Substrate abLatIon as Concomitant trEatment for Left Atrial Macroreentrant Tachycardia

Inclusion Criteria: * Atypical flutter with positive F wave in V1, suspected left atrial origin. * Age ≥ 18 years * Capacity to understand the nature of the study, legal ability and willingness to give informed consent. Exclusion Criteria: * Simultaneous participation in a different trial. * Presence of congenital heart disease. * Suspected flutter of right origin or related to atriotomy scar from previous cardiac surgery. * NYHA IV functional class at the time of recruitment. * Contraindication to chronic anticoagulation or allergy/intolerance to heparin. * Uncontrolled hyperthyroidism. * Life expectancy less than 18 months. * Presence of heart disease that is expected to require surgery or heart transplantation within 18 months. * Pregnancy or the prospect of it in the next 18 months. * Left atrium without pathological substrate: area ≥ 4 cm2 of low voltages (\<0.5 mV) in the left atrium. * Severe fragility (Clinical Frailty Score ≥ 7).