Long-term multimodal imaging, biomarker monitoring and late supraventricular tachycardia-associated collapse in a Maltese dog with giant right atrial diverticulum

Technical Summary: Long-term Multimodal Imaging, Biomarker Monitoring, and Late Supraventricular Tachycardia-Associated Collapse in a Maltese Dog with Giant Right Atrial Diverticulum

Problem Statement
Right atrial diverticulum is a rare cardiac anomaly in dogs characterized by a chamber-like outpouching communicating with the right atrium. While previously described in isolated case reports, the long-term clinical behavior, thromboembolic risks, biomarker trends, and arrhythmia development associated with this condition remain poorly characterized. Differential diagnoses for right-sided thoracic lesions include mediastinal masses, pericardial cysts, and various aneurysms, making accurate diagnosis challenging without multimodal imaging. Furthermore, the potential for intracavitary blood stasis, thrombus formation, and late-onset arrhythmias in clinically compensated dogs is not well established.

Methodology
This case report details the retrospective evaluation and long-term management of a 10-year-old neutered male Maltese dog presenting with recurrent collapse, chronic cough, and excitement-induced syncope. The diagnostic approach relied on multimodal imaging and serial biomarker monitoring over a period of approximately 45 months:

• Imaging: Thoracic radiography was performed initially, followed by contrast-enhanced computed tomography (CT) and echocardiography. CT utilized a Woorien MyVet CT i3D system to assess lesion morphology and contrast pooling. Echocardiography (Philips EPIQ Elite) was used to define the communication between the cystic cavity and the right atrium and to identify intracavitary structures.
• Biomarker Monitoring: Serial measurements included D-dimer (thromboembolic risk), N-terminal pro-B-type natriuretic peptide (cProBNP/c.NT-proBNP; cardiac strain), and cardiac troponin I (myocardial injury). These were measured using a Bionote Vcheck V200 system.
• Management: The dog was managed medically. Initial antithrombotic therapy involved aspirin, which was later switched to rivaroxaban (0.5 mg/kg orally every 12 hours) following a marked elevation in D-dimer. Supportive cardiovascular therapy, including pimobendan, was adjusted based on clinical status and biomarker trends.
• Outcome Assessment: The dog was monitored for clinical signs, rhythm status (via electrocardiography during collapse episodes), and terminal cardiopulmonary function. No necropsy was performed.

Key Results

• Diagnosis: Imaging confirmed a giant right atrial diverticulum measuring approximately 41 × 38 × 34 mm adjacent to the cranial vena cava–right atrial region. CT demonstrated blood-pool enhancement and dependent contrast pooling, indicative of slow or stagnant flow. Echocardiography identified a 7.5-mm communicating orifice and multiple mobile echogenic structures within the cavity, interpreted as suspected intracavitary thrombi.
• Long-term Course: The dog remained clinically stable for approximately 45 months with controlled cough and collapse.
• Biomarker Trends: Serial monitoring revealed intermittent but marked D-dimer elevation (peaking at 3748.35 mg/dL), persistent increases in N-terminal pro-B-type natriuretic peptide, and repeated elevations in cardiac troponin I, supporting ongoing thromboembolic risk, progressive cardiac strain, and recurrent myocardial injury.
• Late Deterioration: Approximately 52 months after the initial collapse, the dog experienced recurrent syncope. Electrocardiography documented a regular narrow-complex supraventricular tachycardia at 178 beats/min. Terminal events included azotemia, hypercapnic respiratory acidosis, and cardiopulmonary decompensation.
• Terminal Event: The dog died approximately 1 hour after emergency presentation. The terminal event was interpreted as acute cardiopulmonary decompensation, potentially involving supraventricular tachycardia-associated low cardiac output, though pulmonary thromboembolism and other causes could not be definitively confirmed without necropsy.

Significance and Claims
The paper claims that this case highlights the diagnostic necessity of combining echocardiography and contrast-enhanced CT for right-sided chamber-like thoracic lesions to distinguish diverticula from aneurysms or mediastinal masses. It suggests that giant right atrial diverticulum may remain clinically compensated for several years but can later become clinically significant due to intracavitary blood stasis, suspected thrombus formation, progressive cardiac strain, recurrent myocardial injury, and supraventricular tachycardia-associated collapse.

The authors assert that multimodal imaging, thromboembolic risk monitoring (via D-dimer), serial cardiac biomarker assessment, and rhythm evaluation are clinically useful tools for managing dogs with this anomaly. The report notes that while medical management provided prolonged stabilization, the condition carries a risk of late deterioration. The paper concludes that further cases are needed to define prognosis and optimal antithrombotic strategies, and it explicitly states that the definitive cause of death could not be confirmed due to the lack of necropsy and terminal rhythm documentation.