Cor triatriatum sinister resembling Lucas type C1a in a cat.

Cardiac CT angiography is essential for accurately classifying cor triatriatum sinister subtypes and guiding feline management.

This case report describes a six-year-old neutered male cat presenting with acute respiratory distress, ultimately diagnosed with cor triatriatum sinister (CTS) resembling Lucas type C1a. Initial transthoracic echocardiography identified a left atrial membrane with a single fenestration and turbulent flow, raising suspicion that the distal chamber received at least one pulmonary vein. The respiratory signs responded to corticosteroids but not to diuretic therapy, prompting further diagnostic workup. Cardiac computed tomography angiography (CCTA) was employed to characterize pulmonary venous anatomy and differentiate CTS from pulmonary vein stenosis or other congenital vascular malformations. CCTA confirmed left atrial subdivision with a single interchamber orifice measuring 5.33 mm. Critically, the imaging revealed an atypical pulmonary venous drainage pattern: three pulmonary veins drained into the proximal chamber, while the left cranial pulmonary vein drained into the distal chamber, which was continuous with the mitral valve. Applying the human Lucas classification system to this feline case, the anatomic configuration most closely resembled Lucas type C1a, a subtype not previously well-documented in veterinary literature. Importantly, no congestive heart failure attributable to CTS was identified. This case highlights the diagnostic value of CCTA in characterizing complex congenital cardiac anomalies in cats, demonstrates the applicability of human cardiac classification schemes to feline patients, and underscores the importance of differentiating CTS subtypes to guide clinical management and prognostication.

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