When Things Go Wrong ECGS : Lecture 2 Flashcards
What are the three different AV heart blocks ?
- First degree heart block
- Second degree heart block ( type 1 Mobitz , type 2 Mobitz )
- Third degree heart block
What are the causes of heart blocks ?
Degeneration of electrical conducting system with age due to fibrosis and sclerosis
Acute MI ischaemia
Medications
Valvular heart disease
What is first degree AV block ?
First degree AV block is caused by delayed conduction through the AV node resulting in consistently prolonged PR interval ( greater than 5 mini boxes )
- there are no skipped beats , all normal P waves followed by QRS complexes.
This can develop into second or third degree heart block
Causes incl hypokalaemia and ischaemic heart disease
What is second degree AV block - Mobitz type 1 ?
- also known as Wenkebach second degree heart block.
- this is where the PR intervals become progressively longer until one of the QRS complexes is dropped ( electrical signal not conducted through the ventricles)
- the PR interval then returns to normal and repeats the cycle.
What is second degree Mobitz type 11 AV heart block ?
The PR intervals do not successively lengthen. Sometimes they can be normal.
- there is just a sudden drop in the QRS complex.
- atrial rhythm is regular , but ventricular rhythm can be irregular.
HIGH RISK PROGRESSION TO COMPLETE HEART BLOCK.
What is third degree heart block ?
Atria and ventricles are depolarising independently. This is due to complete failure of AV conduction.
- ventricular pacemaker takes over which is very slow :20-40bpm
- typically too slow to maintain blood pressure , usually a very wide QRS complex.
AN URGENT PACEMAKER REQUIRED
Atrial rate 100bpm
What are the two areas in the heart where Arrythmias may arise from ?
- The atria ( which are above the ventricles and therefore called the supraventrovular arrythmia )
Eg the sinus node , atrium itself , AV node
2) ventricles : ventricular arrhythmia
How can you tell the difference between a supraventrocular and ventricular arrythmia on a QRS complex ?
SV = they have narrow ( normal) QRS complex
- Ventricular arrythmia would have a wide and bizarre QRS complexes.
What is an atrial fibrillation?
- A supraventricular arrythmia which is characterised by rapid and dirregular beating of the atrial chambers of the heart.
- arises from multiple atrial foci.
- results in rapid chaotic impulses
- cannot detect any P waves
- irregular R-R intervals
- QRS complexs are normal / narrow
- heart rate and pulse irregularly irregular
- wavy baseline
What are variations in Atrial fibrillation ?
They can be slow : less than 60bpm
They can be fast : ventricular response greater than 100bpm
They can be normal rate 61-99bpm
Afib can be with coarse fibrillation ( amplitude greater than 0.5mm) or fine fibrillation ( amplitude less than 0.5mm)
What are haemodynamic consequences of atrial fibrillation?
The quivering atria essentially cause stasis of the blood as the atria are less efficient at pumping blood into the ventricles. This can result in thrombus formation. A thrombus in the left atrium is more common as blood can sit in the left auricle and clot , which can easily embolise and cause ischaemic stroke.
What are causes of AFib?
Dilated left atrium
Hypertension
Ischaemic heart disease
Hyperthyroidism
Alcohol
Cardiomyopathy
What is the most common cardiac arrythmia in the population ?
Afib
What is ventricular ectopic beats ?
- this is where the impulses are generated by ectopic sin the ventricles and do not travel via the HIS-purkyne system and instead spread slowly across the myocardium
Therefore these ectopic give a broad QRS complex as the time taken for the impulse to travel is longer.
What is ventricular tachycardia ?
Caused by an ectopic focus in the ventricular myocardium,
VT is identified as three or more consecutive ventricular ectopic beats - these are seen as very broad and bizarre QRS complexes on the ECG.
This is dangerous because it can develop into ventricular fibrillation
