CLINICAL STATEMENTS AND GUIDELINES resource and does not repeat existing guideline recom- mendations. Abbreviation Meaning/Phrase AAOCA anomalous aortic origin of the coronary artery ACHD adult congenital heart disease AP anatomic and physiological AR aortic regurgitation ASD atrial septal defect AVSD atrioventricular septal defect BAV bicuspid aortic valve CCT cardiac computed tomography CCTGA congenitally corrected transposition of the great arteries CHD congenital heart disease CMR cardiovascular magnetic resonance CoA coarctation of the aorta CPET cardiopulmonary exercise test CT computed tomography CTA computed tomography angiography d-TGA dextro-transposition of the great arteries ECG electrocardiogram ERC evidence review committee GDMT guideline-directed management and therapy HF heart failure ICD implantable cardioverter-defibrillator IE infective endocarditis LV left ventricular LVOT left ventricular outflow tract PA pulmonary artery PAH pulmonary arterial hypertension PDA patent ductus arteriosus PR pulmonary regurgitation PS pulmonary stenosis QoL quality of life Qp:Qs pulmonary systemic blood flow ratio RCT randomized controlled trial RV right ventricular RVOT right ventricular outflow tract SCD sudden cardiac death SubAS subaortic stenosis TEE transesophageal echocardiography TGA transposition of the great arteries TOF tetralogy of Fallot TR tricuspid regurgitation TTE transthoracic echocardiography VHD valvular heart disease VSD ventricular septal defect VT ventricular tachycardia 2. BACKGROUND AND PATHOPHYSIOLOGY 2.1. Anatomic and Physiological Terms The International Society for Nomenclature of Pediatric and Congenital Heart Disease (also known as the No- menclature Working Group) defined, codified, mapped, and archived examples of nomenclatures and devel- oped standards for terminology.S2.1-1 S2.1-5 The Interna- tional Paediatric and Congenital Cardiac Code (IPCCC) nomenclature for anatomic lesions and repairs is used in this guideline (http://ipccc.net).S2.1-6 2.2. Severity of ACHD In a patient with CHD, severity of disease is deter- mined by native anatomy, surgical repair, and current physiology. Prior documents, including the 2008 ACHD relied primarily on anatomic classifica- tions to rank severity of disease. 