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Published on: July 29, 2011
Asymmetric wall-stress heterogeneity defines a stretch-activated arrhythmogenic substrate beyond ejection fraction in
1Independent Researcher, Los Angeles, CA, United States.
Insights
Dilated cardiomyopathy (DCM) patients face unpredictable sudden cardiac death. Asymmetric heart wall thinning, not ejection fraction (EF), creates an arrhythmogenic substrate via stretch-activated channels, offering a new risk predictor.
Area of Science:
- Cardiovascular Physiology
- Computational Biology
- Medical Imaging
Background:
- Dilated cardiomyopathy (DCM) poses unpredictable risks of sudden cardiac death from ventricular arrhythmias.
- Ejection fraction (EF) is an inadequate predictor of arrhythmia risk in DCM due to its insensitivity to regional wall thinning patterns.
Purpose of the Study:
- To investigate the hypothesis that asymmetric myocardial remodeling in DCM, specifically differential wall thinning, generates heterogeneous diastolic wall stress and stretch.
- To determine if this heterogeneity, via stretch-activated channel (SAC) activation, creates an arrhythmogenic substrate not captured by EF.
Main Methods:
- Development of a three-component in silico model integrating left ventricular geometry, regional wall stress, and a human ventricular action potential model with SACs.
- Simulation of DCM across varying severity and asymmetry levels to compute EF and assess electrophysiological changes.
Main Results:
- Ejection fraction (EF) was solely dependent on DCM severity, unaffected by asymmetric remodeling.
- Asymmetric remodeling, unlike uniform dilation, induced significant end-diastolic stretch gradients, leading to regional resting-potential and action potential duration (APD) dispersion.
- A linear correlation was observed between the arrhythmogenic substrate and the septal/lateral wall-stress gradient, which is related to echocardiogram-derived wall-thickness ratios.
Conclusions:
- Asymmetric wall thinning in DCM, not EF, is a key driver of arrhythmogenic substrate formation through mechanical stretch and SACs.
- An echocardiogram-derived wall-thickness ratio may serve as a novel, falsifiable predictor of ventricular arrhythmia risk in DCM, independent of EF.
- This study provides a quantifiable mechanism and prediction for clinical validation of a new arrhythmic substrate index.
Abstract:
In dilated cardiomyopathy (DCM), sudden cardiac death from ventricular arrhythmia occurs unpredictably among patients with similar ejection fraction (EF), and EF performs poorly as an individual risk predictor. EF is a cavity-volume ratio and is, by construction, blind to the spatial distribution of wall thinning. I hypothesized that the pattern of remodeling, specifically asymmetric septal versus lateral wall thinning, produces spatially heterogeneous diastolic wall stress and stretch, which through stretch-activated channel (SAC) activation creates an arrhythmogenic substrate that EF cannot encode. I developed a three-component in silico model coupling a parametric prolate-ellipsoid left ventricular geometry, regional biaxial (Laplace) wall stress, and the O'Hara-Rudy 2011 human ventricular action potential model with an ohmic SAC current engaged during diastole. Across five severity by five asymmetry levels, ejection fraction was computed and depended on severity alone, not on asymmetry. At matched EF, asymmetric remodeling produced a regional gradient of end-diastolic stretch that uniform dilation did not: at severe asymmetric DCM the thinned septum was depolarized by 2.25 mV relative to baseline, with 1.32 mV of regional resting-potential dispersion and 2.19 ms of action potential duration (APD) dispersion, against essentially none for uniform dilation at the same EF. The substrate rose approximately linearly with the septal/lateral wall-stress gradient, which equals the lateral-to-septal wall-thickness ratio measurable on a standard echocardiogram (slope 1.81 mV per unit gradient), and saturated at the sarcomere stretch ceiling. This in silico study quantifies a known mechanism and converts it into a specific, falsifiable prediction: an echo-derived wall-thickness ratio indexes an arrhythmic substrate orthogonal to EF, motivating retrospective and prospective clinical validation.
