Final answer:
The return of the ST segment elevation to baseline on an ECG is a clinical sign that indicates successful reperfusion after thrombolytic therapy for a myocardial infarction.
Step-by-step explanation:
The clinical manifestation that indicates to the nurse that reperfusion has been successful after a client has received thrombolytic therapy following a myocardial infarction is an elevation of the ST segment returning to baseline. This is because an elevation of the ST segment is oftentimes observed in patients with an acute myocardial infarction (MI), and its return to baseline can indicate successful reperfusion. It's worth noting that the treatment options for myocardial infarction may include thrombolytic agents such as streptokinase, which dissolve blood clots that are obstructing blood flow to the heart muscle.