Functional Interplay Between Upper Loop Reentry and Clockwise Cavotricuspid Isthmus-Dependent Flutter in a Non-surgical Right Atrium: A Case of Dual-Loop Macroreentry

Figures

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  Figure 1. Surface electrocardiogram showing atrial flutter. Black arrows indicate the characteristic predominantly negative f waves in the inferior leads (II, III, and aVF, where arrows point up to negative deflections) and predominantly positive f waves in lead V1 (arrows point down to positive peaks).

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  Figure 2. Intracardiac electrograms demonstrating activation sequence. The tracing displays surface ECG leads (II, aVR, V1) and intracardiac recordings from the ablation (ABL), CS, and duodecapolar lateral right atrial (HALO) catheters. Black arrows highlight the sequential atrial activation within a single tachycardia cycle, illustrating a craniocaudal (proximal-to-distal) sequence along the HALO catheter (from HALO 1-2 to HALO 19-20). This activation pattern is consistent with a clockwise cavotricuspid isthmus-dependent atrial flutter. The tachycardia cycle length is stable at 264 ms (indicated by vertical lines). CS: coronary sinus; ECG: electrocardiogram.

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  Figure 3. Electroanatomical local activation time map. Electroanatomical local activation time map in the left anterior oblique projection using the CARTO® 3 electroanatomical mapping system (Biosense Webster, Irvine, CA, USA), demonstrating a dual-loop macroreentrant pattern. Yellow arrows indicate the two concurrent wavefronts: a typical CTI-dependent circuit and a superior right atrial loop encircling the superior vena cava. The "early-meets-late" zone is clearly visualized, confirming the macroreentrant nature of the arrhythmia.

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  Figure 4. Three-dimensional electroanatomical clockwise activation map. Activation map generated using the CARTO® 3 system (Biosense Webster). Yellow arrows indicate the clockwise activation front around the tricuspid annulus. A clear conduction bottleneck is visualized at the cavotricuspid isthmus (CTI). The transition from the late activation zone (purple) back to the early activation zone (red/orange) confirms the reentrant mechanism.

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  Figure 5. Intraprocedural prolongation of the tachycardia cycle length from 264 ms to 308 ms during radiofrequency ablation, as recorded by the LabSystem™ Pro (Boston Scientific), indicating modification of the superior loop component without arrhythmia termination. The purple arrow indicates the site of radiofrequency application at the ablation catheter (ABL D), leading to circuit modification. Black arrows illustrate the maintained atrial activation sequence along the coronary sinus catheter despite the cycle length increase.

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  Figure 6. Post-ablation cavotricuspid isthmus block verification. Electroanatomical activation map (RAO projection) generated using the CARTO® 3 system. The yellow "X" over the white arrow visually indicates complete, bidirectional block at the cavotricuspid isthmus, where the activation wavefront is stopped. The vertical yellow arrow highlights the continuous radiofrequency ablation line (red points) responsible for terminating the reentrant circuit. RAO: right anterior oblique.

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  Figure 7. Acute termination of atrial flutter to sinus rhythm during CTI ablation, confirmed by intracardiac recordings and surface ECG obtained with the LabSystem™ Pro (Boston Scientific). The long black arrow clearly indicates the precise moment of tachycardia cessation and the subsequent period of silence. The green arrows mark the restoration of organized sinus rhythm, confirmed by surface ECG and organized intracardiac signals in the CS and ablation (ABL) catheters. CS: coronary sinus; CTI: cavotricuspid isthmus; ECG: electrocardiogram.

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  Figure 8. Final ablation site at the CTI–IVC junction demonstrating abrupt termination of atrial flutter and confirmation of bidirectional CTI block by differential pacing maneuvers using the CARTO® 3 system. Diagonal yellow arrow pointing towards the precise CTI location where successful arrhythmia termination was achieved. Lower panels display real-time electrogram recordings; vertical blue arrows indicate the organized return of stable sinus rhythm, confirmed by simultaneous surface ECG and organized intracardiac signals. CTI: cavotricuspid isthmus; IVC: inferior vena cava; ECG: electrocardiogram.