Is cutting stress responsible for the limited durability of heart valve bioprostheses?

The limited durability of the valve bioprostheses made from calf pericardium is partially due to the calcification of this biomaterial and to mechanical fatigue of the tissue. The object of this study is to determine the harmful effect on the pericardial membrane of cutting caused by the suture thread by showing the different elastic behaviors of the biomaterials employed. This cutting stress is established during the process of molding the valve leaflet, creating a vulnerable point from the very moment of construction, which is an important factor in the limited duration of the bioprosthesis.

[Thrombosis from prosthetic materials: prevention with different antiaggregatory agents. Low dose aspirin?]

Using an ex vivo shunt in dogs, platelet deposition on 6 prosthetic materials used in the construction of cardiovascular prostheses [highly porous Knitted Dacron (intervascular HP 800, 1,400 ml/cm2/min/120 mmHg), Woven Dacron of low porosity (intervascular LP 200, 200 ml/cm2/min/120 mmHg), Doble Velour Knitted Dacron, Avcothane 51 elastomere and the mesothelial and epipericardial surfaces of bovine pericardium] was quantified. The study of the prevention of platelet thrombi formation on these materials was carried out in 6 groups of 8 animals: group 1 (control), group 2 (5 mg/kg body weight/day acetylsalicylic acid), group 3 (20 mg/kg body weight/day acetylsalicylic acid), group 4 (15 mg/kg body wt/day triflusal plus 5 mg/kg body wt/day dipyridamole), group 5 (15 mg/kg body wt/day triflusal) and group 6 (5 mg/kg body wt/day acetylsalicylic acid plus 5 mg/kg body wt/day dipyridamole). Platelets were labeled with 111In-oxine. The least thrombogenic material was Avcothane 51 elastomere. The only effective treatment for reduction of platelet deposition on the 6 materials was that used in group 2. The treatment used in group 3 only decreased the deposition of platelets on 3 of the 6 materials. The treatments employed in groups 4, 5 and 6 did not significantly diminish the deposition of platelets on any of the materials when compared with the control group. The platelet count was not modified in the animals in groups 2 and 4 while in the rest it decreased after the test.

The relationship between stress and relaxation in calf pericardium used in the construction of cardiac bioprostheses

Assessment of relaxation (loss of load within a given time) without apparent deformation is a necessary step before durability assay of biomaterials. From results obtained using calf pericardium, the following conclusions were drawn: (a) there is no limit to relaxation for this biomaterials; (b) the lesser the load applied, the greater the relaxation; and (c) the relaxation curve follows the logarithmic function y = K1 - K2 - Int. These findings demonstrate the poor behaviour of the biomaterial at supposedly low loads and suggest that rupture-point load is not a reliable reference to determine the safety coefficient of calf pericardium used in cardiac bioprostheses.

Posterior sagittal anorectoplasty for adults. A sphincter-saving operation

We performed posterior sagittal anorectoplasty to treat two adult patients. One patient had an idiopathic stricture extending from the proximal sigmoid colon to the anus. The second patient was born with a high imperforate anus and, following a pull-through procedure as an infant, remained totally incontinent of feces. Both patients now have excellent fecal continence following this operation. The posterior sagittal anorectoplasty may be used to preserve rectal continence in selected adults.

Left heart and biventricular bypass

Various forms of circulatory assist devices are currently under investigation. Clinical use of ventricular bypass devices ranging from roller-pump-driven units to pneumatically powered VADs have been in use for several years. These devices are indicated for patients in cardiogenic shock following cardiac surgery or myocardial infarction when all other forms of conventional therapy have failed. Success, though modest, is encouraging in these patients with a dismal prognosis. An increasing role for the VAD may be found in supporting patients whose condition deteriorates while awaiting cardiac transplantation.

Symptomatic malignant melanoma of the gastrointestinal tract. Operative treatment and survival

Malignant melanoma involving the gastrointestinal tract is a common autopsy finding in patients who die with this disease. Melanoma metastatic to bowel infrequently causes symptoms. Some investigators suggest that survival following the onset of gastrointestinal symptoms is very poor and, as a result, surgical intervention to relieve symptoms should be avoided. We reviewed the clinical courses of 15 consecutive patients with symptomatic malignant melanoma of the bowel who underwent resection alone or in combination with bypass of symptomatic intestinal lesions. There were no deaths within 30 days of operation; 14 patients obtained relief of intestinal symptoms; 11 patients survived a mean of 7.9 months; and four patients are alive 2, 7, 22, and 23 months after operation. These results suggest that operations to treat symptomatic intestinal melanoma provide reasonable palliation and survival for patients with this disease.

Radiographic evaluation of patients with schistosomiasis

Plain films of the abdomen in advanced states of schistosomiasis reveal massive splenomegaly without evidence of splenic calcification. The liver may be enlarged in the early stages but ultimately decreases and becomes small. Ascites is evident in far advanced disease. Chest films are negative in the early stages, but in advanced disease, dilated pulmonary arteries, right ventricular enlargement, and dilatation of the azygous vein may be recognized. Granulomata are seen as multiple small rounded densities scattered throughout both lung fields. The routine barium swallow will reveal unsuspected esophageal varices. Nine patients were studied preoperatively by panhepatic angiography and 14 post-operatively following splenorenal shunt. Thrombosis of the shunt and hepatic encephalopathy were common postoperative complications.