HETEROGENEITIES IN [K-FIBRILLATION DURING ACUTE REGIONAL ISCHEMIA IN THE ISOLATED-PERFUSED PORCINE HEART(](0) AND TQ POTENTIAL AND THE INDUCIBILITY OF VENTRICULAR)

Background The relation between the inducibility of ventricular fibril lation (VF) and heterogeneity of the extracellular potassium concentra tion ([K+](o)) and of TQ potential is unknown. Methods and Results Dat a from 78 epicardial DC electrodes or from up to 32 intramural K+ elec trodes were acquired simultaneously. induction of VF was attempted wit h one or two ventricular premature beats induced in normal myocardium in isolated porcine hearts during (1) regional perfusion of the left a nterior descending artery (LAD) with a normoxic, hyperkalemic solution ([K+] 6 to 19.6 mmol/L), (2) simulated ischemia, ie, LAD perfusion wi th a glucose-free, hypoxic solution ([K+] 4 to 16 mmol/L, PO2 <5 mm Hg , pH 6.98), and (3) regional ischemia produced by stopping LAD flow. D uring normoxic, hyperkalemic LAD perfusion, no VF could be induced (12 interventions, 7 hearts) During simulated ischemia (27 interventions) , VF could be induced only when [K+](o) was between 8 and 13.5 mmol/L. After 5 minutes of true regional ischemia, more sites with [K+](o) be tween 8 and 13.5 mmol/L were present than after 10 minutes. VF could b e induced with 1 ventricular premature beat in 11 of 17 interventions after 5 minutes and in 0 of 14 interventions after 10 minutes of ische mia (P<.001). Regional simulated ischemia presents a relatively homoge neous condition compared with 5 minutes of regional ischemia (SD+/-SEM of TQ potential in LAD tissue, 0.9+/-0.05 versus 2.1+/-0.13 mV, respe ctively). True ischemia superimposed on regional simulated ischemia ca used the rapid development of heterogeneities in [K+](o) and TQ potent ial and caused VF after 45+/-7 seconds in ah interventions. Activation maps of induction of VF suggest a different mechanism of unidirection al block during simulated ischemia from that in true ischemia. Conclus ions (1) In the presence of hypoxia and acidosis, [K+](o) between 8 an d 13.5 mmol/L provides the conditions necessary for the induction of V F; (2) after 5 minutes of ischemia, these conditions are present in a larger area and inducibility of VF is higher than after 10 minutes of ischemia; and (3) small heterogeneities within the intermediate K+-con centration domain (8 to 13.5 mmol/L) are associated with high inducibi lity of VF.