Working formulation nomenclature of heart transplant pathology: A retrospective evaluation of 1037 endomyocardial biopsies.

Working Formulation (WF) was recently introduced by the International Society for Heart Transplantation to grade acute cellular rejection, as well as additional lesions observed in endomyocardial biopsies (EMBs). The aim of this study was to evaluate the actual advantages of this grading system in terms of feasibility and predictive value. To this purpose, we reclassified 1037 EMBs performed in our heart transplantation units according to the WF. Our results show that multifocal mild rejection (grade IA), when worsening, tends to progress to multifocal moderate (3A), whereas diffuse mild (1B) generally worsens to diffuse moderate (3B), thus following the same focal or diffuse pattern. Unifocal moderate rejection (grade 2) has a peculiar behavior, in that it almost always resolves, though in our units it is treated the same way as is grade 113. Finally, we found a significant relationship between Quilty B effect and chronic rejection. In conclusion, this retrospective study shows that WF is effective in using both qualitative and quantitative criteria and, particularly, in separating focal and diffuse forms of rejection and devoting a distinct grade to unifocal moderate rejection.