Related Experiment Video
Updated: Jun 22, 2026
Real-Time Cardiac Mapping with a Noninvasive Imageless Electrocardiographic Imaging System
Published on: April 11, 2025
Assessment of clockwise cavotricuspid isthmus block based on conduction times during transient entrainment: a
Eduardo Castellanos1, Jesús Almendral, Alberto Puchol
1Department of Cardiology, Hospital Virgen de la Salud, Toledo, Spain. ecastellanos@secardiologia.es
Insights
Transient entrainment during atrial flutter ablation accurately identifies cavotricuspid isthmus block. Comparing conduction times during entrainment and sinus rhythm pacing confirms successful CTI block, aiding ablation procedures.
Area of Science:
- Electrophysiology
- Cardiac Arrhythmias
- Interventional Cardiology
Background:
- Typical counterclockwise atrial flutter (AFL) impulse propagation to the anteroinferior right atrium (AIRA) is expected to follow a specific path during transient entrainment (TE) from the coronary sinus (CS).
- This expected propagation pattern during TE in AFL is similar to that during sinus rhythm (SR) pacing from the same CS site if cavotricuspid isthmus (CTI) block is present.
- Identifying CTI block is crucial for successful ablation of typical AFL.
Purpose of the Study:
- To evaluate the utility of comparing conduction times during TE from the CS with pacing during SR to confirm CTI block in patients with typical AFL.
- To determine if TE can reliably indicate the presence or absence of CTI block during catheter ablation procedures.
Main Methods:
- Thirty-six patients with typical AFL underwent CTI ablation.
- Coronary sinus (CS) pacing was performed at a cycle length 20 ms shorter than the AFL cycle length before ablation.
- Pacing was also performed during sinus rhythm (SR) with and without CTI conduction, and conduction times were measured.
Main Results:
- Transient entrainment (TE) with orthodromic activation of the anteroinferior right atrium (AIRA) occurred in all patients.
- Conduction time from CS to AIRA during TE was significantly longer than during SR pacing, both with and without CTI conduction.
- A "TE index" derived from these conduction times demonstrated high sensitivity (97%) and specificity (91%) for identifying CTI block.
Conclusions:
- Comparing conduction times during TE from the CS and SR pacing from the same site is effective for establishing CTI block in typical AFL.
- This method provides a reliable way to confirm successful CTI ablation during electrophysiology procedures.
Background:
In typical counterclockwise atrial flutter (AFL), the route of impulse propagation to anteroinferior right atrium (AIRA) during transient entrainment (TE) from the coronary sinus (CS) is expected to be similar to that during pacing from the same CS site during sinus rhythm (SR) when cavotricuspid isthmus (CTI) block has occurred. This could be used to identify CTI block during ablation procedures.
Methods:
Thirty-six patients with AFL (cycle length [CL], 240 +/- 25 ms) underwent CTI ablation during AFL. CS pacing was performed at a CL of 20 ms less than AFL CL before ablation (n = 36), and at several CL during SR with conduction through the CTI (n = 21) and after CTI block (n = 36).
Results:
TE with orthodromic activation of AIRA occurred in all 36 patients. Conduction time from CS to AIRA during TE (T-entr, 199 +/- 29 ms) was significantly longer than during pacing in SR (T-CTI) at the same rate not only with CTI conduction (T-CTI-C, 135 +/- 24 ms, P < 0.001), but also with CTI block (T-CTI-B, 186 +/- 24 ms, P < 0.01). T-entr did not correlate with T-CTI-C, but there was an excellent correlation between T-entr and T-CTI-B (r = 0.874, P < 0.001). A "TE index" that corrected T-CTI for individual T-entr identified CTI block with 97% sensitivity and 91% specificity. T-CTI at low rates differed from T-CTI at high rates but correlated significantly with them.
Conclusion:
Comparison of conduction times during TE from the CS and during pacing from the same site and rate in SR can help to establish whether clockwise CTI block has been achieved in patients with typical AFL.
Related Concept Videos
01:18Dysrhythmias IV: Characteristics of Bradyarrhythmias
01:17Assessment of apical pulse
Assessing the apical pulse is a critical nursing procedure, particularly indicated for:
01:25Assessment of apical radial pulse
The A-R pulse assessment involves simultaneous evaluation of the apical and radial pulses. When the apical and radial pulse rates vary, this assessment helps identify a pulse deficit.
Pre-Procedural Preparation
01:30Acute Coronary Syndrome III: Diagnostic Studies