What differentiates a SVT from Sinus Tachycardia?

• A. SVT has a consistent R-R interval
• B. SVT has a variable R-R interval
• C. Sinus Tachycardia has a consistent R-R interval
• D. Sinus Tachycardia has a variable R-R interval

Answer: (A)

The rhythm regularity is what this question is testing. Supraventricular tachycardia typically produces a rapid, narrow-complex rhythm with a highly regular cadence—the time between heartbeats (R-R interval) stays essentially the same beat to beat. In other words, SVT tends to have a consistent R-R interval.

Sinus tachycardia, on the other hand, is driven by the sinus node firing faster but remains a true sinus rhythm. In children, breathing can cause variation in the R-R interval (sinus arrhythmia), so the intervals may not be perfectly constant, even though each beat has a normal P wave preceding the QRS.

So the differentiator here is that SVT usually shows a consistent R-R interval, whereas sinus tachycardia may exhibit some variability in R-R intervals due to physiological factors like respiration.