An 11-year-old, 2.6 kg, castrated male Maltese (case 1) was presented with lethargy and respiratory distress. Vital signs included a body temperature of 38.8°C, heart rate of 180 bpm respiratory rate of 54 bpm, and blood pressure of 120 mmHg. chocardiography and abdominal ultrasonography showed a heterogenous heart-base mass compressing the cranial vena cava (CrVC), accompanied by pleural effusion, plethoric CdVC, hepatic congestion, and ascites. (Fig. 1A and B). Thoracocentesis and paracentesis identified the pleural effusion and ascites as modified transudate, without evidence of infection, active inflammation, or neoplasia. The owner declined cytologic or histologic evaluation of the cardiac tumor due to the high risk of complications, including bleeding. The pleural effusion and ascites progressively worsened despite the oral administration of furosemide. Transatrial stent placement is meant to resolve tumor-induced compression and alleviate symptoms. Pre-procedural coagulation assessments yielded normal results. Computed tomography (CT) was performed to guide stent placement. CT revealed a 28.5 × 27.9 × 28.6 mm mass between the ascending aorta and CrVC, cranial to the right atrium, with heterogenous enhancement with hypodense parenchyma. The mass significantly compressed the CrVC, causing luminal narrowing and dilation cranial to the stenosis (Fig. 1C and D). The selected stent diameter was approximately 1.1 to 1.2 times the measured diameter of the CrVC. The stent length was selected to ensure adequate coverage of the CrVC, right atrium, and CdVC to prevent migration. Two self-expanding metallic stents (SEMS) (K-easy Vet Vascular Stent; S&G Biotech, Korea) measuring 10 × 80 mm and 12 × 80 mm were selected. The dog was anesthetized per standard hospital protocol, positioned in right lateral recumbency, and an 8-Fr vascular introducer sheath (Accu-Sheath; Sungwon Medical, Korea) was inserted via the left jugular vein. The introducer's distal end was positioned in the CrVC for direct administration of a 1:1 diluted contrast solution of iohexol 300 mgI/mL and normal saline. A filling defect was visualized in the inflow segment of the CrVC and the cranial right atrium during contrast administration (Fig. 1E). The azygos vein was engorged due to CrVC obstruction and retrograde blood flow [10]. The diameters of the dilated CrVC, tumor-constricted CrVC lesion, and CdVC were reassessed on fluoroscopic angiography, using an esophageal marker catheter to determine the appropriate stent size. The 10 × 80 mm SEMS was selected as the most suitable. A 0.035-inch guidewire (Weasel wire; Infiniti, USA) was advanced through the introducer sheath to traverse the CrVC, right atrium, and CdVC. The stent was carefully positioned with its proximal end at the midpoint between the heart and diaphragm. After stent deployment, contrast imaging via the introducer sheath confirmed adequate expansion of the constricted lesion (Fig. 1F). The left jugular vein was repaired using a simple continuous absorbable monofilament suture (PDS II 5-0; Ethicon, USA), followed by skin closure using a non-absorbable suture (Blue nylon 4-0; Ailee Co., Ltd., Korea). The dog recovered uneventfully and was discharged the day after the procedure. Six days after the procedure, hepatic congestion and ascites were resolved, and a small amount of pleural effusion persisted. The patient showed improved vitality and appetite compared to before the procedure. Two months after the procedure, the patient presented with a small amount of ascites and hepatic congestion on ultrasonography. Ascites were modified transudate, and there were no signs of tumor metastasis. Echocardiography revealed no evidence of tumor invasion or thrombosis within the stent. Three months after the procedure, the amount of ascites was increased, and paracentesis was performed to relieve abdominal discomfort. The patient is doing well, sixteen months after the stent placement, receiving toceranib (Palladia; Zoeits, Korea) chemotherapy and intermittent paracentesis. The only complication present is ascites, with no other issues reported.

A 15-year-old, 6.38 kg, castrated Poodle (case 2) presented with cyanosis. On physical examination, marked subcutaneous edema in the head and neck region, distention of jugular veins, and low oxygen saturation (SpO₂: 60-80%) were observed. Thoracic radiography showed prominent pleural effusion. A total of 350 mL of pleural effusion was aspirated and confirmed to be a modified transudate, without any inflammatory and neoplastic cells on cytology. Echocardiography identified right atrial inflow obstruction of the CrVC due to a cardiac tumor (Fig. 2A). CT revealed a mass (1.66 × 1.77 × 2.68 cm) with strong heterogeneous contrast enhancement at the site of the right atrial appendage, causing significant compression of the CrVC (Fig. 2B) and severe dilation of CrVC just cranial to the stenotic region. This compression resulted in dilation of the CrVC, azygos vein, internal thoracic veins, and multiple tortuous venous shunt vessels forming along the pericardium that drain to the CdVC (Fig. 2C). The head and neck edema was attributed to venous congestion in the head and neck, secondary to CrVC compression caused by the tumor identified on imaging. Therefore, transatrial stenting was performed to improve venous circulation. The patient was placed in the left lateral recumbent position underwent anesthesia. A surgical cut down was performed via the right jugular vein, and an 8-Fr vascular introducer sheath (Accu-Sheath) was inserted. A CrVC angiogram confirmed significant vascular constriction in the cranial portion of the right atrium, leading to slow contrast agent outflow and aneurysmal dilation at the constriction site. Several small, tortuous venous collateral vessels were observed, allowing retrograde blood flow into the azygos vein and alleviation of CrVC pressure. A 12 mm × 80 mm SEMS was positioned from the CrVC, traversing the right atrium, to the CdVC. The stent expanded to approximately 30% of its maximum diameter at the constriction site. A repeat angiogram showed improved blood flow (Fig. 2D and E). The introducer sheath was removed, and vascular repair was performed. The procedure lasted a total of 120 minutes. The patient was discharged two days later without any complications. The stent expanded to approximately 80% of its normal diameter three days after the procedure and maintained that diameter thereafter (Fig. 2F and G). Over the course of several days, the cervical edema rapidly resolved. Clopidogrel (Prabic; Shinil, Korea) was initiated at 2 mg/kg once daily starting the day before the procedure. Despite this, a non-obstructive thrombus was observed within the stent the following day (Fig. 3). Rivaroxaban (Xarelto; Bayer, Germany) was subsequently added at 1 mg/kg once daily. Thrombus formation persisted without causing complete stent obstruction. By the 9th postoperative day, pleural effusion had improved. The owner declined further anesthesia-dependent tests or treatments, including CT and thrombus removal. Despite the thrombus, the dog remained stable for two months. After two months, the dog was euthanized at the owner's request due to recurrent pleural effusion and respiratory distress.

Two dogs presented with pleural effusion and ascites (case 1) or cervical swelling and pleural effusion (case 2) due to central venous obstruction and congestion from a cardiac tumor. Clinical symptoms in both dogs improved following transatrial stenting, a non-invasive approach. Jugular vein access is generally not recommended in the presence of significant cervical swelling, elevated jugular venous pressure, or concerns about radiation exposure [10]. In these dogs, the small body size made femoral vein access with an 8-Fr introducer sheath challenging, prompting the use of jugular access instead. Stents placed in the cranial or CdVC on one side are prone to migration due to directional blood flow. However, transatrial stents are relatively resistant to migration because of the opposing flow between the cranial and CdVC. To prevent migration, the distal end of the stent should be placed just before the bifurcation of the brachiocephalic vein into the subclavian veins, while the proximal end should be positioned just before the CdVC bifurcates into the hepatic veins, ensuring the stent clears the tumor-constricted segment and passes through the right atrium [4]. Following these criteria, the stent was successfully deployed without migration, resulting in significant improvement in clinical signs. Pleural effusion and respiratory distress were resolved in both dogs, and the owners were satisfied with the improved quality of life post-procedure. Weisse at al. [4] reported no thrombus formation in dogs after vascular stent placement, and anticoagulants were not routinely used. In this report, transatrial stenting for vena cava compression due to a cardiac tumor improved the patient’s clinical symptoms and achieved the palliative goal of enhancing quality of life. However, unlike the findings in the report, thrombus formation developed within the stent after the procedure in case 2. Human studies highlight risk factors for stent thrombosis, such as diabetes mellitus (DM), renal dysfunction, small stent diameter, and insufficient antiplatelet response [11]. In veterinary patients, hypercoagulable states linked to protein-losing nephropathy, enteropathy, or systemic inflammation further increase thrombotic risk [12, 13]. Careful patient selection, appropriate anticoagulation therapy, and close monitoring are crucial for stenting success.

The limitations of this study include the lack of cytological or histological confirmation of cardiac tumors, absence of pre- and post-procedural pressure gradient measurements, short follow-up duration, and small sample size, limiting prognostic assessment and generalizability. Despite these constraints, endovascular transatrial stenting may serve as a favorable palliative treatment option for cardiac tumors causing venous return obstruction, particularly when owners are hesitant to pursue aggressive treatments like en bloc tumor resection or radiation therapy. This minimally invasive approach shows promise in alleviating clinical symptoms and offers a viable option for patient management.