Symptomatic partial anomalous pulmonary venous connection in a kitten

Abstract A 3‐month‐old intact female American Shorthair cat, with syncope and tachypnea, underwent cardiac examination which identified no heart murmur or gallop. Thoracic radiography disclosed mild generalized enlargement of the cardiac silhouette and a bronchial and interstitial pattern throughout the lungs. Echocardiography identified tubular structures near the left atrium. After agitated saline contrast imaging, persistent left cranial vena cava with unroofed coronary sinus was suspected. Computed tomography angiography showed the right cranial, right caudal and left caudal pulmonary veins draining into the coronary sinus and flowing into the right atrium. The left cranial pulmonary vein drained normally into the left atrium. Partial anomalous pulmonary venous connection (PAPVC) was diagnosed. The kitten was treated with diuretics but died of heart failure 2 months later. Permission for necropsy was not granted. This case represents symptomatic PAPVC in a kitten. Most pulmonary veins were connected abnormally with the coronary sinus. The prognosis was grave because of refractory heart failure.


| INTRODUCTION
Partial anomalous pulmonary venous connection (PAPVC) is a rare congenital cardiovascular abnormality. In veterinary literature, anomalous pulmonary venous connection (APVC) or drainage has been reported in dogs, 1-7 cats, 8 a foal, 9 and chickens. 10 In fetal life, the primitive pulmonary veins from the lung buds develop from the splanchnic plexus, which communicates with the systemic venous system, and connects to the left atrium. As development proceeds, the connection between pulmonary veins and the systemic venous system disappears. If the communication between pulmonary veins and the systemic venous system persists, total APVC or PAPVC would be diagnosed depending on the degree of persistent connections. 11

| CASE PRESENTATION
A 3-month-old intact female American shorthair cat was admitted to the Veterinary Medical Teaching Hospital of the National Chung-Hsing University for cardiac examination. An episode of syncope was observed 1 month earlier, which was followed by 2 weeks of tachypnea. The kitten was hospitalized for supportive care at a local animal hospital and the referring veterinarian suspected congestive heart failure secondary to congenital heart disease.
On presentation, the kitten was bright, alert, and responsive, and weighed 1.45 kg with mild muscle loss. Thoracic auscultation was normal, and the heart rate was 216 beats per minute. The kitten was sedated using 0.3 mg/kg butorphanol IM (Butomidor, richter pharma AG, Wels, Oberösterreich, Austria) combined with 0.003 mg/kg dexmedetomidine (DEXDOMITOR, Zoetis, Parsippany, New Jersey) to minimize stress and facilitate evaluation. Thoracic radiography disclosed generalized cardiomegaly with a vertebral heart score of 8.3 (normal, 7.3 ± 0.49), 12  Treatment is to surgically reconstruct the pulmonary veins, which is accomplished by cardiopulmonary bypass, but cardiopulmonary bypass was not possible in a kitten weighing only 1.45 kg because of F I G U R E 1 Thoracic radiography after admission. Diffuse bronchial and interstitial pattern on the A, ventraldorsal; B, right recumbent; and C, left recumbent views small blood volume, risks of electrolyte disturbance, hemodilution, and limitation of small vessel diameter for cannulation. 14 After discussion with the owner, cardiac medications including furosemide (4.3 mg/kg PO q12h), pimobendan (0.25 mg/kg PO q12h), benazepril (0.32 mg/kg PO q12h), and spironolactone (1.6 mg/kg PO q12h) were prescribed to control heart failure and maintain quality of life. Two months after diagnosis, the referring veterinarian reported that the kitten had died of heart failure; permission for necropsy was denied.

| DISCUSSION
This case report describes PAPVC, a rare congenital cardiovascular abnormality, in a kitten. Descriptions for this type of abnormality include the terms "connection" and "drainage." The term "connection" indicates an anomalous venoatrial connection, whereas the word "drainage" describes the concept of abnormal pulmonary venous return, despite normal anatomical connection. 15 Depending on the diagnostic evaluation performed, "connection" is the preferred description in this case. Tubular structures, seen in both long-and short-axis echocardiographic views, were indicative of PLCVC, which also is a rare congenital cardiovascular abnormality in cats, but it is more common in dogs.
Furthermore, microbubbles injected from the left cephalic vein were visible in the tubular structure and then appeared in the left atrium.
However, PLCVC alone cannot explain why microbubbles appeared in the left atrium, because PLCVC in 90% of cases in humans is connected to the CS and eventually drains into the right atrium. 16 Unroofed CS is another developmental disorder that frequently is identified together with PLCVC and was considered a concomitant abnormality. The CS collects blood supplied from the myocardium and serves as the final portion of coronary venous circulation. It is transversely located in the left atrioventricular groove on the dorsal aspect of the heart. Unroofed CS represents either single or multiple defects in the shared wall between the CS and the left atrium, allowing blood communication between the right and left atria through the incomplete CS. Therefore, it is considered a type of atrial septal defect. 17 Before advanced imaging, a diagnosis of PLCVC combined with unroofed CS seemed likely in this case.  20 The anomaly in our kitten closely resembled cardiac type total APVC, in which the pulmonary veins drain into the right atrium directly or through the CS. A previous case report described a cat with PAPVC and suspected pulmonary hypertension. 8 In contrast to our case, the cat of the previous report was asymptomatic at 14 months of age and was referred for evaluation of a heart murmur that was heard incidentally. Computed tomography identified that pulmonary veins from the caudal lung lobes drained into the caudal vena cava with bilateral cranial pulmonary veins that were connected normally to the left atrium. No structural cardiac disease that could result in the left parasternal systolic murmur could be identified. By comparing these 2 cases, it seems that PAPVC could be tolerated, and clinical manifestations and prognosis could vary depending on the extent of abnormal pulmonary veins.
During fetal life, the foramen ovale is a route by which blood can bypass the uninflated lungs, and it should close after birth because of decreased right-sided pressure. As the right-sided heart pressure and volume remain high after birth, the foramen ovale cannot close, and still allows communication between the right and left atria, a condition known as PFO, which permits some mixture of oxygenated and deoxygenated blood to enter the systemic circulation. In our case, the presence of PFO could be indirectly identified by the slightly lower SpO 2 , because no other shunting was observed. Moreover, contrast material entered the left atrium after the right atrium, also supporting the presence of a PFO.
In conclusion, we described symptomatic PAPVC in a kitten. The clinical manifestation of this rare congenital cardiovascular disease can vary depending on the individual. In veterinary patients, conventional radiography and echocardiography are supportive for PAPVC diagnosis, whereas advanced diagnostic imaging, such as CTA, that provides 3-dimensional images can improve understanding. Future reports, including studies before and after death, could provide more information and advance knowledge of this disease.

ACKNOWLEDGMENT
No funding was received for this study. We are grateful to Dr. Ming-Chih Lin and Dr. Chen-Hao Wu who served as diagnostic imaging advisors and to all associates who contributed to this case in Taichung Veterans General Hospital and National Chung Hsing University Veterinary Medical Teaching Hospital. We also thank the reviewers and editor for their comments.

CONFLICT OF INTEREST DECLARATION
Authors declare no conflict of interest.

OFF-LABEL ANTIMICROBIAL DECLARATION
Authors declare no off-label use of antimicrobials.

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Authors declare human ethics approval was not needed for this.