A new heuristic description for electromigration-induced early resistance changes is given. The basis is formed by two coupled partial differential equations, one for vacancies, and one for imperfections. These equations are solved numerically for a grain boundary bamboo structure. It is shown that this model is capable of simulating the typical effects as observed in early resistance change measurements. These early resistance changes are due to the redistributions of the vacancies and the generation of imperfections. Simulations are performed that closely match the measured resistance change curves.