Cardiac arrhythmogenesis in Experimental Autoimmune Myocarditis (EAM) model

Introduction: Myocarditis is an inflammatory heart disease linked to a high risk of arrhythmias and sudden cardiac death (SCD). However, the mechanisms underlying myocarditis-related arrhythmias are not fully understood, and specific therapies or risk prediction strategies are lacking. Identifying these mechanisms is crucial for developing novel therapies to prevent SCD.

Objective: To evaluate the incidence of arrhythmias and to investigate underlying proarrhythmic remodeling in the acute phase of a myocarditis using the EAM mouse model. 

Method: We used the Experimental Autoimmune Myocarditis (EAM) mouse model. In BALB/c mice (9-12 weeks old) α-myosin heavy chain peptide was injected together with Complete Freund’s adjuvant on day 0 and 7 to induce an autoimmune myocarditis at day 21. Control mice (sham) received an emulsion of CFA and PBS in a 1:1 ratio. Comprehensive in vivo phenotyping included serial echocardiography (on d0, d7, d14, d21), telemetry ECG recordings (from d0 to d21), and invasive EP studies (on d21). Immune cell infiltration and interstitial fibrosis were histologically quantified by analysing HE and Masson trichrome staining on hearts harvested on day 21.

Results: EAM mice showed an increased risk of atrial arrhythmias constituting of atrial tachycardia, atrial fibrillation episodes with episode duration >1000 ms (sham: 2% vs EAM: 3.49%, *p=0.01, Figure 1A) and ventricular arrhythmias comprising of couplets, triplets, NSVT (sham: 0.09% vs EAM: 0.73%, *p=0.02, Figure 1B). Heart rate (HR), PR interval, QRS duration, P wave duration was not altered (Figure 1C-F) but QTc interval was significantly prolonged (sham: 50.64 ms vs EAM: 62.21 ms, **p=0.008, Figure 1G) in EAM mice on day 21. Echocardiography did not show changes in LV diameter, wall thickness and EF (Figure 1H-J) but showed a significant LA dilatation in EAM mice (sham: 1.792 mm vs EAM: 2.321 mm, ****p<0.0001, Figure 1K) on day 21. EP studies did not show significant differences in sinus node recovery time (SNRT), AV conduction properties, or tissue refractoriness between groups (Figure 1L-P). Histological evaluation showed a significant increase in immune cell infiltration as evident from the EAM score across atria and ventricles (Left atrium(LA), sham: 0.538 vs EAM: 1.250, *p=0.0370; Right atrium (RA), sham: 0.545 vs EAM: 1.350, *p=0.039; Left ventricle (LV), sham: 0.250 vs EAM: 1.840, ****p<0.0001; Right ventricle(RV), sham: 0.647 vs EAM: 2.176, ***p=0.0001, Figure 1Q). Increased fibrosis was found in both left and right atrium as well as in left ventricle (LA, sham: 0.91% vs EAM: 1.90%, *p=0.014;  RA, sham: 2.47% vs EAM: 4.54%, *p=0.04; LV, sham: 0.55% vs EAM: 1.476%, *p=0.028; RV, sham: 1.44% vs EAM: 2.34%, p=0.1049, Figure 1R). 

Conclusion: Our study showed a higher susceptibility of arrhythmogenesis paralleled by a significant structural remodeling as observed by LA dilatation and increased fibrosis in mice with acute autoimmune myocarditis. Future studies are warranted to further elucidate the underlying pathophysiologic mechanisms to allow development of novel strategies for treatment, risk assessment, or prevention in patients with myocarditis.