RESUMO
BACKGROUND: New echocardiographic contrast agents are commonly tested in the dog model. However, this species has a number of drawbacks, including difficulties in experimentation, cost, and ethical considerations. The rabbit has a number of advantages due to its relative simple coronary circulation. The present study was designed to evaluate the rabbit model for determination of areas of risk (ARs) by contrast echocardiography. METHODS: Eight rabbits were intubated and mechanically ventilated after occlusion of the left coronary artery with a ligature. The transducer (operating at 7.5 MHz) was positioned on the right ventricle through a right thoracotomy. The images were obtained after intra-aortic injection of 1 ml of Albunex, followed by 3 ml of dye (Blue Uniperse) for histological analysis postmortem. The ARs were obtained after circumscription of the various echocardiographic and histological images. RESULTS: Excellent echocardiographic images were obtained, largely due to the hemodynamic stability of the rabbit to ischemia. Echocardiographic ventricular areas, absolute AR, and relative AR correlated closely with postmortem data (r = 0.86, 0.94, and 0.94, respectively). The measurements were highly reproducible with low variability. CONCLUSIONS: The rabbit model shows promise for study by contrast echocardiography of myocardium subjected to ischemia. This method for determination of ARs was validated against postmortem findings. The method also should be of value in the evaluation of reperfusion.
RESUMO
The purpose of the present study was to determine the optimal management of nonobstructive thrombi in the early postoperative period after mitral valve replacement.Twenty cases of early thrombi were revealed by systematic transesophageal echocardiography (TEE) performed 9 days after surgical implantation of 229 St. Jude prostheses. Patients were prospectively randomized into two groups: the first group received oral anticoagulants (fluindione), and the second group was treated with a combination of oral anticoagulants and aspirin. The impact of the different therapies on prosthetic thrombi was assessed by systematic TEE at 5 months. All thrombi were nonobstructive and disappeared without fibrinolytic agents or surgery. Seven large (>/= 5 mm) thrombi disappeared: in two patients after reintroduction of intravenous heparin and in five patients with an optimized oral treatment (anticoagulants alone in one patient, anticoagulants associated with aspirin in four patients). In the 13 small (< 5 mm) thrombi, 11 disappeared with an optimized oral treatment: anticoagulants alone in nine patients and anticoagulants associated with aspirin in two patients. The other two small thrombi treated with heparin alone initially persisted and finally disappeared with heparin associated with aspirin. In the group with large thrombi, we recorded a 43% rate of thromboembolic events, with more deaths and severe cerebral embolic events than in the patients with small thrombi. Embolic events were associated with mobile thrombi. An optimized oral anticoagulation therapy with correction of the parameters of Virchow et al. is effective in the treatment of small prosthetic thrombi. For large thrombi, the high rate of thromboembolic events would appear to require a more aggressive approach such as an association of heparin with aspirin and TEE follow-up.