Figure 2. Characteristic P wave morphology of focal tachycardias originating from pulmonary vein ostia. Notice that these tachycardias are inferiorly directed and positive throughout the precordial leads. Leads I, aVL and V1 are important in distinguishing left from right pulmonary vein origin and amplitude in the inferior leads help differentiating superior from inferior pulmonary veins. See text for details. LSPV left superior pulmonary vein, RSPV right superior pulmonary vein, LIPV left inferior pulmonary vein, RIPV right inferior pulmonary vein.