CAL: ECG Interpretation Flashcards
How should you work out the HR from an ECG?
If you have time, count every single QRS during a minute
T/F: P waves have their own T waves
True - often - but often you can’t see this
Name 4 conditions associated with there not always being a P wave for every QRS
- Premature beats – ventricular or supraventricular
- Sinus arrest with escape complexes
- Atrial standstill
- Atrial fibrilliation
Distinguish complexes of ventricular and supraventricular origin
- VENTRICULAR - wide and bizarre, AV dissociation or no associated P waves
- SUPRAVENTRICULAR - narrow upright QRS complexes in appropriate leads (unless concurrent hypertrophy or conduction disturbance), may be associated with P waves (may have AV dissociation if junctional), same QRS as sinus complexes where present.
What happens in atrial standstill?
Bradycardia (<70 bpm) without any P waves
What can cause a P wave without a QRS complex? 2
Failure of conduction through AVN – 2nd (intermittent) or 3rd degree (persistent)
What are the different types of 2nd degree block?
- Mobitz type 1 = progression prolongation of PR interval, prior to failure of P wave conduction. This is almost always due to disease of the AVN.
- Mobitz type 2 = this is almost always a disease of the distal conduction system. The ECG has intermittently non-conducted P waves, not preceded by PR prolongation and not followed by PR shortening. There is usually a fixed number of non-conducted P waves for every successfully conducted QRS complex.
Describe what happens in 1st degree AV block?
all the P-wave are conducted but some of them are conducted with delay leading to lengthy P-Q intervals.
Typically what is meant by HR on an ECG trace?
the ventricular rate
What implies the atria and ventricules are depolarising autonomously?
varied interval between atrial and vetricular depolarisations. . This is called “atrioventricular dissociation” = 3rd degree AV block.
What are DDx for P wave absence 4
- Atrial fibrillation (this trace)
- Atrial standstill
- Ventricular tachycardia/fibrillation
- Asystole (flatline)
Describe ventricular fibrillation
has an absence of any organized ventricular or atrial activity. You would not be able to recognize any QRS complexes.
What are features of atrial standstill?
absence of P-waves and supraventricular QRS complexes, usually bradycardic (<70bpm)
Define asystole
when there is a “flatline” or a complete absence of any electrical activity.
What does the presence of P waves on any trace suggest?
The atria are depolarizing in an organized way and therefore they cannot be fibrillating.
What does a VPC look like on an ECG?
relatively normal appearance but just appears early (i.e. premature)
What pathology can ECGs indicate? 3
- changes in myocardial mass
- metabolic abnormalities affecting the myocardium
- alterations in conductivity between heart and skin
Can you determine the mean electrical axis from an ECG?
yes
DDx for not a P for every QRS - 3
- Premature complexes (VPC or
Junctional premature) - Sinus arrest with escape complexes
(Ventricular escape and Junctional escape) - No organised atrial depolarisation (Atrial standstill or Atrial fibrillation)
Define AF
Enlarged atria with multiple waves of depolarisation spreading in a disorganised fashion simultaneously. No evidence of P-waves. Coarse oscillation of the baseline demonstrates the presence of f-waves.
DDx - No QRS following a P wave
FAILURE OF AV CONDUCTION:
- Second degree AV block (Intermittent failure of AV conduction, Mobitz type I - Prolongation of P-R interval, Mobitz type II - No prolongation of P-R interval)
- Third degree AV block (Complete failure of AV conduction, Complete AV dissociation)
What do P wave variations indicate? 3
- May be normal - wandering pacemaker
- May indicate atrial ectopy
- P-wave should be positive in lead II
What does variation in QRS complex indicate?
- Some variation may be normal
- May indicate variable conduction
- May indicate electrical alternans
What is the main determinant of the significance of rhythm disturbance?
- where the rhythm disturbance is causing clinical signs
- why is the rhythm disturbance present
- always treat the patient and not the ECG
Why might abnormalities of generation or conduction of the depolarisation arise? 7
- Intrinsic cardiac disease
- Hypoxia
- Autonomic influence
- Mechanical abnormalities
- Metabolic abnormalities
- Electrolyte disturbances
- Drugs
