Partial pericardial agenesis presenting with positional palpitations

Congenital pericardial agenesis is a rare anomaly resulting from defective development of the pleuropericardial membrane. While often clinically silent, partial defects carry a higher risk of myocardial herniation, coronary compression or ventricular arrhythmias compared to complete absence. Symptomatic presentations are non-specific, frequently leading to diagnostic delays. We report the case of a 40-year-old man presenting with intermittent palpitations exacerbated by the left lateral decubitus position. Past medical history was unremarkable and patient did not take any medication. Physical examination as well as laboratory studies were innocent. Initial evaluation revealed sinus bradycardia and frequent polymorphic premature ventricular contractions (PVC). Transthoracic echocardiography (TTE) provided the first diagnostic clue, demonstrating a “pseudo-right-ventricular-overload” pattern characterized by paradoxical interventricular septal motion, exaggerated diastolic flattening of the posterolateral wall and right ventricular predominance in the formation of the cardiac apex. Significant apicolateral left ventricular hypermobility was also noted. Cardiac magnetic resonance imaging (MRI) confirmed partial pericardial agenesis involving the apical regions of both ventricles, with diastolic bulging suggestive of early herniation. Structural mimics, including arrhythmogenic right ventricular cardiomyopathy and dilated cardiomyopathy, as well as hemodynamic conditions like constrictive pericarditis and pulmonary hypertension, were excluded through multimodal imaging. Given the mild symptoms and absence of coronary compromise, herniation or significant arrythmias, conservative management was adopted with structured surveillance consisting of annual TTE and periodic Holter monitoring. The patient remains clinically stable at follow-up. This case highlights an unusual presentation of partial pericardial agenesis manifesting as positional palpitations. It underscores the importance of recognizing peculiar echocardiographic signs of pericardial defects and the role of cardiac MRI as the gold standard for diagnosis confirmation and risk stratification. Structured long-term monitoring is essential to detect potential progression toward myocardial entrapment or coronary compromise, enabling timely and targeted therapeutic interventions.