence outcome, but mortality rate was higher with more extensive resection: 43% with resection including the descending aorta died versus 14% with only ascending aorta or hemiarch replacement. Overall 5- and 10-year survival was 71% and 54%, respectively; among discharged patients (median follow-up 41 months) survival was 84% and 64% versus expected US survival of 92% and 79%. CONCLUSIONS: Immediate surgical treatment of all acute type A dissections with resection of the intimal tear and use of hypothermic circulatory arrest for distal anastomosis results in acceptable early mortality rates and excellent long-term survival.

Predictors of adverse outcome and transient neurological dysfunction after ascending aorta/hemiarch replacement.

BACKGROUND: This study was undertaken to determine predictors of adverse outcome and transient neurological dysfunction after replacement of the ascending aorta with an open distal anastomosis. METHODS: All 443 patients (300 male, median age 63) undergoing replacement of the ascending aorta with an open distal anastomosis between 1986 and 1998 were included in the analysis. The ascending aorta alone was replaced in 190 (42.9%); 253 (57.1%) also had proximal arch replacement. Median hypothermic circulatory arrest (HCA) time was 25 minutes (range 12 to 68). Either death or permanent neurological dysfunction were considered adverse outcome (AO). RESULTS: Adverse outcome occurred in 11.5% (51 of 443) of patients overall: in 7.4% of elective (20 of 269) or urgent (4 of 54) operations, but in 17% (19 of 113) of emergencies. Multivariate analysis of the group as a whole revealed that significant (p < 0.05) independent preoperative predictors of AO were age greater than 60 [odds ratio (OR) 2.2], hemodynamic instability (OR 2.7), and dissection (OR 1.9). For the 435 operative survivors, procedural variables predictive of AO were contained rupture (OR 2.8) and HCA time (OR 1.03/min). When only the 271 elective patients were analyzed separately, the need for a concomitant procedure (p = 0.009, OR 3.6) and HCA time (p = 0.002, OR 1.06/min) were the only predictors of AO in multivariate analysis. Transient neurological dysfunction (TND) occurred in 86 of 392 patients (22%). Significant predictors of TND for all patients without AO were age (OR 1.06/y), HCA time (OR 1.04/min), coronary artery disease (OR 2.2), hemodynamic instability (OR 3.4), and acute operation (OR 2.2). Survival of discharged patients was 93% at 1 year and 83% at 5 years. CONCLUSIONS: Early elective operation and shorter HCA time during ascending aorta/hemiarch surgery will reduce both AO and TND.

Surgical techniques. Aortic arch and deep hypothermic circulatory arrest: real-life suspended animation.

Surgical reconstruction of the aortic arch is a complex procedure requiring careful preoperative analysis of the pathology and forethought toward surgical approach. Development of surgical techniques has brought dramatic improvement survival and reduction of neurological events associated with these procedures, yet significant morbidity is still encountered. New approaches to the patient with these pathologies include antegrade and retrograde perfusions to the brain. Continued research into physiology of hypothermic circulatory arrest offers the promise of pharmacological protection of the brain during aortic reconstruction and potentially development of therapeutic modalities to treat and limit ischemic brain damage.

Surgical treatment of the dilated ascending aorta: when and how?

BACKGROUND: The aorta is considered pathologically dilated if the diameters of the ascending aorta and the aortic root exceed the norms for a given age and body size. A 50% increase over the normal diameter is considered aneurysmal dilatation. Such dilatation of the ascending aorta frequently leads to significant aortic valvular insufficiency, even in the presence of an otherwise normal valve. The dilated or aneurysmal ascending aorta is at risk for spontaneous rupture or dissection. The magnitude of this risk is closely related to the size of the aorta and the underlying pathology of the aortic wall. The occurrence of rupture or dissection adversely alters natural history and survival even after successful emergency surgical treatment. METHODS: In recommending elective surgery for the dilated ascending aorta, the patient's age, the relative size of the aorta, the structure and function of the aortic valve, and the pathology of the aortic wall have to be considered. The indications for replacement of the ascending aorta in patients with Marfan's syndrome, acute dissection, intramural hematoma, and endocarditis with annular destruction are supported by solid clinical information. Surgical guidelines for intervening in degenerative dilatation of the ascending aorta, however, especially when its discovery is incidental to other cardiac operations, remain mostly empiric because of lack of natural history studies. The association of a bicuspid aortic valve with ascending aortic dilatation requires special attention. RESULTS: There are a number of current techniques for surgical restoration of the functional and anatomical integrity of the aortic root. The choice of procedure is influenced by careful consideration of multiple factors, such as the patient's age and anticipated survival time; underlying aortic pathology; anatomical considerations related to the aortic valve leaflets, annulus, sinuses, and the sino-tubular ridge; the condition of the distal aorta; the likelihood of future distal operation; the risk of anticoagulation; and, of course, the surgeon's experience with the technique. Currently, elective root replacement with an appropriately chosen technique should not carry an operative risk much higher than that of routine aortic valve replacement. Composite replacement of the aortic valve and the ascending aorta, as originally described by Bentall, DeBono and Edwards (classic Bentall), or modified by Kouchoukos (button Bentall), remains the most versatile and widely applied method. Since 1989, the button modification of the Bentall procedure has been used in 250 patients at Mount Sinai Medical Center, with a hospital mortality of 4% and excellent long-term survival. In this group, age was the only predictor of operative risk (age > 60 years, mortality 7.3% [9/124] compared with age < 60, mortality 0.8% [1/126], p = 0.02). CONCLUSIONS: This modification of the Bentall procedure has set a standard for evaluating the more recently introduced methods of aortic root repair.

Temporary neurological dysfunction after deep hypothermic circulatory arrest: a clinical marker of long-term functional deficit.

BACKGROUND: With increasing clinical experience, it has become clear that two distinct forms of neurological injury occur after operations on the thoracic aorta that require temporary exclusion of the cerebral circulation. Traditionally, evaluation of neurological outcome was limited to reporting the incidence of postoperative stroke related to ischemic infarcts due to particulate embolization. More recently, the symptom complex defined as "temporary neurological dysfunction" (TND) was recognized as a functional manifestation of subtle and presumably transient brain injury, but whether this early postoperative syndrome is associated with long-term deficits of cognitive and intellectual functions has not been established. METHODS: With Institution Review Board approval, 105 patients undergoing elective thoracic aortic surgery were entered into a protocol involving neuropsychological evaluation with a battery of tests preoperatively, and 1 and 6 weeks postoperatively. Patients who could not be tested adequately or had documented strokes were eliminated from final analysis. Seventy-one patients completed the neuropsychological evaluation, which consisted of eight tests consolidated into five domains: attention, cognitive speed, memory, executive function, and fine motor function. Independent observers also determined whether temporary dysfunction was present, and graded its severity based on a fixed but subjective clinical scale, ranging from simple disorientation and lethargy or confusion (grade 1-2) to prolonged extreme agitation or psychotic behavior requiring treatment with psychotropic drugs (grade 3-5). Data were normalized to baseline values, and were analyzed using analysis of variance, analysis of covariance (ANCOVA), and chi2 as necessary. RESULTS: A previous analysis had shown that patients who could not be tested or had poor scores 1 week postoperatively were more likely to perform poorly at 6 weeks (odds ratio 5.27, p < 0.01). In the current study, in order to determine the clinical relevance of TND, patients were analyzed retrospectively according to their performance in neuropsychological testing: patients with no change or a decline of less than 50% in tests of memory, motor function, and attention 1 week postoperatively (group 1, n = 49) were compared with those with a negative change exceeding 50% in the same functions at 1 week (group 2, n = 22). The overall incidence of TND was 28.1% (20/71). The incidence of TND in group 2 (14/22, 63%) was significantly higher than in group 1 (6/49, 12%; p = 0.0006). Similarly, the severity of TND (as assessed by clinical score > 2) was also significantly higher in group 2 (11/14) compared with group 1 (0/6; p = 0.006.) CONCLUSIONS: The incidence and severity of clinically apparent temporary neurological dysfunction correlates significantly with poor performance on neuropsychological tests 1 week postoperatively. Such poor performance predicts continued deficits in memory and motor function at 6 weeks. Thus, TND may not be a benign self-limited condition as previously supposed, but rather a clinical marker for insidious but significant neurological injury associated with measurable long-term deficits in cerebral function. A concerted effort to reduce the incidence of this complication is therefore necessary.

Cerebral metabolic suppression during hypothermic circulatory arrest in humans.

BACKGROUND: Hypothermic circulatory arrest (HCA) is used in surgery for aortic and congenital cardiac diseases. Although studies of the safety of HCA in animals have been carried out, the degree to which metabolism is suppressed in patients during hypothermia has been difficult to determine because of problems with serial measurements of cerebral blood flow in the clinical setting. METHODS: To quantify the degree of metabolic suppression achieved by hypothermia, we studied 37 adults undergoing operations employing HCA. Cerebral blood flow was estimated using an ultrasonic flow probe on the left common carotid artery, and cerebral arteriovenous oxygen content differences were calculated from jugular venous bulb and arterial oxygen saturations. Cerebral metabolic rates while cooling were then ascertained. The temperature coefficient, Q10, which is the ratio of metabolic rates at temperatures 10 degrees C apart, was determined. RESULTS: The human cerebral Q10 was found to be 2.3. The cerebral metabolic rate is still 17% of baseline at 15 degrees C. If one assumes that cerebral blood flow can safely be interrupted for 5 min at 37 degrees C, and that cerebral metabolic suppression accounts for the protective effects of hypothermia, the predicted safe duration of HCA at 15 degrees C is only 29 min. CONCLUSIONS: The safe intervals calculated from measured cerebral oxygen consumption suggest that shorter intervals and lower temperatures than those currently used may be necessary to assure adequate cerebral protection during hypothermic circulatory arrest.

Natural history of descending thoracic and thoracoabdominal aneurysms.

BACKGROUND: A review of 165 patients with chronic dissecting and degenerative aneurysms of the descending thoracic and thoracoabdominal aorta initially managed nonoperatively was carried out to ascertain factors associated with a high risk of rupture. METHODS: Changes in the aneurysms were followed with three-dimensional reconstructions of computed tomograph scans. Risk factors were compared in patients with dissecting and nondissecting aneurysms who experienced rupture, in whom operation was recommended during the course of follow-up, and in those without rupture or operation. RESULTS: Nondimensional variables associated with an enhanced risk of rupture include age, the presence of chronic obstructive pulmonary disease, and even uncharacteristic continued pain. Patients with rupture of dissections had significantly higher blood pressures than survivors, and significantly smaller maximal descending thoracic aortic diameters (median 5.4 cm) than patients with rupture of degenerative aneurysms (median 5.8 cm). The extent of the aneurysm, as reflected by the maximal abdominal aortic diameter, was a significant risk factor for rupture only in nondissecting aneurysms. Mortality from rupture was significantly higher in patients with chronic dissections than in patients with nondissecting aneurysms: 9/10 vs 26/34 (p = 0.004). CONCLUSIONS: Almost 20% of patients followed nonoperatively succumbed to rupture, suggesting that a more aggressive surgical approach toward patients with chronic aneurysms of the descending thoracic and thoracoabdominal aorta is warranted. An individualized risk of rupture within 1 year can now be calculated, and patients whose operative risk is lower than their calculated risk should be offered elective surgery.

Use of somatosensory evoked potentials for thoracic and thoracoabdominal aortic resections.

BACKGROUND: Despite tremendous development in surgical and anesthetic techniques, resection of the thoracic and thoracoabdominal segments of the aorta remain associated with the risk of paralysis. Routine use of somatosensory-evoked potential (SEP) monitoring in patients undergoing surgery of the thoracic aorta has become a standard intra- and postoperative procedure at our institution since its first use in 1993. METHODS: One hundred forty nine (149) thoracic aortic operations were performed during January 1993 through January 1998 using SEP-directed serial sacrifice of paired intercostal arteries. Full, partial, or no cardiovascular bypass was variably used, dictated by anatomy; 49 patients required deep hypothermic circulatory arrest (DHCA). Patients were monitored during both the intraoperative procedure as well for the post-anesthesia period until neurologic stability and/or ability to reproducibly demonstrate lower extremity neurologic competency was established. Postoperative neurologic function was compared to ischemic intervals, extent of aortic resection, number of intercostal arteries sacrificed, type of perfusion, and underlying aortic pathology. RESULTS: Overall mortality in the group was 13 patients (8.7%), with no one cause predominating. Nine patients sustained permanent paraplegia, only 1 of whom lost SEPs during the procedure. Abnormal SEPs were seen in 19 patients, 14 of whom had normal neurologic function after awakening. Three of 19 (15.8%) developed late paraplegia that resolved with medical therapy. Eleven patients (7.4%) developed cerebrovascular accidents (CVA), with the majority (8) appearing in the group undergoing DHCA. The risk of CVA was significantly higher in DHCA patients (p < 0.01) than other patients. No patient with CVA had abnormal SEPs; 4 DHCA patients developed abnormal SEPs, 1 with permanent paralysis. CONCLUSIONS: The routine use of SEP monitoring during thoracic and thoracoabdominal aortic surgery as well as during the postoperative period may be useful in decreasing the observed incidence of paraplegic events associated with these procedures.

Subtypes of acute aortic dissection.

BACKGROUND: This series consists of a 12-year experience with a policy of identifying and replacing the aortic segment containing the primary intimal tear for repair of acute aortic dissection. METHODS: Patients with type A dissection underwent urgent surgery. Patients with type B dissection were referred for surgery based on selective criteria, including aortic dilatation greater than 5 cm. A classification system for acute dissection is described that specifies the site of intimal tear while retaining the clinical relevance of the Stanford system. RESULTS: Of 168 acute dissections, 139 were type A and 29 were type B. The site of intimal tear was as follows: ascending aorta, 83 cases; arch, 32 cases; descending aorta, 29 cases; multiple tears, 11 cases (10 included arch tears); no tear (intramural hematoma), 6 cases; not noted, 7 cases. Only 60% of acute type A dissections arose from solitary intimal tears in the ascending aorta, whereas 30% had arch tears. Hospital mortality for type A dissection was 13.7% (18.8% for arch tears, NS) and 0% for type B. False lumen patency was 57.1% for type A dissection and 18.8% for type B dissection (p = 0.002), yet survival was similar for these groups. Ten-year survival for type A dissection with arch tear (0.51 +/- 0.12) was lower than 10-year survival for type A dissection with ascending tear (0.74 +/- 0.05; p = 0.77), and significantly lower than for type A dissection with descending tear (0.88 +/- 0.12; p = 0.029). CONCLUSIONS: Systematic resection of the primary tear yielded similar hospital mortality, 5-year survival, and aorta-related event-free survival rates for subtypes of acute type A dissection. Excellent results were obtained with a selective approach to type B dissection.

Risk factors for rupture of chronic type B dissections.

OBJECTIVE: This study was an attempt to determine risk factors for rupture and to improve management of patients with type B aortic dissection who survive the acute phase without operation. METHODS: We studied 50 patients by means of serial computer-generated 3-dimensional computed tomographic scans. All patients who did not undergo operative treatment before the completion of at least 2 computed tomographic scans a minimum of 3 months apart after an acute type B dissection were included in the study. The median duration of follow-up was 40 months (range 0.9-112 months). Only 1 patient died of causes unrelated to the aneurysm during follow-up. Nine patients had fatal rupture (18%); 10 patients underwent elective aneurysm resection because of rapid expansion or development of symptoms, and 31 patients remained alive without operation or rupture. Possible risk factors for rupture in patients in the rupture, operative, and event-free groups were compared, as were dimensional data from first follow-up and last computed tomographic scans. RESULTS: Older age, chronic obstructive pulmonary disease, and elevated mean blood pressures were unequivocally associated with rupture (rupture versus event-free survival, P <.05), and pain was marginally significantly associated. Analysis of dimensional factors contributing to rupture was complicated by the fact that patients who underwent elective operation had significantly larger aneurysms and faster expansion rates than did either of the other groups, leaving comparisons of aneurysmal diameter between groups with and without rupture showing only marginal statistical significance. The last median descending aortic diameter before rupture in the rupture group was 5.4 cm (range 3.2-6. 7 cm). CONCLUSIONS: In an environment in which patients with large and rapidly expanding aneurysms are usually referred for surgical treatment, older patients with chronic type B dissections, especially if they have uncontrolled hypertension and a history of chronic obstructive pulmonary disease, are significantly more likely to have rupture than are younger, normotensive patients without lung disease. Neither the presence of a persistently patent false lumen nor a large abdominal aortic diameter appears to increase the risk of rupture. Overall, our nondimensional data strikingly resemble the natural history of patients with nondissecting aneurysms, suggesting that calculations derived from data on chronic descending thoracic and thoracoabdominal aneurysms would provide an overly conservative individual estimate of rupture risk for patients with chronic type B dissection, who tend toward earlier rupture of smaller aneurysms. A more aggressive surgical approach toward treatment of patients with chronic type B dissection seems warranted.

Retrograde cerebral perfusion enhances cerebral protection during prolonged hypothermic circulatory arrest: a study in a chronic porcine model.

BACKGROUND: This study was undertaken to confirm earlier findings that retrograde cerebral perfusion (RCP) can improve cerebral outcome after prolonged hypothermic circulatory arrest (HCA), and to determine whether RCP with inferior vena caval occlusion, which is more effective in removing particulate emboli, is superior to conventional RCP in enhancing cerebral protection. METHODS: Sixty-two pigs (27 to 30 kg) were randomly assigned to undergo one of the following for 90 minutes at 20 degrees C: antegrade cerebral perfusion (ACP); conventional RCP (RCP); RCP with occlusion of the inferior vena cava (RCP-O), or HCA with the head packed in ice. RCP flow was regulated to a sagittal sinus pressure of 20 mm Hg. Hemodynamic, electrophysiologic, and metabolic monitoring were carried out until 4 hours after rewarming, daily behavioral and neurologic assessments until elective sacrifice on day 7, and histologic analysis of the brain after death. RESULTS: Complete behavioral recovery was seen in all surviving animals by day 5 after ACP or RCP, but in only 83% after RCP-O and 50% after HCA (p = 0.001). A histopathologic score of 2 or more, indicating more than mild injury, was not found in any animal after ACP, in 27% after RCP, in 47% after HCA, and in 68% after RCP-O (p = 0.002). The median oxygen consumption was 6.66 mL/min after ACP, 1.37 mL/min with RCP, and 1.02 mL/min with RCP-O (p < 0.0001). The median amount of fluid sequestered was 2,450 mL after RCP-O, 760 mL after RCP, and -200 mL after ACP (p < 0.0001). CONCLUSIONS: Conventional RCP without inferior vena caval occlusion results in a significantly better outcome than RCP-O after prolonged HCA, despite more efficient cerebral perfusion during RCP-O, and also provides cerebral protection superior to prolonged HCA alone, but care must be taken during its implementation to minimize cerebral edema and other possible causes of retroperfusion-related cerebral injury.

Can retrograde perfusion mitigate cerebral injury after particulate embolization? A study in a chronic porcine model.

OBJECTIVE: We assessed the impact on histologic and behavioral outcome of an interval of retrograde cerebral perfusion after arterial embolization, comparing retrograde cerebral perfusion with and without inferior vena caval occlusion with continued antegrade perfusion. METHODS: Sixty Yorkshire pigs (27 to 30 kg) were randomly assigned to the following groups: antegrade cerebral perfusion control; antegrade cerebral perfusion after embolization; retrograde cerebral perfusion control; retrograde cerebral perfusion after embolization; retrograde cerebral perfusion with inferior vena cava occlusion, retrograde cerebral perfusion with inferior vena cava occlusion control, and retrograde cerebral perfusion with inferior vena cava occlusion after embolization. After cooling to 20 degrees C, a bolus of 200 mg of polystyrene microspheres 250 to 750 (microm diameter (or saline solution) was injected into the isolated aortic arch. After 5 minutes of antegrade cerebral perfusion, 25 minutes of antegrade cerebral perfusion, retrograde cerebral perfusion, or retrograde cerebral perfusion with inferior vena cava occlusion was instituted. After the operation, all animals underwent daily assessment of neurologic status until the time of death on day 7. RESULTS: Aortic arch return, cerebral vascular resistance, and oxygen extraction data during retrograde cerebral perfusion showed differences, suggesting that more effective flow occurs during retrograde cerebral perfusion with inferior vena cava occlusion, which also resulted in more pronounced fluid sequestration. Microsphere recovery from the brain revealed significantly fewer emboli after retrograde cerebral perfusion with inferior vena cava occlusion. Behavioral scores showed full recovery in all but one control animal (after retrograde cerebral perfusion with inferior vena cava occlusion) by day 7 but were considerably lower after embolization, with no significant differences between groups. The extent of histopathologic injury was not significantly different among embolized groups. Although no histopathologic lesions were present in either the antegrade cerebral perfusion control group or the retrograde cerebral perfusion control group, mild significant ischemic damage occurred after retrograde cerebral perfusion with inferior vena cava occlusion even in control animals. CONCLUSIONS: Although effective washout of particulate emboli from the brain can be achieved with retrograde cerebral perfusion with inferior vena cava occlusion, no advantage of retrograde cerebral perfusion with inferior vena cava occlusion after embolization is seen from behavioral scores, electroencephalographic recovery, or histopathologic examination; retrograde cerebral perfusion with inferior vena cava occlusion results in greater fluid sequestration and mild histopathologic injury even in control animals. Retrograde cerebral perfusion with inferior vena cava occlusion shows clear promise in the management of embolization, but further refinements must be sought to address its still worrisome potential for harm.

Prospective study of the natural history of thoracic aortic aneurysms.

BACKGROUND: The decision whether or not to recommend resection of moderately large descending thoracic and thoracoabdominal aneurysms requires weighing the relatively high mortality and significant risk of paraplegia associated with operation against the likelihood that the aneurysm will rupture spontaneously, with an almost invariably fatal outcome. To better define the risk of aneurysm rupture, we undertook a prospective study of patients who had not had operation on their moderately large descending thoracic and thoracoabdominal aneurysms. METHODS: Patients were enrolled at the time of their second computed tomographic scans: three-dimensional computer-generated reconstructions allowed determination of several dimensional parameters for each study, including diameters and cross-sectional areas at the site of maximal dilatation in the descending aorta and in the abdomen as well as total thoracoabdominal surface area. Comparisons of serial studies permitted calculation of yearly rates of change in these dimensions. RESULTS: Of 114 patients, 8 died of causes unrelated to the aneurysm, 26 died of rupture, 20 met previously determined criteria for operation, and 60 survived without operation or rupture. Multivariate regression analysis identified maximal diameter in the descending and in the abdominal aorta as independent risk factors for rupture, as well as older age, the presence of even uncharacteristic pain, and a history of chronic obstructive pulmonary disease. A piecewise exponential model enabled construction of an equation allowing calculation of rate of rupture in patients in whom the values of the risk factors are known, and also of the probability of rupture in a given individual over a specified time interval. CONCLUSIONS: Because using this equation--based on easily determined risk factors (age, pain, chronic obstructive pulmonary disease, maximal thoracic and maximal abdominal aortic diameter)--allows the risk of aneurysm rupture within a given interval to be estimated fairly accurately for each individual patient, it is our current practice to recommend operation when the calculated risk of rupture within 1 year exceeds the anticipated mortality of elective operation, rather than relying on general operative guidelines based almost exclusively on aneurysm size.

The Bentall procedure in patients with Marfan's syndrome.

From 1985 to 1996, 18 patients with Marfan's syndrome underwent the Bentall procedure at Mount Sinai Hospital. They are compared with 38 patients aged < 40 without Marfan's syndrome who also underwent composite valve-graft replacement of the ascending aorta. The mean age of the non-Marfan group was 33 while that of the Marfan group was 29. Nearly three-quarters of each group were male. Aortic dissection was present in 33% of the Marfan group but only in 18% of the other group. Seventy-eight percent of the Marfan patients and 89% of the non-Marfan patients had aortic regurgitation. Twenty-one percent of the patients in the control group nevertheless had gross aortic pathology suggestive of Marfan's syndrome and may have had variants of the syndrome; 26% of the non-Marfan group had a bicuspid aortic valve. A modification of the Bentall procedure with implantation of coronary artery buttons was performed in the majority of the patients in both groups. Three patients, all in the group with Marfan's syndrome, required a concomitant mitral valve procedure. There was one death in each group. Two non-Marfan patients required reoperation; neither had dissection. Four patients with Marfan's syndrome underwent reoperation for distal disease in the aorta; they comprised one third of the Marfan patients who had aortic dissection. Three late complications occurred in the group with Marfan's syndrome: progressive cardiomyopathy; myocardial infarction; and late tamponade. There were also two late sudden deaths in the group with Marfan's syndrome, which may have been the consequence of aortic rupture. No difference in immediate operative mortality following the Bentall procedure was noted between patients with and without Marfan's syndrome, but young patients without Marfan's syndrome seem to have better event-free and long-term survival. In patients with Marfan's syndrome, the presence of acute dissection makes reoperation more likely, and sudden death from rupture still occurs despite careful postoperative surveillance. A higher incidence of severe mitral valve disease was found among young patients with Marfan syndrome than in controls.

Identification of risk factors in patients undergoing thoracoabdominal aneurysm repair.

Developments and advances in surgical and anesthetic techniques have lead to increased survival in patients undergoing complex thoracic aortic aneurysm repairs. The decision to operate, however, continues to be based in a large degree on the clinical impression of the patient's ability to withstand the rigors of the procedure. As part of the ongoing effort of our department to further elucidate those parameters that impart added risk to patients, the diameters and volumes of CT-imaged aortas were determined for 67 surgical and nonoperatively managed patients. Significant differences were found between those patients not requiring surgery, and both those undergoing operation and those that died of rupture. Similarly, the average yearly increase in volume in surgical and rupture patients was higher than that of nonoperatively managed patients. Those patients who smoked also were found to have a significant yearly increase in size of their aortas relative to those patents that did not. An algorithm for managing patients presenting with thoracoabdominal aneurysms based upon size at initial presentation, change in annual diameter and volume, and estimated risk for paraplegia is presented.

Use of hypothermic circulatory arrest for cerebral protection during aortic surgery.

Optimal use of hypothermic circulatory arrest during aortic surgery requires understanding of its physiology. Research in laboratory animals and clinical observations have now documented that considerable residual cerebral metabolism remains with cooling to levels of 15-18 degrees C, especially if cooling intervals are short, reflected by persistent jugular venous desaturation. Cooling should be continued to below 15 degrees C if the duration of HCA is expected to exceed 20 minutes, and continued until jugular venous saturations exceed 95%. There is considerable laboratory evidence that even short durations of HCA are followed by a prolonged interval of increased cerebral vascular resistance during which cerebral metabolism is maintained at normal levels by markedly increased oxygen extraction. Clinical observations have now confirmed that considerable jugular venous desaturation is present in patients following HCA: it is more pronounced with prolonged HCA, and is still present as late as six hours after the start of rewarming. This reinforces the concept of a prolonged postoperative vulnerable interval following HCA, during which any compromise in oxygen delivery has the potential for producing cerebral injury. Several adjunctive measures have been shown to improve outcome following HCA. The simplest and most important is topical hypothermia: packing the head in ice during the interval of HCA. Retrograde cerebral perfusion (RCP) has also been shown to improve EEG recovery as well as histological and behavioral outcome in laboratory animals following prolonged HCA, but some of its effect may be secondary to its efficacy in keeping the brain cold, since RCP provides very low rates of flow and supports metabolism at a much lower level than antegrade perfusion at the same temperature. But despite the clear superiority of antegrade perfusion, and the documentation of some benefits of RCP in laboratory measures of cerebral protection, clinical results using RCP and ACP have not yet demonstrated the superiority of these methods over use of HCA alone, perhaps because these modalities are usually employed in patients with unusually high risk of neurological injury: those with dissection or with clot or atheroma in the aorta. Nevertheless, recent years have seen considerable reduction in mortality following aortic surgery, especially in older patients, and a trend toward a lower incidence of permanent neurologic dysfunction. The presence of preoperative rupture or hemodynamic compromise, and of clot or atheroma in the aorta, remain the most significant risk factors both for death and occurrence of stroke.