24th April 2024

Physiology

An understanding of the cardiac action potential and its different phases will help clarify the mechanisms of different antiarrhythmic medications (see image and table below). Cardiac myocytes have a resting membrane potential of -90mV, like skeletal muscle but lower than that of neurons (-70mV) and smooth muscle (between -50mV and -60mV). 

Medications affecting the cardiac action potential. Depolarisation phase 0, is due to a net flow of positive charge into the cell from sodium ions. Dips 1 and 3 occur when sodium channels are inactivated and there is an efflux of potassium ions, restoring the negative potential of the cardiac myocyte (repolarisation). The plateau phase 2, results from inward movement of calcium ions. 

Image Source: Wikimedia Commons (2021). Cardiac action potential, Licensed under a creative commons licence. Available for free at: https://en.wikipedia.org/wiki/Cardiac_action_potential (Accessed: 23 April 2024).

Table 2: Cardiac action potential