Diagnosis by Intraoperative Transesophageal Echocardiography of Acute Thrombosis of Mechanical Aortic Valve Prosthesis Associated with the Use of Biological Glue

Mechanical aortic valve thrombosis is an uncommon complication of valve replacement. Inadequate anticoagulation is observed in 45% of patients presenting with this complication and it occurs as close as 15 days postoperation (1). Failure to wean from cardiopulmonary bypass (CPB) after aortic valve replacement may be because of a multitude of pathologies. We present a case where easy access to transesophageal echocardiography (TEE) allowed a rapid diagnosis of acute mechanical aortic valve occlusion with subsequent successful surgical management. Case Discussion A 59-yr-old hypertensive male with a mechanical aortic valve was admitted to the coronary care unit with New York Heart Association Class IV dyspnea. Six months previously he had undergone insertion of a CarboMedics #23 valve (CarboMedics, Austin, TX) in the aortic position with anastomosis of the left internal mammary artery to the second marginal coronary artery. Echocardiography demonstrated severe aortic incompetence secondary to a large paravalvular leak. Right-sided cardiac catheterization demonstrated pulmonary hypertension of 83/6 mm Hg with pulmonary occlusion pressure of 16 mm Hg and cardiac output by thermodilution of 5.4 L/min. There was also a history of end-stage renal failure secondary to interstitial nephritis, treated with a cadaveric renal transplant 9 yr previously. His serum creatinine had been stable at 170 μmol/L. Medications included cyclosporin, prednisolone, and warfarin sodium. The patient was scheduled for repeat aortic valve replacement. Heparin was started on the sixth day after admission and continued for 10 days until the day of surgery. On the day of surgery, laboratory investigations revealed hemoglobin of 97 g/L, a platelet count of 392 × 109/L, normal electrolytes, urea 19.6 mmol/L, and creatinine 217 μmol/L. His electrocardiogram demonstrated sinus rhythm and first-degree atrioventricular (AV) block. The patient was placed under general anesthesia and both hydrocortisone 100 mg and 10 g of tranexamic acid were given before CPB. The patient was resistant to heparin and received 45,000 IU of heparin and 2 U of fresh frozen plasma before CPB. Using Celite as the activator, the first activated clotting time (ACT) was 403 s prebypass and decreased to 394 s on bypass. After a further decrease in ACT to 343 seconds, he required in total, another 60,000 IU heparin and a further 2 U of fresh frozen plasma on bypass to maintain an ACT between 494 s and 511 s for the remainder of the bypass period (283 min). The surgery was remarkable for the delicate, friable nature of the ascending aorta. Once the aorta was opened, a large defect was found at the posterior aspect of the AV ring. The surgeon elected to remove the valve completely and replace it with a new valve (CarboMedics #23) that was sutured in place with Tycron 2–0 sutures. Closure of the ascending aorta was problematic and biological glue (Gelatin-reorcin-formaldehyde-glutaraldehyde) was used. Despite the use of an intraaortic balloon pump, milrinone, and epinephrine, separation from CPB was not successful. A TEE probe that was inserted revealed a grossly dilated left ventricle containing spontaneous echo contrast with profound depression of systolic function. The bileaflet mechanical valve in the aortic position was unrecognizable with a large tissue-density mass in the ascending aorta (Fig. 1). There was flow acceleration from the aortic cannula around the obstruction, through the posterior aspect of the valve and into the left ventricle.Figure 1: Long axis view of the aortic valve demonstrating thrombus in prosthetic aortic valve. The arrow points to thrombus occluding the prosthetic valve and the proximal ascending aorta. Asc Ao = ascending aorta; LV = left ventricle; LA = left atrium; *the acoustic shadow of the prosthetic valve ring.The aorta was reopened and fresh thrombin clot was extracted from the ascending aorta. The valve was completely occluded and therefore excised. The aorta was closed with the use of a Dacron patch without biological glue. Weaning from CPB was accomplished with the aid of an intraaortic balloon pump and three inotropes (Fig. 2). The patient required 15 days in the cardiovascular intensive care unit because of severe right ventricular failure requiring the use of nitric oxide. He fully recovered and was discharged from the hospital on his 25th postoperative day.Fig. 2: Long axis view of the aortic valve after removal of obstructed prosthetic aortic valve. Asc Ao = ascending aorta; LV = left ventricle; LA = left atrium; *the acoustic shadow of the prosthetic valve ring.Discussion Prosthetic AV thrombosis as early as 15 days postoperatively has been described in the literature (1). However, there have been no descriptions of this complication occurring while a patient was fully heparinized on CPB. Although biological glue is now commonly used in the repair of aortic dissections with preservation of the native AV (2), it is not commonly used in repeat AV surgery. This agent is extremely potent and the containment of the glue to the anastomotic site is mandatory (3). The only complication with the use of this agent that has been reported is cerebral embolization after aortic arch replacement, resulting in multiple small infarcts (4). Problems with acute AV occlusion associated with the use of this agent have not been reported. We believe that this is the first report of acute prosthetic valve thrombosis and aortic occlusion associated with biological glue occurring in a fully anticoagulated patient. Acute mechanical valve obstruction is rare. In our patient there was difficulty in achieving adequate heparinization before the commencement of CPB. This was attributed to heparin resistance, as there was little improvement in ACT after administration of fresh-frozen plasma. An antifibrinolytic drug was also administered. Although the ACT was adequate during bypass, these factors may have contributed to the acute thrombosis. The pathology report, however, revealed that both surfaces of the semilunar discs were covered with solidified “gelfoam-like” material. This material immobilized the discs and extended beyond the disk for 0.5 cm on the aortic side. It is likely that the biological glue applied to the surface of the aorta had gained access to the aortic lumen and precipitated an acute obstruction. This life-threatening complication associated with the use of biological glue may not be readily detectable without the use of intraoperative TEE. Indeed TEE has become increasingly desirable in both cardiac and noncardiac operations where it is the most important guiding factor in 25% of interventions, particularly when hemodynamic instability is present (5–7). The use of TEE would be desirable in cases where applied biological glue might gain access to the aorta lumen.

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