Which of the following would you expect to see in a patient with a heart rate of 180 bpm from narrow-complex tachycardia?

In a patient experiencing narrow-complex tachycardia with a heart rate of 180 bpm, it is common to see decreased cardiac output as a primary consequence. Narrow-complex tachycardia, which typically originates from the atria or the AV node, results in the heart beating at a significantly accelerated rate. When the heart beats this quickly, there is insufficient time allocated for the ventricles to fill with blood between contractions, leading to a reduced stroke volume. This decline in stroke volume ultimately translates to a decreased cardiac output, which is critically important for maintaining blood flow to vital organs.

While other physiological responses such as changes in blood pressure can occur, the key point here is that the rapid heart rate compromises the heart's ability to pump effectively. Thus, decreased cardiac output is a direct result of the increased heart rate in this scenario, causing potential symptoms such as fatigue, dizziness, or even syncope due to less effective circulation.

The presence of ventricular ectopy, increased blood pressure, or heart murmurs would require additional context or conditions that are not inherently associated with the situation of narrow-complex tachycardia alone.