1. ECG IN HYPERKALEMIA

2. Potassium is most abundant intracellular cation
Most important determinant of resting membrane potential (RMP)

3. Mild to moderate levels of hyperkalemia
Decrease TP(less negative)
Decrease RMP (less negative)
Decrease RMP more than decrease TP
Diminish difference between two and increase excitability

4. Decrease in slope of upstroke of AP (dV/dT)
Major determinants of conduction velocity
Counterbalanced by decrease in RMP to TP difference
Result in ultimate increase in conduction velocity initially

5. Disproportional effects of varying levels of hyperkalemia on RMP and the TP
Initial increase in excitability and conduction velocity followed by their decrease as potassium level increases further

6. Severe hyperkalemia
Associated with increase in difference between RMP and TP
Leading to decrease in excitability
Further decrement in AP upstroke (dV/dT) overwhelms positive effect of TP decrease on conduction velocity

7. Rate of rise of phase 0 of AP (Vmax) is directly proportional to value of RMP at the onset of phase 0
Decrease in V max levels causes a slowing of myocardial conduction manifested by progressive prolongation of P wave, PR interval and QRS complex

8. Mechanism for early ECG manifestations of hyperkalemia (ST depression, peaked T waves, and short-QT)
Ikr is mostly responsible for K+ efflux in phases 2 and 3
Ikr currents are sensitive to extracellular K+ levels
As potassium levels increase in extracellular space potassium conductance through these currents is increased
Leads to increase in slope of phases 2 and 3
shorten repolarization time

9. Modulation of potassium currents by electrolyte concentration

10. Effects of hyperkalemia depend on tissue involved
Atrial myocardium most sensitive
ventricular myocardium less sensitive
Specialized tissue (SA node and His bundle) least sensitive

11. References
1.Electrolyte disorders and arrhythmogenesis ,Nabil El-Sherif1, Gioia Turitto2, Cardiology Journal 2011, Vol. 18
2.Hyperkalemia Revisited, Walter A. Parham, MD,Ali A. Mehdirad, MD, FACC ,Kurt M. Biermann, BS ,Carey S. Fredman, MD, FACC, Tex Heart Inst J 2006