Repolarization
[1] Repolarization is a stage of an action potential in which the cell experiences a decrease of voltage due to the efflux of potassium (K+) ions along its electrochemical gradient.
The lack of repolarization means that neuron stays at a high voltage, which slows sodium channel deactivation to a point where there is not enough inwards Na+ current to depolarize and sustain firing.
Further study of K+ channels shows that there are four types which influence the repolarization of the cell membrane to re-establish the resting potential.
Areas with dense Kv3 channels include the neocortex, basal ganglia, brain stem and hippocampus as these regions create microsecond action potentials that requires quick repolarization.
When the Kv4 channel is blocked, the action potential becomes broader, resulting in an extended repolarization period, delaying the neuron from being able to fire again.
When large quantities of Ca2+ ions enter the cell due to extended repolarization periods, the neuron may die, leading to the development of stroke or seizures.
Due to the complexity of the heart, specifically how it contains three layers of cells (endocardium, myocardium and epicardium), there are many physiological changes effecting repolarization that will also affect these waves.
[18] Early repolarization is a phenomenon that can be seen in ECG recordings of ventricular cells where there is an elevated ST segment, also known as a J wave.
Early repolarization occurs mainly in males and is associated with a larger potassium current caused by the hormone testosterone.
[20] As mentioned in the previous section, early repolarization is known as appearing as elevated wave segments on ECGs.
The condition is shown in both ventricular fibrillation without other structural heart defects as well as an early depolarization pattern, which can be seen on ECG.
[21] The primary root of early repolarization syndrome stems from malfunctions of electrical conductance in ion channels, which may be due to genetic factors.
Changes in these currents may result in overlap of myocardial regions undergoing different phases of the action potential simultaneously, leading to risk of ventricular fibrillation and arrhythmias.
[22] Upon being diagnosed, most individuals do not need immediate intervention, as early repolarization on an ECG does not indicate any life-threatening medical emergency.
[23] In addition, a patient may be more prone to atrial fibrillation if the individual has early repolarization syndrome and is under sixty years of age.
[21] Patients who suffer from obstructive sleep apnea can experience impaired cardiac repolarization, increasing the morbidity and mortality of the condition greatly.
