9. ECG Common Abnormalilites Flashcards
What 2 things can abnormal rhythms be due to?
Abnormal pulse formation
Abnormal conduction
Where can supraventricular rhythms arise from?
Sinus node
Atrium
AV node
Do you get normal or abnormal ventricular depolarisation with supraventricular rhythms? What can be seen on the QRS complexes?
Normal ventricular depolarisation
Normal QRS complexes
What happens to the length of depolarisation in ventricular rhythms (ventricular ectopic beats)? What happens to the QRS complexes on an ECG?
Depolarisation takes longer, as not via usual His-purkinje system
Wide and bizarre QRS complexes
Give 2 examples of ventricular rhythms
Ventricular premature beats
Ventricular fibrillation
(Ventricular tachycardia)
What changes on an ECG depending on where the origin of the impulse is, which allows the diagnosis of an arrhythmia?
P wave and QRS complex
What is the rhythm strip on an ECG?
Lead II (sometimes also V1 and V5) best for looking at P waves
What is atrial fibrillation?
Multiple atrial foci making impulses chaotic
What is seen on an ECG in atrial fibrillation?
No P waves - wavy baseline
Narrow QRS complexes, irregularly irregular
What is heart block (AV conduction blocks)?
Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of His
What are 2 causes of heart block?
Acute myocardial infarction (most common)
Degenerative changes
What happens in first degree heart block?
Atrioventricular conduction lengthened due to slow conduction in AV node and bundle of His
What is seen on an ECG in first degree heart block?
Normal P wave
PR interval prolonged (>5 small squares)
Normal QRS
What is seen on an ECG in Mobitz type 1 (Wenkebach) 2nd degree heart block?
Progressive lengthening of PR interval until one P is nor conducted, then cycle begins again
What is seen on an ECG in Mobitz type 2 second degree heart block?
PR interval normal
Sudden dropped QRS
Which type of second degree heart block has a high risk of progression to complete heart block?
Mobitz type 2
What happens in third degree heart block?
Atrial depolarisation normal Impulses not conducted to ventricles Ventricular pacemaker takes over HR too slow to maintain BP and perfusion Urgent pacemaker insertion required
What is seen on an ECG in third degree heart block?
No relationship between P waves and QRS complexes
More P waves than QRS complexes
Wide QRS
HR slow 30-40bpm
What is ventricular tachycardia?
Run of 3 or more consecutive ventricular ectopics. Is a broad complex tachycardia. If persists then is a dangerous rhythm, as high risk of VF need to shock to reset.
What is ventricular fibrillation?
Abnormal ventricular depolarisation
Impulses from numerous ectopic sites in ventricular muscle
No coordinated contraction, ventricles quiver
No cardiac output - cardiac arrest
What is seen on an ECG in VF?
Very rapid, irregular reading
What changes are seen on an ECG in ischaemia and MI?
Need to look at PQRST in all 12 leads, changes seen in leads facing affected area
Leads facing affected area show ST segment depression, T wave inversion
What are of the heart is most vulnerable in ischaemia and MI? Why?
Sub endocardial, as furthest from major coronary arteries
When are ischaemic ECG usually seen?
During exercise (as flow through atherosclerosed coronary artery is usually during diastole, but diastole is shorter during exercise)
