1. Definition/Overview

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1 VCAwestlaspecialty.com VCA West Los Angeles recently performed closure of a patent ductus arteriosus via percutaneous transarterial embolization with an Amplatz canine ductal occluder on a female, four-month-old Newfoundland. We would like to share her case and provide a review on PDA s in dogs. 1. Definition/Overview Patent ductus arteriosus (PDA) is a persistent communication between the pulmonary artery and the descending aorta that diverts blood away from the non-functional fetal lungs. The ductus should close shortly after birth but in some patients remains open. It is the second most common congenital malformation after subaortic stenosis and the most common congenital abnormality requiring intervention. The poor prognosis if left untreated and potential fast progression of disease makes recognition and prompt intervention very important with PDA s. 2. Etiology/Pathophysiology PDA s occur due to histologic abnormalities within the ductal wall. In dogs with PDA s, the contractile smooth muscle fibers are replaced to varying degrees with elastic fibers, which inhibits proper closure. Immediately after birth, the lungs fill with oxygen and release bradykinin. Bradykinin along with local inhibition of prostaglandin, causes constriction of the smooth muscle that forms the ductus resulting in functional closure. When closure fails, blood is shunted from left (descending aorta) to the right (pulmonary artery) because systemic blood pressure in the aorta is much higher than the blood pressure in the 1

2 pulmonary artery. The continuous flow of blood across the PDA is what creates the continuous murmur heard on auscultation. In time, the volume overload to the left atrium and ventricle can lead to congestive heart failure because a portion of the cardiac output is recirculating through the pulmonary vasculature and returning to the left side of the heart. 3. Signalment/History Our recent case was a patient named Pink, an intact female, four-month-old Newfoundland that presented to our cardiologist Dr. Kirstie Barrett at VCA West Los Angeles Animal Hospital. PDA s are more common in female dogs than males with an odds ratio of 3:1. Although any dog can develop a PDA, the most common breeds are Chihuahua, Collie, Maltese, German Shepherd, Newfoundland, Poodle, Pomeranian, English Springer Spaniel, Keeshond, Bichon Frise, and Shetland Sheepdog. 4. Clinical Evaluation On presentation Pink had a grade 5/6 continuous heart murmur with a point of maximum intensity towards the heart base. A grade 2/6 left apical systolic murmur over the mitral valve was also present. She had a normal sinus rhythm, was eupneic, and had pink mucus membranes. She had synchronous and bounding, water-hammer like femoral pulses. By 7-10 days of age the ductus should be closed, and a continuous murmur after this age is abnormal. The murmur will be continuous with a point of maximum intensity near the base of the heart (axillary region). A mitral valve murmur may also be auscultated due to left atrial enlargement secondary to volume overload. Another common finding with PDA s is a bounding femoral pulse due to increased aortic systolic and decreased aortic diastolic pressures. Depending on severity, the patient may be otherwise normal or may have signs consistent with congestive heart failure. If pulmonary hypertension is developing the murmur may be absent to faint during diastole. 2

3 5. Diagnostics At initial presentation, we performed thoracic radiographs, an echocardiogram, and laboratory testing. A PCV/TS was 32%/5.2 g/dl and a CBC/chemistry profile was within normal limits. Thoracic radiographs revealed a characteristic bulge of the descending aorta with dilation of the main pulmonary artery due to over-circulation on the VD projection. The left atrium was not enlarged on lateral projections but there was distension of the cranial pulmonary artery and vein. A PDA was confirmed on echocardiography along with mitral regurgitation and mild elevation in pulmonary systolic pressure. Any time a continuous heart murmur is found on physical exam, a PDA should be suspected. Additional diagnostics to confirm the diagnosis should be completed so that treatment can be instituted promptly. Thoracic radiographs and echocardiography are often used to confirm the presence of a PDA. 6. Treatment We elected to close Pink s PDA with percutaneous, fluoroscopically guided, trans-arterial embolization with an Amplatz canine ductal occluder (ACDO) via the femoral artery. Prior to device deployment, angiographic evaluation of the PDA was performed to visualize the size and shape of the PDA. The procedure and anesthesia were uneventful. Radiographs obtained the following day confirmed the ACDO had not migrated. Her continuous murmur was absent but a mitral valve murmur was still present. Treatment options for PDA closure include surgical ligation or embolization with a thrombogenic coil or an expandable plug-like device (ACDO). Transarterial closure is advantageous to surgical closure due to lower morbidity, shorter hospitalization, and faster recovery. The size and shape of the ductus is important in embolization device selection. Both coil embolization and ACDO placement is done with fluoroscopy through a small 3

4 incision into the femoral artery so the patient must be large enough to accommodate catheters and deployment devices. ACDO s are currently limited to patients 2.5kg while coils can be placed in smaller patients. A coil is most successful in smaller, funnel shaped PDA s. Advantages to ACDO s include use in patients with larger PDA s that are conical or cylindrical in shape, closer can be obtained with a single device, and they have a lower rate of dislodgement. In patients that do not undergo PDA closure, the success of medical management varies based on degree and direction of shunting. Right-to-left shunting results from pulmonary hypertension, causing hypoxemia and polycythemia and is managed with phlebotomy, hydroxyurea and treatment for pulmonary hypertension. Left-to right shunting can lead to left sided congestive heart failure and is managed with diuretics, ace-inhibitors, and pimobendan. A B C Figure A: Contrast angiogram prior to ACDO deployment. Contrast is seen leaving the catheter and crossing the PDA into the pulmonary artery. Figure B: ACDO device is being deployed into the ductus. Figure C: Contrast angiogram after ACDO deployment demonstrating resolution of blood flow across the PDA. 7. Prognosis The prognosis for Pink is excellent and she should go on to live a happy, normal life. The prognosis was due to early and prompt diagnosis and surgical correction. 4

5 Patients diagnosed with a left-to-right shunting PDA carry a poor prognosis with 60% dying within 1 year after diagnosis if there is no intervention. Dogs with small, modest shunts can go on to live beyond 10 years of age. If the PDA is surgically corrected prior to heart failure or shunt reversal the prognosis is quite good. It is important to quickly investigate any murmur suspected to be a PDA so that the window of opportunity to intervene is not missed. Closure of a PDA should never be delayed because development of irreversible cardiac damage and progressive clinical signs inhibit our ability to arrive at a successful outcome. A B C 5

6 Suggested Reading: Achen, S.E., Miller, M.W., Gordon, S.G., Saunders, A.B., Roland, R.M. and Drourr, L.T. (2008), Transarterial Ductal Occlusion with the Amplatzer Vascular Plug in 31 Dogs. Journal of Veterinary Internal Medicine, 22: doi: /j x Bonagura, J.D., Twedt, D.C. Patent Ductus Arteriosus. In: Kirk s Current Veterinary Therapy XIV. St. Louis, Missouri: Saunders Elsevier, 2009; Buchanan, J. W. and Patterson, D. F. (2003), Etiology of Patent Ductus Arteriosus in Dogs. Journal of Veterinary Internal Medicine, 17: doi: /j tb02429.x Côté, E. and Ettinger, S. J. (2001), Long-Term Clinical Management of Right-to-Left ( Reversed ) Patent Ductus Arteriosus in 3 Dogs. Journal of Veterinary Internal Medicine, 15: doi: /j tb02295.x Oyama, M.A., Sisson, D.D., Thomas, W.P., Bongura, J.D. Congenital Heart Disease. In: Textbook of Veterinary Internal Medicine. 7 th ed. St. Louis, Missouri: Saunders Elsevier, 2010; A B C Moore, K. W. and Stepien, R. L. (2001), Hydroxyurea for Treatment of Polycythemia Secondary to Right-to-Left Shunting Patent Ductus Arteriosus in 4 Dogs. Journal of Veterinary Internal Medicine, 15: doi: /j tb02340.x Saunders, A.B., Gordon, S.G., Boggess, M.M. and Miller, M.W. (2014), Long-Term Outcome in Dogs with Patent Ductus Arteriosus: 520 Cases ( ). Journal of Veterinary Internal Medicine, 28: doi: /jvim Singh, M. K., Kittleson, M. D., Kass, P. H. and Griffiths, L. G. (2012), Occlusion Devices and Approaches in Canine Patent Ductus Arteriosus: Comparison of Outcomes. Journal of Veterinary Internal Medicine, 26: doi: /j x 6