ECG interpretation Dr Ally Duncan May 2012 SpR In Anaesthesia & Clinical Fellow in Undergraduate Medical Education Manchester 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 Cardiac conducting system

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 It’s vital to have a system in place to interpret the ECG.

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 Small square 0.04s; Large square 0.2s

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 It’s vital to have a system in place to interpret the ECG.

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 Can use lead II

Axis The normal axis is around 60 degrees.

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 The normal axis is around 60 degrees.

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 It’s vital to have a system in place to interpret the ECG.

P wave Are there P waves present? Bifid = P mitrale (LA hypertrophy) Pointy = P pulmonale (RA hypertrophy) Not very useful signs.

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) Short PR interval can be accessory pathway or can be normal

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 It’s vital to have a system in place to interpret the ECG.

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 It’s vital to have a system in place to interpret the ECG.

ST segment ST depression - downsloping or horizontal = ABNORMAL ST elevation - infarction - pericarditis (widespread)

ST segment

ST segment

ST segment ST segment changes are usually in “territories”

T wave Small = hypokalaemia Tall = hyperkalaemia Inverted/biphasic = ischaemia/previous infarct Tall = can be normal young man

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 Long QT syndrome. Amiodarone, sotalol.

QT interval Long QT syndrome is associated with Torsades de pointes

ECG quiz

ECG 1 AF

ECG 2 INFERIOR MI

ECG 3 LBBB with lateral MI

ECG 4

Any questions?

Summary Discussed the indications for performing an ECG Introduced an approach to interpreting ECGs Discussed common ECG abnormalities