ECG interpretation

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.”

The ECG

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

Calibration

Calibration

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

Rate

Rhythm

• Are there P waves?• Are they regular?• Does one precede every QRS complex?

• Regular vs. irregular

Axis

Axis

Axis

Positive in I and II = NORMAL

Positive in I and negative in II = LAD

Negative in I and positive in II = RAD

Axis

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)

P mitrale

P pulmonale

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

• Normal = <0.12 seconds

• >0.12 seconds = Bundle Branch Block

QRS complex

W I LL ia m = LBBB

M a RR o w = RBBB

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

Q waves

• Q waves are allowed in V1, aVR & III

• Pathological Q waves can indicate previous MI

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)

ST segment

ST segment

ST segment

T wave

• Small = hypokalaemia

• Tall = hyperkalaemia

• Inverted/biphasic = ischaemia/previous infarct

T wave

T wave

T wave

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

QT interval

ECG quiz

ECG 1

ECG 2

ECG 3

ECG 4

Any questions?

Summary

• Discussed the indications for performing an ECG

• Introduced an approach to interpreting ECGs

• Discussed common ECG abnormalities