Relationship between sinus rhythm late activation zones and critical sites for scar-related ventricular tachycardia: systematic analysis of isochronal late activation mapping

Abstract

Background: It is not known whether the most delayed late potentials are functionally most specific for scar-related ventricular tachycardia (VT) circuits.

Methods and results: Isochronal late activation maps were constructed to display ventricular activation during sinus rhythm over 8 isochrones. Analysis was performed at successful VT termination sites and prospectively tested. Thirty-three patients with 47 scar-related VTs where a critical site was demonstrated by termination of VT during ablation were retrospectively analyzed. In those who underwent mapping of multiple surfaces, 90% of critical sites were on the surface that contained the latest late potential. However, only 11% of critical sites were localized to the latest isochrone (87.5%-100%) of ventricular activation. The median percentage of latest activation at critical sites was 78% at a distance from the latest isochrone of 18 mm. Sites critical to reentry were harbored in regions with slow conduction velocity, where 3 isochrones were present within a 1-cm radius. Ten consecutive patients underwent ablation prospectively guided by isochronal late activation maps, targeting concentric isochrones outside of the latest isochrone. Elimination of the targeted VT was achieved in 90%. Termination of VT was achieved in 6 patients at a mean ventricular activation percentage of 78%, with only 1 requiring ablation in the latest isochrone.

Conclusions: Late potentials identified in the latest isochrone of activation during sinus rhythm are infrequently correlated with successful ablation sites for VT. The targeting of slow conduction regions propagating into the latest zone of activation may be a novel and promising strategy for substrate modification.

Keywords: ablation techniques; tachycardia; ventricular.

Conflict of interest statement

Conflict of Interest Disclosures: None

© 2015 American Heart Association, Inc.

Figures

Figure 1

Manual annotation of electrograms during sinus rhythm to the offset of the local electrogram for ILAM construction. In electrograms with continuous and fractionated activity, determination of the onset or maximum slope is subject to more interpretation than return to baseline.

Figure 2

Patient with inferior myocardial infarction with extensive right ventricular involvement with biventricular dense scar. The ILAM demonstrates that the latest isochrone of combined activation is in the basal inferior region in the right ventricle. Two VTs with left bundle branch morphology were terminated in the second latest isochrone of sinus rhythm activation (VAP of 75% and 79%) in the right ventricle.

Figure 3

Distribution of sites critical to reentry by ventricular activation percentage in ILAM. The latest isochrone of activation was least frequently associated with a successful ablation site.

Figure 4

ILAM and voltage map in a patient with NICM and ejection fraction of 15% with VT storm. A patchy lateral wall scar is seen in the left ventricle and the termination sites for the two induced VTs were localized to the second and third latest isochrone (VAP 72% and 86%).

Figure 5

ILAM and voltage map in a patient with NICM and ejection fraction of 30% with VT storm that demonstrates for extensive scarring on the epicardium compared to the endocardium. The latest zone of activation is seen in the endocardium and the critical site is located in the thinnest portion of second latest isochrone where 3 isochrones are seen within a 1 cm radius.

Figure 6

Potential factors that may influence ventricular activation percentage of critical sites include A) intrinsic vs paced complex B) diastolic activation time during VT C) anatomic location in septal to lateral dimension D) anatomic location in apical to basal dimension. Sites in the mid-isthmus had a later VAP compared to sites in the distal isthmus closer to the exit. The anatomic location of the critical site did not significantly influence the VAP.

Figure 7

Prospective case of inferoseptal patchy infarct with rapid, untolerated VT localized by pacemapping with induction outside of the latest isochrone of activation. Termination of VT was achieved at this exact site, which was not in the latest region of activation in both sinus rhythm and a lateral pacing wavefront. Ablation lesions are shown around the termination site and circumferentially outside the latest isochrone of activation.

Figure 8

Prospective case of extensive dense scar from inferior infarction. ILAM demonstrates centripetal activation into the latest region of activation (purple isochrones). The latest LP was a bystander with 2:1 passive activation during VT 1 with long stimulus-QRS interval during sinus rhythm and VT2 was successfully entrained and terminated outside the latest isochrone (green dot).