ECG interpretation Flashcards
What is the normal width of the P wave
<120 ms wide (3 small squares)
What is the normal height of the P wave
<1.3 mV (3 small sqaures)
What could cause a P wave to have low amplitude
Atrial fibrosis
Obesity (fat between SAN and ECG electrodes)
Hyperkalaemia (can inhibit sodium channels)
What could cause a tall P wave?
Right atrial enlargment
What could cause a bifid p wave?
Left atrial enlargement (delayed depolarisation of different parts of atrium)
What could cause focal atrial tachycardia?
Alternative pacemaker foci (ectopic pacemaker, excitable cells outside of SAN)
What is the normal time for PR interval?
120-200 ms
What could cause a longer PR interval?
Disorders of AV node
Disorders of specialised conducting tissue
What could cause a shorter PR interval?
Younger patients
Wolf-Parkinson-White syndrome
What is Wolf-Parkinson-White syndrome?
There is an abnormal accessory electrical pathway called the Bundle of Kent between the atria and ventricles. Signals travel more quickly than through AV node leading to premature activation of ventricles
Delta wave characteristic feature - initial part of ventricular contraction before main pathway contraction.
Rapid and irregular heartbeat, supraventricular tachycardia.
Symptoms of Wolf-Parkinson-White Syndrome
Palpitations, raid heartbeat, chest pain, dizziness, fainting.
Can be asymptomatic.
How fast is normal QRS complex?
<120ms
What is the normal frontal axis between
-30 and +90
What can cause QRS >120 ms?
ventricular conduction delay
Bundle branch block
Pre-excitation (delta wave in WPW syndrome)
What can cause small amplitude QRS complex
Obese patients (fat between ventricles and ECG electrode)
Pericardial effusion (fluid between ventricles and ECG electrode, may compress heart and hinder transmission through myocardium)
Infiltrative cardiac disease (disorders which deposit abnormal substances into heart eg amyloids. can cause fibrosis and impaired myocardial conduction)
What can cause tall QRS complexes?
Left ventricle hypertrophy
Thin patient (minimal fat between ventricles and ECG electrodes)
What can cause an elevated ST segment?
Myocardial infarction (convex, damaged myocardial cells have influx of calcium ions which shows on ECG)
Pericarditis (concave, electrical changes due to irritated epicardium)
Inversion of the T wave may indicate…
Ischaemia or infarction (influx of calcium, leads to delayed repolarisation, T-wave changes)
Myocardial strain/hypertrophy (increased stress on heart, increased calcium influx, delayed repolarisation)
Myocardial disease/ cardiomyopathy
What is the normal range for heart rate?
60-100 bpm
What are types of tachycardias?
Atrial fibrillation
Atrial flutter
Supraventricular tachycardia
Ventricular tachycardia
Ventricular fibrillation
What is atrial flutter?
Regular, organised and rapid heartbeat originating in the atria due to reentrant circuits, typically has a regular ventricular response
What is the characteristic ECG of atrial flutter?
Sawtooth pattern
What are some causes of bradycardia?
Conduction tissue fibrosis
Ischaemia
Inflammation/infiltrative disease
Drugs
What is the difference between AV block and Bundle Branch block?
AV block refers to delay or interruption between atrial and ventricles at AV node
BBB refers to delay or blockage along a bundle branch in the ventricle
What is first degree AV block?
Slow conduction between atria and ventricles, all impulses still conducted
What is second degree AV block?
Slow conduction with some of the signals being blocked between the atria and the ventricles
What is third degree AV block?
No atrial impulses reach the ventricles so independent rhythm for atria and ventricles.
What does Mobitz type 1 refer to?
Type of second degree AV block.
Progressive prolongation of PR until a P wave is not followed by QRS
What does Mobitz type II refer to?
Type of second degree AV block
consistent PR interval but intermittent non-conducted P wave without QRS. May progress to complete heart block.
What are ECG findings for right bundle branch block?
MaRrow
V1 = M shape
V6 = W shape
What are ECG findings for left bundle branch block?
WiLliam
V1 = W shape
V6 = M shape
Which leads show high lateral side of heart?
I, aVL
Which leads show the inferior wall of the heart?
aVF, II, III
Which leads show septal activity?
V1,V2
Which leads show anterior wall of heart?
V2, V3, V4
Which leads show the lateral wall of heart?
V5, V6
What does hyperkalaemia show on ECG?
Flattened P waves, broad QRS, tall T waves
Flat p waves - decreased excitability of atrial cells
Broad QRS - reduced resting potential of ventricular cells slowing conduction
Tall T waves - increase in K+ as it leaves the cell during repolarisation and already high concentration
What does hypokalaemia show on ECG?
QT prolongation (longer for ventricles to depolarise and repolarise) and flat T waves
What does hypercalcaemia show on ECG?
QT shortening
What does hypocalcaemia show on ECG?
QT prolongation
