In atrial flutter ablation, which strategy is used to interrupt the circuit?

• A. Create a line of block connecting two non-conducting structures.
• B. Create a small focal lesion at the isthmus.
• C. Isolate the pulmonary veins.
• D. Create a line of block connecting two non-conducting structures and confirm bidirectional block.

Answer: (D)

The central idea is to stop a macro-reentrant atrial flutter by breaking the circuit with a complete linear block. In typical flutter circuits, the reentry path goes around the tricuspid annulus through a narrow isthmus; placing a continuous lesion across that isthmus creates a barrier that prevents the impulse from circulating. Crucially, the block must be bidirectional, meaning conduction across the line is halted in both directions. After ablation, pacing from either side should not cross the line, confirming the circuit cannot re-enter. This is why the best strategy includes both creating the line of block and verifying bidirectional block. Other options either target a different rhythm mechanism (focal lesions) or refer to pulmonary vein isolation, which is for atrial fibrillation, not flutter.