Arrhythmias-Narrow Complex Tachycardias Flashcards
outline the classification of tachycardias
- narrow complex
- broad complex
what are narrow complex?
SVT’s
symptoms of SVT?
- dizziness
- palpitations
- chest pain
- collapse
define narrow complex
- rate >100bpm
- QRS width <120ms
what can SVT’s be
- focal
- re-entry
what are the types of focal SVT’s?
- Sinus tachycardia
- focus on SA node
- Atrial tachycardia
- heart’s electrical rhythm comes from an ectopic pacemaker in atria; hence a different focus in atria takes over from SA node
causes of sinus tachycardia?
numerous physiological causes…
- fever
- thyrotoxicosis
- hypotension
- hypoxia
- any form of stress
aetiology of atrial tachycardia?
- structural heart abnormality
- CAD
- lung disease
what is seen in atrial tachycardia on ECG?
abnormally shaped P waves
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what are the types of re-entry tachycardias?
- atrial flutter
- atrial fibrillation
- atrio-ventricular re-entrant tachycardia (AVRT)
- atrioventricular nodal re-entrant tachycardia (AVNRT)
what are the 3 main types of SVT?
- AVRT
- AVNRT
- Atrial tachycardia
pathophysiology of re-entry?
electrical signal re-enters atria from ventricles –> travels through AV node –> causes another ventricular contraction
essentially causes a self-perpetuating electrical loop without an end point & results in a fast, narrow complex tachycardia
describe AVRT and Rx of it
- electrical signal re-enters through accessory pathway - WPW
Rx:
- best initial treatment: electrical cardioversion
* curative option: ablation of pathway
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what is contraindicated in patients with AVRT who develop AFib or Atrial Flutter?
AV node blockade, as by doing so you are encouraging use of accessory pathway & if there are fibrillatory waves from atria these can transmit to ventricles & cause VFib
describe AVNRT & Rx of it
- re-entry back through AV node
Rx:
AV node blockade
- mechanical
- carotid sinus massage, vasovagal maneouvres
- chemical
- adenosine
- beta blockers
- verapamil (CCB)
ECG features of AVRT & AVNRT
- AVRT- inverted P waves after QRS
- AVNRT- no P waves seen
Mx of pts w SVT?
stepwise approach trying each step & seeing if it works before moving on
make sure on continuous ECG monitoring
- if haemodynamically compromised
- sedate + DC cardioversion
- if stable - identify rhythm & treat accordingly
- vagal maneouvres
- valsalva
- carotid sinus massage
- Adenosine
- Verapamil
- DC Cardioversion if above fails
- vagal maneouvres
what should valsalva and carotid massage do?
terminate an SVT
how is carotid sinus massage done?
massage carotid gently on one side w 2 fingers
what is the difference between Defibrillation and Cardioversion?
defibrillation:
- unsynchronised, random administration of shock throughout any point of cardiac cycle
cardioversion:
- synchronised administration of shock during R wave / QRS complex of cardiac cycle
how does adenosine work?
- slows cardiac conduction mainly through AV node
- interrupts AV node/accessory pathway during SVT & resets back to sinus rhythm
- must be given as rapid bolus
- will often cause brief period of asystole / bradycardia that can be scary
when should adenosine be avoided?
- asthma
- COPD
- HF
- Heart block
- severe hypotension
what drug reduced function of adenosine?
theophylline
what drug increases function of adenosine?
dipyridamole
when adminstering, what should you warn pt about and where is it administered into
warn about scary feeling of dying / impending doom
administered into a large proximal cannula (eg grey cannula in antecubital fossa)
can adenosine be used in pregnancy?
yes, safe to use
how much adenosine is adminstered?
6mg then 12mg then a further 12mg if no improvement in between doses
prophylaxis of SVT?
- B Blockers, CCB or amiodarone
- radiofrequency ablation
pathophysiology of WPW?
- extra electrical pathway connecting atria & ventricles- bundle of kent
- causes no problems and is asymptomatic
- when this pattern can facilitate certain arrhythmias (ie AVRT), or worsen pre-existing atrial arrhythmias–> WPW Syndrome
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what may happen with a pre-existing atrial arrhythmia in WPW?
atrial conduction too fast so AV node blocks it so then goes down accessory pathway –> Vfib –> cardiogenic shock as heart barely has time to fill up/pump blood
aetiology of WPW?
congenital
WPW on ECG?
Wide QRS (>0.12seconds)
PR interval short <0.12seconds
Wave- Delta wave (slurred upstroke of QRS)
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Rx of WPW?
definitive - radiofrequency ablation of accessory pathway
what drugs are contraindicated in WPW pts with AFib or Atrial flutter?
anti-arrhythmics
- beta blockers
- CCB
- adenosine
pathophysiology of Atrial flutter?
- caused by re-entrant rhythm in either atrium
- signal goes round & round the atrium without interruption & stimulates atrial contraction at 250-300bpm
- due to refractory period of AV node, signal makes its way to the ventricles every 2nd lap causing ventricular contraction at 150bpm
atrial flutter on ECG
- characteristic saw tooth appearance of P waves
- QRS regular
- blocks can be 2/3/4/5:1 depending on how many P waves per QRS complex
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associated conditions with Atrial flutter?
- HT
- IHD
- Cardiomyopathy
- thyrotoxicosis
- can be precipitated by acute cardiac / respiratory problems
Rx of atrial flutter?
- rate /rhythm control
- beta blockers / cardioversion
- radiofrequency ablation of re-entrant rhythm
- anti-coagulation based on CHAD2DVASC score
- treat reversible underlying condition