7. Interpreting ECGs Flashcards
Where could supra ventricular rhythms arise form?
SA node (sinus)
Ectopic atrium
AV node
What are the characteristics of supra ventricular rhythms?
Conducted into and within ventricles via normal his-purkinje system, so NORMAL ventricular depolarisation will occur with narrow QRS complexes.
What are the characteristics of ventricular rhythms?
Depolarisation takes longer as not via his-purkinje system, widened and bizarre QRS complexes.
What are 3 types of abnormal ventricular rhythms?
- Ventricular premature beats
- Ventricular tachycardia
- Ventricular fibrillation
What would you see on the ECG if an ectopic atrial beat is present?
P wave no perfectly rounded
QRS normal
What would you see on an ECG if there was an AV node beat?
P wave inverted as depolarising away from the apex
QRS normal
What would you see if there was a ventricular ectopic beat?
Widened QRS
RV - upwards
LV - downwards
How can you determine if there is normal sinus rhythm?
If every QRS is preceded by a P wave
What would be visible on an ECG of atrial fibrillation?
No P waves, wavy baseline.
What happens to ventricular depolarisation during atrial fibrillation?
Impulses arrive at AV node at rapid irregular rate, only some conducted to ventricles at irregular intervals.
Ventricles depolarise and contract normally.
Which rhythm abnormality can be described as ‘irregularly irregular’?
Atrial fibrillation
What is a complication of atrial fibrillation?
Stagnant blood in atria can form thrombosis and enter systemic circulation - Stroke
How is CO affected during atrial fibrillation?
Cardiac output remains ok
What are the 3 types of heart block (AV conduction block)?
1st degree
2nd degree- mobitz 1 +2
Third degree - complete heart block
What ECG changes are visible in first degree heart bloc?
PR interval prolonged (> 0.20 seconds)
What happens in first degree heart block?
Slow conduction in AV node and His bundle.
What is the outcome/mangagement of first degree heart block?
Usually benign and no treatment needed, but worse blocks may follow.
What is mobitz type 1 HB called?
Wenkebach rhythm
What ECG changes are visible in mobitz type 1 HB?
Progressive lengthening of PR interval until a QRS complex is dropped. Cycle begins.
What is the prognosis of wenkebach rhythm?
Generally benign, less likely to progress to CHB.
How does mobitz type 2 differ to mobitz type 1?
PR interval normal
Sudden dropped QRS and skipping of a beat.
What is the prognosis of type 2 mobitz?
High risk of progression to CHB
What is third degree heart block?
Atrial depolarisation remains normal but is not conducted to the ventricles. No link between atria and ventricles.
* Ventricular escape rhythm kicks takes over
How does ventricular escape rhythm differ to sinus rhythm?
Very slow, 30-40 bpm
What ECG changes would you see in third degree heart block?
Normal, regular P waves but no relationship to wide QRS complexes
What is the outcome of third degree HB?
Often too slow to maintain BP and organ perfusion
Urgent pacemaker insertion required.
How can wenkebach rhythm be described?
Regularly irregular - regular rate with a dropped beat
How is VT defined?
> =3 consecutive ventricular ectopics
What is the risk of VT?
Dangerous rhythm which has a high risk of leading to VF (cardiac arrest)
What is happening to the ventricles in VF?
Quivering , no coordinated contraction.
NO CARDIAC OUTPUT - CARDIAC ARREST
NO PULSE
What leads to myocardial ischaemia?
Reduced perfusion due to coronary atherosclerosis.
Which area of the heart is most vulnerable to ischaemia?
Endocardium- vessels are on epicardial surface
Explain what would you expect to see on ECG leads facing an area of myocardial ischaemia?
ST segment depression and/or T wave inversion due to abnormal current during repolarisation.
What causes ST elevation MI?
Complete occlusion of a coronary artery.
What would you expect to see in an acute ECG of a STEMI?
ST elevation in leads facing infarcted region
What evolving changes would you see following a STEMI?
Acute - ST elevation Hours -Smaller R wave Day 1/2 - Q wave deepens, T wave inversion Days later - T wave inverted Weeks - Deep Q wave persists
How can you define pathological Q waves?
> 1 small square wide
2 small squares deep
(Depth >1/4 of height of R wave)
What ECG changes would you see in a patient with hyperkalaemia?
Tall, tented T waves
Big Pot, High tea
What ECG changes would you see in a patient with hypokalaemia?
Low T waves
What is the most common ventricular arrythmia?
Ventricular premature beats
