ECG Interpretation Flashcards
What are the steps in looking at an ECG ?
- Identity, Standardisation
- Rate
- Rhythm
- P Wave
- P–R Interval
- QRS Complex
- QT Interval
- ST Segment
- T Wave
- Axis
- Other Abnormal Components
- Formulate an Interpretation
Explain what you look for when looking at identity and standardization of an ECG.
First confirm patient’s name and age and ECG’s date
Standardisation
- Make sure that 1cm = 1mV and
- Paper speed 25mm/sec
Explain what you look for when looking at Rate of an ECG.
Calculation:
- Divide 300 by the number of big squares per R – R interval (i.e. by number of 0.20 s segments per R-R interval)
- Calculate this in the second lead
- Normal rate 60-100 b.p.m (Bradycardia <60 and Tachycardia >100)
What is the scale that is usually used for an ECG per small square or big square ?
A small square = 0.04 s (40 ms)
A large squares = 0.2 s (200 ms)
Define R-R interval.
Intervals between successive heartbeats
Explain what you look for when looking at Rhythm of an ECG.
Are the normal P waves present (<0.25mV, and upright in II III and AVF)?
Are the QRS complex narrow-normal <120 ms (0.12s) or wide >120 ms (0.12s)?
Relationship between P waves and QRS complexes. (One P wave followed by one QRS complex)
Is the rhythm regular or irregular (arrhythmia)?
How can you ensure whether the rhythm is regular or irregular ?
Mark position of 3 successive R waves
Slide the mark forward and check that intervals are equal
Define sinus rhythm.
"normal cardiac rhythm proceeding from the sinoatrial node" Hence, Normal P waves Normal QRS complexes One P wave followed by one QRS complex Regular rhythm
What are possible abnormalities if the rhythm is found to be irregular (arrhythmia).
1) Atrial Fibrillation (=”atrial contractions are rapid and random”): No discernible P waves and irregular QRS complexes
2) Atrial Flutter (=” atrial contractions are rapid but regular”): More than 1 P wave per QRS complex (ventricular activation may in the meantime be completely regular)
3) Junctional (Nodal) Tachycardia (=”Tachycardia resulting from a focus in the atrioventricular node”): Normal QRS complexes but absent P wave
4) Ventricular Tachycardia (=”Tachycardia originating in a ventricle”): Broad QRS complexes, T waves possibly difficult to identify. (> 120 ms)
What event within the heart does the P-Wave represent ?
Atrial Depolarisation
Explain what you look for when looking at the P-wave of an ECG.
<0.25mV, and upright in II III and AVF
Normally precedes each QRS complex
Give examples of abnormal P waves.
Absent P-wave due to:
Atrial fibrillation
Nodal (junctional) rhythm
P-Mitrale: Bifid P wave, signifying left atrial hypertrophy
P-Pulmonale: Peaked P wave (more than 0.25 mV height), signifying right atrial hypertrophy
What is the P-R interval ?
The time between atrial and ventricular depolarisation.
Explain what you look for when looking at the P-R interval of an ECG.
Measure from the beginning of P to the beginning of Q wave, normal range 120-200 ms (0.12-0.2 s).
Identify possible abnormalities in the P-R interval, explaining why each might occur.
Prolonged P-R interval >200 ms (0.2 s) implies delayed AV conduction (= Heart Block)
What event in the heart does the QRS complex represent ?
Ventricular Depolarisation (also hides atria repolarisation)
Explain what you look for when looking at the QRS complex of an ECG.
- Measure from the beginning of Q to the end of S wave.
Normal Duration <120 ms (0.12 s)
Normal Q wave <40 ms (0.04 s) and <2mm depth
Identify possible abnormalities in the QRS complex, explaining why each might occur.
If >120ms (0.12 s):
-ventricular conduction defects (L or R bundle branch block)
Low voltage (<5 mm):
- Hypothyroidism
- Chronic Obstructive Airways Disease (COAD)
- Myocarditis
- Pericarditis and Pericardial effusion
Left ventricular hypertrophy:
-R wave in V5 >25mm or
sum of the S wave in V1 and R wave in V5 or V6 >35mm (=Sokolow-Lyon index)
Right ventricular hypertrophy:
- Dominant R wave in V1 (> 7mm tall)
- Deep S wave in V6 (> 7mm deep)
- T wave inversion in V1-V3 or V4
Significant Q wave: - >40ms (0.04 s) - Depth >2 mm Present couple of hours/days after acute MI If present in lead III consider PE.
What is the Q-T interval ?
“the period from onset of depolarisation to completion of repolarisation of the ventricular myocardium”
Explain what you look for when looking at the QT Interval of an ECG.
- Measure from start QRS to end of T wave (varies with rate)
-Calculate QTc interval (“adjusts the QT interval correctly for heart rate extremes”)
QTc= QT/√RR
Normal is 380-420 ms (0.38-0.42 sec)
Identify possible abnormalities in the QT interval, explaining why each might occur.
Prolonged QT Interval:
- Acute Myocardial Ischaemia
- Myocarditis
- Bradycardia
- Head Injury
- Hypothermia
- U&E Imbalance (K+ Ca2+ Mg2+ )
- Congenital
- Drugs (Quinidine, Antihistamines, Macrolides, Amiodarone, Phenothiazines)
What is the ST segment ?
Time from the end of ventricular
depolarisation to the start of ventricular repolarisation
Explain what you look for when looking at the ST Interval of an ECG.
Usually isoelectric
Identify possible abnormalities in the ST interval, explaining why each might occur.
Elevation > 2mm in two adjacent chest leads
OR
Elevation > 1mm in two adjacent limb leads
=Myocardial Infarction
ST depression upon exercice
=Myocardial Ischemia
What is the T wave ?
Ventricular Repolarisation
Explain what you look for when looking at the T wave of an ECG.
Normally inverted in VR and V1 and in V2 in young
Identify possible abnormalities in the T wave, explaining why each might occur.
T wave inverted in I, II and V4 -V6
=Ischaemia /Infarction
T wave inversion and ST segment sloping depression
=Digitalis Effect (due to Digoxin)
Explain what you look for when looking at the Axis of an ECG.
Sum of all ventricular forces during ventricular depolarisation (expect leads I II and III to be predominantly positive )
Normally, between -30° and +90°.
Identify possible abnormalities in the Axis of the heart, explaining why each might occur.
Left Axis Deviation (-30 to -90°)
- Negative QRS deflections in leads II and III
- Could signify LV hypertrophy, MI
Right Axis Deviation (+90° to +180°)
- Negative QRS deflection in lead I
- Could signify RV hypertrophy, PE, MI
Describe the ECG changes which take place in an MI.
During an Acute MI, the ECG evolves through 3 stages: - T wave peaking followed by T wave inversion - ST segment elevation -Appearance of new Q waves
Which leads will we see changes in for an infarction of which area of the heart ?
Anterior Infarction:
-Any of precordial leads (V1 through V6)
Lateral Infarction:
-Leads I, AVL, V5 and V6
Inferior Infarction:
-Leads II, III, and AVF
Posterior Infarction:
-Reciprocal changes in lead V1 (ST- segment depression, tall R wave)
What changes would you expect to see in an anterior infarction ?
- Sinus rhythm
- Q waves in leads V2-V4
- Inverted T waves in leads V4-V6
What changes would you expect to see in an anterolateral infarction ?
- Sinus rhythm
- Q waves in leads I, II, AVL, V3-V5
- Raised ST segments in leads V2-V6
What changes would you expect to see in an inferior infarction ?
- Sinus rhythm
- Q waves in leads III and AVF
- Depressed (ischemic) ST segment in leads AVL and V6
What changes would you expect to see on an ECG in a pulmonary embolism (PE) ?
- Large S wave in lead I
- Deep Q wave in lead III
- Inverted T wave in lead III
Identify metabolic abnormalities for which you could see differences on the ECG (name the differences).
- Hyperkalaemia:
Tall, tented T wave, widened QRS
Hypokalaemia:
Small T waves, prominent U waves (successor of T wave)
Hypercalcaemia:
Short QT interval
Hypocalcaemia:
Long QT interval, small T waves
