title: Metabolic protection by verapamil during graded coronary flow reduction independent of effect on baseline systolic function. Separation of mechanical and ionic markers of ischemia.
abstract: Pretreatment with the calcium channel-blocking agent verapamil lowers the coronary flow associated with the first rise in myocardial extracellular potassium [( K+]e). The mechanisms underlying this effect are unclear. It is not known whether this effect is a manifestation of verapamil-induced reduction in baseline cardiac work before the reduction in coronary flow, is dependent on a selective depression of contractility within the low-flow region, or is independent of an effect on myocardial work. This study was performed to determine the relations between changes in regional contractility and [K+]e before and after verapamil (0.2 mg/kg followed by 6.5 micrograms/kg/min) when left anterior descending (LAD) coronary flow is progressively reduced and when verapamil-induced alterations in baseline myocardial work are prevented by atrial pacing and by dobutamine (4.3 +/- 2.2 micrograms/kg/min) to maintain systemic arterial blood pressure and contractility. Before verapamil-dobutamine, myocardial [K+]e rose and regional contractility fell when LAD coronary flow was reduced to 87.7 +/- 9.6% and 83.4 +/- 7.4%, respectively, of the unrestricted control value (p = NS). After verapamil-dobutamine, the threshold flow for rise in [K+]e decreased to 56.4 +/- 13.5% of the unrestricted control flow (p = 0.003), but the threshold flow for regional contractility fall was unchanged (84.8 +/- 11.3%). Our results indicate that the protective effect of verapamil on preventing ischemia-induced [K+]e release is not dependent on a reduction in baseline myocardial work. In this setting, calcium channel blockade by verapamil results in a dissociation between the ionic and mechanical events that occur when coronary flow is reduced.
authors.affiliation: Division of Cardiology, School of Medicine, University of North Carolina at Chapel Hill.
authors.forename: M G
authors.initials: MG
authors.lastname: Jenkins
authors.forename: T A
authors.initials: TA
authors.lastname: Johnson
authors.forename: C
authors.initials: C
authors.lastname: Engle
authors.forename: L S
authors.initials: LS
authors.lastname: Gettes
mesh_terms: D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects*; D003327:Coronary Disease / Q000188:drug therapy* / Q000503:physiopathology; D004280:Dobutamine / Q000627:therapeutic use; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D013552:Swine; D014700:Verapamil / Q000627:therapeutic use*
chemical_list: D004280:Dobutamine; D014700:Verapamil; D011188:Potassium