Key result
In silico LQT2 models show ~14-fold more stress-induced arrhythmic events versus LQT1.
Why the study?
The penetrance of LQT1 and LQT2 mutations is highly variable, and how physiological variability in other cardiac ionic currents influences the arrhythmic phenotype was unclear.
Does simulated blockade of L-type Ca²⁺ channels reduce action potential duration and arrhythmic events in in silico models of LQT1 and LQT2?
Does simulated blockade of L-type Ca²⁺ channels reduce action potential duration and arrhythmic events in in silico models of LQT1 and LQT2?
Absolute Event Rate: 7.6% vs 0.55%
In silico modeling suggests that natural variability in ionic currents influences LQTS penetrance and supports calcium channel blockers as a potential therapy for patients unresponsive to beta-blockers.
Should not yet alter LQT genotype-guided surveillance; leaves open how other ionic current variability modulates penetrance and phenotype.
Congenital Long QT Syndrome types 1 and 2 (LQT1 and LQT2) are caused bymutations in the KCNQ1 and KCNH2 genes, responsible for the IKs and IKr currents, respectively. However, the penetrance of these mutations is highly variable, since some carriers remain asymptomatic, while others exhibit severe clinical manifestations. To elucidate how physiological variability in other cardiac ionic currents may influence the arrhythmic phenotype, human ventricular action potentials were simulated in silico using the O'Hara-Rudy dynamic model implemented in the Virtual Assay software. Conductances of nine key ionic currents were randomly modified within physiologically plausible ranges and the resulting population of models was validated under stress conditions. LQT1 and LQT2 cohorts were generated by reducing IKs by 80% and IKr by 60%, respectively. These cohorts were stratified into four risk categories based on action potential duration (APD) under different conditions and the occurrence of arrhythmic events. LQT1 models demonstrated impaired adaptation to adrenergic stimulation, whereas LQT2 models showed marked APD prolongation at rest. Risk stratification revealed a higher incidence of arrhythmic events in LQT2 (7.6%) compared to LQT1 (0.55%). Regression analyses identified IKr and IK1 as protective currents, while INaL and ICaL were major contributors to APD prolongation in both types. Simulated blockade of L-type Ca²⁺ channels effectively shortened APD and reduced the proportion of high-risk models. The natural variability in ionic current profiles contributes to the phenotypic expression of LQTS and support the potential use of calcium channel blockers as therapeutic alternatives in patients unresponsive to β-blockers.
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Casis et al. (2026) studied Congenital Long QT Syndromes (LQTS) types 1 and 2 (n=3,052). Simulated LQT2 (60% reduction in IKr) vs. Simulated LQT1 (80% reduction in IKs) was evaluated on Incidence of arrhythmic events under cardiac stress. In silico modeling of long QT syndromes demonstrated a higher incidence of arrhythmic events in LQT2 models (7.6%) compared to LQT1 models (0.55%) under cardiac stress conditions.
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