Disturbed repolarisation-relaxation coupling during acute ischaemia permits systolic mechano-arrhythmogenesis
Authors: Cameron Breanne A. , Baumeister Peter A. , Lawen Tarek , Rafferty Sara A. , Taeb Behzad , Stoyek Matthew R. , Greiner Joachim , Uzelac Ilija , Fenton Flavio H. , Peyronnet Rémi , Kohl Peter , Quinn T Alexander 
Published: January 2025

Background

The heart’s mechanical state feeds back to its electrical activity, potentially contributing to arrhythmias. ‘Mechano-arrhythmogenesis’ has been mechanistically explained during electrical diastole, when cardiomyocytes are at their resting membrane potential. During electrical systole, cardiomyocytes are refractory right from the onset of depolarisation, while during repolarisation they appear to be protected from mechano-arrhythmogenesis by near-simultaneous restoration of resting membrane potential and cytosolic calcium concentration ([Ca2+]i): repolarisation-relaxation coupling (RRC). Yet, systolic mechano-arrhythmogenesis has been reported in ischaemic myocardium, with unclear underlying mechanisms. We hypothesise that ischaemia-induced alteration of RRC gives rise to a vulnerable period for mechano-arrhythmogenesis.

Methods

Acute left-ventricular (LV) regional ischaemia was induced by coronary artery ligation in Langendorff-perfused rabbit hearts, with mechanical load controlled by an intraventricular balloon. Mechanical activity was assessed by echocardiography and arrhythmia incidence by electrocardiogram. Single LV cardiomyocytes were exposed to simulated ischaemia or pinacidil (ATP-sensitive potassium channel opener). Stretch was applied in diastole or late systole using carbon fibres. Stretch characteristics and arrhythmia incidence were assessed by sarcomere length measurement. In both models, RRC was assessed by simultaneous voltage-[Ca2+]ifluorescence imaging and mechano-arrhythmogenesis mechanisms were pharmacologically tested.

Results

In whole heart, acute regional ischaemia leads to systolic stretch and disturbed RRC at the ischaemic border. These electro-mechanical changes were associated with waves of arrhythmias, which were reduced by mechanical unloading, electro-mechanical uncoupling, or buffering of [Ca2+]i. In LV cardiomyocytes, physiological RRC is associated with a low incidence of systolic mechano-arrhythmogenesis, while a vulnerable period emerged by prolonged RRC during ischaemia. The increase in systolic mechano-arrhythmogenesis was reduced by restoring RRC, chelating [Ca2+]i, blocking mechano-sensitive transient receptor potential kinase ankyrin 1 channels (TRPA1), or buffering reactive oxygen species (ROS) levels.

Conclusion

Prolonged RRC allows for systolic mechano-arrhythmogenesis in acute ischaemia, involving contributions of elevated [Ca2+]i, TRPA1 activity, and ROS, which represent potential anti-arrhythmic targets.

GRAPHICAL ABSTRACT LEGEND

Role of disturbed repolarisation-relaxation coupling (RRC), transient receptor potential kinase ankyrin 1 (TRPA1) channels, cytosolic calcium concentration ([Ca2+]i), and reactive oxygen species (ROS) in ventricular systolic mechano-arrhythmogenesis.Schematic of the proposed mechanisms underlying the TRPA1- and Ca2+-mediated increase in systolic mechano-arrhythmogenesis with disturbed RRC. AITC, Allyl isothiocyanate (TRPA1 channel activator); AP, action potential; BAPTA ([Ca2+]ibuffer); CaT, Ca2+transient; DNT, dantrolene (ryanodine receptor stabiliser); DPI, diphenyleneiodonium (ROS production blocker); GLIB, glibenclamide (KATPchannel blocker); HC-300031 (TRPA1 channel blocker); KATP, ATP-sensitive potassium channel; NAC, N-acetyl-L-cysteine (ROS chelator); NCX, sodium-Ca2+exchanger; PIN, pinacidil (KATPchannel activator); ROS, reactive oxygen species; SI, simulated ischaemia; STP, streptomycin (non-specific mechano-sensitive ion channel blocker).