Final answer:
Adenosine is considered the best treatment for SVT and regular wide complex tachycardias during pregnancy due to its safety profile. Potassium channel blockers like amiodarone affect the ventricular repolarization phase of the cardiac action potential but are generally avoided in pregnancy.
Step-by-step explanation:
The best treatment for Supraventricular Tachycardia (SVT) and regular wide complex tachycardias during pregnancy is typically adenosine (a). While other treatments like amiodarone, procainamide, and digoxin are available for arrhythmias and have their own uses, adenosine is often preferred in emergency settings for SVT because it has a short half-life and fewer side effects, making it generally safer for both the mother and the fetus. It is vital to handle cardiac arrhythmias cautiously during pregnancy due to the altered physiological state and the potential impact on the fetus.
Potassium channel blockers, like amiodarone and procainamide, affect the ventricular repolarization (b) phase of the action potential as they impede the movement of potassium through voltage-gated K+ channels. This makes them useful in treating cardiac dysrhythmia, by controlling the electrical activity that leads to arrhythmias. Nonetheless, their use during pregnancy is typically avoided unless absolutely necessary due to potential adverse effects on the fetus.