Case B4. First Degree AV Block. St Emlyn’s ECG Library


First degree AV block


The EGG was recorded from a 78 year old woman with a history of heart failure treated by her general practitioner withan ACE inhibitor and diuretics.


Rhythm: Sinus rhythm is present. Each P wave is followed by a QRS complex – there are no pauses or dropped beats. The PR interval is the time interval between the onset of the P wave and the start of the QRS complex (whether this begins with a Q wave or R wave) and normally lies tvithin the limits of .12 seconds – .21 seconds. In this case the PR interval is prolonged – to .32 seconds. Morphology: The ECG also shows ST segment depression in I,aVL and V5 and V6. There is T wave flattening or inversion in these leads in addition. There is no evidence from the presence of Q waves or loss of R wave of previous myocardial infarction.


First degree AV block is a common finding and represents delayed conduction in the AV junction (the AV node and bundle of His). This may result from ischaemia or primary conducting system disease. Several drugs also delay conduction in the AV node- digoxin, beta blockers, and certain calcium channel blockers including verapamil and diltiazem. The ST segment and T wave abnormalities seen here are non specific and may be they caused by myocardial ischaemia.


Cite this article as: Simon Carley, "Case B4. First Degree AV Block. St Emlyn’s ECG Library," in St.Emlyn's, October 29, 2018,

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