title: Effects of calcium and sodium concentrations on atrioventricular conduction: experimental study in rabbit hearts with clinical implications on heart block and slow calcium channel blocking agent usage.
abstract: Effects of electrolyte concentrations on atrioventricular (AV) conduction were studied in isolated, perfused rabbit hearts by recording the His bundle electrogram. Initial calcium (Ca++), sodium (Na+), and potassium (K+) concentrations were 2.4, 144.8, and 4.5 mM, respectively. Lowering of Ca++ to 0.8 mM slightly prolonged the AH interval, whereas elevation of Ca++ to 4.8 or 7.2 mM more markedly prolonged this interval, often causing intranodal block. High Ca++-induced depression of intranodal conduction was antagonized by high K+ (7.5 mM). Verapamil (0.5 to 1.0 mg/L) produced second-degree intranodal block. High Na+ (172 mM) restored 1:1 conduction, whereas high Ca++ did not. These results suggest that: (1) an optimal Ca++ concentration for intranodal conduction exists; (2) high K+ counteracts high Ca++-induced intranodal block; (3) verapamil effect on AV node is antagonized by high Na+; and (4) slow Na+ current may play a role in AV nodal action potentials.
mesh_terms: D000818:Animals; D001283:Atrioventricular Node / Q000187:drug effects; D002118:Calcium / Q000008:administration & dosage* / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004562:Electrocardiography; D006329:Heart Conduction System / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects; D011188:Potassium / Q000008:administration & dosage; D011817:Rabbits; D012964:Sodium / Q000008:administration & dosage*; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D013779:Tetrodotoxin; D012964:Sodium; D014700:Verapamil; D011188:Potassium; D002118:Calcium