Approach to ECG Flashcards
What are the first three steps of ECG interpretation?
- Rate
- Rhythm
- Axis
How would you calculate ventricular rate on an ECG?
Take the number of large squares on ECG paper in 1 minute (300) and divide by the number of squares between two sequential R waves
How would you assess rhythm?
Look at rhythm strip: lead II
Should be defined as regular, regularly irregular, or irregularly irregular
What does the axis represent in an ECG?
Since the left ventricle makes up most of the heart muscle under normal circumstances, normal cardiac axis is directed downward and slightly to the left:
Normal Axis = QRS axis between -30° and +90°.
How would you assess axis in an ECG?
Look at lead 1 and aVF (quadrant method)
- QRS wave should be positive (R wave should be more positive than S is negative)
- Should be done in lead 1 and aVF
How would you assess the P wave?
Best seen in lead II
Should precede each QRS complex
What are P-wave abnormalities?
- P-mitrale – elongation of the P-wave (>120 ms) due to left atrial enlargement
- P-pulmonale – increased amplitude of the P-wave (>2.5 mm) due to right atrial enlargement
How would you assess the PR interval?
Should have a consistent duration
Shortening (<120 ms) suggests an accessory pathway bypassing the AV node
Elongation (>200 ms) suggests impaired AV conduction
What does PR shortening suggest?
An accessory pathway bypassing the AV node
What does PR elongation suggest?
Impaired AV conduction
How would you assess the QRS complex?
Normally consistent amplitude within leads
Elongation (>120 ms) suggests delayed conduction within the His bundle or Purkinje fibres
Increased amplitude suggests ventricular hypertrophy or abnormal ventricular conduction
What are causes of QRS elongation?
- Left bundle branch block
- Right bundle branch block
- Ventricular origin
- Idiopathic ventricular conduction delay
- Hyperkalaemia
- Ventricular paced rhythm
- Ventricular pre-excitation (WPW pattern)
How would you differentiate between left and right bundle branch block?
If the QRS complex is widened and downwardly deflected in lead V1, a left bundle branch block is present.
If the QRS complex is widened and upwardly deflected in lead V1, a right bundle branch block is present.
How would you assess the ST segment?
Should be isoelectric, elevation/depression suggests pathology
Pathological deviation usually presents in adjoining leads
What are causes of ST elevation?
- Infarction
- Pericarditis
- Bundle branch block
- LV aneurysm
- Brugada syndrome
- Benign early repolarization
What artery do leads II, III and aVF represent?
Inferior
Right coronary artery
What artery do leads V1 and V2 represent?
Septal
Left coronary artery
What artery do leads V3 and V4 represent?
Anterior
Left anterior descending artery
What artery do leads V5, V6 and I represent?
Lateral
Left circumflex
How would you assess the T-wave?
Should be positive in most leads
Normally negative in aVR and V1 (occasionally V2)
In what leads could the T wave be negative (physiologically)?
aVR and V1
How long is a normal PR interval?
12-200 ms
How long is a normal QRS?
Narrow (<100 ms), normal amplitude
What does inhalation do to heart rate?
Inhalation decreases vagal tone, increasing heart rate
What does exhalation do to heart rate?
Exhalation increases vagal tone, decreasing heart rate
What happens during blood pressure during inspiration?
Goes down
What happens during blood pressure during expiration?
Goes up
What are abnormal cardiac axes?
Left Axis Deviation = QRS axis less than -30°.
Right Axis Deviation = QRS axis greater than +90°.
Extreme Axis Deviation = QRS axis between -90° and 180°
See lead I as -90 to +90 (vertical half)
See lead aVF as 0 to 180 (horizontal half)
If lead I is positive and aVF is negative, what is the deviation?
Possible Left Axis Deviation
If lead I is negative and aVF is positive, what is the deviation?
Right Axis Deviation
If lead I is negative and aVF is negative, what is the deviation?
Extreme Axis Deviation
What are causes of Left Axis Deviation?
Left ventricular hypertrophy
Left bundle branch block
Inferior MI
Wolff-Parkinson-White Syndrome
What are causes of Right Axis Deviation?
Right ventricular hypertrophy PE Lateral STEMI COPD Hyperkalaemia
What are causes of Extreme Axis Deviation?
Ventricular rhythms – e.g.VT, AIVR, ventricular ectopy
Hyperkalaemia
Severe right ventricular hypertrophy
In what condition are p waves often absent?
Atrial fibrillation
What are the normal durations of the interval in waves?
PR: 120-200 ms (3-5 small squares)
QRS: <120 ms
QT: <45ms in men; <47 ms in women
What is a normal R wave amplitude in I, II and III?
< 20 ms
What does an isolated Q wave in lead III present?
Respiration
What are causes of pathological Q waves?
Left-sides pneumothorax
Dextrocardia
Perimyocarditis
Cardiomyopathy
What are delta waves associated with?
WPW
Slurred upstroke of QRS complex
What are tall T waves associated to?
Hyperkalaemia
Hyperacute STEMI
They are tall if - > 5mmin thelimb leadsAND
- > 10mmin thechest leads
What causes biphasic T waves?
Ischaemia and hypokalaemia
What causes U waves?
Hypothermia
Electrolyte imbalances
Antiarrythmic therapy (digoxin)
How would diagnose first degree heart block on an ECG?
fixedprolongedPR interval (>200 ms)
How would diagnose second degree (2.A) heart block on an ECG?
Progressive prolongation of the PR intervaluntil eventually the atrial impulse is not conducted and theQRS complex is dropped
AV conduction is picked up after
How would diagnose second degree (2.B) heart block on an ECG?
Consistent PR interval durationwithintermittently dropped QRS complexesdue to a failure of conduction
The intermittent dropping of the QRS complexes typically follows arepeating cycleof every3rd (3:1 block)or4th (4:1 block)P wave.
How would diagnose third degree heart block on an ECG?
No AV association
Narrow-complex escape rhythms(QRS complexes of <0.12 seconds duration) originateabove the bifurcationof thebundle of His
Broad-complex escape rhythms(QRS complexes >0.12 seconds duration) originate frombelow the bifurcation of the bundle of His
