Heterogeneous ventricular chamber response to hypokalemia and inward rectifier potassium channel blockade underlies bifurcated T wave in guinea pig

Abstract

It was previously demonstrated that transmural electrophysiological heterogeneities can inscribe the ECG T wave. However, the bifurcated T wave caused by loss of inward rectifier potassium current ( IK1) function is not fully explained by transmural heterogeneities. Since right ventricular (RV) guinea pig myocytes have significantly lower IK1 than left ventricular (LV) myocytes, we hypothesized that the complex ECG can be inscribed by heterogeneous chamber-specific responses to hypokalemia and partial IK1 blockade. Ratiometric optical action potentials were recorded from the epicardial surface of the RV and LV. BaCl2 (10 μmol/l) was perfused to partially block IK1 in isolated guinea pig whole heart preparations. BaCl2 or hypokalemia alone significantly increased RV basal (RVB) action potential duration (APD) by ∼30% above control compared with LV apical (LVA) APD (14%, P < 0.05). In the presence of BaCl2, 2 mmol/l extracellular potassium (hypokalemia) further increased RVB APD to a greater extent (31%) than LVA APD (19%, P < 0.05) compared with BaCl2 perfusion alone. Maximal dispersion between RVB and LVA APD increased by 105% ( P < 0.05), and the QT interval prolonged by 55% ( P < 0.05) during hypokalemia and BaCl2. Hypokalemia and BaCl2 produced an ECG with a double repolarization wave. The first wave (QT1) corresponded to selective depression of apical LV plateau potentials, while the second wave (QT2) corresponded to the latest repolarizing RVB myocytes. These data suggest that final repolarization is more sensitive to extracellular potassium changes in regions with reduced IK1, particularly when IK1 availability is reduced. Furthermore, underlying IK1 heterogeneities can potentially contribute to the complex ECG during IK1 loss of function and hypokalemia.