Background – Obesity is one of the most relevant and lately most increasing risk factors for cardiovascular disease in western societies. Independent of coronary heart disease, obesity promotes a multimodal arrhythmic substrate and increases the susceptibility to ventricular arrhythmias (VA) eventually leading to sudden cardiac death. Aim of the present study was to develop an ex-vivo mouse model for obesity‑induced arrhythmogenesis and to characterize left ventricular (LV) myocardial disruption of calcium homeostasis.

Methods – All experiments were performed ex vivo in retrogradely perfused hearts from 32 – 36 week-old C57Bl/6J mice (n=14). Five mice received a normal chow diet (NCD), 9 mice were fed a sustained high-fat diet (HFD) over a 6-month period to generate diet‑induced-obesity (DIO). We combined an endocardial catheter‑based technique to assess VA susceptibility with an epicardial dual fluorescence imaging approach employing a potentiometric (Rh237) and a calcium sensitive (Rhod2) dye to assess action potential and calcium cycling characteristics of the LV anterior wall. Optical mapping data was analysed using a MATLAB‑based algorithm. VA susceptibility was quantified by an established scoring system.

Results – Mice receiving a sustained high-fat diet were significantly heavier than control (NCD: 34.8±2.1g, DIO: 53.3±3.2g, P<0.0001). The number of induced VAs, VA susceptibility as well as the inducibility of ventricular tachycardias (VT) were increased in DIO mice compared to control (number of induced VAs: NCD: 1.4±0.7, DIO: 6.3±0.8, P=0.005; VA susceptibility: NCD: 1.4±0.7, DIO:  18.1±2.3, P=0.001; VT inducibility: NCD: 0.0 %, DIO: 88.9 %, P=0.001, Figure 1A). Epicardial optical mapping of the anterior LV wall showed a prolonged action potential duration (APD) and prolonged calcium transient duration (CaTD) in DIO mouse hearts (APD₉₀ at CL 100 ms: NCD: 45.1±1.5 ms, DIO: 50.8±1.8 ms, P=0.03, Figure 1B; CaTD₉₀ at 100 ms pacing cycle length (PCL): NCD: 61.0±2.3 ms, DIO: 66.6±0.6 ms, P=0.02, Figure 1C). Additionally, CaT alternans (ALT) threshold defined as amplitude alternans > 10 % of two consecutive beats was decreased (PCL ALT threshold: NCD: 60.0±1.6 ms, DIO: 67.8±1.2 ms, P=0.006), with mean ALT being increased in DIO hearts (mean ATL at 60 ms PCL: NCD: 15.4±2.4 %, DIO: 25.7±3.0 %, P=0.04, Figure 1C).

Conclusions – Our findings show that sustained high-fat diet in mice increases ventricular susceptibility to VA, mimicking the situation in humans. It leads to disruption of LV myocardial calcium homeostasis as demonstrated by a decreased ALT threshold and increased mean ALT. Our data suggest that LV calcium mishandling may be a driver for arrhythmogenesis in DIO and modulation may present a perspective therapeutical approach. Further experiments will address molecular mechanisms and identify potential targets of modulation. 

Figure 1: (A) Inducibility of ventricular arrhythmias (VA) was elevated in hearts diet-induced-obesity (DIO) mice compared to normal-chow-diet (NCD) hearts. (B) Left ventricular action potential duration (APD₉₀) were prolonged in DIO hearts. (C) Calcium homeostasis in DIO hearts was disturbed with prolonged calcium transient duration (CaTD₉₀) and decreased ALT threshold pacing cycle length (PCL) in DIO hearts. NCD: n=5, DIO: n=9, *P<0.05, **P<0.01.