Ana Paula Martins

Intra-atrial temperatures in radiofrequency endocardial ablation: histologic evaluation of lesions.

BACKGROUND Because of the limited information on the effects of ablation in human tissues, we studied intra-atrial temperatures during endocardial radiofrequency applications. We correlated the intra-tissue temperatures with the tissue thickness and with the histologic appearance of the lesions. METHODS Radiofrequency currents were delivered to human atrial tissue, simulating conditions in endocardial ablation during surgery at set temperature of 70 degrees and 80 degrees C, and intra-tissue temperatures were measured with thermocouples. Radiofrequency applications at 70 degrees C were performed in patients undergoing mitral valve surgery and biopsy specimens were obtained. Samples from in vitro studies and from patients were assessed histologically. RESULTS The subepicardial temperatures were usually over 60 degrees C in applications in vitro at 70 degrees C and over 70 degrees C in applications at 80 degrees C. Values were higher when the interior of the tissue was warmer than its surface as a result of consecutive radiofrequency applications over the same area. Histologic examination of 12 in vitro samples showed that 10 had transmural lesions. Five of 10 samples from patients with mitral valve surgery had lesions confined to the endocardium, 3 had damaged variable portions of the myocardium, and 2 had transmural lesions. CONCLUSIONS Although it is possible to obtain transmural lesions in vitro and in vivo with endocardial applications at 70 degrees C, it is significantly more difficult to achieve transmural lesions in patients with mitral valve disease than in normal atrial tissue in vitro. Consecutive applications can raise the intra-tissue temperatures to values significantly higher than those used for application. Our findings suggest that the composition of the endocardium and of the myocardium is a major determinant in lesion formation.

Mechanisms underlying degeneration of cryopreserved vascular homografts

OBJECTIVE To analyze the mechanism(s) underlying homograft degeneration, we designed an experimental model in which the behavior of cryopreserved autografts and homografts, as well as fresh autografts, implanted in the same animal was compared. METHODS A cryopreserved homograft was implanted in the aorta of 14 sheep. The excised aortic autologous segment was then subjected to cryopreservation, and 1 to 8 weeks later it was implanted 1 to 2 cm below the cryopreserved homograft. The intermediate segment of the native aorta, the fresh autograft, was dissected at this point. Animals were put to death at different times and the implanted segments were harvested together with a portion of native aorta. Histologic and immunohistochemical analyses, as well as cell viability assessments, were then performed on the explanted segments. Similar studies were also conducted on fragments of cryopreserved autografts and homografts before implantation. RESULTS With the exception of a partial loss of the endothelium, cryopreserved specimens retained cell viability and morphologic integrity before implantation. Explanted cryopreserved homografts showed profound changes affecting all strata, as well as a decline in cell viability. Lymphocyte infiltrates were found up to 12 months after implantation. Endothelium was always absent in cryopreserved homografts. However, a reendothelialization of the cryopreserved autografts was observed. After an initial period of neuronal degeneration, reenervation of the cryopreserved autograft segment occurred 6 to 12 months after the operation. Findings regarding the fresh autografts were similar to those of the cryopreserved autografts. CONCLUSION Our results suggest that the immunologic reaction rather than the cryopreservation process is responsible for the degenerative process occurring in cryopreserved homografts.

Glutathione S transferase mu polymorphism and gastric cancer in the Portuguese population

The glutathione S-transferases appear to form part of a protective mechanism against the development of cancer where environmental chemical carcinogens are involved. In humans one member of the mu class gene family (GSTM1) has been shown to be polymorphic and is only expressed in ~50% of individuals. Previous studies have shown a possible link between the null phenotype and susceptibility to cancer but have been equivocal regarding stomach cancer. To evaluate any association in Portuguese gastric cancer individuals with GSTM1 variability, we performed GST M 1 polymorphism by PCR amplification in 148 gastric cancer patients and in 84 healthy control individuals. We found no statistical differences between the gastric cancer and control populations (wild type phenotype: 52%, 48%; null phenotype: 48%, 52%, respectively). A subset analysis into site of tumour also revealed no significant differences between the groups, although we found a slight increase of the wild type phenotype in the samples of the antrum compared with the control population (57% vs 48%, respectively; 2= 1.18; p 0.28) and a slight increase of the null phenotype in the signet ring cells/mucocellular group (2= 1.05; p 0.3). However, in both cases it did not reach statistical significance. A subset analysis of the histological groups following the WHO criteria revealed a statistically significant difference (2= 3.704; p 0.05) between the moderately differentiated gastric adenocarcinoma and the presence of the wild type phenotype. These results do not support the hypothesis that the GSTM1 null phenotype predisposes to gastric cancer in the Portuguese population and the moderately differentiated gastric adenocarcinoma seems to be associated with the presence of the G STM 1 wild type phenotype.

Hamartoma of the mitral valve with blood cysts: A rare tumor detected by echocardiography

A 16-year-old boy was submitted to a cardiac examination after an episode of faintness. A transthoracic echocardiogram was performed, which revealed a very mobile multicystic tumor attached to the mitral valve. A small solid mass adherent to the cysts was better defined by transesophageal echocardiography. The patient was submitted to cardiac surgery consisting of tumor resection and a mitral prosthesis implant. The surgery was successful. The tumor consisted of three bright red tense cysts with hematic content, each 1 to 2 cm in diameter. The cysts were coalescent and adherent to a solid mass attached to the posterior papillary muscle head. Histopathologic examination revealed a hamartoma with a cystic part composed of the proliferation of myofibroblast cells in a stroma with vessels, collagen, and elastin fibers. Valvular hamartoma with blood cysts is a very rare cardiac tumor both for its histopathology and its localization.

Utility of Radiofrequency Ablation in Atrial Fibrillation Surgery

Atrial fibrillation surgery is an evolving procedure. The maze operation, developed by James Cox,1 has been the standard operation since the early nineties. However, the maze operation is a complex procedure with bleeding potential that always requires the use of cardiopulmonary bypass and a long myocardial ischemic time. Because of the complexity of the maze operation, different alternatives have been proposed aiming at simplifying the techniques and reducing the time and risks of the operation.2–4 The final goal of each particular procedure is to create scars in the atrial wall in such a way that the initiators, the perpetuators or both mechanisms of atrial fibrillation will be eliminated.