Interventions in Congenital Heart Disease for Small Animals--In Detachable Coil Embolyzation for PDA
About 40 years ago, trans-catheter treatment (balloon angioplasty) was attempted to vascular dilatation in human medicine . In 1987, similar techniques were used to congenital heart disease (pulmonary stenosis) in veterinary medicine . Since its introduction, many techniques and devices have been described in various reports. As it is described in recent reports for veterinary medicine, these techniques have documented the safety and effectiveness to treat for congenital heart disease.
Complications of the Trans-Catheter Treatment
Balloon valvuloplasty to PS, AS and MS, and coil embolyzation to PDA are most effective heart diseases. It, however, was also described that there are some complications during or after treatment. Re-stenosis was reported to PS and AS by balloon valvuloplasty. In PDA, in recently, Raskind coil or Jackson detachable coil are used very often for treatment, but severe hemolysis is reported after embolyzation in some cases. As the other problems to PDA, an embolyzed coil moves to the peripheral pulmonary artery. If it happened, we must decide to have a rescue to collect the shifted coil from pulmonary artery. However it is very hard to collect such a shifted coil. Sometime, it is left in pulmonary artery because the patient has no hemodynamical abnormality.
Epidemiological study for PDA from 1999 to 2003 in Azabu University
78 cases for PDA have diagnosed for past four years. 78% (61 cases) of PDA was treated by Jackson method (thirty cases) and detachable coil embolyzation (twenty four cases). Mortality was about 7 % (four cases) in treated cases which were used by both methods. Body weight of the dogs which were treated by Jackson method was about 5.1±6.7 kg, and 4.0±2.2 kg by coil embolyzation. Age of PDA cases which were diagnosed was variable. 50 % cases of PDA, that is, were under 6 months old and 25 % of cases were between seven to twelve months old. Remaining 25 % of cases were over one year old. To 17 cases of coil embolyzation, one coil was used. Three coils were inserted to two cases and two coils were used to remaining seven cases of PDA. In complications, hemolysis was happened to four cases. Protrusion of the coil to the aorta was found to one case and shift of the coil to the peripheral pulmonary artery was found to the other case.
Hemolysis Caused by Coil Embolyzation for PDA
The other hand, the hemolysis caused by coil embolyzation usually has a big problem to the patients. I have had one case of severe hemolysis after finishing detachable coil embolyzation. A one-year-old female, 4.0 kg Miniature Dachshund was referred for closure of the PDA by coil embolyzation. In spite of the cardiomegary for the X-ray findings, she has no clinical sign except continuous murmur. Selective aortic angiography revealed her configulation was type E, which indicates for coil embolyzation. We used one detachable coil (Jackson, 5mm diameter, five loops), and detected small residual shunt (1.58m/sec) by color doppler. Hemolysis started from right after the coil procedure. Three days later, RBC (x 10000) decreased very much from 702 to 71, and PCV also diminished 49.5% to 4.6%. We tried to remove the coil, but it moved to the caudal pulmonary artery. Hemolysis was getting decreased after the coil movement. However, an acute renal failure happened and pulmonary edema was also found. During these days, medical treatments were carried out including blood transfusion, but she died five days later from coil procedure.
We have planned an experimental study to know the cause of such severe hemolysis because it is suggested that there are two major reasons about hemolysis. One is a residual shunt and the other is the fragility of erythrocyte membrane. To the former, there was no relationship between a residual shunt flow velocity and hemolysis in our clinical cases. However, there was a relationship between the presence of a residual shunt and hemolysis after coil embolyzasion in the same clinical cases. To the latter, by using normal blood without fragile and model blood with fragile erythrocyte membrane due to depletion of ATP by 50 %, there were no significant changes between two of them in spite of a development of the hemolysis in both models. It was suggested that one of major causes of hemolysis might rather have physical damage of erythrocyte due to presence of residual blood flow passing through the coil after insertion of it than influence of fragile erythrocyte membrane due to the depletion of ATP.
Future of Trans-Catheter Treatment for Congenital Heart Diseases
We have two ways to treat the congenital heart diseases, one is open-heart surgery and the other is trans-catheter treatment. In human medicine area, they are using the trans-catheter techniques for treatment not only PS, AS, PDA and VSD cases but also more severe cardiovascular malformations . Both of these treatments must be developed as both wheels of the treatment for congenital heart diseases. However, many devices, including balloon catheters and coils, which are used for veterinary medicine were developed for human medicine originally. So, in the future, these treatments including VSD will also be carried out and the fitted devices have to be developed for small animal medicine. One report in human medicine describes about the future of interventional cardiology in pediatrics that catheter-mediated treatment is certain to continue, care must be taken to regulate safely the introduction of novel techniques and devices into clinical use in pediatric cardiology .
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