The clinical classification of pulmonary hypertension (PH) has gone through a series of changes since the first classification was proposed in 1973 at the World Health Organization international conference on primary pulmonary hypertension (PPH) in Geneva, Switzerland.[1,2] The initial classification designated only two categories, primary pulmonary hypertension (PPH) and secondary PH, depending on the presence or absence of identifiable causes or risk factors.
Twenty-five years later, a second World Symposium on Pulmonary Arterial Hypertension (PAH) was held in 1998 in Evian, France. Based on the research that had ensued in studying the pulmonary circulation since 1973, by 1998 significant advances had been made in our understanding of PH. Further, the first drug for PPH was approved during this time, i.e., in 1995. Thus, because the aim of a clinical classification is to individualize different categories sharing similarities in pathobiology, clinical presentation, and therapeutic approaches, the “Evian Classification” was based on defining categories of PH that shared similar histopathology and clinical characteristics. The Evian Classification expanded the prior 1973 classification from 2 groups to 5 major groups with Group 1 PH being the most studied, i.e., PAH. In 2003, during the third World Symposium on PH held in Venice, Italy, the clinical classification was slightly modified, with further modification most recently during the fourth World Symposium held in Dana Point, California in 2008