This is the ECG of a 73 year old man who was noticed to have a slow pulse rate. He has a past  history  of  ischemic  heart  disease  and  is  being  treated  with  digoxin  and  beta- adrenergic blockers.

What is the rhythm?  What is the conduction abnormality?  Please justify your responses.

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College Answer

The rhythm is Atrial Flutter with a high degree (but apparently consistent) AV block, and a ventricular rate of approximately 40/minute. There is an obvious saw-tooth pattern of atrial depolarisations (at  a  rate  of  approximately 250/min)  seen  in  many  leads.  Association between the flutter and the ventricular depolarisations is based on the finding of a constant PR interval (with a fixed relationship between the P wave and the QRS complex), which excludes AF, and complete heart block.

The conduction abnormality is a tri-fascicular block as it includes:

•    Second degree (Mobitz II) AV block (as evidenced by constant relationship between P waves and the QRS)

•    Right bundle branch block (QRS > 0.12, RSR in V1, S in lead 1)

•    Left anterior hemiblock implied by left axis deviation (slightly positive in 1, negative with small R waves in II and III)

Discussion

The accuracy and completeness of the college answer makes it difficult to discuss this question.

Certainly, I cannot improve on their response.

One can read further about these ECG abnormalities within the body of this site:

Or one could review the topic properly at LITFL.