The University of California, San Diego (UCSD) classification; a proposed new surgical classification of chronic thromboembolic pulmonary hypertension
| Surgical level | Location of thromboembolic disease |
| 0 | No evidence of thromboembolic disease |
| I | Starts in the main pulmonary arteries (patients with complete occlusion of one lung are classified as level IC) |
| II | Starts at the level of the lobar or intermediate pulmonary arteries |
| III | Starts at the level of segmental arteries only |
| IV | Starts at the subsegmental branches only |
Preliminary results (M. Madani, Division of Cardiovascular and Thoracic Surgery, University of California, San Diego, La Jolla, CA, USA; unpublished data).