The importance of bidirectional block during pulmonary vein isolation

The definition of a successful ablation of atrial fibrillation can vary among electrophysiologists. A commonly described endpoint is bidirectional block of the four pulmonary veins. A case is described in which entrance block into a pulmonary vein was achieved early during pulmonary vein isolation. However, triggers from the pulmonary vein continued to conduct into the atrium, revealing the block was only unidirectional. Further ablation resulted in true electrical isolation and highlights the importance of achieving bidirectional block.