ECG Interpretation Flashcards
How do you calculate rate?
300 divided by the number of big squares between each QRS complexes
What are the four criteria’s for sinus rhythem?
- Are normal P waves present (shorter than 0.25mm and upright in 1/2/3)
- Are the QRS complex narrow (less than 0.12s) or wide (more than 120ms)
- P wave ALWAYS come before a QRS complex
- Is the rhythm regular or irregular
How can you physically tell if the rhythm is regular
Mark positions of 3 successive R waves then slide marker along to check intervals are equal
Describe what is seen on an EGC for atrial fibrillation
There are no visable P wave and irregular QRS complexes
How does atrial flutter appear on ECGs?
Where P waves are seen at a rate of 300BMP giving saw tooth appearance.
What does a normal P wave look like?
Less than o.25mV in height and it deflects upwards in leads 1, 3 and AVF
In what defects are the P waves absent?
Atrial fibrillation and Nodal rhythm
Name and describe an abnormal P wave
P-mitrale - Bifid P waves that indicate left atrial hypertrophy.
P-Pulmonale - Peaked P wave which indicates right atrial hypertrophy.
How to you measure the P-R interval?
From beginning of P wave to beginning of Q wave. Normal range is 0.12-0.2s.
A prolonged P-R imples?
Delayed AV conduction
How do you measure the QRS complex and what does a normal QRS complex look like?
From beginning of Q wave to end of S wave. Normal duration - 0.12s and the normal Q wave is 0.04s and less than 2mm depth.
If the QRS wave lasts for longer than 0.12s what does this indicate?
Ventricular conduction defects such are left and right bundle branch defects
If the voltage of the QRS complex is below 5mm then what does this indicate?
Hypothyroidism, COAD (chronic obstructive airway disease), myocarditis, pericarditis and pericardial effusion.
How does left ventricular hypertrophy appear on an ECG and is the most common cause?
R wave in V5 is bigger than 25mm. This is most often due to high blood pressure
How does right ventricular hypertrophy appear on an ECG?
Dominant R wave in V1, T wave inversion in V1-V3 or V4, and Deep S wave in V6
What is a significant Q wave defined as and when might you see this
- Longer than 0.04s and deeper than 2mm. It can be present a couples hours/days after acute MI and if its present in lead 3 then consider PE.
How calculate the correct QTc intercal?
QT/Square root of RR interval.
What can cause a prolonged QT interval?
- Acute myocardial ischaemia,
- Myocarditis,
- Bradycardia,
- Hypothermia,
- U&E imbalance,
- Congenital
- Drugs
What is the ST segment?
Time from end of ventricular depolarisation to the start of ventricular repolarisation. Usually isoelectric (sits at baseline)
Describe when you have an abnormal ST segment and why this might occur
- If there is elevation in two adjacent limb or chest leads then indicates infarction.
- If the st segment is depressed then it indicates ischaemia
Describe the normal and abnormal inverted T wave
Normal - aVR, V1 and (V2 in young folk)
Abnormal - Inversion all other leads (ischaemia/infarction)
What are the effects of digoxin
T wave inversion and ST segment sloping depression
What is the cardiac axis?
Average direction of spread of the depolarisation wave through the ventricles. Normal axis means all QRS complexes in leads 1-3 deflect up with lead 2 having the highest peak.
Describe what occurs when there is deflections in the cardiac axis
If there is left axis deviation - there will be negative deflections in lead 2 and 3. Indicates LV hypertrophy or MI.
If there is right axis deviation then there will be negative QRS deflections in lead one. Indicates RV hypertrophy, PE or MI
Describe the MI ECG changes
- T wave peaked followed by T wave inversion.
- ST elevation.
- Appearance of new Q waves
Describe how you can use the ECG to localise the infarct causing the Infarct
Anterior infarction - Any precordial (chest) leads
Lateral infarction - Leads 1, AVL, V5 and V6.
Inferior - Leads 2, 3,and AVF
Posterior - Reciprocal changes in lead V1
Describe how pulmonary embolism presents on ECG
Large S wave in lead 1,
Deep Q wave in lead 3 and inverted T wave in lead 3
How do hyperkalaemia and hypokalaemia show on ECG?
Hyper - Tall, tented T waves and widened QRS.
Hypo - Small T waves and prominent U wave
How does hyper/hypocalcaemia present on ECGs
Hyper - Short QT interval,
Hypo - Long QT interval and small T waves
