Came in with shortness of breath. What is the rhythm ?
This is a regular narrow QRS rhythm at rate of about 90 bpm (or about 16.5 small squares). There is poor R wave progression and low voltage limb leads (~ 5 mm)
The P waves are inverted or negative in II, III and aVF , upright or positive in aVR, aVL and V1. The atrial rate is best computed in V1 where it can be seen at about 188 bpm (1500/ 8 small squares or at cycle length of 320 ms). In between P waves is a clear ISOELECTRIC lime. There are 2 P waves for 1 QRS or there is 2:1 AV conduction.
What is this rhythm?
Atrial tachycardia is typically defined as a regular atrial rhythm with a rate around 100 - 240 bpm with an isoelectric baseline. Atrial flutter on the other hand is defined a reentrant arrhythmia with a regular pattern at a rate above 240 bpm with characteristics flutter waves.
I would like to quote "verbatim" the thoughts of Drs. Das and Zipes regarding the semantics of using atrial tachycardia and atrial flutter from their book Electrocardiography of Arrhythmias:
"Atrial tachycardia (AT) is defined as a regular atrial rhythm originating from the atrium at 100 bpm to 240 bpm. The presence of an atrial rate above 100 bpm with three different P wave morphologies signifies different foci of atrial depolarization and is called a multifocal atrial tachycardia (MAT). Previous classifications of AT had been based exclusively on the routine electrocardiogram (ECG) with a constant rate and an isoelectric line between the two consecutive P waves. Atrial flutter (AFL) is typically a reentrant arrhythmia defined as having a pattern of regular tachycardia with a rate above 240 bpm without an isoelectric baseline between deflections. The typical (cavotricuspid dependent) AFL usually shows sawtooth pattern in inferior ECG leads. ATs can also have a reentrant mechanism, usually seen around a scar in the atrium. The ECG pattern can mimic an atypical (noncavotricuspid dependent) AFL. However, neither rate nor lack of isoelectric baseline is specific for any tachycardia mechanism. A rapid AT in a scarred atrium can mimic AFL, and, on the other hand, a typical AFL can show distinct isoelectric intervals between flutter waves, in diseased atria, or in the presence of antiarrhythmic drug therapy. Therefore it becomes a matter of semantics to define an AT or an atypical AFL."
If we follow those thoughts then this is atrial tachycardia vs. atrial flutter with 2:1 AV conudction.