• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.429-438
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• 1997

Mechanical valve is one of the most widely used implantable artificial organs of which the reliability is so important that its failure means the death of patient. Therefore early noninvasive detection is essentially required, though mechanical valve failure with thrombosis is the most common. The objective of this paper is to detect the thrombosis formation by spectral analysis and neural network. Using microphone and amplifier, we measured the sound from the mechanical valve which is attached to the pneumatic ventricular assist device. The sound was sampled by A/D converter(DaqBook 100) and the periodogram is the main algorithm for obtaining spectrum. We made the thrombosis models using pellethane and silicon and they are thrombosis model on the valvular disk, around the sewing ring and fibrous tissue growth across the orifice of valve. The performance of the measurment system was tested firstly using 1 KHz sinusoidal wave. The measurement system detected well 1KHz spectrum as expected. The spectrum of normal and 5 kinds of thrombotic valve were obtained and primary and secondary peak appeared in each spectrum waveform. We find that the secondary peak changes according to the thrombosis model. So to distinguish the secondary peak of normal and thrombotic valve quantatively, 3 layer back propagation neural network, which contains 7, 000 input node, 20 hidden layer and 1 output was employed The trained neural network can distinguish normal and valve with more than 90% probability. As a conclusion, the noninvasive monitoring of implanted mechanical valve is possible by analysing the acoustical spectrum using neural network algorithm and this method will be applied to the performance evaluation of other implantable artificial organs.

• Journal of Chest Surgery
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• v.41 no.4
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• pp.484-488
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• 2008

During long-term anticoagulation treatment with using heparin in a pregnant patient with a mechanical mitral prosthesis, we observed several anticoagulation-related complications, including repeated prosthetic valve thrombosis. This was found to be caused by heparin resistance due to an anti-thrombin III deficiency. Thrombolytic therapy using urokinase or tissue plasminogen activator (tPA) was successful and safe for her as well as her baby.

• Journal of Chest Surgery
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• v.37 no.4
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• pp.369-372
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• 2004

Acute myocardial infarction due to coronary occlusion by emboli originating from the prosthetic valve thrombosis is very rare but fatal disease which needs immediate diagnosis and urgent treatment. We report a case of acute myocardial infarction after left anterior descending embolic occlusion in whom had previous mitral valve replacement. Redo valve replacement following the interventional catheterization and anti platelet therapy lead to successful results.

• Journal of Chest Surgery
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• v.32 no.1
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• pp.70-74
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• 1999

Thrombosis in valve or left atrium after mechanical mitral valve replacement causes prosthetic valve dysfunction or thromboembolism. Early and adequate therapy is very important but clinically not easy. Thrombolysis can avoid reoperation-related risks and act as an optimal therapy for prosthetic valve thrombosis. This report describes three patients who were treated by using low molecular weight heparin (LMWH) and wafarin. Two patients, including one pregnant woman, had prosthetic valve thrombosis and immobility of valve leaflets, and one patient with recent cerebral infarction due to thromboembolism had thrombus in left atrium. Fraxiparine 0.3 cc (7,500 ICU AXa) was administrated subcutaneously twice or triple daily. At discharge, thrombosis in valve and left atrium were completely or near totally lysed and valve leaflets were normally mobile. During the period of thrombolysis and follow up, there were no complications in all patients.

• Journal of Chest Surgery
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• v.29 no.6
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• pp.651-654
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• 1996

Recently, we report a surgical experience of one case of acute prosthetic valve failure due to throe- bosis. The patient was 39-year old male who complained of dyspnea and orthopnea for 3 days before admission. The patient had not taken anticoagulant therapy for recent 4 months against medical ad- vice. The limitation of valve motion was revealed on echocardiography. We performed emergency reoperation with thrombectomy and prosthetic valve replacement. The patient had anuncomplicated postoperative course and have been followed up.

• Journal of Chest Surgery
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• v.35 no.11
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• pp.826-830
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• 2002

Prosthetic valve thrombosis(PVT) may be a life-threatening complication requiring prompt intervention. This is a case report of thrombolytic therapy for thrombosis of prosthetic mitral valve. A 47 year-old male admitted to the emergency room for abrupt onset of dyspnea. He had undergone mitral valve replacement(On-Ⅹ valve, 29mm) for mitral stenosis 8 months ago. The patient's international normalized ratio(INR) on admission was 1.09. The mechanical clicks were muffled and rales were heard in both lung fields. A transesophageal echocardiography(TEE) revealed prosthetic valve thrombosis with increased transvalvular pressure gradient(34 mmHg). The patient's condition needed to intubation for mechanical ventilation due to hemodynamic compromise, however his wife and relatives refused the surgical intervention due to financial problems. The patient was transferred to the cardiac care unit and we decided to perform thrombolytic therapy. A bolus of 1,500,000 IU of urokinase was given, followed by a drip of 1,500,000 IU for 1 hour. The patient did not improved hemodynamically; therefore, we gave 100 mg of tissue plasminogen activator(t-PA) for over 2 hours. During that time mechanical clicks were audible and hemodynamics of the patient improved progressively. A TEE showed disappearance of thrombus and decreased pressure gradient(1.7 mmHg) after 6 hours of thrombolytic therapy. The patient was recovered without any neurologic sequale and was discharged with administration of warfarin.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.421-430
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• 2004

Clinically, it is almost impossible for a physician to distinguish subtle changes of frequency spectrum by using a stethoscope alone especially in the early stage of thrombus formation. Considering that reliability of mechanical valve is paramount because the failure might end up with patient death, early detection of valve thrombus using noninvasive technique is important. Thus the study was designed to provide a tool for early noninvasive detection of valve thrombus by observing shift of frequency spectrum of acoustic signals with computer aid diagnosis system. A thrombus model was constructed on commercialized mechanical valves using polyurethane or silicon. Polyurethane coating was made on the valve surface, and silicon coating on the sewing ring of the valve. To simulate pannus formation, which is fibrous tissue overgrowth obstructing the valve orifice, the degree of silicone coating on the sewing ring varied from 20％, 40％, 60％ of orifice obstruction. In experiment system, acoustic signals from the valve were measured using microphone and amplifier. The microphone was attached to a coupler to remove environmental noise. Acoustic signals were sampled by an AID converter, frequency spectrum was obtained by the algorithm of spectral analysis. To quantitatively distinguish the frequency peak of the normal valve from that of the thrombosed valves, analysis using a neural network was employed. A return map was applied to evaluate continuous monitoring of valve motion cycle. The in-vivo data also obtained from animals with mechanical valves in circulatory devices as well as patients with mechanical valve replacement for 1 year or longer before. Each spectrum wave showed a primary and secondary peak. The secondary peak showed changes according to the thrombus model. In the mock as well as the animal study, both spectral analysis and 3-layer neural network could differentiate the normal valves from thrombosed valves. In the human study, one of 10 patients showed shift of frequency spectrum, however the presence of valve thrombus was yet to be determined. Conclusively, acoustic signal measurement can be of suggestive as a noninvasive diagnostic tool in early detection of mechanical valve thrombosis.

• Proceedings of the KTCVS Conference
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• 1996.10a
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• pp.46-46
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• 1996

• Journal of Chest Surgery
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• v.29 no.12
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• pp.1337-1341
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• 1996

From September 1989 to March 1996, 13 patients with prosthetic valve thrombosis underwent reoperdtion on 16 occasions. The mean interval between implantation and reoperation was 27.8 months. The anticoagulation status was inadequate in 44% of th Instances. The majority(75%) were in NYHA functional class IV, 6 of them being in shock. Reoperation was performed for valve replacement(15 of 16 occasions) or thrombectomy(1 of 16 occasions) within 3 to 192 hours(mean 33.5 hours). Operative mortality at reoperation was 25%(4 patients). Re-thrombosis occurred In 3 patients. Long-term outcome was satisfactory in all survivors with a mean follow-up of 30.B months. The present results indicate that an early diagnosis and prompt surgical intervention is needed to decrease operative mortality.

• Journal of Chest Surgery
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• v.31 no.6
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• pp.591-597
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• 1998

Background: The aim of the current study was to analyze the early and intermediate-term performance of aortic valve replacement. Material and Method: Between January 1986 and January 1996, records of 61 consecutive patients who had received aortic valve replacement were reviewed. 38 were male and 23 were female patients, ranging from 10 to 71 years of age(mean: 40.5${\pm}$11.2). Results: The early death rate was 4.9%(3/61). A thorough follow-up rate of 93.1% was accomplished in these 58 patients who left the hospital(mean: 51.5${\pm}$32.0 patient-months) under the assistance of the same operator. Three of these patients who left the hospital died. The late death rate was 5.2%(3/58). Five patients experienced anticoagulant-related hemorrhage(all were minor). Three patients had thromboembolic episodes. There was no clinical evidence of hemolysis and structural failure of valves used. Of those patients who survived, the NYHA functional class improved significantly. Linearized rate were 1.58%/patient-year and 2.0%/patient-year respectively for thromboembolism and anticoagulant-related hemorrhage. The 10 year actuarial survival rate was 83.6%. Conclusion: This early and intermediate-term follow-up suggests that the mechanical valve is a reliable and durable prosthesis with good hemodynamic function and low rate of prosthesis-related complication.