B50-40 Not All Lines Who Wander Are Lost: Persistent Left-Sided Superior Vena Cava Mimicking Arterial Cannulation

Abstract Introduction Unexpected catheter courses on post-procedure imaging can quickly raise alarm for arterial cannulation, particularly after left internal jugular (IJ) access. Yet not every “wrong” trajectory is a mistake. A persistent left-sided superior vena cava (PLSVC) can make a correctly placed line appear aberrant. This congenital anomaly—caused by failure of regression of the left cardinal vein—is the most common thoracic venous variant, occurring in about 0.3-0.5% of the general population and up to 10% of patients with congenital heart disease. Because its course parallels the aortic arch and left heart border, it can convincingly mimic an arterial path, prompting premature line removal and delayed therapy if not recognized. Case Report A 64-year-old man with hypertension and alcohol use disorder presented in undifferentiated shock. A triple-lumen catheter was placed emergently into the left IJ vein under ultrasound guidance for vasopressor administration. Post-procedure chest radiograph showed the catheter tracking along the left mediastinal border rather than crossing to the right atrium, raising concern for carotid or other arterial placement. At the bedside, however, the line produced non-pulsatile, low-pressure flow. The catheter was transduced, revealing a venous waveform, and a blood gas drawn from the distal port showed pH 7.42, pCO2 35 mmHg, pO2 30 mmHg, and oxygen saturation 50%, consistent with central venous blood. Computed tomography of the chest subsequently identified a PLSVC draining into an enlarged coronary sinus, confirming correct venous positioning and allowing continued use of the catheter. Discussion When a central line appears to trace the left heart border, the default assumption is of a technical error. PLSVC is an important mimic of arterial cannulation that intensivists, emergency physicians, and interventionalists should recognize. In time-sensitive shock states, automatic removal of a “suspicious” line risks losing hard-won access and exposing the patient to repeat cannulation without benefit. A simple, physiology-first algorithm—pressure transduction, waveform inspection, and venous blood gas analysis—can rapidly distinguish venous from arterial placement at the bedside. Once PLSVC is identified, awareness of its anatomy matters for left-sided procedures such as pacemaker or defibrillator insertion and pulmonary artery catheterization, where angulation, looping, or coronary sinus cannulation can complicate device advancement. This case highlights a practical point for trainees and proceduralists: when radiography and physiology disagree, confirm before you pull. This abstract is funded by: None