Surgical treatment of a persistent right aortic arch with concurrent patent ductus arteriosus in a 4‐month‐old German shepherd dog

Abstract A 4‐month‐old intact female German shepherd dog was presented with a history of postprandial regurgitation, a palpably distended cervical oesophagus after eating, and poor weight gain despite a ravenous appetite. Computed tomography angiography, esophagoscopy and echocardiography identified a persistent right aortic arch with a concurrent patent ductus arteriosus (PDA) causing extraluminal oesophageal compression leading to marked segmental megaoesophagus. A heart murmur was not detectable. A left lateral thoracotomy was performed to ligate and transect the PDA without complication. The dog was discharged with mild aspiration pneumonia which resolved with antimicrobial therapy. Twelve months post‐surgery the owners reported no regurgitation.


INTRODUCTION
The ductus arteriosus (DA) is a foetal vessel that connects the permanent arch of the aorta to the pulmonary artery. The DA allows blood to shunt from the pulmonary artery to the aorta, allowing maternal oxygenated blood to bypass the foetal lungs and flow directly into circulation. Shortly after birth, the DA closes, but its attachments to the aorta and pulmonary artery remain as a fibrous structure known as the ligamentum arteriosum (LA). Occasionally, the DA will not close during development and a patent vessel connecting the aorta and the pulmonary artery remains, known as a patent ductus arteriosus (PDA) (Buchanan, 2003). representing 95% of clinical cases (Buchanan, 2004). Surgical treatment, via transection of the LA, is indicated in these patients. It has been estimated that PDA occurs concurrently in only 10%-14% of animals with PRAA (Buchanan, 2004;Schorn et al., 2021;vanGrundy, 1989).

CASE DESCRIPTION
A 4-month-old intact female German shepherd dog was presented with a history of daily postprandial regurgitation, a palpably distended cervical oesophagus after eating and poor weight gain despite a ravenous appetite. Clinical signs had been present since adoption at 7 weeks of age. The body weight at the time of adoption was 2.3 kg; significantly lower than other littermates. Inc., Weston, Ontario). The dog was being elevated for 15 min after being fed kibble from a non-elevated slow feeder. Mild improvement in frequency of regurgitation was noted following implementation of these changes.
Upon presentation, the dog was bright, alert and responsive with a body weight of 11.9 kg, and a body condition score of 3/9. All vital parameters were within normal limits. Cardiac auscultation revealed a normal rhythm and no detectable murmur. Normal bronchovesicular lungs sounds were appreciated in all fields, with normal respiratory effort. A 3 cm tubular soft-tissue structure, presumed to be the oesophagus, was palpated along the ventral aspect of the cervical region. The remainder of the physical exam was unremarkable.
Based on the dog's clinical signs, age of onset and the preliminary radiographic findings, the primary differential was a vascular ring anomaly, with a PRAA being considered most likely. Other differential diagnoses to consider based on clinical signs and age of onset included idiopathic primary megaoesophagus, hiatal hernia and gastroesophageal intussusception. Post-operative right lateral and ventrodorsal thoracic radiographs confirmed appropriate thoracostomy tube placement and resolution of the iatrogenic pneumothorax while also revealing a diffuse patchy interstitial coalescing to alveolar pulmonary pattern, most prominent in the right hemithorax; this was consistent with atelectasis or chronic aspiration pneumonia. Anaesthesia recovery proceeded without complication. and amoxicillin and clavulanic acid (Aventiclav; Norbrook Laboratories Limited, Newry, Northern Ireland) (13.75 mg/kg PO q12h). Antimicrobial therapy was recommended to be continued for 2 weeks beyond radiographic resolution of suspected aspiration pneumonia. Diet recommendations included a gradual transition from a liquid diet to kibble, accompanied with a transition from elevated feeding to non-elevated feeding over a 6-8-week period, if no regurgitation was occurring.
Twelve months post-surgery, the dog weighed 26 kg, was in good body condition and was being fed a mixture of canned food and kibble from an elevated slow feeder. The owners reported no further regurgitation.

DISCUSSION
Previous retrospective studies have estimated the prevalence of congenital cardiovascular defects in dogs to be 1%, with PRAA representing 8% of all cardiovascular defects (Paterson, 1971). PRAA is the most common clinically relevant vascular ring anomaly, representing 95% of clinically affected animals (Buchanan, 2004). Vascular comorbidities with PRAA are not uncommon with reports of up to 44% of dogs with PRAA having at least one coexisting compressive arterial anomaly (Buchanan, 2004). PDA is a far less common comorbidity in dogs with PRAA, being identified concurrently in only 10%-14% of dogs (Buchanan, 2004;Schorn et al., 2021;vanGrundy, 1989). Although many reports of combined PRAA and PDA in both neonatal dogs and humans have identified the usual high-grade continuous murmur of a PDA, the dog in this report lacked an audible heart murmur (Christiansen et al., 2007;Dundie et al., 2017;Holt et al., 2000;Reed & Bonasch, 1964;Salamat & Lyon, 2009;Saunders et al., 2013). Preoperatively identifying a PDA in dogs with PRAA is crucial as it may alter the surgical approach to reduce the risk of life-threatening haemorrhage; the leading cause of operative death in cases of PDA (Birchard et al., 1990). Therefore, it is especially important that a PDA not be excluded based on lack of audible heart murmur.
Diagnostic evaluation for PRAA often begins with thoracic radiography; however, multiple diagnostic imaging modalities are beneficial in pre-operative planning. CTA, while more invasive than radiography, can provide more detailed information about vascular comorbidities in animals with PRAA, including coexisting compressive anomalies (Buchanan, 2004). Despite its utility, a recent retrospective study evaluating dogs with PRAA from 1998 to 2015 found that only 7% of surgical interventions for PRAA used CTA for preoperative planning (Nucci et al., 2018). This likely underrepresents the overall use of CTA for vascular ring anomaly evaluation, as minimally invasive surgical (MIS) techniques for the treatment of PRAA have become more popular (Townsend et al., 2016). Thus, the use of advanced imaging to collect more anatomic information preoperatively is paramount to ensure correct selection of animals for these approaches (Townsend et al., 2016).
Beyond, the use for determination of suitability for MIS techniques, advanced imaging further enhances the utility of other advanced presurgical planning techniques such as 3D printing for these complex vascular anomalies (Dundie et al., 2017). Furthermore, echocardiography can complement CTA findings by confirming the presence of a concurrent PDA, such as in this case where an audible murmur was not identified and by evaluating the secondary cardiovascular effects of PDA preoperatively, such as presence of left ventricular and atrial dilation (Hamabe et al., 2015). Without the combined CTA and echocardiogram, a PDA was not suspected in this dog and may have led to life-threatening haemorrhage had it been transected intraoperatively, without this knowledge.
Although both PRAA and PDA can be treated with minimally invasive surgery when occurring in isolation, occlusion or ligation of the PDA alone when occurring simultaneously with a PRAA would not resolve the vascular ring causing oesophageal compression and clinical signs for the affected animal (Gordon & Miller, 2005;Nucci et al., 2018;Townsend et al., 2016). Therefore, when PDA and PRAA occur simultaneously ligation and division of the PDA is required to resolve the compression from the vascular ring. Although it is not uncommon for the LA to be ligated during surgical treatment of PRAA in isolation to minimize the risk of haemorrhage, the uses of vessel sealing devices are commonly employed when PRAA is treated with MIS techniques (Nucci et al., 2018;Townsend et al., 2016). In a recent human case report, the uses of vessel sealing devices for division of PDA have been questioned due to the decreased amount of collagen present in the PDA relative to other vessels and the resultant significant haemorrhage that had been encountered during its use (Zamfir et al., 2007).
Considering these factors, when a PDA is identified simultaneously with a PRAA, surgical approaches should be carefully considered. For this reason, a MIS approach was exchanged for an open thoracotomy with PDA ligation and division for the dog in this report.

CONCLUSION
This case is the first report of a dog with a combined PRAA and PDA, with the lack of an audible heart murmur. This case highlights the importance of using multiple diagnostic imaging modalities for preoperative surgical planning when a PRAA is suspected to best characterize the vascular anomaly. Specifically, the use of multiple imaging modalities may be required to identify a concurrent PDA as a PDA cannot be definitively ruled out by lack of audible murmur when occurring simultaneously with a PRAA.

AUTHOR CONTRIBUTIONS
Writing-original draft (lead); review and editing: Marco T. Duguay.