Figure 2 shows another ECG with atrial flutter. Increasing the paper speed to 50 mm/s or applying carotid massage (which increases the atrioventricular block) will be helpful in such situations. Note that with paper speed 25 mm/s, which is standard in the US and many other countries, a 2:1 block will be difficult to discern because the flutter wave may fuse with the preceding T-wave. One should always consider atrial flutter when confronted with a regular tachyarrhythmia at 150 beats per minute. In typical cases of atrial flutter the atrial rate is around 300 beats per minute with a 2:1 block, which yields a ventricular rate of about 150 beats per minute. If there are 2 flutter waves before each QRS complex then it is 2:1 block. If 3 flutter waves occur before each QRS complex then it is 3:1 block. The degree of blocking in the atrioventricular node is specified by counting the number of flutter waves preceding each QRS complex. The atrioventricular node is not capable of conducting all impulses, which is why some impulses will be blocked. The atrial rate (i.e the rate measured between flutter waves) typically ranges between 250 and 350 beats per minute (which is slower than the atrial rate in atrial fibrillation). Please note that for most clinicians it is not necessary to be able to determine the direction of the re-entry loop. If the re-entry has a clockwise direction, the flutter waves are positive in lead II, III, aVF and the P-waves typically have a notch on the apex.
This yields negative flutter waves in II, III and aVF and positive flutter waves in V1 ( Figure 1). In the most common type of atrial flutter, the re-entry loops around the tricuspid valve in a counter-clockwise direction. The exact appearance of the flutter waves will depend on the location and direction of the re-entry circuit. Flutter waves are typically best seen in leads II, III aVF, V1, V2 and V3. The flutter waves (on the contrary to f-waves in atrial fibrillation) have identical morphology (in each ECG lead). Atrial flutter is the only diagnosis causing this baseline appearance, which is why it must be recognized on the ECG. The ECG shows regular flutter waves ( F-waves not to be confused with f-waves seen in atrial fibrillation) which gives the baseline a saw-tooth appearance. Impulses spread rapidly through the atria from this re-entry circuit. In the vast majority of cases, the re-entry circuit in atrial flutter is located in the right atrium and it typically loops around the tricuspid valve. This is due to the fact that atrial flutter is caused by a macro re-entry circuit (a large re-entry circuit) and re-entry circuits are vulnerable processes that usually self-terminate within minutes, hours or days.
Thus, as compared with atrial fibrillation, atrial flutter is not capable of persisting for longer periods of time. Acute and paroxysmal cases are common in clinical practice.
The observant will notice that the classification differs slightly from that of atrial fibrillation.
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