Local Conduction Velocity in the Presence of Late Gadolinium Enhancement and Myocardial Wall Thinning: A Cardiac Magnetic Resonance Study in a Swine Model of Healed Left Ventricular Infarction

Abstract

Background: Conduction velocity (CV) is an important property that contributes to the arrhythmogenicity of the tissue substrate. The aim of this study was to investigate the association between local CV versus late gadolinium enhancement (LGE) and myocardial wall thickness in a swine model of healed left ventricular infarction.

Methods: Six swine with healed myocardial infarction underwent cardiovascular magnetic resonance imaging and electroanatomic mapping. Two healthy controls (one treated with amiodarone and one unmedicated) underwent electroanatomic mapping with identical protocols to establish the baseline CV. CV was estimated using a triangulation technique. LGE+ regions were defined as signal intensity >2 SD than the mean of remote regions, wall thinning+ as those with wall thickness <2 SD than the mean of remote regions. LGE heterogeneity was defined as SD of LGE in the local neighborhood of 5 mm and wall thickness gradient as SD within 5 mm. Cardiovascular magnetic resonance and electroanatomic mapping data were registered, and hierarchical modeling was performed to estimate the mean difference of CV (LGE+/-, wall thinning+/-), or the change of the mean of CV per unit change (LGE heterogeneity, wall thickness gradient).

Results: Significantly slower CV was observed in LGE+ (0.33±0.25 versus 0.54±0.36 m/s; P<0.001) and wall thinning+ regions (0.38±0.28 versus 0.55±0.37 m/s; P<0.001). Areas with greater LGE heterogeneity ( P<0.001) and wall thickness gradient ( P<0.001) exhibited slower CV.

Conclusions: Slower CV is observed in the presence of LGE, myocardial wall thinning, high LGE heterogeneity, and a high wall thickness gradient. Cardiovascular magnetic resonance may offer a valuable imaging surrogate for estimating CV, which may support noninvasive identification of the arrhythmogenic substrate.

Keywords: conduction velocity; electroanatomic mapping; late gadolinium enhancement; magnetic resonance imaging; myocardial infarction; myocardial wall thickness; ventricular tachycardia.

Figure 1.

Study flowchart. Animal model of healed myocardial infarction (MI) was created by mid left anterior descending (LAD) coronary artery ischemia-reperfusion. After 9 weeks of surviving periods, in-vivo cardiovascular magnetic resonance (CMR) was performed. After 0–5 days of recovery, an electrophysiology (EP) study was performed and electroanatomic maps were acquired while pacing from the RV apex (RVA) at cycle length of 400 ms. CMR and EP data were processed to extract CMR features including late gadolinium enhancement (LGE) and left ventricular wall thickness. Conduction velocity (CV) was estimated using triangulation technique. CMR and CV data were spatially registered to study their associations.

Figure 2.

Analysis pipeline for investigating association between CMR features and conduction velocity (CV). (A) CV was estimated based on the local activation time (LAT) map using triangulation technique. (B) Endo-/epicardial contours were delineated to perform CMR feature projection on left ventricular endocardial surface model. (C) CV and CMR data were then spatially registered using fiducial registration based on right coronary artery (RCA), left main stem (LMS), and apex. CV and CMR data were then 2D projected on the semi-hemisphere map to minimize the surface area distortion using a Hammer mapping.

Figure 3.

Conduction velocity (CV) and CMR features from 2 animals. CV was estimated based on the local activation time (LAT). CV and CMR data were registered in the same spatial coordinates. Slower CV was observed in the region of hyperenhancement on LGE and wall thinning. The pattern of CV was inhomogeneous throughout the scar with maximal slowing in the region of dense scar with higher LGE heterogeneity or wall thickness gradient.

Figure 4.

Scatter plots of LGE, wall thickness, LGE heterogeneity, and wall thickness gradient vs. conduction velocity (CV) of all 6 animals. Smoothing splines of each animal are overlaid on the scatter plots.

Figure 5.

Conduction velocity (CV) in the presence and absence of LGE averages over all animals (A) and for each individual animal (B). Slower CV was observed in the areas of hyperenhancement on LGE (LGE+).

Figure 6.

Conduction velocity (CV) in the presence and absence of wall thinning averages over all animals (A) and for each individual animal (B). Significantly slower CV was observed in areas of wall thinning+ compared to regions of wall thinning-.