Background. Pulmonary veins (PV) reconnection is the most common reason for atrial fibrillation (AF) recurrence. The ablation-index is a marker of ablation lesion quality which use achieves high percentages of first pass isolation and improved results of AF ablation. Most operators use a double trans-septal approach with confirmation of PV isolation with a circular mapping catheter. In the present study we aimed to show that an ablation-index guided procedure using a single trans-septal approach and ablation catheter only would achieve adequate PV isolation while demonstrating the critical role of the carina in PV isolation. Methods. 76 consecutive patients with paroxysmal AF: 34 patients underwent WACA, 32 patients underwent WACA+ (including empiric carina isolation) and 10 patients underwent a staged procedure of WACA followed by WACA+ in case of lack of first pass isolation. All procedures were performed via single trans-septal. Results. Compared to WACA-only, WACA+ increased the odds of PV isolation from 65% to 91%, p=0.012. In WACA-only, ablation of the carina was needed to achieve PV isolation. The role of the carina was confirmed in 10 patients with sequential ablation. PV isolation was confirmed by inserting a circular mapping catheter through the single trans-septal sheath. At 18 months of follow-up [IQR 15.2-20.8 months], freedom from AF was 84% for the entire cohort. Conclusion. Our study confirms the high success rate of PV isolation using ablation index and shows that this can be achieved via single trans-septal crossing. Our study confirms the role of the carina in PV isolation.