A Case of Pulmonary Arteriovenous Shunt Diagnosed by Microbubble Test via a Swan-Ganz Catheter

When encountering severe hypoxemia that does not respond to oxygen supplementation, it is essential to consider underlying right-to-left shunting. Among various diagnostic approaches, the microbubble test via transthoracic echocardiography (TTE) is a simple, noninvasive method for detecting pulmonary arteriovenous shunts, particularly in hepatopulmonary syndrome (HPS). Although microbubbles are usually administered peripherally, using a Swan-Ganz (SG) catheter to inject microbubbles directly into the pulmonary artery may provide even more definitive diagnostic information. We report a case of a woman in her 60s who was admitted in cardiac arrest after several months of progressive dyspnea and one month of poor appetite. While resuscitation was successful, severe hypoxemia persisted despite intubation, mechanical ventilation, and oxygen therapy. Immediately after resuscitation, TTE revealed no intracardiac shunt but did show microbubbles in both heart chambers. The patient exhibited refractory hypoxemia, high-output status, and pulmonary hypertension. Based on a history of severe dietary irregularities, beriberi heart disease was suspected, and empirical thiamine administration improved pulmonary hypertension and high-output state; however, the hypoxemia remained unresolved. Since microbubbles had been observed in the left heart without an intracardiac shunt, a pulmonary arteriovenous shunt was suspected. Peripheral microbubble testing showed Grade 4 opacification of the left heart three to four heartbeats subsequent to the filling of the right heart. Concerns regarding hemodynamic instability and timing prompted a microbubble test via the already-placed SG catheter. Injection of microbubbles directly into the pulmonary artery again demonstrated Grade 4 opacification in the left heart alone, confirming a pulmonary arteriovenous shunt independent of intracardiac pathways. The patient later died on day six due to irreversible brain damage. The autopsy revealed cirrhosis with histopathological features of autoimmune hepatitis and pulmonary changes suggestive of a pulmonary arteriovenous shunt. Postmortem evaluations indicated low vitamin B1 levels, consistent with beriberi heart disease, and the presence of autoimmune markers suggesting Sjögren's syndrome. In beriberi heart disease, high output is associated with reduced vascular resistance and increased metabolic demand. In liver disease, excessive nitric oxide and carbon monoxide production may worsen these hemodynamic conditions, promoting pulmonary vasodilation and pulmonary arteriovenous shunt formation. Using the SG catheter for the microbubble test proved practical and effective, especially when standard peripheral methods are complicated by hemodynamic instability, difficulty visualizing the right heart, the potential presence of intracardiac shunts, or contraindications to transesophageal echocardiography (TEE). This technique, relying on commonly available cardiovascular equipment, may facilitate earlier diagnosis of shunt-related diseases in complex clinical scenarios.