Thread by @ZiadIssaMD

#IssaTweetorials
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What are the types of CTI-dependent atrial macroreentry?

CTI-dependent macroreentrant atrial tachycardias (MRATs) are confined to the RA & incorporate the CTI as a critical part of the circuit. All these MRATs can be eliminated by CTI ablation.
#EPeeps

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CTI-dependent MRATs include:
(1) peritricuspid reentry (clockwise and counterclockwise typical atrial flutter [AFL])
(2) peritricuspid double-wave reentry
(3) lower loop reentry
(4) intra-isthmus reentry.

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PERITRICUSPID REENTRY
In typical AFL the wavefront rotates around the tricuspid annulus. A line of conduction block in the RA free wall is usually required to as a critical lateral boundary that prevents short-circuiting of the flutter wavefront around the IVC.

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DOUBLE-WAVE REENTRY
Typical AFL circuits with a large excitable gap may allow a second excitation wave to be introduced in the same circuit by a critically timed extrastimulus. The 2 wavefronts occupy the circuit simultaneously. This rhythm rarely lasts more than a few beats.

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LOWER LOOP REENTRY (LLR)
In LLR, the wavefront rotates around the IVC.

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LLR vs Typical AFL
LLR often coexists with typical AFL. Significant RA disease and slow conduction across the lower crista terminalis to enable reentry around the IVC instead of around the TA. In contrast conduction block across the posterlateral RA is required for typical AFL

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INTRA-ISTHMUS REENTRY
Small reentry circuits confined to the CTI (often the medial aspect of CTI) can develop, especially in patients with prior extensive CTI ablation for typical AFL, which provides the substrate for reentry (even in the presence of bidirectional CTI block).