Abstract 17708: Cardiac Nut-Cracker: Paroxysmal Left Main Coronary Compression by Inducible Pulmonary Trunk Dilatation in Pulmonary Hypertension

Case Presentation: A 56yo woman with a 12-year history of idiopathic pHTN and severe RV dysfunction presented with worsening exertional angina (CCS III). Perfusion imaging demonstrated a large apical-septal defect, corresponding to an 80% eccentric stenosis of the LMCA on angiography ( Fig 1AB ) due to compression on ostium and shaft by a severely dilated pulmonary trunk ( Fig 1C ). Right heart catheterization revealed pulmonary artery pressures (PAPs) of 90/40/68mmHg. Operative risk for CABG was deemed prohibitive, thus the patient underwent high-risk PCI of the LMCA under IV conscious sedation. Initial angiography confirmed a patent LMCA with minimal longitudinal compression. Opening PAPs (102/37/64mmHg) with supplemental oxygen (FiO 2 /PaO 2 0.76/168mmHg) were similar to preop findings ( Fig 1D ). To replicate her symptomatology, supplemental oxygen was discontinued, resulting in rapid worsening of LMCA compression with severe reduction in LMCA cross-sectional area at room air conditions (FiO 2 /PaO 2 0.21/70mmHg), with corresponding suprasystemic PAP (122/44/73mmHg) ( Fig 1E) . Under IVUS guidance, a preselected stent was deployed producing complete LMCA patency without evidence of dynamic compression; minimal stent areas were unchanged at supraphysiologic and physiologic conditions: 19 vs 20mm 2 , FiO 2 0.73 vs 0.21 ( Fig 1F ). Discussion: LMCA stenosis from extrinsic compression of the vessel by an enlarged pulmonary artery is a rare etiology of acute coronary syndromes. Treatment options include PCI, CABG, reimplantation, or PA reduction plasty. While preop imaging clearly demonstrated LMCA compression by a dilated PA, during PCI true and dynamic severity of LMCA compression was revealed only under “normoxic conditions” (FiO 2 0.21). This paroxysmal “nut-cracker” phenomenon from inadvertent reversal of dynamic LMCA compression highlights the importance of normoxia in making the diagnosis of such anomalies in susceptible individuals with pHTN.