Dx – Atrial flutter with variable block

• In this ECG, the baseline has saw tooth shaped P waves. They are known as flutter waves.
• Atrial flutter waves discharge at a rate of 300 but ventricular rate is reduced because of atrioventricular block. 
• In case of regular block, the rhythm is regular and ventricular rate is approximately 150/min, 100/min or 75/min depending on 2:1, 3:1 or 4:1 block.
• Atrial flutter should be suspected in case of narrow complex arrhythmia of about 150/min (Because saw tooted pattern may not be obvious in 2:1 block)
• If there is variable AV block, the rhythm is irregular (as in this ECG).