Arrhythmias Flashcards
What is a cardiac arrhythmia?
An abnormality of the cardiac rhythm
May cause sudden death, syncope, heart failure, chest pain, dizziness, palpitations
What sit the physiological cardiac pacemaker?
Sinoatrial node
Depolarises spontaneously and is controlled by parasympathetic nervous system
What is a sinus arrhythmia?
Fluctuations in autonomic tone result in phasic changes of the sinus discharge rate
What causes a physiological sinus arrhythmia?
Inspiration will increase HR
Typical sinus arrhythmia results in predictable irregularities of the pulse
What mechanisms can cause arrhythmias?
- Accelerated automaticity
- Triggered activity
- Re-entry
What is the mechanism behind accelerated automaticity in arrhythmias?
Normal depolarisation depends on parasympathetic input but can be influenced by:
- Epinephrine
- Specific drugs
What is the mechanism behind triggered activity in arrhythmias?
Myocardial damage can result in oscillations of the transmembrane potential at the end of an action potential, which are called after depolarisatioins
- Delayed after depolarisations (increased calcium in the SR)
- Early after depolarisations (caused by stimuli that increase calcium or AP duration)
What is the mechanism behind re-entry in arrhythmias?
Tachyarrhythmias are generally due to re-entry, which causes the most serious arrhythmias especially during or after a myocardial infarction as conduction is slower in some parts of the heart
What are the four steps of re-entry?
- In re-entry, the pulse is trapped in one region of the heart
- In adjacent tissue, the depolarising stimulus is no longer in its refractory period
- The delayed impulse then re-enters the adjacent tissue and spreads throughout the heart which can create a premature beat or sustained tachycardia
- Can occur whenever adjacent areas of the myocardium have different conduction rates and refractoriness
What are the basic requirements for re-entry?
- A conducting pathway with a non-excitable core around which the impulse can cycle
- Zones of differential conductivity or refractoriness within the pathway
- Unidirectional block
What are rotors?
Interaction of waves of depolarisation with obstacles or zones of impaired conduction is thought to lead to breaking up the waves and formation of spiral waves of excitation
Can give rise to fibrillation
What extrinsic factors can cause sinus bradycardia?
- Hypothermia
- Hypothyroidism
- Cholestatic jaundice
- Raised intracranial pressure
- Drug therapy with beta-blockers, digitalis and other anti-arrhytmic drugs
- Neurally mediated syndromes
What are the types of bradycardia?
- Atrioventricular heart block
- Sinus bradycardia
- Sick sinus syndrome
- Bundle branch block
What are the three types of an atrioventricular heart block?
- First degree AV block
- First degree AV block (Mobitz 1 and 2)
- Complete heart block
What is the difference between Mobitz 1 and Mobitz 2?
Mobitz 1 - progressive PR interval prolongation until a P wave fails to conduct (Normal atrial rhythm)
Mobitz 2 - constant PR with intermittent QRS absence
What is a third-degree heart block and how is this seen on an ECG?
Atria and ventricles contract independently
- Narrow complex escape rhythm
- Broad complex rhythm
What is sick sinus syndrome?
This syndrome encompasses a number of conduction system problems: persistent sinus bradycardia not caused by drugs, sinus pauses, AV conduction disturbances, and paroxysms of atrial arrythmias. It is usually diagnosed by ambulatory cardiac monitoring.
What enzymes will be raised in ventricular fibrillation?
Troponin
How would you manage ventricular fibrillations?
Defibrillation and cardioversion
Careful post-resuscitation care is essential to survival because recurrence rates average at about 50%
Most survivors of VF should be treated with implantable cardioverter defibrillators
What is the prognosis for ventricular fibrillation?
Prognosis is poor without intervention by 4-6 minutes after onset of VF
What distinctions should you make while diagnosing a arrhythmia?
- Tachy (>120 bpm) versus Brady (60 bpm)
- Narrow (<120 ms) versus broad
- Regular versus irregular
How would you determine if a tachycardia is ventricular or supra ventricular?
Is the QRS complex broad (>120 ms)?
Yes—ventricular in origin
No—supraventricular.
What are the types of tachyarrhythmias?
- Atrial tachyarrhythmias
- Supraventricular tachyarrhythmias
- Ventricular tachyarrhythmias
What are examples of atrial tachyarrhythmias?
- sinus tachycardia
- sinus node re-entrant tachycardia (SNRT)
- atrial fibrillation (AF)
- atrial flutter
What are examples of atrioventricular tachyarrhythmias?
- AVRT
- AVNRT
- junctional tachycardia
What are examples of ventricular tachyarrhythmias?
- VT (monomorphic VT; polymorphic VT (torsades de pointes))
* ventricular fibrillation (VF).
On an ECG, what may suggests a tachycardia is of ventricular origin?
- AV dissociation
- QRS width >140 ms
- QRS axis +90
- Concordance of QRS complexes in precordial leads
What questions do you ask when interpreting a tachyarrhythmic ECG?
- Is the tachycardia regular?
- Is the QRS complex broad (>120 ms)?
- Identify P waves, their morphology and P:R ratio
- Response to AV block (adenosine or carotid massage)
If the rhythm is not regular, what is the most likely diagnosis?
Atrial fibrillation
If the rhythm is regular and the QRS is >120ms, what is the most likely diagnosis?
VT
What are the ECG characteristics of atrial fibrillation?
No P waves, fibrillating chaotic F waves around the baseline
Irregular rhythm
What are the ECG characteristics of atrial flutter?
- P waves absent
- saw-tooth (!) F waves visible at rate of ~300
- Regular rate
What are the ECG characteristics of sinus tachycardia?
Normal shape and size; 1:1 correspondence with ventricular complexes, normal PR interval, P waves can merge with T waves if very fast
What are the common causes of atrial fibrillation?
- Hypertension
- Ischaemic heart disease
- Heart failure
- Valvular heart disease (e.g. rheumatic)
- Idiopathic/lone AF
- Alcohol!
What two conditions can AF lead to?
Stroke: major concern with AF is the formation of thrombi in the atria leading to systemic thromboembolism
Heart failure: two-fold increase in rate of development of heart failure
What are the three causes of thrombus formation of Virchow’s triad?
- Haemodynamic
- Endothelium
- Hypercoagulability
What valvular cause can lead to AF?
Mitral stenosis
What are the 4 subtypes of AF?
- Paroxysmal: spontaneous return to sinus rhythm without need for intervention
- Persistent: return to sinus rhythm possible following intervention
- Long-standing persistent: arrhythmia lasting longer than 1 year without return to sinus rhythm
- Permanent: sinus rhythm is not achievable even with intervention, or intervention is no longer considered
What are the management options for AF?
- Rate control
2. Rhythm control
When would you consider rate control in AF?
This should be considered in older patients or in those with long-standing AF that have little chance of reverting to sinus rhythm
What medication is given for rate control in AF?
- Beta-blockers
- Rate-limiting CCBs
- Amiodarone
- Digoxin – as monotherapy only for relatively sedentary patients
When would you consider rhythm control in AF?
Maintenance of sinus rhythm following cardioversion (rhythm control) should be considered in young patients and those with paroxysmal AF
What are the causes of atrial flutter?
- Hypertension
- Ischaemic heart disease
- Heart failure
- Valvular heart disease (e.g. rheumatic)
- Idiopathic/lone AF
- Alcohol!
What is a supra ventricular tachycardia?
An arrhythmia consisting of a rapid heart rate other than atrial fibrillation or flutter originating at or above the AV node.
What is the cause of supra ventricular tachycardias?
Usually occurs in young healthy adults.
Re-entrant circuit is normally present from birth but may not become apparent until adult life.
What adverse condition can a supra ventricular tachycardia lead to?
Ventricular tachycardia
How would you manage SV tachycardias?
Conservative -> vagal manoeuvres
Medical -> termination of tachycardia
Adenosine
Longterm can use beta-blocker
What is the definition of a ventricular tachycardia?
A tachycardia with three or more consecutive beats that originate from the
ventricles, independent of atrial or AV nodal conduction
What is the definition of Torsades de pointes?
A form of polymorphic ventricular tachycardia with characteristic beat-to-beat
changes in the QRS complex
What can cause ventricular tachycardias?
- Previous MI
- Structural heart problems
- Inherited ion-channel abnormalities (long QT)
- Drugs
- Electrolyte disturbances
- Tension pneumothorax, cardiac tamponade, PE
What electrolyte disturbances can lead to VT?
Hyperkalaemia
Hypokalaemia
Hypomagnesaemia r Hypocalcaemia
What is Wolff-Parkinson-White syndrome?
Wolff-Parkinson-White (WPW) syndrome is the most common of the ventricular pre-excitation syndromes
WPW syndrome is a congenital abnormality which can result in supraventricular tachycardia (SVT) that uses an atrioventricular (AV) accessory tract
How would you identify WPW on an ECG?
Classic ECG findings of WPW syndrome include a short PR interval (less than 120 ms), a prolonged QRS complex of longer than 120 ms with a slurred onset producing a delta wave in the early part of QRS and secondary ST-T wave changes
How would you classify WPW based on ECG findings?
Type A: the delta wave and QRS complex are predominantly upright in the precordial leads. The dominant R wave in lead V1 may be misinterpreted as right bundle branch block.
Type B: the delta wave and QRS complex are predominantly negative in leads V1 and V2 and positive in the other precordial leads, resembling left bundle branch block.
What is absolutely contraindicated in WPW?
Digoxin! Can be lethal
What does AVNRT stand for?
Atrioventricular nodal re-entrant tachycardia
Re-entrant circuit is located within the AVN which has two pathways with different conduction properties:
1. Fast pathway: fast conduction velocity, long refractory period 2. Slow pathway: slow conduction velocity, fast refractory period
What is Ebstein’s anomaly?
Congenital heart defect
Septal leaflet of the tricuspid valve is displaced towards apex of the right ventricle r Causes enlargement of the aorta
Is associated with Wolff–Parkinson–White syndrome
What vagal manoeuvres can be performed too low down the AV-node?
a. Valsalva manoeuvre
b. Carotid sinus massage
c. Head immersion in cold water
