Local myocardial electrogram and potassium concentration changes in superficial and deep intramyocardium and their relations with early ischaemic ventricular arrhythmias

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Abstract
Bipolar myocardial electrograms and extracellular potassium concentrations were simultaneously monitored using double barrelled probes during 30 min of acute ischaemia in 15 dogs in vivo. The responsiveness of the time from the onset of the limb lead electrocardiogram to the peak deflection of the local electrogram to extracellular potassium changes was more prominent in superficial intramyocardium than in deep intramyocardium, despite similar changes in potassium concentration in both layers. The changes in electrogram duration and amplitude were related to extracellular potassium concentration both in superficial and deep intramyocardium. Immediate phase ventricular arrhythmias (within the first 10 min of acute ischaemia) were characterised by delayed activity mainly due to an increase in the time to peak of the electrogram in superficial intramyocardium. In contrast, in dogs showing delayed phase arrhythmias (within 10-30 min of acute ischaemia) delayed activity associated with pronounced changes in potassium concentration and electrogram duration and amplitude were noted in deep intramyocardium. Thus the two phasic appearances of early ischaemic ventricular arrhythmias with different origins seem to be related to the features of the conduction pathway in superficial intramyocardium and the severe local electrogram changes associated with a pronounced increase in extracellular potassium concentration in deep intramyocardium.