To achieve a successful CTI ablation, which type of block must be confirmed?

To achieve a successful CTI ablation, which type of block must be confirmed?

• A. Unidirectional block
• B. Bidirectional block
• C. Partial block
• D. No block required

Answer: (B)

The essential idea is that a CTI ablation must stop electrical conduction across the isthmus in both directions. Typical atrial flutter relies on a circuit that travels through the cavotricuspid isthmus in either direction around the tricuspid annulus. If the ablation line only blocks one direction, the circuit can still propagate in the other direction, allowing flutter to persist or recur. Confirming bidirectional block means showing that no conduction crosses the ablation line from either side. In practice, this is demonstrated with pacing and activation mapping to ensure there is no entrance into the line from either chamber side and no exit from the line to either side. Because a unidirectional block still leaves a path for reentry in the unblocked direction, or a partial block indicates incomplete ablation, or no block means the flutter circuit remains intact, bidirectional block is the goal for a durable, successful CTI ablation.

The essential idea is that a CTI ablation must stop electrical conduction across the isthmus in both directions. Typical atrial flutter relies on a circuit that travels through the cavotricuspid isthmus in either direction around the tricuspid annulus. If the ablation line only blocks one direction, the circuit can still propagate in the other direction, allowing flutter to persist or recur.

Confirming bidirectional block means showing that no conduction crosses the ablation line from either side. In practice, this is demonstrated with pacing and activation mapping to ensure there is no entrance into the line from either chamber side and no exit from the line to either side.

Because a unidirectional block still leaves a path for reentry in the unblocked direction, or a partial block indicates incomplete ablation, or no block means the flutter circuit remains intact, bidirectional block is the goal for a durable, successful CTI ablation.