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The "sawtooth" arrhythmia

You are presented the following monitoring ECG in a 6 y/o boy who is in pediatric intensive care following heart surgery for atrial septal defect closure:

Heart rate of 89 bpm, oxygen saturation 100%, mean BP 46mmHg. Looking at the ECG you see a fast atrial rhythm. However, QRS complexes seem to appear arrhythmic, showing changing cycle lengths.

What diagnosis do you make of this?

?? atrial fibrillation ??

?? atrial flutter ??

?? atrial tachycardia ??

Since this is your first on call shift on PICU you think about administering adenosine. If it is a AV node dependent reentry arrhythmia adenosine might terminate it. If it doesn't terminate, it might help with the diagnosis.

The following picture shows the adenosine response:

Adenosine blocks AV nodal conduction. Therefore QRS complexes disappear. Now you clearly see fast atrial complexes, sawtooth shaped P waves. These are also called flutter waves and represent the typical appearance of atrial flutter (AFL). AFL is a reentry arrhythmia circling within the atrium, typically using the cavotricuspid isthmus region as part of the circuit.

Two typical forms of AFL exist, counterclockwise (ccw; negative flutter waves in inferior leads) and clockwise AFL (cw; positive flutter waves in inferior leads).

AFL = atrial flutter; CCW = counterclockwise; CW = clockwise; CTI = cavotricuspid isthmus

Since the patient was still intubated you went for electrical cardioversion, which ultimately resulted in restoration of sinus rhythm:

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