What is an expected complication of third-degree heart block following a myocardial infarction?

Third-degree heart block, also known as complete heart block, is characterized by a complete dissociation between atrial and ventricular activity. This can frequently occur following a myocardial infarction, especially when the infarction affects the tissues surrounding the conduction system of the heart.

The expected complication of third-degree heart block is the need for pacemaker insertion. This is necessary because the heart is unable to conduct electrical impulses effectively from the atria to the ventricles, resulting in a significant alteration of the heart's rhythm. A pacemaker helps to restore a proper rhythm by providing electrical stimulation to the heart muscles, ensuring that the ventricles contract at an appropriate rate despite the block.

While other complications can arise from myocardial infarction, they do not directly address the complete blockade of electrical conduction seen in third-degree heart block. For instance, paroxysmal atrial tachycardia and ventricular tachycardia refer to different arrhythmias not specifically tied to the management of third-degree heart block. A shortened PR interval is typically associated with conditions like pre-excitation syndromes and does not pertain to complete heart block. Therefore, the need for a pacemaker is the most appropriate and expected intervention in this scenario.