Low right atrial tachycardia with positive P waves in the inferior leads: explanation by electroanatomical mapping.

The P-wave morphology can help trying to localize the origin of an ectopic atrial tachycardia noninvasively. We describe the case of a 54-year-old male patient with an ectopic right atrial tachycardia and positive P waves in the inferior leads on a 12 lead ECG. Electroanatomical mapping with the CARTO system localized the focus at the low right atrial free wall. With that origin and a very slow conduction through the cavotricuspid isthmus the activation spread clockwise around the tricuspid anulus and resulted in a craniocaudal septal activation pattern, which subsequently caused a positive P-wave morphology in the inferior leads.