Mode of action (for very interested readers)
In order for large quantities of blood to circulate continuously in the body’s circulation, the heart needs to be pumped regularly. Heart muscle cells are excited at regular intervals for this purpose. The heart has its own system of impulse conduction, the excitation of the heart muscle cells takes place in a healthy heart via the so-called sinus node with a natural frequency of approx.
70/min. Action potentials are formed at the heart muscle cells by the influx of certain ions into the cell interior. The heart muscle cell depolarizes and a voltage reversal of the cell interior and exterior from -70 mV to +30 mV occurs.
This is triggered by an increased positive influx of sodium into the cell interior. After a plateau phase at 0 mV, excitation regression and repolarization of the cell occurs. Responsible for this are a positive outflow of potassium and a negative inflow of chloride; they ensure that the heart muscle cells are brought back to a rest potential of -70 mV.
Now one action potential is finished and another can be created. Amiodarone acts as a potassium channel blocker on the repolarisation phase of the action potential. The potassium outflow is reduced and thus the so-called refractory period is prolonged, during which the cell cannot react to a new stimulus because it is still repolarizing.
This effect can prevent circular excitation as in atrial fibrillation and the formation of extrasystoles, while fully maintaining the contractile power of the heart. In addition, amiodarone lowers the heart rate and dilates the coronary arteries, allowing the heart to be better supplied with oxygen.
