Table 1. Clinical classification of pulmonary arterial hypertension in congenital shunt lesions; modified from (28,31).

Group	Class	Definition
A	Eisenmenger syndrome	● All major intra- and extra-cardiac cardiovascular defects with initial systemic to pulmonary blood flow (shunt), in which PVR increases greatly over the course of the disease and in which there is a consecutive bidirectional shunt or a complete shunt reversal (blood flow from the lungs to the systemic circulation) ● In clinical terms, there is cyanosis, secondary erythrocytosis and cyanosis-remultiple organ involvement
B	Left-to-right shunts correctable (by intervention or surgery)	● Medium- to large-size defects with mild to moderate systemic-pulmonary blood flow but no cyanosis at rest
C	PAH, coincidentally associated with a CHD	● PAH is coincidentally associated with a congenital heart defect ● Markedly elevated PVR in the presence of small congenital defects that are not primarily responsible for the development of elevated PVR (in adults this is typically a ventricular septal defect with an effective diameter <1 cm or an atrial septal defect with an effective diameter <2 cm as measured by echocardiography) ● The clinical picture strongly resembles idiopathic PAH ● Defect closure is contraindicated ● The diameter measured does not always indicate the haemodynamic relevance of the defect! ● For a more precise assessment of the shunt haemodynamics, pressure gradients, shunt size and direction and the ratio of pulmonary to systemic flow (Qp/Qs) must be taken into consideration
D	PAH after previous repair	● Persistent PAH that reoccurs within months or years after repair of the CHD, without haemodynamically relevant re- or residual shunts
E	Others	● Segmental PAH ● Pulmonary vascular disease after previous Fontan-Operation

PVR, pulmonary vascular resistance; PAH, pulmonary arterial hypertension; CHD, congenital heart defect.