case_images: PMC11338790_01
case_images: (A) Case 1: the isochronal endocardial propagation map demonstrates the epicardial-endocardial breakthrough during fixed pacing from the proximal dipole of CS. The blue arrows indicate the wavefront traveling from the CS towards the CTI ablation line. Subsequently, the first local activation on the other side of the isthmic ablation line is observed 1,3 cm away from it, displaying a focal-type activation (indicated by white arrows in the green zone). Activation proceeds from the site of pseudo-focal activity both laterally and towards the line of the isthmic block (the activation towards the line of the isthmic block is shown also by the recorded EGMs as indicated by the white arrow); (B) case 2: in the left picture, the local activation map of right atrium illustrates the CTI block following RF application at the epicardial-endocardial breakthrough; the two wavefronts collide at the CTI level with a time delay of at least 100 ms between the first and second component of the double potential recorded on the isthmus line, as depicted in the EGM on the right. CS, coronary sinus; CTI, cavo-tricuspid isthmus; EGM, intracardiac electrograms; RF, radiofrequency.
case_images: fcvm-11-1420916-g001.jpg
case_images: PMC11338790_02_fcvm-11-1420916-g001.jpg
case_images: F1
case_images: This resulted in a further delay between the first and the second atria straddling the line (i.e., Figure 1B).
case_images: PMC11338790_02
case_images: (A) Case 1: the isochronal endocardial propagation map demonstrates the epicardial-endocardial breakthrough during fixed pacing from the proximal dipole of CS. The blue arrows indicate the wavefront traveling from the CS towards the CTI ablation line. Subsequently, the first local activation on the other side of the isthmic ablation line is observed 1,3 cm away from it, displaying a focal-type activation (indicated by white arrows in the green zone). Activation proceeds from the site of pseudo-focal activity both laterally and towards the line of the isthmic block (the activation towards the line of the isthmic block is shown also by the recorded EGMs as indicated by the white arrow); (B) case 2: in the left picture, the local activation map of right atrium illustrates the CTI block following RF application at the epicardial-endocardial breakthrough; the two wavefronts collide at the CTI level with a time delay of at least 100 ms between the first and second component of the double potential recorded on the isthmus line, as depicted in the EGM on the right. CS, coronary sinus; CTI, cavo-tricuspid isthmus; EGM, intracardiac electrograms; RF, radiofrequency.
case_images: fcvm-11-1420916-g001.jpg
case_images: PMC11338790_02_fcvm-11-1420916-g001.jpg
case_images: F1
case_images: This resulted in a further delay between the first and the second atria straddling the line (i.e., Figure 1B).
case_images: PMC11338790_03
case_images: Case 3. (A): The local endocardial activation map during typical atrial flutter after performing an ablation line at the CTI level reveals a counterclockwise loop around the TV, with more than 90% of the cycle length occurring within the RA. The propagation map indicates early activation along the CTI at the red spot, located on the septal side of the isthmus, near the TV but far away from the ablation line. Consequently, the typical atrial flutter appears to be sustained by an epi-endocardial breakthrough that can bypass the lesion line; (B) in the left picture is shown the application of RF at the supposed endocardial breakthrough resulting in the interruption of the atrial flutter. CTI, cavo-tricuspid isthmus; EGM, intracardiac electrograms; RA, right atrium; SR, sinus rhythm; TV, tricuspid valve.
case_images: fcvm-11-1420916-g002.jpg
case_images: PMC11338790_03_fcvm-11-1420916-g002.jpg
case_images: F2
case_images: However, we noted that, after the wavefront reached the lateral side of the CTI, a focal activation appeared from the septal side beyond the ablation line (Figure 2A). The flutter stopped after a few seconds of a single-shot RF application (Figure 2B), restoring SR.
case_images: PMC11338790_04
case_images: Case 4. Top: isochronal activation map during pacing from the CS shows an apparently focal activation pattern, on the left side of the lesion line, approximately 1,4 cm away from the isthmus. The EGM obtained from the distal dipole of the ablation catheter exhibits early atrial activation with a clear rS pattern preceded by a far-field electrogram (epicardial activation?) both on the bipolar and the unipolar recordings in the middle of the red zone. Bottom: RF delivery at this location increases the stimulus-atrium interval during RF leading finally at the achievement of complete CTI block.
case_images: fcvm-11-1420916-g003.jpg
case_images: PMC11338790_04_fcvm-11-1420916-g003.jpg
case_images: F3
case_images: However, careful observation of the activation map highlighted the presence of an early "focal" potential beyond the line, 1 cm away on the lateral side of the isthmus (Figure 3, top). During RF ablation, we observed that the isthmus block occurred about 20 s after the start of RF (Figure 3 bottom), indicating a deep conducting channel with a possible multiple endocardial breakthrough.