Proceedings of the International scientific and practical conference ―Paris Science and Education Forum‖ (March 2-4, 2026) / Publisher website: www.naukainfo.com. – Paris, France, 2026. - 293 p.

242 Introduction In modern cardiology practice, complex clinical cases requiring a multidisciplinary approach to diagnosis and treatment are becoming increasingly common. One such case is the combination of hypertrophic cardiomyopathy with rare anatomical and functional cardiac abnormalities. This case demonstrates how long- term observation, comprehensive assessment, and collaboration among specialists can lead to optimal patient management strategies. Clinical Characteristics The focus is on a patient with hypertrophic cardiomyopathy associated with a subaortic muscular membrane and combined left ventricular outflow tract obstruction. Additionally, she had an implanted dual- chamber cardioverter-defibrillator and a long history of treating atrial fibrillation and flutter. These arrhythmias were associated with hemodynamic instability (EHRA III functional class) and the development of acute left ventricular heart failure. The patient experienced serious complications after multiple sessions of electrical cardioversion and catheter ablation. The rhythm control strategy was successful, with sinus rhythm maintained for over 10 years. Due to the complex intracardiac hemodynamic disturbance and aggressive arrhythmia management, the patient developed stiff left atrium syndrome with subtotal atrial wall calcification, restricting venous return and causing restrictive hemodynamics. This led to severe mixed (post- and pre-capillary) pulmonary hypertension complicated by pulmonary artery aneurysm. Biventricular heart failure developed, predominantly affecting the right ventricle. Despite preserved left ventricular ejection fraction, the anatomical and functional alterations exclude the possibility of isolated lung transplantation. Diagnostic Pathway Over 24 years of follow-up, an extensive diagnostic archive was collected: physical and laboratory exams, ECG and Holter monitoring, chest X- ray, transthoracic and transesophageal echocardiography, contrast-enhanced cardiac MRI, native and contrast-enhanced MSCT pulmonary angiography of the pulmonary artery, right heart catheterization, coronary angiography, spirometry, and ultrasound of abdominal and thyroid organs. All diagnoses conform to ICD-10 codes. An expert