title: Spatially discordant alternans in cardiomyocyte monolayers.
abstract: Repolarization alternans is a harbinger of sudden cardiac death, particularly when it becomes spatially discordant. Alternans, a beat-to-beat alternation in the action potential duration (APD) and intracellular Ca (Cai), can arise from either tissue heterogeneities or dynamic factors. Distinguishing between these mechanisms in normal cardiac tissue is difficult because of inherent complex three-dimensional tissue heterogeneities. To evaluate repolarization alternans in a simpler two-dimensional cardiac substrate, we optically recorded voltage and/or Cai in monolayers of cultured neonatal rat ventricular myocytes during rapid pacing, before and after exposure to BAY K 8644 to enhance dynamic factors promoting alternans. Under control conditions (n = 37), rapid pacing caused detectable APD alternans in 81% of monolayers, and Cai transient alternans in all monolayers, becoming spatially discordant in 62%. After BAY K 8644 (n = 28), conduction velocity restitution became more prominent, and APD and Cai alternans developed and became spatially discordant in all monolayers, with an increased number of nodal lines separating out-of-phase alternating regions. Nodal lines moved closer to the pacing site with faster pacing rates and changed orientation when the pacing site was moved, as predicted for the dynamically generated, but not heterogeneity-based, alternans. Spatial APD gradients during spatially discordant alternans were sufficiently steep to induce conduction block and reentry. These findings indicate that spatially discordant alternans severe enough to initiate reentry can be readily induced by pacing in two-dimensional cardiac tissue and behaves according to predictions for a predominantly dynamically generated mechanism.
authors.affiliation: Cardiovascular Research Laboratory, Department of Medicine, Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
authors.forename: Carlos
authors.initials: C
authors.lastname: de Diego
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Pai
authors.forename: Amish S
authors.initials: AS
authors.lastname: Dave
authors.forename: Adam
authors.initials: A
authors.lastname: Lynch
authors.forename: Mya
authors.initials: M
authors.lastname: Thu
authors.forename: Fuhua
authors.initials: F
authors.lastname: Chen
authors.forename: Lai-Hua
authors.initials: LH
authors.lastname: Xie
authors.forename: James N
authors.initials: JN
authors.lastname: Weiss
authors.forename: Miguel
authors.initials: M
authors.lastname: Valderrábano
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D004594:Electrophysiology; D006329:Heart Conduction System / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology
chemical_list: D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002118:Calcium