The Gasul Phenomenon: A Forgotten yet Fascinating Transformation in Congenital Heart Disease

Abstract The Gasul phenomenon refers to the acquired development of right ventricular outflow tract obstruction (RVOTO) in patients with large perimembranous ventricular septal defects (VSDs). We present the case of an 18-year-old female with progressive exertional dyspnea and fatigue, initially acyanotic during childhood but later exhibiting the features of right ventricular obstruction. Physical examination revealed a harsh systolic murmur and mild clubbing. Electrocardiography and chest radiography demonstrated right ventricular hypertrophy and reduced pulmonary vascular markings, respectively. Transthoracic echocardiography confirmed a large perimembranous VSD with hypertrophied infundibular muscle bundles causing significant subvalvular stenosis, consistent with the Gasul phenomenon. Surgical correction involving VSD patch closure and resection of the infundibular muscle was planned. This case underscores the importance of vigilant long-term follow-up in unrepaired VSDs, as acquired RVOTO can alter the disease course, mimic tetralogy of Fallot, and impact clinical management and prognosis.