Aberrant sinus node firing during β‐adrenergic stimulation leads to cardiac arrhythmias in diabetic mice

Abstract

Aim: Cardiovascular complications, including cardiac arrhythmias, result in high morbidity and mortality in patients with type-2 diabetes mellitus (T2DM). Clinical and experimental data suggest electrophysiological impairment of the natural pacemaker of the diabetic heart. The present study examined sinoatrial node (SAN) arrhythmias in a mouse model of T2DM and physiologically probed their underlying cause. Methods: Electrocardiograms were obtained from conscious diabetic db/db and lean control db/+ mice. In vivo SAN function was probed through pharmacological autonomic modulation with isoprenaline, atropine and carbachol. Blood pressure stability and heart rate variability (HRV) were evaluated. Intrinsic SAN function was evaluated through ex vivo imaging of spontaneous Ca 2+ transients in isolated SAN preparations. Results: While lean control mice showed constant RR intervals during isoprenaline challenge, the diabetic mice experienced SAN arrhythmias with large RR fluctuations in a dose-dependent manner. These arrhythmias were completely abolished by atropine pre-treatment, while carbachol pretreatment significantly increased SAN arrhythmia frequency in the diabetic mice. Blood pressure and HRV were comparable in db/db and db/+ mice, suggesting that neither augmented baroreceptor feedback nor autonomic neuropathy is a likely arrhythmia mechanism. Cycle length response to isoprenaline was comparable in isolated SAN preparations from db/db and db/+ mice; however, Ca 2+ spark frequency was significantly increased in db/db mice compared to db/+ at baseline and after isoprenaline. Conclusion: Our results demonstrate a dysfunction of cardiac pacemaking in an animal model of T2DM upon challenge with a β-adrenergic agonist. Ex vivo, higher Ca 2+ spark frequency is present in diabetic mice, which may be directly linked to in vivo arrhythmias. K E Y W O R D Sautonomic nervous system, baroreflex, calcium, electrophysiology, isoprenaline, type-2 diabetes

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“…These and similar digits were seen before, but were forced to trust and believe that they might have place in nature and science. How it is logical that the RR interval in ECG is apart at 106 versus 113 ms (Lubberding et al, 2020), but the PR and QRS are identical at respective 33 ± 1 and 11 ± 0.2 ms at the same time and conditions for two different groups, control − db/+ and diabetic − db/db mice in table 1? Are these digits, 216 ± 44 versus 260 ± 39% really not apart and statistically insignificant for db/+ versus db/db mice and carbachol effects on RR?…”