Introduction. During cardiac ischaemia-reperfusion, high levels of succinate accumulation and metabolism promote reactive oxygen species mediated cell death and dysfunction [1]. There is also a high risk of both atrial and ventricular arrhythmias following exposure to ischaemia/reperfusion. However, the impact of succinate on cardiac electrical function remains largely uncharacterised and it is unclear if elevated succinate metabolism may have a role in promoting cardiac arrhythmia.
Aims/Objectives. This study analysed the effects of succinate on murine ECGs to identify potential proarrhythmic electrical changes in the atria and ventricles.
Methods. ECGs were recorded from male and female adult FVB mice (n=15) under alfaxalone anaesthesia (Alfaxan®; Vetoquinol UK Ltd), at 20-25 mg kg-1 h-1, i.v., with 0.02 ml boluses as necessary. The left jugular vein was cannulated to allow for infusion of diethyl succinate (DESucc) a cell permeable form of succinate [2]. ECG recordings were measured at baseline (Pre-infusion), throughout 15-20 minutes infusion of Vehicle (n=3) or low dose DESucc (8 mg kg-1 min-1 (n=3)) or high dose DESucc (80 mg kg-1 min-1 (n=9)), and again 10 minutes post-infusion. Analysis was performed in ECG and HRV modules in LabChart v8 (AD Instruments, Oxford, UK). Signal averaged ECGs were used for waveform analysis. The arrhythmia index (number of premature or delayed R-waves per minute) was recorded across the whole experiment. Following the experiment, animals were killed by a schedule 1 method. Values are expressed as mean±SEM. Statistical analysis was performed using a one-way repeated measures Analysis of Variance with Bonferroni post hoc analysis (Prism9, GraphPad, Cal, USA). Significance was taken as P<0.05.
Results. High dose DESucc infusion did not significantly modify heart rate (Pre-infusion: 476±9; high DESucc: 494±25; Post-infusion: 517±41 beats per minute, n=9). However, high dose DEsucc infusion produced an elevation in irregularly spaced R-R intervals and delayed beats as evidenced by an increase in arrhythmia index (Pre-infusion: 0.8±0.3; high DESucc: 4.1±0.9; Post-infusion: 1.9±0.8 abnormal beats per minute, n=9, P<0.05). Similarly, high dose DESucc infusion increased the standard deviation of the R-R interval (SDRR) (Pre-infusion: 5.7±0.5; high DESucc: 20±3; Post-infusion: 7±3 ms, n=9, P<0.05). Analysis of ECG waveforms showed that high dose DESucc significantly prolonged the P-R interval, the QRS duration and the Q-T interval. However, the most striking effect was to cause irreversible prolongation the P-wave duration (Pre-infusion: 9±0.4; high DESucc: 13±1; Post-infusion: 13±1 ms, n=9, P<0.05). Arrhythmia index, SDRR, P-wave duration, P-R interval, QRS duration and Q-T interval were not significantly modified by Vehicle (n=3) or low dose DESucc (n=3) infusion.
Conclusion. High dose DESucc infusion causes acute cardiac arrhythmia and changes in ECG waveforms which are consistent with major conduction disturbances in both the atria and ventricles. More work is required to determine if these actions are dependent on direct modifications in ion channel function, such as Nav1.5, which may be preventable by targeted treatment.