Relationship between Extracellular Potassium Accumulation and Local TQ-Segment Potential During Graded Coronary Flow Reduction in a Porcine Myocardial Ischemia Model

Background: Changes in resting membrane potential due to extracellular potassium ([K+]e) accumulation are thought to be responsible for TQ segment depression in ischemia. However, the nature of the [K+]e-TQ relationship remains to be fully elucidated. Methods: We created a carotid-coronary shunt in 21 pigs, and recorded [K+]e and TQ-segment potentials simultaneously during graded left anterior descending artery (LAD) flow reduction via 4-6 K+-sensitive electrodes placed in the LAD. Only data from K+ electrodes with calibration slopes of 55-65 mV/decade change in K+ were used. Results: While the correlation between the changes in potassium equilibrium potential (EK) and the TQ shift was linear, the regression slopes initially increased and then decreased during graded flow reduction (S = -0.338, Q = 30 mL/minute, S = -3.253, Q = 10 mL/minute, S = -0.312, Q = 0 mL/minute), i.e., TQ depression at all EK values became larger, then smaller as the flow was decreased in a stepwise manner. The inhomogeneity of changes in [K+]e and TQ potential changes and their relationship also decreased initially then increased during graded flow reduction (R = -0.237, LAD flow = 30 mL/minute; R = -0.819, LAD flow = 15 mL/minute; R = -0.115, LAD flow = 0 mL/minute). Conclusions: Although [K+]e and the TQ shift are related linearly, there is large variability in their relationship in the setting of graded coronary flow reduction. Therefore, local TQ-segment potentials cannot be used as indices of the severity of ischemic changes.