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)
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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 |
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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 |
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