Prior documents, including the 2008 ACHD relied primarily on anatomic classifica- tions to rank severity of disease. However, patients with the same underlying anatomy may have very different repairs and experienced variable physiological conse- quences of those repairs. For example, a patient with tetralogy of Fallot (TOF) after a valve-sparing primary re- pair may have excellent biventricular function with nor- mal exercise capacity and no arrhythmias, whereas an- other patient of the same age with TOF may have had palliative shunting followed by a transannular patch repair resulting in severe pulmonary regurgitation (PR) with right ventricular (RV) enlargement, biventricular dysfunction, and ventricular tachycardia (VT). To cate- gorize disease severity in CHD in a more comprehensive way, the writing committee developed an ACHD Ana- tomic and Physiological (AP) classification system (Ta- bles 3 and 4) that incorporates the previously described CHD anatomic variables as well as physiological vari- ables, many of which have prognostic value in patients with ACHD. 2.3. The ACHD AP Classification The ACHD AP classification (Tables 3 and 4), newly elab- orated in this guideline, is intended to capture the com- plexity of ACHD anatomy and physiology, which are not always correlated. Certain anatomic abnormalities of clinical importance are shared across diagnoses (eg, aortic enlargement), which may be found in patients with BAV, coarctation of the aorta (CoA), transposition (Continued) Abbreviation Meaning/Phrase CLINICAL STATEMENTS AND GUIDELINES Table 3. Physiological Variables as Used in ACHD AP Classification Variable Description Aortopathy Aortic enlargement is common in some types of CHD and after some repairs. Aortic enlargement may be progressive over a lifetime. There is no universally accepted threshold for repair, nor is the role of indexing to body size clearly defined in adults, as is done in pediatric populations. 