Inclusion Criteria:

• patients with paroxysmal AF undergoing PVI by PEF energy with documented typical atrial flutter or patients with persistent AF in whom catheter ablation of CTI is planned as a part of a complex procedure
• Age ≥ 18 years at the time of study enrollment
• Signed informed consent

Exclusion Criteria:

• - LA diameter > 65 mm (measured in the parasternal long-axis view)
• History of CTI ablation in the past
• History of cardiac valve surgery
• Significant valvular defect
• Age below 18 years
• Pregnancy, breastfeeding
• Any disease with a life expectancy <1 year
• Uncorrected congenital heart disease or valvular obstruction
• Active myocarditis
• Untreated hypothyroidism or hyperthyroidism
• Recipient of any major organ transplant (e.g., lung, liver, heart)
• HIV positivity with a survival expectancy of less than five years due to HIV
• Chronic dialysis treatment
• Unwillingness to participate.