After a myocardial infarction, how can a nurse best evaluate the effectiveness of the client's ventricular contractions?

Monitoring urinary output hourly is a crucial method for evaluating the effectiveness of the client's ventricular contractions after a myocardial infarction. This is because the kidneys are highly sensitive to changes in cardiac output and perfusion. When the heart is pumping effectively, it ensures adequate blood flow to the kidneys, resulting in normal urine production. A decrease in urinary output can indicate poor renal perfusion due to compromised cardiac function, which can occur after a myocardial infarction. Therefore, consistent monitoring of urinary output provides valuable insight into the patient's hemodynamic status and the heart’s ability to maintain circulation.

The other options do not directly assess the effectiveness of ventricular contractions in the same way. Observing anxiety levels may provide indirect information about the patient's condition but is not a reliable indicator of ventricular function. Evaluating cardiac enzyme results is important for diagnosing the extent of myocardial injury but does not directly measure heart function or contraction effectiveness at a specific moment. Assessing breath sounds can help identify pulmonary complications but doesn't provide specific information about the heart’s contraction effectiveness. Therefore, hourly urinary output is a more direct and effective measure in this context.