POSTOPERATIVE THROMBOTIC COMPLICATIONS

Case report: Management of immediate post-car-diopulmonary bypass massive intra-cardiac thrombosis

PURPOSE

To describe the management of severe acute intracardiac thrombosis in a patient who underwent redo multiple valve replacement and valvular repair. The diagnostic features, associated risk factors, and anesthetic management are reviewed.

CLINICAL FEATURES

A 67-yr-old woman undergoing redo mitral and aortic mechanical valve replacement and tricuspid annuloplasty under aprotinin prophylaxis exhibited severe refractory hypotension that began immediately after protamine reversal of intraoperative heparin anticoagulation following separation from cardiopulmonary bypass. Intraoperative transesophageal echocardiography revealed severe thrombosis in the right atrium, right ventricle and pulmonary artery. The patient was managed by immediate reheparinization and return to cardiopulmonary bypass (CPB), surgical thrombectomy, and intraoperative administration of recombinant tissue-plasminogen activator. After removal of the thrombi, and separation from CPB, no further protamine was given. One hundred units of blood products and two surgical re-explorations were required to manage subsequent massive postoperative bleeding. Acute heparin-induced thrombocytopenia (HIT) was ruled out using sensitive assays for HIT antibodies. After 16 days in the intensive care unit and 30 more days in hospital, the patient was subsequently transferred to a chronic care facility and succumbed several weeks later.

CONCLUSION

Acute intraoperative thrombosis is a rare and potentially fatal complication of cardiac surgery. Intraoperative transesophageal echocardiography was essential for rapid diagnosis in this case. Multiple interacting prothrombotic factors (e.g., aprotinin use, acquired antithrombin deficiency, long pump time, post-protamine status, transfusion of blood components) were likely contributing factors related to this rare complication.

Pulsed high-intensity focused ultrasound enhances thrombolysis in an in vitro model

PURPOSE

To evaluate the use of pulsed high-intensity focused ultrasound exposures to improve tissue plasminogen activator (tPA)-mediated thrombolysis in an in vitro model.

MATERIALS AND METHODS

All experimental work was compliant with institutional guidelines and HIPAA. Clots were formed by placing 1 mL of human blood in closed-off sections of pediatric Penrose tubes. Four experimental groups were evaluated: control (nontreated) clots, clots treated with pulsed high-intensity focused ultrasound only, clots treated with tPA only, and clots treated with pulsed high-intensity focused ultrasound plus tPA. The focused ultrasound exposures (real or sham) were followed by incubations of the clots in tPA with saline or in saline only. Thrombolysis was measured as the relative reduction in the mass of the clot. D-Dimer assays also were performed. Two additional experiments were performed and yielded dose-response curves for two exposure parameters: number of pulses per raster point and total acoustic power. Radiation force-induced displacements caused by focused ultrasound exposures were simulated in the clots. A Tukey-Kramer honestly significant difference test was performed for comparisons between all pairs of experimental groups.

RESULTS

The clots treated with focused ultrasound alone did not show significant increases in thrombolysis compared with the control clots. The clots treated with focused ultrasound plus tPA showed a 50% ([30.2/20.1]/20.1) increase in the degree of thrombolysis compared with the clots treated with tPA only (P < .001), further corroborating the d-dimer assay results (P < .001). Additional experiments revealed how increasing both the number of pulses per raster point and the total acoustic power yielded corresponding increases in the thrombolysis rate. In the latter experiment, simulations performed at a range of power settings revealed a direct correlation between increased displacement and observed thrombolysis rate.

CONCLUSION

The rate of tPA-mediated thrombolysis can be enhanced by using pulsed high-intensity focused ultrasound exposure in vitro.

Treatment of Venous Thromboembolism: Challenging the Unfractionated Heparin Standard

Venous thromboembolism (VTE) is a major public health problem leading to high morbidity and mortality in the United States. Since more then 50% of patients with VTE may have asymptomatic disease, the start of appropriate therapy often is delayed. Traditionally, intravenous unfractionated heparin (UFH) has been used to manage the acute phase of VTE. Although an effective agent, numerous limitations are associated with the use of UFH therapy, such as the need for careful monitoring and frequent dosing adjustments. In addition, the assay used to monitor UFH--the activated partial thromboplastin time (aPTT)--does not correlate reliably with plasma heparin levels or antithrombotic activity. In the early 1990s, the low-molecular-weight heparins (LMWHs) emerged as alternative anticoagulants to UFH and began to successfully challenge the UFH standard for treatment of VTE. Clinical evidence has consistently demonstrated that LMWHs given subcutaneously are at least as safe and as effective, if not better, than intravenous UFH. This anticoagulant class has a much more predictable dose-response relationship, requires little or no monitoring, and provides cost-saving opportunities for outpatient management of VTE. The LMWHs are now considered the treatment of choice for many patients with VTE and are largely replacing UFH for this indication. In the last decade, additional agents, such as direct thrombin inhibitors and factor Xa inhibitors, have emerged as potential future alternatives for treatment of VTE. As clinical data regarding these new agents for treatment of VTE continue to evolve, their role in clinical practice will be elucidated.

Epidemiology of venous thromboembolic disease

From the information presented in this article, it can be concluded that clinical suspicion of VTE should be increased in patients with a history of VTE, recent surgery, spinal cord injury, trauma, or malignancy. A variety of medical illnesses also increase the risk of venous thrombosis, including congestive heart failure, myocardial infarction, stroke with paresis, nephrotic syndrome, cigarette smoking, and obesity. Hypercoagulable states, such as antithrombin III deficiency, protein C deficiency, protein S deficiency, or factor V Leiden mutation should be considered in those patients who develop VTE in the absence of known risk factors. Additionally, the presence of vena caval filters does not exclude the possibility of PE or recurrent DVT. With a careful assessment of risk, physicians can hope to increase the diagnostic yield of VTE and decrease the significant morbidity and mortality of caused by this disease.