ECG’s

Jake Turner

What is an ECG?

• A recording of the electrical activity within the heart.

What you need to know

• Basic pathologies that can be picked up on ECG

• How to calculate heart rate• Shockable rhythms• How to localise a pathology from an ECG• Basic arrhythmias

ECG basics

• Check that this ECG is for the patient in front of you! (Name, DOB, patient number etc)

• Check which lead the rhythm strip is (usually lead II)

• At the bottom left is the 'paper speed' (25 mm/s on the horizontal axis) and the sensitivity of the ECG (10mm/mV).

ECG strips

Localising a pathology on ECG

Coronary arteries

How to calculate heart rate

• Method 1: We always print off 10 second ECG strips, so count the number of QRS complexes, multiply this by 6 and you have the heart rate!

• Method 2: Count the number of large squares between each QRS complex, then divide 300 by this number (this method cannot be used for an irregular rhythm).

• NOTE: To calculate the heart rate using method 1 you must use the rhythm strip!

Arrhythmias on ECG

• Ventricular or atrial• Too fast, too slow or irregular• Sinus rhythm, regularly regular– Normal, tachycardic or bradycardic

• Sinus rhythm, regularly irregular– P-P interval varies by more than 10%.

• Irregularly irregular– Atrial fibrillation (VF is effectively pulseless)

Sinus rhythm

• This just means that every QRS complex is preceded by a P wave!

• Note: It does not necessarily mean that every P wave is followed by a QRS complex.

How to tell if a rhythm is regular?

• Check if the ECG printout tells you!• Paper strip method

How to read an ECG (the official version)

• Step 1: Rhythm• Step 2: Rate• Step 3: Conduction (PQ,QRS,QT)• Step 4: Heart axis• Step 5: P wave morphology• Step 6: QRS morphology• Step 7: ST morphology• Step 7+1: Compare the current ECG with a

previous one

What we need to read from an ECG

• Step 1: What jumps out at you? (VF, VT, irregularly irregular, gross morphological problems, ST elevation indicative of an NSTEMI etc)

• Step 2: Rhythm• Step 3: Rate• Step 4: Conduction (is there conduction?)• Step 5: General morphology (is everything about the right

size?)• Step 6: Compare the current ECG with a previous one (this

is less likely to come up in an OSCE, but could do in an exam)

Normal ECG• Rhythm: sinus• Rate: 60-100 bpm• PQ interval 120-200ms• QRS width 60-100ms• Heart axis: between -30 and +90 degrees

• The maximal height of the P wave is 2.5 mm in leads II and / or III• The p wave is positive in II and AVF, and biphasic in V1• The p wave duration is usually shorter than 0.12 seconds (3 small squares)

• No pathological Q waves• No left or right ventricular hypertrophy• Normal R wave propagation. (R waves increase in amplitude from V1-V5)

• No ST elevation or depression• T waves should be concordant with the QRS complex• The ECG should not have changed from the previous ECG

Normal ECG

Quiz time!

What didn’t I cover?

• Heart blocks• The effects of ion disturbances• QRS complex abnormalities• Bundle branch blocks• Cardiac hypertrophy• Genetic conditions• Treatments• Axis deviation

Any Questions?

ECG denotations.• The letters "Q", "R" and "S" are used to

describe the QRS complex• Q: the first negative deflection after the p-

wave. If the first deflection is not negative, the Q is absent.

• R: the positive deflection• S: the negative deflection after the R-wave• Small print letters (q, r, s) are used to describe deflections of small

amplitude. For example: qRS = small q, tall R, deep S.• R`: is used to describe a second R-wave.

Revision sites

• http://en.ecgpedia.org/wiki/Main_Page

• http://en.ecgpedia.org/wiki/Basics• http://www.medicine-on-line.com/html/ecg/e

0001en_files/14.htm• http://www.nottingham.ac.uk/nursing/practic

e/resources/cardiology/index.php

Specific revision pages

• For bundle branch blocks: http://www.medicine-on-line.com/html/ecg/e0001en_files/13.htm

• For right and left hypertrophy: http://www.medicine-on-line.com/html/ecg/e0001en_files/12.htm