P wave:

Atrial depolarization
location—precedes the QRS complex
amplitude—2 to 3 mm high
duration—0.06 to 0.12 second
configuration—usually rounded and upright
Peaked, notched, or enlarged P waves may represent atrial hypertrophy or enlargement associated with chronic obstructive pulmonary disease, pulmonary emboli, valvular disease, or heart failure.
Inverted P waves may signify retrograde or reverse conduction from the atrioventricular (AV) junction toward the atria.

PR Interval:

QRS Complex

The QRS complex follows the P wave and represents depolarization of the ventricles. Immediately after the ventricles depolarize, as represented by the QRS complex, they contract. That contraction ejects blood from the ventricles and pumps it through the arteries, creating a pulse.
location—follows the PR interval
amplitude—5 to 30 mm high but differs for each lead used
duration—0.06 to 0.10 second, or half of the PR interval. Duration is measured from the beginning of the Q wave to the end of the S wave or from the beginning of the R wave if the Q wave is absent

ST Segment

end of ventricular conduction or depolarization and the beginning of ventricular recovery or repolarization
location—extends from the S wave to the beginning of the T wave
deflection—usually isoelectric (neither positive nor negative); may vary from –0.5 to +1 mm in some precordial leads.
ST-segment depression: An ST segment is considered depressed when it’s 0.5 mm or more below the baseline. A depressed ST segment may indicate myocardial ischemia or digoxin toxicity.
ST-segment elevation: An ST segment is considered elevated when it’s 1 mm or more above the baseline. An elevated ST segment may indicate myocardial injury.

T Wave

ventricular recovery or repolarization.
Duration is not measured
location—follows the S wave
amplitude—0.5 mm in leads I, II, and III and up to 10 mm in the precordial leads
configuration—typically round and smooth

QT Interval

ventricular depolarization and repolarization.
The length of the QT interval varies according to heart rate. The faster the heart rate, the shorter the QT interval.
location—extends from the beginning of the QRS complex to the end of the T wave
duration—varies according to age, sex, and heart rate; usually lasts from 0.36 to 0.44 second; shouldn’t be greater than half the distance between consecutive R waves when the rhythm is regular.

	Created by Sarah-Jean Edmonds over 7 years ago

Nursing Note on ECG Interpretation, created by Sarah-Jean Edmonds on 14/04/2017.