Temporary treatment for a third-degree AV block may involve which of the following?

In cases of third-degree AV block, also known as complete heart block, there is a failure of electrical impulses to be conducted from the atria to the ventricles. This can lead to significant bradycardia and potentially life-threatening situations due to inadequate cardiac output.

Transcutaneous pacing is a temporary external method used to stimulate the heart when there is a complete block in electrical conduction, allowing for a proper heart rate and rhythm to be maintained until more permanent solutions, such as the placement of a pacemaker, can be implemented. It works by delivering electrical impulses through the skin to stimulate cardiac contractions and is particularly useful in emergency situations.

Other options, like defibrillation and cardioversion, are primarily indicated in situations involving arrhythmias such as ventricular fibrillation or unstable tachycardia, where there is a need to restore a coordinated rhythm. Ablation therapy is typically considered for certain types of arrhythmias and is not an immediate/emergency treatment for complete heart block. Therefore, for the temporary management of a third-degree AV block, transcutaneous pacing is the most appropriate and effective intervention.