Model of reentrant ventricular tachycardia based on infarct border zone geometry predicts reentrant circuit features as determined by activation mapping

Abstract

Background: Infarct border zone (IBZ) geometry likely affects inducibility and characteristics of postinfarction reentrant ventricular tachycardia, but the connection has not been established.

Objective: The purpose of this study was to determine characteristics of postinfarction ventricular tachycardia in the IBZ.

Methods: A geometric model describing the relationship between IBZ geometry and wavefront propagation in reentrant circuits was developed. Based on the formulation, slow conduction and block were expected to coincide with areas where IBZ thickness (T) is minimal and the local spatial gradient in thickness (DeltaT) is maximal, so that the degree of wavefront curvature rho proportional, variant DeltaT/T is maximal. Regions of fastest conduction velocity were predicted to coincide with areas of minimum DeltaT. In seven arrhythmogenic postinfarction canine heart experiments, tachycardia was induced by programmed stimulation, and activation maps were constructed from multichannel recordings. IBZ thickness was measured in excised hearts from histologic analysis or magnetic resonance imaging. Reentrant circuit properties were predicted from IBZ geometry and compared with ventricular activation maps after tachycardia induction.

Results: Mean IBZ thickness was 231 +/- 140 microm at the reentry isthmus and 1440 +/- 770 microm in the outer pathway (P <0.001). Mean curvature rho was 1.63 +/- 0.45 mm(-1) at functional block line locations, 0.71 +/- 0.18 mm(-1) at isthmus entrance-exit points, and 0.33 +/- 0.13 mm(-1) in the outer reentrant circuit pathway. The mean conduction velocity about the circuit during reentrant tachycardia was 0.32 +/- 0.04 mm/ms at entrance-exit points, 0.42 +/- 0.13 mm/ms for the entire outer pathway, and 0.64 +/- 0.16 mm/ms at outer pathway regions with minimum DeltaT. Model sensitivity and specificity to detect isthmus location was 75.0% and 97.2%.

Conclusions: Reentrant circuit features as determined by activation mapping can be predicted on the basis of IBZ geometrical relationships.

1

Method to measure IBZ thickness. A–C: histology measurement. Adjacent wax sections were stained with Masson's trichrome stain to distinguish infarcted from surviving myocytes. D–F: MRI measurement. E: The ex-vivo MR scanning provides view of the heart slice from above (Base to Apex).

2

Characteristics of reentrant ventricular tachycardia. A. Diagram of the extrastimulation cycle leading to reentry. B. Schematic of the proposed relationship between IBZ thickness (Z-axis) and wavefront curvature when propagation within the reentrant circuit is in parallel to the plane of the epicardial surface (XY).

3

Mathematical relationships used to formulate the geometric model. A. Wavefront curvature as a circular arc. B. Geometrical configuration for calculating wavefront curvature due to IBZ thickness change. C. Method to determine the maximum thickness change (ΔT_max) in proximity to a particular computational node.

4

IBZ maps for a selected postinfarction canine experiment. A–B: activation during sinus rhythm and ventricular tachycardia. Thin lines separating colors denote isochrones. C. IBZ thickness T determined from histology slides. D. thickness gradient ΔT_max. E. ρ_max estimated from Eq. 9. Overlaid are the locations of estimated (gray-green) and actual (black) lines of block (also in Figure 5–Figure 7). F. the multielectrode grid.

5

IBZ maps for a postinfarction canine experiment in which sustained reentrant tachycardia was inducible by extrastimulation. A–B: activation during sinus rhythm and ventricular tachycardia. C–D. IBZ thickness T determined from MR images. E–F. thickness gradient ΔT_max. G–H. maximum degree of curvature ρ_max estimated from Eq. 9. Estimated block lines computed from panel G (gray), and actual block lines determined from the ventricular tachycardia activation map in panel B (black) are overlaid on the maps in panels C, E and G (also in Figure 6–Figure 7).

6

IBZ maps for postinfarction canine experiment in which only nonsustained reentrant tachycardia was inducible. Panels are same as in Figure 5.

7

IBZ maps for postinfarction canine experiment in which a reentrant circuit was not mappable although ventricular tachycardia was induced. Panels are same as in Figure 5. Note isochronal spacing is ~5ms in the sinus rhythm and ventricular tachycardia activation maps, Panels A-B.

8

Overlap of estimated isthmus location (from maps derived using Eq. 9) with actual isthmus location (from tachycardia activation map).