<prompt> Answer this question truthfullyWhat other channels, in addition to Na channels, do Class IA antiarrhythmics block?  <response>: <reason> Class IA antiarrhythmics not only block Na channels, but also block potassium K channels. This dual mechanism of action helps to prolong the action potential duration and refractory period of cardiac cells, making them effective in treating certain types of arrhythmias. 