Heterogeneity of ventricular fibrillation dominant frequency during global ischemia in isolated rabbit hearts

Caldwell, J., Burton, F., Smith, G. and Cobbe, S. (2007) Heterogeneity of ventricular fibrillation dominant frequency during global ischemia in isolated rabbit hearts. Journal of Cardiovascular Electrophysiology, 18(8), pp. 854-861. (doi: 10.1111/j.1540-8167.2007.00867.x)

Abstract

Introduction: Ventricular fibrillation (VF) studies show that ECG-dominant frequency (DF) decreases as ischernia develops. This study investigates the contribution of the principle ischernic metabolic components to this decline. Methods and Results: Rabbit hearts were Langendorff-perfused at 40 mL/min with Tyrode's solution and loaded with RH237. Epicardial optical action potentials were recorded with a photodiode array (256 sites, 15 x 15 mm). After 60 seconds of VF (induced by burst pacing), global ischernia was produced by low flow (6 mL/min), or the solution changed to impose hypoxia (95 % N-2/5% CO2), low pH(o) (6.7, 80 % O-2/20% CO2), or raised [K+](o) (8 mM). DF of the optical signals was determined at each site. Conduction velocity (CV), action potential duration (APD90), effective refractory period (ERP), activation threshold, dV/dt(max) and membrane potential were measured in separate experiments during ventricular pacing. During VF, ischernia decreased DF in the left ventricle (LV) (to [58 6] %, P < 0.001), but not the right (RV) ([93 5]%). Raised [K+]o reproduced this DF pattern (LV: [67 +/- 12]%, P < 0.001; RV: [95 91%). LV DF remained elevated in hypoxia or low pH,,. During ventricular pacing, ischernia decreased CV in LV but not RV. Raised [K+](o) did not change CV in either ventricle. Ischernia and raised [K+](o) shortened APD90 without altering ERP. LV activation threshold increased in both ischernia and raised [K+](o) and was associated with diastolic depolarization and decreased dV/dt(max),Conclusions: These results suggest that during VF, decreased ECG DF in global ischemia is largely due to elevated [K+](o) affecting the activation thresholds in the LV rather than RV.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Smith, Professor Godfrey and Burton, Dr Francis and Caldwell, Dr Jane and Cobbe, Professor Stuart
• Authors: Caldwell, J., Burton, F., Smith, G., and Cobbe, S.
• College/School: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health; College of Medical Veterinary and Life Sciences
• Journal Name: Journal of Cardiovascular Electrophysiology
• Publisher: Blackwell
• ISSN: 1540-8167