What symptom is indicative of unstable Supraventricular Tachycardia?

Hypotension is considered a key symptom of unstable supraventricular tachycardia (SVT) because it indicates that the heart is not effectively pumping blood to meet the body's demands due to the rapid heart rate. In unstable SVT, the heart beats excessively fast, which can lead to inadequate filling time for the ventricles. This can subsequently reduce cardiac output and lead to symptoms such as low blood pressure. When the brain and other vital organs do not receive enough blood, patients may exhibit signs of instability, including altered mental status, weakness, or signs of poor perfusion.

In contrast, mild headache, a normal heart rhythm, and localized itching do not reflect the critical state associated with unstable SVT. Mild headaches can be caused by many unrelated factors and do not point specifically to cardiovascular instability. A normal heart rhythm directly contradicts the condition of unstable SVT, which is characterized by a rapid heart rate. Localized itching is unrelated to heart function and suggests an allergic reaction or skin condition rather than a cardiovascular issue. Thus, hypotension is the primary indicator of instability in patients experiencing supraventricular tachycardia.