13.01.5 Class III

Class III anti-arrhythmic agents block the delayed outward rectifying K⁺ channel. D-sotalol, the D-isomer of the β-adrenoceptor blocker racemic sotalol, blocks the delayed outward rectifying potassium channel to prolong the action potential in the Purkinje system (Figure 13.5). In a normal heart, D-sotalol prolongs the repolarisation, but this has little effect as there is a period of quiescence between action potentials (and between heart beats). Arrhythmias are often due to re-excitation in what should be the quiescence phase. By prolonging the repolarisation, D-sotalol decreases the likelihood of re-excitation (Figure 13.5).

Figure 13.5 Mechanism of D-sotalol (Copyright QUT, Sheila Doggrell)

D-sotalol is useful in a variety of supraventricular (arising in the atria) and ventricular arrhythmias.