Final answer:
The correct treatment for a patient with third-degree heart block is the implantation of a pacemaker to maintain an adequate heart rate and ensure effective pumping of blood.
Step-by-step explanation:
The patient described is exhibiting signs of a third-degree heart block, as indicated by a heart rate of 40 beats/minute, regular P waves, regular Q waves, and no relationship between the P wave and QRS complex. In a third-degree heart block, none of the impulses from the SA node reach the AV node, resulting in the ventricles initiating their own rhythm at a slower rate. This can severely affect cardiac output and lead to inadequate perfusion. The typical treatment for a patient with symptomatic third-degree heart block is the implantation of a pacemaker. The pacemaker will provide regular electrical impulses to ensure the heart contracts and pumps blood effectively. Other options such as carotid massage, defibrillation, or simply monitoring are not adequate treatments for this type of block.