title: Antiarrhythmic efficacy of combined I(Ks) and beta-adrenergic receptor blockade.
abstract: Suppression of malignant ventricular arrhythmias by selective blockade of the cardiac slowly activating delayed rectifier current (I(Ks)) has been demonstrated with the benzodiazepine L-768673 [(R)-2-(2,4-trifluoromethyl-phenyl)-N-[2-oxo-5-phenyl-1-(2,2,2-trifluoro-ethyl)-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl]acetamide] in canine models of recent and healed myocardial infarction. The present study extends the initial antiarrhythmic assessment of I(Ks) blockade by demonstrating prevention of ischemic malignant arrhythmias in dogs with recent (8.0 +/- 0.4 days) anterior myocardial infarction with the coadministration of a subeffective dose of L-768673 and a subeffective, minimally beta-adrenergic blocking dose of timolol. Administered individually, neither 0.3 microg/kg i.v. L-768673 nor 1.0 microg/kg i.v. timolol prevented the induction of ventricular tachyarrhythmia (VT) by programmed ventricular stimulation (PVS) or the development of malignant ventricular arrhythmia in response to acute coronary artery thrombosis. In contrast, coadministration of 0.3 microg/kg i.v. L-768673 + 1.0 microg/kg i.v. timolol suppressed the induction of VT by PVS (8/10, 80% rendered noninducible versus 1/10, 10% noninducible in vehicle group; p < 0.01) and prevented the development of acute ischemic lethal arrhythmias (3/10, 30% incidence versus 8/10, 80% incidence in vehicle group; p < 0.05). Concomitant administration of low-dose L-768673 + timolol produced modest increases in QTc and paced QT intervals (4.5 +/- 1.2 and 5.5 +/- 1.4%; both p < 0.01), increases in noninfarct zone relative and effective refractory periods (7.0 +/- 1.7 and 12.3 +/- 3.0%; both p < 0.01), and lesser increases in infarct zone relative and effective refractory periods (5.3 +/- 1.6 and 5.8 +/- 1.4%; both p < 0.01). These findings suggest that concomitant low-dose I(Ks) and beta-adrenergic blockade may constitute a potential pharmacologic strategy for prevention of malignant ischemic ventricular arrhythmias.
authors.affiliation: Department of Pharmacology, Merck Research Laboratories, WP46-300, West Point, PA 19486, USA. joseph_lynch@merck.com
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Lynch
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Salata
authors.forename: Audrey A
authors.initials: AA
authors.lastname: Wallace
authors.forename: Gary L
authors.initials: GL
authors.lastname: Stump
authors.forename: David B
authors.initials: DB
authors.lastname: Gilberto
authors.forename: Hossain
authors.initials: H
authors.lastname: Jahansouz
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Liverton
authors.forename: Harold G
authors.initials: HG
authors.lastname: Selnick
authors.forename: David A
authors.initials: DA
authors.lastname: Claremon
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D000889:Anti-Arrhythmia Agents; D001570:Benzodiazepinones / Q000494:pharmacology*; D004285:Dogs; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D006321:Heart / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology; D017202:Myocardial Ischemia / Q000473:pathology; D026902:Potassium Channel Blockers; D013999:Timolol / Q000494:pharmacology; D016276:Ventricular Function
chemical_list: D000081:Acetamides; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D000889:Anti-Arrhythmia Agents; D001570:Benzodiazepinones; C109598:L 768673; D026902:Potassium Channel Blockers; D013999:Timolol; D007545:Isoproterenol