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Virginia Luis Fuentes (Professor of Veterinary Cardiology) and Eve Lo (Resident in Veterinary Cardiology)   

Murphy, a nine-month-old male Cockerpoo was presented to the RVC’s Emergency Referral Service at the end of last April. He had become acutely unwell and weak, and collapsed after an episode of vomiting.

The owners took Murphy to his local vet practice and, after receiving intravenous fluid therapy and antibiotics, he was discharged from his local vets, who referred him to the RVC Emergency Referral Service due to lack of improvement.

On admission Murphy was barely responsive, with pale mucous membranes. Auscultation revealed a grade III/VI left basilar systolic heart murmur, and focal inspiratory pulmonary crackles. His systolic blood pressure was only 82 mmHg.

Murphy was transferred to the RVC Cardiology Service, and an echocardiogram revealed a patent ductus arteriosus (PDA), with low-velocity shunting of blood from the aorta through the PDA to the main pulmonary artery. There was evidence of right-sided cardiac enlargement, suggestive of pulmonary hypertension.

Usually the blood flow through a PDA is very high velocity, with substantial shunting across the ductus that can lead to congestive heart failure. In Murphy’s case, there was very little shunting of blood across the ductus, because of pulmonary hypertension. His pulmonary artery pressures were only slightly lower than the aortic pressure.

The best management for dogs with a left-to-right PDA is to close the ductus, ideally with a catheter intervention. However, ductal closure in dogs with a PDA and severe pulmonary hypertension is contraindicated because once the PDA is closed, the right heart has to pump into a high resistance pulmonary arterial circuit. This sudden increase in pulmonary vascular resistance can result in death. However, without ductal closure, dogs with a PDA and pulmonary hypertension end up severely exercise intolerant and develop erythrocytosis, because of low oxygen levels in the descending aorta.

Murphy was started on sildenafil to reduce pulmonary vascular resistance gradually. We were delighted when Murphy responded well to sildenafil, and PDA closure became a possible option for him. However, although the sildenafil helped Murphy’s cardiovascular system, he remained quiet and poorly responsive. Murphy’s haematology results demonstrated severe thrombocytopenia and leukocytosis, and despite no obvious external petechiae, rectal examination revealed melena.

Working with the Emergency Service, the Diagnostic Imaging team conducted a CT scan that confirmed findings consistent with pneumonia, and Murphy continued his improvement over the next couple of days. His thrombocytopenia was thought to be consumptive in origin, and resolved with management of his pneumonia, and he was discharged with antibiotics and an increased dose of sildenafil, with plans to close his PDA the following week.

Second admission    

A week later, Murphy was bright, alert and clinically well at home. His murmur had changed to a grade V/VI left basilar continuous murmur, more typical of a classic PDA. His haematology and biochemistry results demonstrated a normal platelet count and near-normal biochemistry. Echocardiography showed a more typical cardiac phenotype consistent with a left-to-right shunting PDA, with no evidence of pulmonary hypertension. After discussion with our Internal Medicine and Antibiotic Stewardship teams, PDA closure was planned for the following day.

Murphy was anaesthetised by our Anaesthesia Team, and the Cardiology Team performed the catheterisation procedure via a small incision over the femoral artery. An Amplatz canine ductal occluder (ACDO) device was positioned in the ductus, imaged using a combination of transoesophageal echocardiography and fluoroscopy. The ACDO device was released, preventing blood flow through the ductus.

Murphy recovered from the procedure and the anaesthesia uneventfully, and there were no complications associated with his pulmonary hypertension during or after the intervention. After a month of restricted exercise it was possible to stop the sildenafil, as the pulmonary hypertension had resolved.

Left-to-right shunts are a recognised cause of pulmonary hypertension, but in Murphy’s case it is possible that his pneumonia also contributed. The contributions of the various clinical teams involved all helped to ensure Murphy was in optimum condition for his cardiac intervention, and he now has an excellent chance of a normal life expectancy.

Many thanks to the Animal Care Trust (registered charity of the RVC) who provided grant funding for the QMHA echocardiography machines, CT scanner, and fluoroscopy equipment.