ECG- Recognising Common Abnormalities Flashcards
What are causes of abnormal rhythms? (2)
Abnormal impulse formation
Abnormal conduction (AV block)
Where in the heart can rhythms arise from and what are they called?
SAN-supraventricular rhythms
Atrium- supraventricular rhythms
AV node- supraventricular rhythms
Ventricle- ventricular rhythms
What are the features of supraventricular rhythms?
- conducted into and within ventricles by His-Purkinje system
- normal ventricular depolarisation
- normal (narrow QRS) complexes
What are the features of a ventricular rhythm?
- from foci in ventricle
- conduction not via usual His-purkinje system
- depolarisation takes longer
- wide and bizarre QRS complex (different foci produce different shapes)
What are the 3 types of ventricular rhythms?
Ventricular premature beats
Ventricular tachycardia
Ventricular fibrillation
What is atrial fibrillations?
Random impulses causing chaotic depolarisation- cardiac cannot contract in a coordinated way
What effect does atrial fibrillation have on CO?
It drops it slightly
What is the ECG of atrial fibrillations?
No p waves just wavy baseline (atria quiver rather than contract)
Narrow QRS at irregular intervals
What happens to the heart rate and pulse rate during atrial fibrillations?
They become irregularly irregular
Why would blood thinners be given to those who have atrial fibrillations?
Clots can form in the striatum because there is static blood this can cause strokes etc
What is AV conduction blocks?
Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of His
What are the two main causes of AV conduction block?
Acute MI - full recovery within a few days
Degenerative changes
What are the 3 types of heart blood?
First degree block
Second degree heart block: type 1 and type 2
Third degree heart block (complete heart block)
What happens in complete heart block?
A pacemaker in the ventricle will take over (ventricular escape rhythm)
What is first degree heart block defined by?
Slow conduction in AV node and His Bundle
Normal P wave
Prolonged PR interval (>5 small squares)
Normal QRS
What is type 1, 2nd degree heart block?
Progressive lengthening of PR interval until one P is not conducted (this allows time for AVN to recover) then cycle begins again
What is type 2, 2nd degree heart block?
PR interval normal
Sudden non-conduction of a beat (dropped beat without warning- ie no QRS)
High risk of progression to complete heart block
What is 3d degree heart block?
Atrial depolarisation normal but no impulses are conducted to ventricles
Ventricular pacemaker takes over-wide QRS (ventricular escape rhythm)
No relationship between the P and the QRS wave of an ECG
What are the problems with 3rd degree heart block?
Heart rate is too slow- 30/40
Too slow to maintain BP and perfusion
Urgent pacemaker insertion required
Possible for someone to go into asystole
What are the features of ventricular ectopic beats?
Impulses not spread via the His-purkinje system
Much slower depolarisation of ventricles
Wide QRS complex, different in shape to usual
What is ventricular tachycardia?
Run of 3 or more consecutive ventricular ectopics
Broad complex tachycardia
Why is persistence ventricular tachycardia so dangerous?
Because the person is at high risk of ventricular fibrillation
They will need to be electrically shocked back into rhythm
What is ventricular fibrillation?
Abnormal, chaotic, fast, ventricular depolarisation
Caused by impulses form numerous ectopic site in ventricular muscle
No co-ordinated contraction causing ventricles to quiver
What effect doe VF have on CO?
No cardiac output, cardiac arrest
Ischameia and MIs can effect any part of the heart, how can you tell where the damage is?
Changes seen in leads facing affected area.
Look at which ECG lead is abnormal
What region of tissue in the heart is most vulnerable from lack of perfusion?
Sub-endocardial region
What changes will you see in an ECG lead facing an area of ischaemic cardiac tissue?
ST segment depression
Or T wave inversion
Due to abnormal current during repolarisation
*ischaemic ECG changes may only be seen during exercise but if severe reduction of lumen: ischaemic changes at rest
What is STEMI?
ST segment elevation myocardial infarction
Due to complete occlusion of lumen by thrombus
Occurs when muscle injury extends ‘full thickness’ from endocardium to epicardium
What defines a pathological Q wave?
Wider than 1 small square (longer than 0.04 seconds)
Deeper than 2 small squares
(Depth more than 1/4 of the height of the subsequent R wave
What effect does hyperkalaemia have on the heart?
RMP less negative which inactivates some voltage gates Na+ channels
- heart is less excitable
What are the ECG changes seen with hyperkalaemia?
High T wave
Prolonged PR interval, depressed ST segment
P wave absent
Ventricular fibrillation
What ECG changes are seen in hypokalaemia?
Low T wave
What is the cardiac axis?
The average direction of spread of ventricular depolarisation
Usually Downwards and left
(-30 to +90 degrees)
What is left axis deviation?
When overall direction of ventricular depolarisation is upwards and to the left (less than -30 degrees)
What is left axis deviation associated with?
Conduction block of anterior branch of left bundle
Inferior MI
Left ventricular hypertrophy
What is right axis deviation?
When overall direction of ventricular depolarisation is downwards and to the right (more than +90 degrees)
What is right axis deviation associated with?
Right ventricular hypertrophy
How can you spot left axis deviation?
Look at leads I and aVF (or III)
If QRS is upright in lead I an inverted in aVF (or in III), it is LAD
How can you spot righ axis deviation?
Look at leads I and aVF/III
If QRS is inverted in lead I and upright in lead III (aVF) then it is RAD
In an ECG of complete heart block what its he relationship between the P waves and the QRS complex?
No relationship between them because the atria and ventricle are being stimulated by different pacemakers
What might have happened to cause a widened QRS complex?
Problems with ventricle wall, bundle branch block, ischaemia, drugs, metabolic abnormalities, hypokalaemia
What do pathological Q waves suggest?
Indicates an area of muscle necrosis following ischaemia
What does ST depression suggest?
Reduced perfusion to the myocardial muscle
If a p wave can be seen on an ECG, it is possible for someone to be having AF?
No
