Interplay of electrical and mechanical properties in transgenic rabbit models of long-QT and short-QT syndrome
Authors: Alerni N , Nimani S , Hornyik T , Barbieri M , Louradour J , Giammarino L , Matas L , Perez-Feliz S , Zehender M , Brunner M , Odening K 
Published: May 2024

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): SNF

Introduction
Long-QT syndrome (LQTS) and short-QT syndrome (SQTS) are cardiac disorders primarily affecting electrical function but secondarily also impacting on mechanical features through electro-mechanical coupling (EMC). This study delves into in vivo and cellular electro-mechanical function and explores the impact of acute mechanical changes on the electrical phenotype, termed mechano-electrical coupling (MEC), in transgenic rabbit models.

Aim
This study aims to investigate the interrelationship between electrical and mechanical properties in LQTS and SQTS rabbit models, examining how acute mechanical alterations influence the electrical phenotype and exploring cellular electro-mechanical characteristics.

Methods
We examined 12-lead ECGs in LQT2, wildtype (WT), and SQT1 adult rabbits under various preload and afterload conditions. Additionally, patch-clamp and ionoptix experiments on isolated ventricular cardiomyocytes were conducted to investigate cellular electrical and mechanical characteristics.

Results
Baseline heart-rate corrected QTc intervals were prolonged in LQT2 (p&lt;0.0001) and shortened in SQT1 (p=0.012) compared to WT. QT-dispersion was solely increased in LQT2 (p&lt;0.05).
Acute increase in preload and in afterload prolonged QTc intervals in all groups, while reduced preload shortened QTc intervals. MEC (mechano-induced ΔQTc) varied among genotypes; in LQT2, QTc changes were more significant than in WT (p&lt;0.0001 with increased preload, p&lt;0.001 with decreased preload, and p&lt;0.05 with increased afterload). SQT1 showed a trend towards less pronounced changes compared to WT only after increased preload (p=0.11).
At the cellular level, action potential duration was longer in LQT2 (p&lt;0.001) and shorter in SQT1 (p&lt;0.0001) compared to WT. While cardiomyocytes from WT and SQT1 showed similar Ca2+ transient durations at 1Hz, 0.5Hz, and 0.25Hz, in LQT2 cardiomyocytes Ca2+ transients were significantly prolonged at 0.5 (p&lt;0.001) and 0.25Hz (p&lt;0.05) in line with the pronounced APD prolongation. Additionally, LQT2 exhibited significantly more pro-arrhythmic Ca2+ oscillations, which may contribute to arrhythmia formation in LQT2s. Moreover, LQT2 exhibited a slower calcium transient upstroke velocity and a reduced cellular contraction velocity and peak sarcomere shortening at all frequencies, demonstrating a mechanical impairment compared to WT and SQTS cardiomyocytes.

Conclusions
Acute mechanical alterations induce electrical changes through MEC in LQT2, WT, SQT1 rabbits. The magnitude of these changes correlates with baseline QTc, exhibiting the most prominent effects in LQT2. Consistent findings between cellular electro-mechanical assessments and in vivo measurements underscore the significance of cardiomyocytes in unravelling the mechanisms behind EMC and MEC. This intricate interplay between electro-mechanical properties in cardiac disorders, highlighting the necessity of considering both aspects when investigating arrhythmia mechanisms.