Prolonged reflex bradycardia after occlusion of patent ductus arteriosus with an Amplatz canine duct occluder in a dog

Abstract

A 9-month-old intact male Maltese dog (1.52 kg) was diagnosed with a patent ductus arteriosus (PDA). Transcatheter occlusion of the PDA was performed by using the Amplatz canine duct occluder (ACDO). After occlusion, reflex bradycardia occurred and lasted for at least 15 h with normal systolic arterial pressure and slightly increased diastolic arterial pressure. The bradycardia slowly resolved, and the heart rate was normal in re-examinations after 7 and 30 days. This is the first case of reflex bradycardia after ACDO implantation, in which the bradycardia continued for a long time, even after recovery from anesthesia.Keywords: Amplatz canine duct occluder, Branham-sign, patent ductus arteriosus, reflex bradycardia Patent ductus arteriosus (PDA), in which there is the persistence of ductus arteriosus after the early neonatal period, is one of the most commonly diagnosed congenital cardiovascular anomalies in dogs [4]. Among many approaches and devices currently used in occlusion of PDA, Amplatz canine duct occluder (ACDO) is considered superior in ease of use, complication rate, and completeness of occlusion [10,13].A sudden occlusion of PDA can induce a transient bradycardia in some patients, and this reflex bradycardia is explained by a phenomenon called "Branham sign", which is a decrease in heart rate (HR) and an increase in blood pressure after the sudden occlusion of arteriovenous fistula [2,7,12].Reflex bradycardia after PDA closure has been reported in surgical ligation, and in most of the cases, the postligation bradycardia was transient for a few minutes [3,14,15]. To the author's knowledge, this is the first case report of dog showing long duration of reflex bradycardia after occlusion of PDA with ACDO.A 9-month-old (body weight, 1.52 kg) intact male Maltese dog was referred due to an episode of syncope (loss of consciousness for a few seconds when excited) and abnormal heart sounds. During physical examination, a grade V/VI continuous heart murmur was auscultated at the left base of the heart, with the point of maximal intensity at the pulmonic valve area. Heart rate was 128 bpm and blood pressure was within normal range (systolic pressure 128 mmHg, diastolic pressure 83 mmHg, and mean arterial pressure 95 mmHg; Cardell 9402 Veterinary Monitor; Midmark, USA). Complete blood count and serum chemistry results were within normal range. Thoracic radiographs showed cardiomegaly (vertebral heart size = 11.8), increased pulmonary circulation, and left atrial and ventricular dilation were suspected. A left-to-right PDA was highly suspected on the basis of these findings. Transthoracic echocardiography (EPIQ 7 Cardiology Ultrasound Machine; Philips, USA) was performed for a definitive diagnosis. Dilation of the left atrium and ventricle (left-side volume overload) and a continuous turbulent flow in the main pulmonary artery were detected, and the PDA was visualized from both right parasternal view and left cranial parasternal view, with the minimum ductal diameter of 5 mm (Fig. 1). On continuous wav...