(1136) Pulmonary Hypertension, Right-to-Left Atrial Shunting, and the Complex Interplay of Oxygenation

Introduction: Pulmonary Hypertension (PH), characterized by elevated pulmonary arterial pressure (PAP), presents significant challenges in cardiovascular medicine. Hypoxemia in PH can result from ventilation/perfusion mismatch, low diffusion capacity, and right-to-left (RL) shunting. While traditionally associated with patent foramen ovale, recent findings suggest other intracardiac mechanisms are rarer. This case highlights severe PH with an intra-atrial RL shunt causing profound hypoxemia, stressing the balance between systemic and pulmonary vascular resistance (PVR).

Description: An 84-year-old female with a history of PH and pulmonary embolism (PE) presented with severe dyspnea and hypoxia (SpO2 74%) requiring high-flow nasal cannula. Echocardiography revealed severe PH, right atrial enlargement, atrial shunting, and moderately reduced right ventricular function. Right heart catheterization confirmed PH (mean PAP 65mmHg), leading to ICU admission. A multidrug regimen of Sildenafil, Treprostinil, Inhaled Nitric Oxide, and loop diuretics was initiated. Despite this, the patient progressed to right ventricular (RV) failure requiring Dobutamine. However, significant hypoxemia persisted. Vasopressin was added to preserve Systemic Vascular Resistance (SVR), minimizing RL shunting and hypoxemia while attempting to reduce PVR. Despite significant therapeutic interventions, improvement in oxygenation was minimal, likely due to the confounding RL intra-atrial shunt.

Discussion: RL shunting in severe PH presents a challenge in preventing hypoxemia. Since hypoxemia is a potent pulmonary vasoconstrictor contributing to the progression of PH, maintaining O2 saturations >90% is conventional. However, oxygen therapy is often ineffective, shifting the focus to pulmonary and systemic vascular dynamics. Increasing SVR with vasopressors can improve hypoxemia but may worsen heart failure, as seen in this patient, potentially leading to death. This case underscores the complexity of managing PH with RL shunting, emphasizing the need for personalized treatment and further research to understand the pathophysiology and develop targeted interventions for this intricate clinical scenario.