What kind of abnormal anatomy can cause an arrhythmia?
- Left ventricular hypertrophy - Accessory pathways - Congenital Heart Disease
What can be causes of arrhythmias in relation to the autonomic nervous system?
- Sympathetic stimulation (stress, exercise, hyperthyroidism) - Increased vagal tone (parasympathetic system - causes bradycardia)
What metabolic factors can cause arrhythmias?
- Hypoxia (chronic pulmonary disease, PE) - Ischaemia Myocardium (acute MI or angina) - Electrolyte imbalances (K+, Ca2+, Mg2+)
What type of inflammation can cause arrhythmias?
Viral myocarditis
How can drugs cause arrhythmias?
Direct electrophysiological effects or via the ANS
What genetic factors can cause arrhythmias?
Mutations of genes encoding cardiac ion channels (e.g. congenital long QT syndrome)
What are the two electrophysiological mechanisms?
- Ectopic Beats
- Re-entry
What are ectopic beats?
When the heart skips a beat or adds an extra beat
How are ectopic beats caused?
Beats / rhythms originating in places other than the SA node - Altered automaticity - Triggered activity
What is altered automaticity?
- The cell depolarising itself - So accelerated generation of action potential by either normal pacemaker tissue or abnormal tissue within the myocardium
Give two examples of when altered automaticity occurs?
- Ischaemia (when cardiac cells lack oxygen they become depolarized) - Catecholamines (i.e. adrenaline)
What is triggered activity?
Impulse initiation that depend on afterdepolarisations (Oscillations in membrane potential after an action potential)
What are two examples that cause triggered activity?
- Digoxin (increases automaticity in His-purjinke system) - Long QT syndrome (affects repolarisation)
What is Re-entry?
Continuous circulating activity, where an impulse re-enters and continuously excites a certain region of the heart
What are three examples of conditions related to re-entry?
- Accessory pathway tachycardia (extra pathway between hearts atria and ventricles) - Previous myocardial infarction (scarring) - Congenital heart disease
What causes re-entry?
Ectopic beats (premature)
How does an increase in phase 4 slope of the action potential affect the heart?
Increase heart rate
What causes an increase in phase 4 of the action potential?
Hyperthermia Hypoxia Hypercapnia Cardiac dilation Hypokalaemia (prolongs repolarisation)
How does a decrease in phase 4 slope of the action potential affect the heart?
Slowed conduction - bradycardia - heart block
What causes the decrease in phase 4 slope of the action potential?
Hypothermia Hyperkalaemia
What is the mechanism of triggered activity?
- In phase 3 of the action potential an afterdpolarisation occurs - This afterdepolarisation may reach a depolarisation threshold - This can lead to a sustained train of triggered depolarisations
What is the mechanism of re-entry?
There is a slow depolarisation and fast depolarisation on one circuit. - Fast depolarisation leaves behind a long refractory period - When a premature beat occurs the slow action potential goes along the circuit and finishes the circuit when the refractory period wears off. - After this it splits at the end and one half goes back round and splits at the start - The whole thing starts again
What are the two characteristics of the fast action potential?
- fast depolarisation - long refractory period
What are the two characteristics of the slow action potential?
- slow depolarisation - short refractory period
What are the main symptoms of arrhythmias?
Palpitations SOB Dizziness Syncope Faintness (presyncope) Sudden cardiac death Angina Heart Failure
What are the usual investigations carried out to determine an arrhythmia?
- 12 lead ECG - CXR - Echocardiogram - Stress ECG - 24 Hour ECG - Event recroder - Electrophysiological (EP) study
What is an ECG used for?
- Assess rhythm - Shows signs of… - Previous MI (q waves) - Pre-excitation (wpw syndrome)
What is an exercise ECG used for?
- Assess ischaemia - Shows exercise induced arrhythmias
What is the purpose of 24 hour Holter ECG?
- assess for paroxysmal arrhythmia - link symptoms to underlying heart rhythm
Purpose of an echocardiography?
Assesses for structural heart disease e.g. - enlarged atria in AF - LV dilation - Previous MI scar - Aneurysm
Purpose of an EP study?
- Triggers the arrhythmia to study its mechanism - May be able to treat by delivering radiofrequency ablation to the extra pathway (destroys the tissue)
What is a normal sinus arrhythmia?
- Variation in heart rate due to changes in vagal tone from the respiratory cycle - on inspiration vagal tone is reduces so heart rate increases
What are common extrinsic causes of sinus bradycardia?
Hypothermia
Hypothyroidism
Raised intracranial pressure
Drug Therapy (BETA BLOCKERS, DIGOXIN etc.)
What are common intrinsic causes pf bradycardia?
Acute ischaemia/ infarction of the sinus node
Chronic Degenrative changes (e.g. fibrosis and shock sinus syndrome)
What heart rate is required to be classed as bradycardia?
Under 60 beats/min
What mechanisms could cause bradycardia?
What is the treatment for bradycardia?
Atropine (if acute e.g. acute MI)
Pacing if haemodynamic compromise (i.e. hypotension collapse)
What heart rate is required to be classed as sinus tachycardia?
Heart rate over 100 beats/min
What cause cause sinus tachycardia?
Anxiety
Fever
Hypertension
Anaemia (heart compensates for lack of red blood cells)
Drugs
What is the treatment for sinus tachycardia?
Treat te underlying cause
Beta-adrenergic blockers
What are symptoms of atrial ectopic beats?
Can be asymptomatic
Palpitations
What is the treatment for atrial ectopic beats?
Generally no treatment
Beat blockers may help
Avoid stimulants e.g. coffee
What are the three main causes of regular supraventricular tachycardia
- AV nodal re-entrant tachycardia (AVNRT)
- AV re-entrant tachycardia (via accessory pathway) (AVRT)
- Ectopic atrial tachycardia (EAT)
What is AV nodal re-entrant tachycardia (AVNRT)?
There are two different pathways within the AV node, one with slow conudction and fast refarctory period the other with fast conduction and long refarctory period
- In sinus rhythm the impulse normally conducts through the fast pathway
- If atrial impusle is premature when fast pathway is still refractory, slow pathway takes over
- then travels back through fast pathway which has already recovered its excitability causing the “slow-fast”
- Thus AVRNT
What is atrioventricular re-entrant tachycardia?
Atrial activation occurs after ventricular activation
- SO P wave is seen between the QRS and T wave
- Re-entry occurs outside of AV node through an accessory pathway made of myocardial fibres from ventricles back to the atrium (multiple pathways can occur)
What are AVRT patients more prone to?
Atrial fibrillation
What do AVRT patients show on their ECG?
- P wave is seen between the QRS and T wave
- Narrow QRS complexes
- Short PR interval
- Delta wave: slurred beggining of the QRS complex
What is AVRNT the most common cause for?
What is seen on an AVNRT patients ECG?
- Narrow QRS complexes
- P waves cannot be seen
What are the three types of AVRT?
- Pre-excitation
- Orthodromic AVRT
- Antidromic AVRT
What is pre-excitation AVRT?
Premature conduction through accessory pathways
- Short PR interval
What is orthodromic AVRT?
Forward moving conduction through the atrioventricular node
- No delta wave
- Retrograde P-wave after QRS
What is antidormic AVRT?
Retrograde conduction through atrioventricular node
- Wide QRS complex with delta wave
- P wave rarely seen
What is the management for acute supraventricular tachycardia?
Increase vagal tone
Slow condcution in the AVN
- IV adenosine
- IV verapamil (calcium channel blockers)
What is the management for chronic supraventricular tachycardia management?
- Avoid stimulants
- EP study and radiofrequency abltation
- Beta blockers
- Antiarrhythmic drugs (i.e. sodium channel blockers, beta blockers, potassium channel blockers and calcium channel blockers)
What are some causes of heart block?
- Age
- Acute MI
- Myocarditis
- Drugs (beta blockers, calcium channel blockers
- Aortic valve disease
- Post-aortic valve surgery
- Genetic
What is a first degree heart block?
- PR interval longer than normal
- Conduction follows each P wave so not really a block
- More advanced block could form so long term follow up is required
What is a 2nd degree heart block?
Some P waves conduct, others do not (intermittent block at AV node)
- Two types; Mobitz I and Mobitz II
What is Mobitz I?
- Progressive lengthening of the PR interval
- Eventually results in a dropped beat
- Vagal tone is usual origin
What is Mobitz II?
- Pathological
- Could develop into complete heart block
- QRS is wide
- Dropped QRS complex is not preceded by progressive PR intrverval prolongation
- Only every second or third P wave conducts to the ventricle
- Permanant pacemaker required
What is 3rd degree AV heart block (complete heart block)?
- Complete heart block
- All atrial activity fails to conduct to the ventricles
What are the causes of ventricular ectopics?
- LVH
- Herat failure
- Myocarditis
- Ischaemic heart disease
- Inherited cardiac condition
- Exercise
- Beta-blockers
What are some features of ventricular tachycardia?
- Life threatening but may be haemodynamically stable
- Most patients have significant heart disease
- Cardiomyopathy can be a rare cause
- Brugada and long QT syndrome could also be rare causes
What are some ECG characteristics that help define VTs?
- Rapid, wide and distorted QRS
- Large T waves
- Regular rhythm
- P waves not usually visible
- PR interval not measureable
What is the treatment used to treat acute VT?
- Direct current cardioversion (DCCV)
- If stable use antiarrhythmic drugs whilst preparing for DCCV
- Consider adenosine to make diagnosis if unsure
What is the long term treatment for VT
- Correct ischaemia
- Optimise CHF therapies
- Anti-arrhythmic drugs CAUSE WORSE OUTCOMES
- If life threatening use implantable cardiovertor defibrillators (ICD)
- VT catheter ablation
What is the most serious arrhythmia?
Ventricular tachycardia
What can ventricular fibrillation lead to?
Heart attack
What effects can supraventricular tachycardia have?
- Syncope
- Severe SOB
What is more serious?
- supraventricular arrhythmias
OR
- Ventricular arrhythmias
Ventricular arrhythmias
What is supraventricular tachycardia?
- Where the heart occasionally breats around 150-250 beats per minute
- more commonly occurs in young people
- can be caused by caffeien, stress and alcohol
What is atrial fibrillation a big cause of?
Stroke
How can atrial fibrillation cause strokes?
- Causes pools of blood to form in the upper chambers of the heart
- Can lead to blood clots
- These blood clots can travel up to the brain
What is Wolff-Parkinson White syndrome?
- Extra muscle pathways between atria and ventricles
- Thse pathways cause electrical signals to arrive at the ventricles too soon
- So signal is sent back too soon
- Causes a very fast heart rate
WPW syndrome can predispose someone to what other arrhythmia?
Supraventricular tachycardia
What is atria flutter?
Atria beat very fast affecting the efficiency of the ventricles to pump blood
What is postural orthostatic tachycardia syndrome?
- When standing up the blood vessels to do not contrsict in some people to keep the blood flow moving to the brain
- The heart tries to make up for this by pumping faster
- iIf the heart cannot pump fast enough, less blood is pumped to the brain
- Causing lightheadedness, syncope and blurry vision
How do heart blocks occur?
When the SA node sends the signal correctly but it is not sent through the AV node or lower electrical pathways as quickly as it should be
What can be the cause of heart block?
- Ageing
- Swelling/scarring of the heart caused by coronary artery disease
- Cardiac amyloidosis (protein deposits take the place of cardiac muscle)
What is sick sinus syndrome?
- SA node isnt sending inpulses properly
- Heart rate alternates between bradycardic and tachycardic
- Can be caused by scarring along the sinus node
What arrhythmia is this ECG indicative of?
- Heart rate <60bpm
- Normal P wave before every QRS
Sinus Bradycardia
What arrhythmia is this ECG indicative of?
- PR interval >200ms
First Degree AV block
What arrhythmia is this ECG indicative of?
- Progressive lengthening of the PR interval until a beat is dropped
Second degree AV block Mobitz I
What arrhythmia is this ECG indicative of?
- Irregular dropped beats
Second degree AV block Mobitz II
What arrhythmia is this ECG indicative of?
- No relationship between P waves and QRS complexes
Third degree AV block
What arrhythmia is this ECG indicative of?
- Regular rhythm
- Tachycardic
- P waves occur before every QRS
- Sawtooth appearance of P waves in II, III and aVF
- Narrow QRS complex
Atrial FLutter
What arrhythmia is this ECG indicative of?
- Rhythm irregularly irregular
- Rate is 350-450 bpm
- Unclear P waves
- Narrow QRS complex
Atrial Fibrillation
What arrhythmia is this ECG indicative of?
- Abrupt onset
- Regular rhythm
- Rate 150-250
- Inverted P wave
- P wave occurs after the QRS complex
- May contain a delta wave (slurred QRS and short PR interval)
Atrioventricular Reentry Tachycardia (AVRT)
What arrhythmia is this ECG indicative of?
- Regular rhythm
- Rate 150-250
- P waves either not visible or after QRS complex
- Narrow QRS complex
Atrioventricular Nodal Reentry Tachycardia (AVRNT)
What arrhythmia is this ECG indicative of?
- Regular, rapid rhythm
- Wide QRS complexes
- AV dissociation (P waves may not be visible)
Ventricular Tachycardia
What arrhythmia is this ECG indicative of?
- Associated with long QT syndrome
- Rapid, irregular QRS complexes twisting around the baseline
Torsade de Pointes
What arrhythmia is this ECG indicative of?
- Heart rate >300bpm
- Arrhythmic fibrillatory baseline
- Erratic undulations with non visible QRS complexes
Ventricular Fibrillation