THE IB PHASE OF VENTRICULAR ARRHYTHMIAS IN ISCHEMIC IN-SITU PORCINE HEART IS RELATED TO CHANGES IN CELL-TO-CELL ELECTRICAL COUPLING

Background This study was designed to test the hypothesis that the los s of cell-to-cell electrical interaction during ischemia modulates the amplitude of ischemia-induced TQ-segment depression (ie, the injury p otential) and the occurrence of ventricular fibrillation (VF) during t he so-called Ib phase of ventricular arrhythmias. Methods and Results Regional ischemia was induced by 60 minutes of mid-left anterior desce nding coronary artery ligation in open-chest swine (n=10). Cell-to-cel l electrical uncoupling was defined as the onset of the terminal rise in whole-tissue resistivity (R(t)). Local activation times and TQ-segm ent changes (injury potential) were determined from unipolar electrogr ams. Extracellular K+ ([K+](e)) and pH (pH(e)) were measured with plun ge-wire ion-selective electrodes. VF occurred in 6 of 10 pigs during r egional no-flow ischemia between 19 and 30 minutes after the arrest of perfusion. The occurrence of VF was positively correlated to the onse t of cell-to-cell electrical uncoupling (R(2)=.885). Cell-to-cell elec trical uncoupling superimposed on changes of [K+](e) and pH(e) contrib uted to the failure of impulse propagation between 19 and 30 minutes a fter the arrest of perfusion. During ischemia, maximum TQ-segment depr ession was -10 mV at 19 minutes, after which TQ-segment depression slo wly recovered. The onset of the TQ-segment recovery was correlated to the second rise in R(t) (R(2)=.886). Conclusions In the regionally isc hemic in situ porcine heart, loss of cell-to-cell electrical interacti on is related to the occurrence of VF and changes in the amplitude of the injury current. Cellular electrical uncoupling contributes to fail ure of impulse propagation in the setting of altered tissue excitabili ty as a result of elevated [K+](e) and low pH(e). These data indicate that Ib arrhythmias and ECG changes during ischemia are influenced by the loss of cell-to-cell electrical interaction.