ECG Basics Flashcards
List the Limb leads.
I
II
III
AVR (IV)
AVL (V)
AVF (VI)
Which leads are in the frontal plane axis?
I
II
III
AVR (IV)
AVL (V)
AVF (VI)
What are the stages of approaching an ECG (in order)?
- Identity, standardisation
- Rate
- Rhythm
- P-wave
- P-R interval
- QRS complex
- QT interval
- ST segment
- T wave
- Axis
- Abnormal component
- Formulate and interpret
How do you perform identity and standardisation and what step is this?
Step 1 ≈ identity and standardisation ≈
a) Confirm ID: Name, Age and ECG Date
b) Standardisation: 1cm = 1mV; Paper speed 25mm/sec
For a young child, what changes may you have to make to the Standardisation of the ECG?
Subject to change e.g. young child will have faster HR thus may alter paper speed or mV
How do you determine rate and what step is this?
Rate is the second step ≈ calculation from second lead
300 / R-R boxes
What are the thresholds of rate in an ECG?
Normal: 60-100bpm
Bradycardia: < 60bpm
Tachycardia: 100bpm
How would you report a rate which varies?
Patient heart rate irregular from X to Y
Use X and Y, reporting range and make an average
How do you determine the rhythm of an ECG and what step is this?
Rhythm of ECG is step 3 ≈ determine by criteria + normal rhythm (sinus rhythm) ≈ mark 3 consecutive R waves on another piece of paper then slide across ECG to intervals equal ≈ rhythm is regular
How do you determine a normal P wave and what step is this?
P wave is step 4 ≈ present + upright (<0.25mV and upright in II, III and AVF) + precedes QRS complex (1:1) ≈ atrial depolarisation
1) P-wave present: upright in leads II, III and AVF + <0.25mV
2) P-wave precedes each QRS complex
Absent P wave:
- Atrial fibrillation
- Nodal (junctional) tachycardia
What would an absent P wave suggest?
Absent P wave:
- Atrial fibrillation
- Nodal (junctional) tachycardia
How do you determine the P-R interval and what step is this?
P-R interval is the time form beginning of P to beginning of Q wave ≈ 0.12-0.2s ≈ P-R interval on ECG ≈ AV conduction - 120-200ms (0.12-0.2s) (3 to 5 small boxes) ≈ time between atrial and ventricular depolarisation ≈step 5
How do you determine the QRS complex and what step is this?
Measure from beginning of Q wave to end of S wave ≈ step 6 ≈ Normal duration of < 0.12s (120ms) + Normal Q wave (<40ms ≈ 0.04s) and <2mm depth ≈ Ventricular depolarisation
What could an abnormal QRS complex suggest?
Dependent on time or magnitude
Time: X > 120ms (0.12s)
- Ventricular conduction defect
- Bundle branch block (R or L Bundle Branch Block)
Amplitude: i) Low voltage < 5mm - Hypothyroidism - COAD - Myocarditis - Pericarditis - Pericardial effusion
High voltage
a) ∑ S wave in V1 + R wave in V5 or V6 > 35mm
- Left Ventricular Hypertrophy
b) Dominant R wave in V1;
T wave inversion in V1-V3/V4; Deep S wave in V6
- Right ventricular hypertrophy
What is the QT interval and how can it be measured? How can it be calculated?
Start QRS complex to end of T wave (varies with rate) ≈ calculated by Corrected QTc interval ≈ step 7 in ECG procedure
Corrected QTc interval ≈ 380-420ms (0.38-0.42s)
What does a planar elevation (> 1mm) or planar depression (> 0.5mm) indicate on an ECG at the QTc?
Infarction
What is the ST segment?
Time from S wave to beginning of T wave ≈ isoelectric ≈ time from end of ventricular depolarisation to start of ventricular repolarisation
What is a normal T wave?
T wave ≈ ventricular repolarisation
What are the normal and abnormal T wave findings and in what leads may you see this?
- Inverted in VR and V1 and V2 in young
- Abnormal if inverted in I, II and V4-V6 ≈ ischaemia/infarction
What is a normal axis of an ECG?
Normal: -30º to +90º
What is the J wave?
Camel’s Hump/Osborn wave ≈ QRS-ST junction ≈ deflection occurring at positive defection at J point (negative in aVR and V1) ≈ normally isoelectric
Give 3 causes of tachycardia.
- Anaemia - Anxiety - Exercise - Pain - Temperature / pyrexia - Hypovolemia - Heart failure - PE - Pregnancy - Thyrotoxicosis - BeriBeri - CO2 retention - Autonomic neuropathy - Sympathomimetics (caffeine, adrenaline and nicotine)
Give 3 causes of bradycardia.
- Physical fitness
- Vasovagal attacks
- Sick sinus syndrome
- Acute MI (especially inferior) - Drugs (ß-blockers, digoxin, amiodarone, verapamil) - Hypothyroidism
- Hypothermia
- Increased intracranial pressure
- Cholestasis
What is notable with AF? Causes?
- Rhythm: No discernible P waves
- IHD
- Thyrotoxicosis
- Hypertension
What is notable in 1st and 2nd degree heart block? Causes?
Electrical impulse moves more slowly than normal but conducts via AVN
1st º = PR > 0.2s
2nd º = PR > 0.2s + QRS fails
Causes: - Normal variant - Athletes - Sick sinus syndrome - IHD - Acute carditis - Drugs (digoxin, ß-blockers)
What is notable in 3rd degree complete heart block?
Electrical signal not sent from atria to ventricles
- P wave present but not related to QRS complex and < 0.12s
List some causes of 3rd Degree complete Heart Block.
- Idiopathic - Congenital - IHD - Aortic valve calcification - Cardiac surgery/trauma - Digoxin toxicity - Infiltration (abscesses, granulomas, tumours and parasites)
What could cause a prolonged QT interval?
- Acute MI
- Myocarditis
- Bradycardia
- Head injury
- Hypothermia
- U+E imbalance
- Congenital
- Drugs (Quinidine, Antihistamines, Macrolides, Amiodarone, Phenothiazines)
What makes an abnormal T wave and in what leads?
Inversion in leads I, II and V4-V6 ≈ ischaemia/infarction
What iatrogenic/toxin may cause this change in the ECG and what is the abnormality?
[Digoxin] elevated ≈ digitalis effect ≈ T wave inversion + ST segment sloping depression
What is left axis deviation? What may left axis deviation be caused by?
Negative QRS deflections in II and III ≈ -30º to -90º ≈ LV hypertrophy, MI
What is right axis deviation? What may cause right axis deviation?
Negative QRS deflections in I ≈ +90º to +180º ≈ RV hypertrophy, PE or LV atrophy
What are the ECG changes seen in MI?
1) T wave peaking then T wave inversion
2) ST segment elevation
3) Appearance of new Q waves
How can the ECG be used to localise an infarct?
1) Anterior infarction
- Any precordial leads (V1 to V6)
2) Lateral infarction
- Leads I, AVL, V5 and V6
3) Inferior infarction
- Leads II, III and AVF
4) Posterior infarction
- Reciprocal changes in lead V1 (ST-segment depression, tall R wave)
What impact would hyperkalemia have on an ECG?
Tall, tented T waves
Widened QRS complex
What impact would hypokalemia have on an ECG?
Small T waves
Prominent U waves
What impact would hypercalcemia have on an ECG?
- Short QT interval
What impact would hypocalcemia have on an ECG?
- Long QT interval
- Small T waves
