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A part of a learning module on ecg interpretation from docsity.com. It covers the analysis of pr, qrs, and qt intervals, and the identification of right and left atrial and ventricular hypertrophy in a 12-lead ecg. The document also includes criteria for diagnosing right atrial enlargement, left atrial enlargement, right ventricular hypertrophy, and left ventricular hypertrophy.
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In Module VII a we introduced a 6 step approach for analyzing a 12-lead ECG and covered the first 3 steps. In this module we will cover the last 3 steps.
QRS complex
< 0.10 s 0.10-0.12 s > 0.12 s
Normal Incomplete bundlebranch block
Bundle branch block PVC Ventricular rhythm
Remember: If you have a BBB determine if it is a right or left BBB. If you need a refresher see Module VI.
3 rd^ degree AV block with ventricular escape rhythm
Incomplete bundle branch block
QT interval
The duration of the QT interval is proportionate to the heart rate. The faster the heart beats, the faster the ventricles repolarize so the shorter the QT interval. Therefore what is a “normal” QT varies with the heart rate. For each heart rate you need to calculate an adjusted QT interval, called the “corrected QT” (QTc):
QTc = QT / square root of RR interval
PR interval? QRS width? QTc interval? 0.16 seconds 0.08 seconds 0.49 seconds
QT = 0.40 s RR = 0.68 s Square root of RR = 0. QTc = 0.40/0. = 0.49 s
Interpretation of intervals? Normal PR and QRS, long QT
Tip: Instead of calculating the QTc, a quick way to estimate if the QT interval long is to use the following rule:
A QT > half of the RR interval is probably long.
Normal QT Long QT
QT
RR
10 boxes
23 boxes 17 boxes
13 boxes
Right atrial enlargement
The P waves are tall, especially in leads II, III and avF. Ouch! They would hurt to sit on!!
Left atrial enlargement
The P waves in lead II are notched and in lead V1 they have a deep and wide negative component.
Notched
Negative deflection
Left atrial enlargement
Normal LAE A common cause of LAE is LVH from hypertension.
Right ventricular hypertrophy
Normal RVH
Right ventricular hypertrophy
A common cause of RVH is left heart failure.