Which arrhythmia is characterized by a ventricular rate of 150-250 beats per minute?

Atrial flutter is characterized by a ventricular rate that typically ranges between 150 to 250 beats per minute. This arrhythmia results from a reentrant circuit within the right atrium, leading to rapid atrial contractions. The ventricular response can vary based on the conduction ratio through the AV node, but when it is unregulated, the ventricular rate often falls within that specified range.

In contrast, ventricular fibrillation represents a chaotic and disorganized electrical activity in the ventricles, leading to no effective heartbeat, and thus the rate cannot be precisely defined in the same way as atrial flutter. Narrow-complex tachycardia refers to a tachyarrhythmia with a rapid rate but does not specify the regularity of the rhythm or confinement to the 150-250 beats per minute range like atrial flutter does. Bradycardia, defined as a heart rate of less than 60 beats per minute, is clearly outside the parameters of the specified rates in the question.