Supraventricular Tachycardia Flashcards
another name for supraventricular tachycardia
narrow complex tachycardia
is SVT a diagnosis
no
SVT is an umbrella term for any cause of rapid heart rate originating from above or within the atrioventricular node
two main categories of SVT
focal tachycardais
re-entrant tachycardias
focal tachycardias
a tachycardia that originates from a single point (or points) in the atrium or AV node
sinus tachycardia
this counts as a focal tachycardia
the ‘focus’ is the sinoatrial node
usually regular
atrial tachycardia
a different focus in the atrium takes over from the sinoatrial node resulting in abnormal p waves preceding QRS complexes
often seen in patients with chronic lung disease
normally > 100bpm and regular
p waves will be positive in the inferior leads as they originate from the top of the atrium and propagate towards the inferior lead
atrial tachycardia is often seen in patients with
chronic lung disease
multifocal atrial tachycardia
the p waves will have different morphologies as the atrial focus changes from beat to beat
junctional rhythms
the impulse originates from the AV node and propagates to the atrium and the ventricles simultaneously
p waves are not visible because they are buried in the QRS complex
management of inappropriate sinus tachycardia
can be slowed using bet blockers or ivabradine (selective sinus node blocker), however it is usually best left alone
management of appropriate sinus tachycardia
may be due to concurrent sepsis, anaemia, thyrotoxicosis, pain
should be left alone and the underlying cause treated
management of atrial tachycardias
can usually be rate controlled with beta-blockers or calcium channel blockers
re-entry tachycardias - atrial flutter
well known for it’s sawtooth baseline
classified as a macro-re-entrant tachycardia
this means there is a single re-entry circuit around the atrium which stimulates the AV node every time it passes
Typical vs. atypical atrial flutter
typical atrial flutter runs nit-clockwise around the right atrium and across the cavotricuspid valve isthmus
atypical flutter can be clockwise in the right atrium, in the left atrium or around sites of previous surgery and can be difficult to identify as they lack the typical sawtooth appearance
the sawtooth appearance of atrial tachycardia in best seen in
the inferior leads becaause it is caused by the circiut alternately heading toward and way from the leads as it speeds round the atrium
atrial fibrillation
micro-re-entrant tachycardia
lots of tiny circuits contributing to chotic random fibrillation of tha atrium
irregularly regular
AVNRT (atrio-ventricular node re-entrant tachycardia)
activates ventricles and atria almost simultaneously
pseudo R wave: retrograde p wave superimposed on the QRS complex
rapid regular tachycardia
treatment involves complete transient AV node blockade
AVRT (atrio-ventricular re-entrant tachycardia)
this requires two pathways: the normal AV conduction system and an accessory pathway (AP)
accessory pathways my conduct antegrade (atria to ventricles) retrograde (ventricle to atria
orthodromic AVRTs
down the AV node and up the accessory pathway
antidromic AVRTs
down the accessory pathway and up the normal AV conduction
management of AVRTs
electrically cardiovert the patient back to sinus rhythm
flecanide can be used to prevent AVRTs but ablation is usually the mainstay of treatment given risk of VF and sudden death
what is the treatment of choice in a haemodynamically unstable patient due to the underlying SVT
cardioversion
rate control for atrial fibrillaation and atrial flutter
beta blockers
calcium channel blockers
digoxin
rhythm control for atrial fibrillation and atrial flutter
chemical cardioversion (amiodarone, flecanide)
electrical cardioversion (DC shock)
ablation for atrial fibrillation and atrial flutter
more likely to succeed in atrial flutter than atrial fib
more likely to succeed in paroxysmal AF than persistent AF
anticoagulation in atrial fibrillation and atrial flutter
according to stroke risk vs bleeding risk (CHADS2 VASc score)
AF patients who should not be considered for AF
AF is not life-threatening
a patient with well-controlled AF and normal LV function has the same life expectancy as someone in sinus rhythm
symptomatic patients will well rate controlled AF will not feel better or life longer by returning them to sinus rhythm
patients who should be considered for cardioversion
new-onset AF
symptomatic AF
LV dysfunction secondary to AF
patients with a reversible cause of AF (eg. post-surgical, post-infection)
pateints who have a reasonable chance of maintaining sinus rhythm
patients who have a reasonable chance of maintaining sinus rhythm will
previous successsful cardioversion - although each subsequent cardioversion becomes less successful
minimal dilatation of the left atrium
no signiificant mitral valve disease
management of AVNRT
induce AV node blockade
mechanical: vasovagal manouvres, carotid sinus massage
chemical: adenosine, beta blockers, verapamil
management of AVRT
avoid AV node blockade as this can promote conduction down the AP and AF can convert to VF
electrical cardioversion is the best initial option although flecanide can be used to chemically cardiovert
ablation of the pathway is the curative option
what is adenosine
a purine nucleoside that, administered intravenously, causes transient complete AV node blockade
it is a useful diagnostic tool as well as a treatment in the setting of narrow complex tahcycardia
is adenosine safe in pregnancy
yes (its endogenous)
can adenosine be used in asthma
usually can be used safetly in asthmatic unless they have brittle severe asthma
effects of adenosine
you will see a few seconds of total AV block
if you administer adenosine and you do not see AV block
one of two things have occurred:
1. you have not administered the adenosine properly and the adnosine has not reached the heart in time given its very short half life
2. the rhythm is not involving the AV node - it is therefore, ventricular tachycardia
