Supraventricular tacchycardias (Complete) Flashcards
What is supraventricular tacchycardia?
Refers to any tacchycardia that is not ventricular in origin
What is the pathophysiology of supraventricular tacchycardia?
Normally electrical signal travels from SA node to AV node and then to ventricles. The signal never travels back to atria in normal circumstances.
In SVT, there is re-entering of elecrtical signal from ventricles back to the atria, creating a loop.
This results in fast complex narrow tacchycardia
List 3 examples of types of supraventricular tacchycardias
AF (Technically supraventricular but SVT tends to focus more on AVRT and AVNRT)
AV re-entry tacchycardia (AVRT): Accesory pathway between the atria and ventricles (e.g. WPW syndrome)
AV nodal re-entry tacchycardia (AVNRT): electrical signal from ventricles travels back up the AV node
What tacchycardia can be seen on ECG in patients with SVT?
Narrow complex tacchycardia
Narrow: QRS complex < 0.12s (<3 small squares)
QRS complex followed by T wave and then QRS complex (absent p-wave)
How can SVT be differentiated from AF on ECG?
SVT/narrow complex tacchycardia: Distance between the QRS complexes are equal (Regularly irregular)
AF: Distance between QRS complexes vary (Irregularly irregular)
Atrial flutter vs narrow complex tacchycardia
T-waves absent as theyre obscured by rapid atrial activity
SVT causes a narrow complex tacchycardia in most cases. If a person has SVT and bundle branch block, what tacchycardia tends to arise?
Broad complex tacchycardia
What is the management plan for patients with SVT?
Depends on type of SVT and whether there is adverse features (e.g. HF, Ischaemia, Shock, Syncope)
SVT with adverse features:
Synchronised DC shock (usually done under sedation of general anaesthetic)
SVT in stable patient:
Regularly irregular rythym:
1st line: Valsalva maneouvre or carotid massage
2nd line: IV adenosine 6mg (temporarily blocks AV node)
Irregularly irregular rythym (e.g. AF):
Refer to AF management
In acute management, what should always be attempted first in a stable patient with SVT?
Vasovagal manouvres such as:
Valsalva manouvre
Carotid sinus massage
If vasaovagal maenouvres fail in management of SVT in a stable patient, what is the next treatment option?
IV adenosine 6mg
How does adenosine work in treatment of SVT?
Blocks AV node, slowing down conduction.
This resets the sinus rythym
What should patients be informed of before being given IV adenosine in management of stable SVT?
How should it be given?
Might experience difficulty breathing, chest tightness and flushing
IV adenosine should be given rapidly over 1-3 seconds followed by 20 ml IV Normal Saline bolus.
N.B. If this fails can try 12mg adenosine followed by another 12mg if that also fails
What are contraindictions of adenosine in management of SVT?
Asthmatics (use verampil instead)
Administration via central line access
Patients on carbamazepine (used to treat epilepsy) [Causes AV node block so addition of atropine will exagerate effect]
Patients on dipyridamole (antiplatelet) [Pronlongs effects of adenosine]
IV adenosine should be replaced with what medication in asthmatic patients?
Verampil
What adverse features of SVT would warrant use of synchronised DC shocks?
Mnemonic: HISS
H: Heart failure
I: Ischaemia
S: Shock
S: Syncope
Why is synchronised DC cardioversion only used in patients who have a pulse?
Pulse helps defibrillator to detect R waves which is where shock is administered.
If shock accidentally occurs during a T-wave this can cause a ventricular fibirillation and send patient into cardiac arrest.
What is long-term management for patients with recurrent SVT?
Pharmacological: (Cardioversion)
Beta blockers
CCB
Amiodarone
Surgical/invasive:
Radiofrequency ablation: Burns the abnormal pathway
