applied sciences lecture course ecg interpretation dr ally duncan spr in anaesthesia & clinical...
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Applied Sciences Lecture Course
ECG interpretation
Dr Ally DuncanSpR In Anaesthesia & Clinical Fellow in Undergraduate Medical EducationManchester Royal Infirmary
May 2012
Objectives
• Justify the reasons for performing an ECG
• Develop a structured approach to interpreting an ECG
• Practice interpreting ECGs
The ECG
“The ECG (electrocardiogram) is a transthoracic interpretation of the electrical activity of the
heart.”
Why perform an ECG?
• It’s part of the admission bundle• Indicated by the patient’s symptoms
- symptoms of IHD/MI- symptoms associated with dysrhythmias
• Indicated by the patient’s examination findings- cardiac murmur
ECG interpretation• Quality of ECG?
• Rate • Rhythm• Axis
• P wave• PR interval• QRS duration• QRS morphology• Abnormal Q waves• ST segment• T wave• QT interval
Quality of the ECG
• Patient name • Date of the ECG• Is there any interference?• Is there electrical activity from all 12 leads?
• Calibration:- speed = 25mm/second- height = 1cm/mV
ECG interpretation• Quality of ECG?
• Rate • Rhythm• Axis
• P wave• PR interval• QRS duration• QRS morphology• Abnormal Q waves• ST segment• T wave• QT interval
Rate
• 300/number of big squares between R waves
• Rate is either:- normal- bradycardic- tachycardic
Rhythm
• Are there P waves?• Are they regular?• Does one precede every QRS complex?
• Regular vs. irregular
Axis
Positive in I and II = NORMAL
Positive in I and negative in II = LAD
Negative in I and positive in II = RAD
ECG interpretation• Quality of ECG?
• Rate • Rhythm• Axis
• P wave• PR interval• QRS duration• QRS morphology• Abnormal Q waves• ST segment• T wave• QT interval
P wave
• Are there P waves present?
• Bifid = P mitrale (LA hypertrophy)• Pointy = P pulmonale (RA hypertrophy)
PR interval
• Start of P wave to start of QRS complex
• Normal = 0.12 - 0.2 seconds (3-5 small squares)
• Decreased = can indicate an accessory pathway
• Increased = indicates AV block (1st/2nd/3rd)
ECG interpretation• Quality of ECG?
• Rate • Rhythm• Axis
• P wave• PR interval• QRS duration• QRS morphology• Abnormal Q waves• ST segment• T wave• QT interval
QRS complex
• Is there LVH?
• Sum of the Q or S wave in V1 and the tallest R wave in V5 or V6>35mm is suggestive of LVH
ECG interpretation• Quality of ECG?
• Rate • Rhythm• Axis
• P wave• PR interval• QRS duration• QRS morphology• Abnormal Q waves• ST segment• T wave• QT interval
ST segment
• ST depression- downsloping or horizontal = ABNORMAL
• ST elevation- infarction - pericarditis (widespread)
T wave
• Small = hypokalaemia
• Tall = hyperkalaemia
• Inverted/biphasic = ischaemia/previous infarct
QT interval
• Start of QRS to end of T wave
• Needs to be corrected for HR
• Normal QTc = < 400ms
• Long QT can be genetic or iatrogenic