Final answer:
Atrial flutter is characterized by a sawtooth pattern on ECG, known as flutter waves, reflecting the re-entry circuit within the atria. It typically presents with a regular rhythm, not a prolonged PR interval nor necessarily a rapid ventricular response.
Step-by-step explanation:
Atrial flutter is characterized by an ECG pattern showing a sawtooth appearance called flutter waves, which is due to a rapid re-entry circuit within the atria. Unlike atrial fibrillation, which presents with irregular rhythms and an abnormal electrical pattern on the ECG, atrial flutter typically has a regular pattern. However, when ventricular response is rapid, it may become variable and seem irregular due to variation in atrioventricular conduction.
The third-degree block or complete heart block, as shown in Figure 19.25e, demonstrates a complete lack of correlation between atrial and ventricular contractions on the ECG, not associated with atrial flutter. The P wave represents atrial depolarization, and the QRS complex represents ventricular depolarization. Atrial repolarization is not typically visible on an ECG as it is masked by the larger QRS complex.
It is crucial to know that atrial flutter is not characterized by a prolonged PR interval or necessarily a rapid ventricular response, although it may occur based on how the atrioventricular node responds to the increased atrial rate.