Atrial flutter is characterized by what abnormality?

Atrial flutter is primarily characterized by a rapid and organized electrical activity in the atria, specifically displaying a distinctive "sawtooth" pattern on an electrocardiogram (ECG), often observed in the inferior leads. This is due to a reentrant circuit or a single circuit loop within the atria, leading to a rapid atrial rate, typically between 240 to 340 beats per minute. Consequently, this results in an abnormal and regular pattern of atrial contractions, but not irregular, which might cause a discordant or varying response in the ventricles.

The other options relate to different heart conditions. For instance, rapid ventricular contractions could indicate a separate arrhythmia, while normal heart rhythm suggests a lack of any arrhythmia or abnormality. Heart block refers to a delay or interruption in the electrical conduction pathways between the atria and ventricles, which does not directly describe the primary electrical pattern and rate variation seen in atrial flutter. Understanding these nuances helps clarify the specific nature of atrial flutter as focusing on its unique organized atrial activity rather than a chaotic rhythm or other heart conditions.