TABLE 1.

AUTOANTIBODIES AND BRADYARRHYTHMIAS

Arrhythmias	Autoantibodies	Associated Diseases	Mechanisms
Sinus Bradycardia	Anti-sinus node	Sick sinus syndrome
	Anti-Ro/SSA, Anti-La/SSB	Neonatal lupus syndrome	Cross-reaction with α1D and α1C subunits of T- and L-type Ca2+ channels ↓ ICa,L, ↓ICa,T
	Anti-M2 receptor	Dilated cardiomyopathy and Chagas” disease	Agonist-liked activity on M2 receptor ↓cAMP, ↑ IKACh, ↓ ICa,L
Conduction Abnormalities	Anti-β1 and anti-β2- adrenergic receptor	Idiopathic conduction disturbances (AV block and intraventricular conduction block) Dilated cardiomyopathy	Agonist-liked activity on β2-adrenergic receptor in conduction tissue ↑ Gi, ↑ GIRK, ↓ ICa,L
	Anti-M2 receptor	Chagas’ disease	Agonist-liked activity on M2 receptor ↓cAMP, ↑ IKACh, ↓ ICa,L
	Anti-Ro/SSA	Systemic lupus erythematosus	↓ICa,L, ↓ICa,T
Congenital Complete Heart Block	Anti-Ro/SSA	Neonatal lupus syndrome	Cross-reaction with α1C subunit of L-type Ca2+ channels → L-type Ca2+ channel internalization → [Ca2+]i dysregulation → cell death → inflammation → fibrosis ↓ ICa,L

I_Ca,L, L-type calcium currents; I_Ca,T, T-type calcium currents; I_KACh, acetylcholine-activated potassium currents; M2 receptor, muscarinic cholinergic type 2 receptor; Gi, inhibitory G protein; GIRK, G-protein activated inward rectifier K⁺ channel