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First degree AV block


See brief interpretation of 12 lead EKG above

First degree heart block (or first degree atrioventricular, AV, block) is characterized by PR prolongation more than 0.22 seconds, but all P waves conduct to the ventricles. The conduction from the atria to the ventricles are delayed and the lesion is most often located at the AV node.

A detail from the EKG above:

detail first degree av block First degree AV block

Note that the prolongation may be so marked, that the P wave is integrated in the preceding T wave or is mistaken for an U wave.

First degree heart block is considered a benign condition and a minor prolongation may be seen in normal individuals and athletes, though it is also associated with electrolyte disturbances, digitalis intoxication, myxedema and myocardial infarction.

— Mathias

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