Arrythmias Flashcards
What is first degree heart block?
This occurs when the electrical signal from the SA node is conducted to the ventricles, but the conduction is delayed more than normal
What are the criteria for the diagnosis of first degree heart block on ECG?
PR interval being longer than normal (>0.2s)
What can cause first degree heart block?
- Coronary Artery Stenosis
- Acute rheumatic Carditis
- Digoxin Toxicity
- Electrolyte disturbances
What are the different types of second degree heart block?
- Wenckeback (Mobitz type 1)
- Mobitz type 2
What is the general definition of second degree heart block?
When excitation intermittently fails to pass through the AV node or the bundle of His
What is a Wenckbach?
Mobitz type 1 Second degree heart block
This is characterised by progressive lengthening of the PR interval, and then failure to conduct an atrial beat. This is then followed by a conducted beat with a shorter PR interval, after which the cycle repeats.
What is a mobitz type II second degree heart block?
This occurs when most beats are conducted with a constant PR interval, but occasionally atrial depolarisation occurs without subsequent ventricular depolarisation.
The PR interval of the conducted atrial beats is normal.
What is important to remember about Mobitz type II second degree heart blocks?
They can descend into complete heart block
What are the subtypes of type II 2nd degree heart block?
- 2:1 Block
- 3:1 block
What is 2:1 type II 2nd degree heart block?
When there are alternate conducted and non-conducted atrial beats. In the case of 2:1, this means that there is one conducted beat, followed by two non-conducted beats. This gives twice as many P waves as QRS complexes.
The PR interval again remains constant for conducted beats.
What is 3:1 type II 2nd degree heart block?
There are three P waves to every QRS complex. This means that only 1/3 of the P waves are conducted. The PR interval of the conducted P waves remains constant.
What are the causes of wenckebach phenomena?
- Drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone
- Increased vagal tone (e.g. athletes)
- Inferior MI
- Myocarditis
- Following cardiac surgery (mitral valve repair, Tetralogy of Fallot repair)
What is the mechanism of third degree heart block?
Atria are contracting but there is no conduction to the ventricles (no relationship between P and QRS complex). Ventricles are excited by a slow escape rhythm which takes over, from a depolarising focus with the ventricular muscle.
This causes the QRS complexes to become abnormally shaped due to the abnormal spread of depolarisation from ventricular focus. The complexes can also become broader than normal.
What are causes of third degree heart block?
MI
What can cause mobitz type II heart block?
- Anterior MI - septal infarction with necrosis of the bundle branches
- Idiopathic fibrosis of the conducting system
- Cardiac surgery
- Inflammatory conditions - rheumatic fever, myocarditis, Lyme disease
- Autoimmune - SLE, systemic sclerosis
- Infiltrative myocardial disease - amyloidosis, haemochromatosis, sarcoidosis
- Hyperkalaemia.
- Drugs - beta-blockers, calcium channel blockers, digoxin, amiodarone.
What is the difference between mobitz type I and mobitz type II heart block in terms of mechanism?
Mobitz I is usually due to a functional suppression of AV conduction (e.g. due to drugs, reversible ischaemia), whereas Mobitz II is more likely to be due to structural damage to the conducting system (e.g. infarction, fibrosis, necrosis).
Mobitz I is produced by progressive fatigue of the AV nodal cells, whereas Mobitz II is an “all or nothing” phenomenon whereby the His-Purkinje cells suddenly and unexpectedly fail to conduct a supraventricular impulse.
What are causes of complete heart block?
- Inferior myocardial infarction
- AV-nodal blocking drugs - calcium-channel blockers, beta-blockers, digoxin
- Idiopathic degeneration of the conducting system
What is atrial flutter?
When the atrial rate is > 250/min and there is no flat baseline between the P-waves, atrial flutter is present.
Any arrhytmia should be identified from the lead in which P-waves can most easily be seen
What are the criteria for atrial flutter?
- P-waves seen at a rate >250/min - often in a sawtoothed appearance.
- Ventricular activation remains constant
What is atrial fibrillation?
When the atrial muscle fibres contract independently of ventricular muscle fibres. The AV node is bombarded with depolarisation waves of varying strength from the independently fibrillating cardiac muscles.
Depolarisation spreads down the bundle of His at irregular intervals in an all or nothing fashion. This means that the depolarisation is of constant intensity. However, the ventricles contract irregularly (rhythm wise).
What are the characteristics of atrial fibrillation on an ECG?
- No P waves, and an irregular baseline
- Irregular QRS complex, which are normally shaped
- Waves can be seen in V1 which resemble atrial flutter
How much does cardiac output drop by in atrial fibrillation?
10-20%
What is the main risk from atrial fibrillation?
Embolic stroke
Why is atrial fibrillation associated with left or right atrial enlargement?
An enlarged atrium increases the potential for re-entrant circuits
What are causes of AF?
- MI
- Heart failure/Ischaemia
- Hypertension
- Hyperthyroidism
- PE
- Pneumonia
- Caffeine
- Alcohol
- Decreased K+, Mg2+
- Cardiomyopathy
- Constrictive pericarditis
- Sick Sinus syndrome
- Lung Cancer
- Endocarditis
- Atrial myxoma
- Haemochromatosis
Why is atrial fibrillation potentially dangerous?
Compromisation of cardiac output -> Hypertension and pulmonary congestion
Blood stasis in the atria -> thrombus formation (particularly left atrial appendage)
What are the main aspect of approaching the management of AF?
- Ventricular rate control
- Restore sinus rhythm
- Assessemtn for need to anticoagulate
What are the symptoms of someone with AF?
Can be asymptomatic
If symptomatic
- Chest pain
- Palpitations
- Dyspnoea
- Syncope
- Fatigue/Faintness
What are signs of AF?
- Irregularly Irregular rhythm
- Apical pulse rate > radial pulse rate
- S1 of variable intensity
- Signs of LVF
What is re-entry?
A reentry arrhythmia occurs when the electrical wave front in the heart gets caught in a loop. When this happens, the depolarization will repeatedly cycle through the tissue utilized in the loop until something interrupts it.
For re-entrance to occur, there has to be a unidirectional block within a conducting pathway.
What are the ECG characteristics of AF?
- Absent P-waves
- Irregular baseline
- Irregular QRS - normally shaped
If someone presented with Chest pain, palpitations and syncope, what investigations would you do?
- ECG
- Bloods - U+E’s, Troponin, TFTs
- ECHO
What is AV node re-entry tachycardia?
https://www.youtube.com/watch?v=36MT8hR-gDg
Two functionally and anatomically different pathways present within the AV node. One of these pathways conducts quicker with a long refractory period, and the other conducts more slowly with a quicker refractory period.
In sinus rhythm, the fast one is involved in depolarisation of the ventricles. If depolarisation occurs early, this is conducted by the slow pathway as the fast pathways is still refractory. It then travels back through the fast pathway which is no longer refractory (slow-fast conduction)
What are the characteristic features on AVNRT on ECG?
- Characterised by no P-waves, or P-waves directly before or after the QRS complex
- Regular normal QRS complex
What is AV re-entry tachycardia?
Can cause Wolff-Parkinson White syndrome
Characterised by an abnormal connection of myocardial fibres from the ventricle back to the atrium (accessory pathway). This results from incomplete separation of the atria during development
Conduction occurs through this pathway without the delay of the AV node, meaning that the ventricles are excited early. The accessory pathway conductivity and location are significant factors, and the location can be determined
What is Wolff Parkinson white syndrome?
Caused by congenital accessory conduction pathway between atria and ventricles.
A constellation of symptoms associated with WPW ECG patterns. Symptoms can include an tachycardia, palpitations, shortness of breath, lightheadedness, or syncope.
What is the name of the accessory pathway found in WPW?
Bundle of kent
What are the characteristic features of WPW on ECG?
- Delta-Wave
- Short PR interval
- Wide QRS complex
- Dominant R-wave in V1 - type A
- Deep S-wave in V1 - type B
What is ventricular fibrillation?
https://www.youtube.com/watch?v=kETghJagzOY
This is a very rapid ventricular activation with no mechanical effect. It is caused by uncoordinated contraction of the ventricles, which causes them to quiver. This rhythm rarely resolves by itself.
What are the characteristic features of VF on ECG?
- Chaotic irregular deflections of varying amplitude
- No identifiable P waves, QRS complexes, or T waves
- Rate 150 to 500 per minute
- Amplitude decreases with duration (coarse VF -> fine VF)
What is ventricular tachycardia?
https://www.youtube.com/watch?v=xAfj5AHxC2I
A type of tachycardia which originates in the ventricles and is usually broad complex tachycardia (QRS >140 bpm). This causes heart rate to exceed 150-200 bpm.
The ventricular rate of contraction starts driving the heart beat, rather than the SA node
What are the characteristic features of VT on ECG?
- Very broad complexes (>160ms).
- Absence of typical RBBB or LBBB morphology.
- Extreme axis deviation (“northwest axis”)
- AV dissociation (P and QRS complexes at different rates).
- Capture beats/Fusion beats
- Brugada’s sign – The distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms.
- Josephson’s sign – Notching near the nadir of the S-wave.
What is a capture beat?
Occur when the sinoatrial node transiently ‘captures’ the ventricles, in the midst of AV dissociation, to produce a QRS complex of normal duration.
The sinus node “captures” the ventricles producing a narrow-complex beat
What is a fusion beat?
Occur when a sinus and ventricular beat coincide to produce a hybrid complex of intermediate morphology.
The first of the narrower complexes is a fusion beat (the next two are capture beats).
What is an atrial ectopic beat?
Also known as supraventricular ectopic
Occurs when the atria depolarise earlier than it should. The accompanying heartbeat is called an extra systole. The term ectopic refers to the depolarisation occurring in an abnormal location. These have abnormal p-waves. QRS complexes remain the same.
What is a ventricular ectopic beat?
These are caused by early firing of the ventricles. They have abnormal QRS complexes, which are typically wide and can be of almost any shape. These are common and usually of no importance.
