Joseph Megerman

Vascular complications associated with spontaneous aortic dissection

Three hundred twenty-five cases of spontaneous aortic dissection seen at two institutions between 1965 and 1986 were reviewed to assess the incidence, morbid sequelae, and specific management of aortic branch compromise. Noncardiac vascular complications occurred in 33% of the study group, and in these patients the overall mortality rate (51%) was significantly (p less than 0.001) higher than in patients without (29%) such complications. Although aortic rupture was the strongest correlate of mortality (90%), death specifically related to vascular occlusion was common when such occlusion occurred in the carotid, mesenteric, and renal circulation. There was a strong correlation between stroke and carotid occlusion (22/26 cases), yet specific carotid revascularization was only used during the chronic phase of the disease. Similarly, peripheral operation was ineffective in reducing the mortality rate in the setting of mesenteric (87%) and renal (50%) ischemia. Fifteen patients required either fenestration or graft replacement of the abdominal aorta for acute obstruction, rupture, or chronic aneurysm development. Thirty-eight patients (12%) demonstrated some degree of lower extremity ischemia, and one third of these required a direct approach on the abdominal aorta or iliofemoral segments to restore circulation. Selected patients with acute aortic dissection may require peripheral vascular operation in accordance with a treatment strategy that directs initial attention to the immediate life-threatening complications.

Effect of compliance mismatch on vascular graft patency

The hypothesis that a mismatch in compliance between a vascular graft and its host artery is detrimental to graft patency was tested by implanting paired arterial autografts, prepared with differential glutaraldehyde fixation of carotid arteries in the femoral arteries of dogs. These grafts differed only in circumferential compliance: they were 100% (compliant) vs. 40% (stiff) as compliant as the host artery. Their flow surfaces were equivalent, as determined by physicochemical measurements and scanning electron microscopy; both lacked viable cells, as determined by in vitro cell culture. In 14 dogs, eight stiff and two compliant grafts became occluded within 3 months, the latter doing so within 24 hours after their contralateral counterparts. Cumulative patencies were 85% and 37% for compliant and stiff grafts, respectively (p less than 0.05) and 100% and 43%, excluding the two dogs with bilateral graft failures (p less than 0.01). We conclude that even with near optimal flow surfaces, compliance mismatch is deleterious to graft patency.

Transperitoneal versus retroperitoneal approach for aortic reconstruction: A randomized prospective study*

A prospective, randomized study was conducted to compare the retroperitoneal versus transperitoneal approach for elective aortic reconstruction. One hundred thirteen patients (transperitoneal = 59, retroperitoneal = 54) were randomized between March 1987 and October 1988. In addition, to assess the changing course of patients undergoing aortic reconstruction similar data were gathered retrospectively on a group of 56 patients undergoing aortic reconstruction by the same surgeons performed via a transperitoneal approach in 1984 to 1985. Randomized patients were identical in age, male to female ratio, smoking history, incidence and severity of cardiopulmonary disease, indication for operation, and use of epidural anesthetics. Details of operation including operative and aortic cross-clamp times, crystalloid and transfusion requirements, degree of hypothermia on arrival at the intensive care unit, and perioperative fluid and blood requirements did not differ significantly for patients undergoing transperitoneal versus retroperitoneal reconstruction. Respiratory morbidity, as assessed by percent of patients requiring postoperative ventilation, deterioration in pulmonary function tests, and the incidence of respiratory complications, was identical in randomized patients. Other aspects of postoperative recovery including recovery of gastrointestinal function, the requirement for narcotics, metabolic parameters of operative stress, the incidence of major and minor complications, and the duration of hospital stay were similar for randomized patients undergoing transperitoneal and retroperitoneal reconstruction. When compared to retrospectively reviewed patients having aortic reconstruction, randomized patients undergoing transperitoneal and retroperitoneal operations had highly significant (p less than 0.001) reductions in postoperative ventilation, transfusion requirements, and length of hospital stay. Such trends were all independent of transperitoneal versus retroperitoneal approach.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunosuppressive treatment of aortic allografts

Immunosuppression with cyclosporine (CsA) was explored as a means of preventing arterial allograft rejection and failure. Aortic allografts across the major histocompatibility barrier were studied in Brown-Norway and Lewis inbred rats. Grafts 1 cm long were interposed into the infra-abdominal aorta of Lewis recipients; five groups included two groups of untreated isograft and allograft control animals and three groups had allograft-CsA treatment regimens. The grafts were examined at 30, 60, and 100 days for patency, aneurysmal dilation, gross structural changes, inflammatory responses, and infiltration of W3/25- and OX8-positive lymphocytes. Only three allograft controls became occluded; the rest showed significant dilation (p less than 0.01), medial thinning and necrosis, intimal proliferation, and prominent cellular infiltration at 30 days. With all CsA regimens, aneurysmal dilation was significantly reduced or prevented (p less than 0.01), correlating with medial smooth muscle cell preservation. Cellular infiltration was delayed by an average daily dose of 5 to 10 mg/kg subcutaneous CsA for 30 days and was suppressed at 100 days by a continuous 5 mg/kg dose every 4 days. Intimal thickening in the graft was delayed but not prevented. We conclude that a low maintenance dose of CsA provides effective immunosuppression, thereby preventing aneurysm formation, and that the potential use of arterial allografts in vascular surgery may need to be readdressed.

Utility of transcutaneous oxygen tension measurements in peripheral arterial occlusive disease

The use of transcutaneous oxygen tension (TCpO2) measurements to objectively and noninvasively diagnose peripheral arterial occlusive disease (PAOD) and to aid in the planning of vascular surgery was investigated. Thirty-two normal subjects and 100 patients with PAOD were studied. TCpO2 values decreased with age; when normalized by measurements on the chest, they did not. Absolute and normalized values of TCpO2 were equally effective in identifying the presence of PAOD and accurately characterized different degrees of severity (claudication vs. rest pain vs. impending gangrene; p less than 0.001). This was true even in diabetic patients, in whom tests based on hemodynamic function were less reliable. Healing of amputations was observed when TCpO2 greater than or equal to 38 mm Hg either preoperatively or after reconstruction; failure to heal in the absence of infection was associated with TCpO2 less than or equal to 38 mm Hg. The need for revascularization was associated with TCpO2 less than 30 mm Hg. A similar distribution of TCpO2 values was associated with success vs. failure of ulcer healing. TCpO2 is a useful complement to standard hemodynamic tests in the diagnosis and management of PAOD and, in addition, provides some distinct advantages.

Increased compliance near vascular anastomoses

Mismatch in mechanical properties (compliance mismatch) between host artery and prosthetic graft has been suggested as a cause of graft failure, but no mechanism linking the two has been identified. With the use of a simplified model based on isocompliant arterial grafts, pulsed ultrasound was used to generate detailed longitudinal profiles of diameter and compliance near the anastomoses. These longitudinal profiles revealed that although arterial diameter decreases monotonically to a minimal level at an anastomosis, arterial compliance first increases by approximately 50% before decreasing to 60% of the control value. This para-anastomotic hypercompliant zone (PHZ) is centered 3.6 mm from the anastomosis. PHZ also occurs in the artery adjacent to compliant or stiff grafts and is probably caused by transmitted effects of the suture line on the arterial wall. PHZ adds to any mismatch in compliance that already exists between artery and graft and can produce a compliance mismatch even between an artery and a nominally isocompliant prosthetic graft. It is hypothesized that PHZ, a region of increased cyclic stretch, promotes subintimal hyperplasia near anastomoses and may thus be a link between the mechanical properties of arteries and the failure of bypass grafts.

The impact of selective use of dipyridamole-thallium scans and surgical factors on the current morbidity of aortic surgery.

Preoperative cardiac testing in patients undergoing vascular surgery remains controversial. We have advocated selective use of dipyridamole-thallium scans based on clinical markers of coronary artery disease before aortic surgery. The present study assessed both the efficacy of this policy and the role of surgical factors in the current morbidity of aortic reconstruction. Two hundred two elective aortic reconstructions (151 abdominal aortic aneurysms, 51 aortoiliac occlusive disease) performed in the period from January 1989 to June 1990 were reviewed. Preoperative dipyridamole-thallium scanning was performed in 29% of all patients, prompting coronary angiograms in 11% and coronary artery bypass grafting/percutaneous transluminal coronary angioplasty in 9% of patients before aortic reconstruction. The overall operative mortality rate was 2%, with one cardiac-related death. Major cardiac (nonfatal myocardial infarction, unstable angina) and pulmonary complications occurred in an additional 4% and 6%, respectively, of patients. Coronary artery disease clinical markers and surgical factors were analyzed with stepwise logistic regression for the prediction of operative mortality rates and major cardiopulmonary complications. Variables retaining significance in predicting postoperative death or cardiopulmonary complications included prolonged (more than 5-hour) operative time (p less than 0.004), operation for aortoiliac occlusive disease (p less than 0.010), and a history of ventricular ectopy (p less than 0.002). Prolonged operative time (p less than 0.006) and the detection of intraoperative myocardial ischemia (p less than 0.030) were predictive of major cardiac complications after univariate analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcutaneous oxygen tension in selection of amputation level

The utility of transcutaneous oxygen tension measurements in selection of a reliable amputation level was evaluated. Measurements were made at the proposed level of amputation in 37 patients, 22 of whom underwent major limb amputation and in 15 amputation was confined to the forefoot or toes. In patients with successful amputation healing, mean transcutaneous oxygen tension on the anterior skin surface was 50 +/- 8 mm Hg (index 0.79 +/- 0.1 mm Hg). In contrast, patients with failure of healing had a mean transcutaneous oxygen tension of 22 +/- 16 mm Hg (index 0.32 +/- 0.19 mm Hg) (p less than 0.001). Measurements on the posterior or plantar skin surface and posteroanterior differences provided even greater separation between success and failure groups, with no overlap of transcutaneous oxygen tension values or index. Transcutaneous oxygen tension measurement is easily obtained and noninvasive, and can be applied to all patients irrespective of Doppler signals, noncompressible vessels, or painful lesions. Transcutaneous oxygen tension appears to predict successful healing with accuracy, and should be a useful addition to clinical judgment in selection of optimal amputation level.

Endothelial preservation in reversed and in situ autogenous vein grafts. A quantitative experimental study.

The hypothesis that superior endothelial preservation occurs when in situ (as opposed to harvested and reversed) autogenous veins are used as arterial grafts was investigated in a canine model by quantitating endothelial loss as seen on scanning electron micrographs. In situ grafts were compared to atraumatically dissected, nondistended, reversed grafts and to grafts distended to 500 mmHg pressure. Two hours after arterial transplantation, endothelial denudation averaged 3.9 +/- 6.7% on in situ grafts, 18.6 +/- 5.9% on reversed grafts (p less than 0.01), and 35.3 +/- 5.4% on reversed and distended grafts (p less than 0.001). At 24 hours after grafting, a significant increase (p less than 0.01) in endothelial destruction on in situ grafts resulted in a smaller, yet still significant difference in endothelial preservation between in situ and reversed grafts (15.2 +/- 9.5% vs. 25.1 +/- 23.4%, p less than 0.05). Endothelial healing was largely accomplished at 2 weeks regardless of technique. No difference in endothelial fibrinolytic activity could be detected between in situ and gently handled, reversed grafts at 24 hours or 6 weeks after surgery. An obligatory, although modest, degree of endothelial destruction occurred on the undissected portion of in situ grafts as a consequence of exposure to arterial hemodynamics. However, in the immediate postoperative period, endothelial preservation on in situ grafts surpassed that seen in even the most gently handled reversed vein grafts.

A Biomechanical, Scanning Electron, and Light Microscopic Evaluation

Two currently available brands of PTFE grafts (Goretex and Impra) were studied in a canine femoral artery model to determine whether changes in the manufacturing processes of the two grafts, which increased their strength, had altered the biophysical properties and the histological reactivity of either graft. Both grafts were found to be similar except for differences in their suturability. Their in vivo dynamic compliances were almost identical (1.2 +/- 0.35 vs. 1.2 +/- 0.45). (Scanning electron microscopy showed endothelialization of the grafts only adjacent to the anastomoses, and light microscopy demonstrated similar degrees of histologic incorporation by the host tissues, though of slower tempo than that previously described. These results are examined and discussed with regard to the suitability of this model for characterizing new arterial prostheses of small to medium diameter.