Supraventricular Tachycardia Flashcards
Aetiology and Pathophysiology of SVT
-A supraventricular tachycardia arises at or above the level of the AV node (140-200 bpm)
-They occur when a re-entry circuit is established
-Two common types
=Atrioventricular nodal re-entry tachycardia (AVNRT)
==A functional second pathway exists within the AV node itself
=Atrioventricular re-entry tachycardia (AVRT)
==Extra accessory pathway / cardiac conductive tissue separate to the AV node, less common (circuit)
Symptoms of SVT
-May present with palpitation, shortness of breath or chest pain
AVNRT:
=Most common in young women (75%)
=Patients may feel pre-syncopal but syncope is unusual
=A safe rhythm
-AVRT
=Shorter refractory period than normal cardiac tissue
=Can conduct rhythms much faster
=If AF occurs can be conducted 1:1 without AV block (safety mechanism)= can be fatal
Clinical signs of SVT
AVNRT:
=Regular, narrow complex tachycardia (V1)- less than 3 small boxes
=Fixed R-R interval
=Often cannot see a P wave or P is seen after QRS (retrograde)
AVRT:
=Sinus rhythm ECG with ‘delta wave’ evident
=Short PR interval?
=Variable R-R interval
This tells you there is an accessory pathway
Investigations of SVT
-ECG
-Echocardiogram= structural abnormalities, LV failure
-24 hour tape= frequent palpitation
-Implantable loop recorder= under skin, 3 years, arrhythmias recorded
-EP study- catheter in heart
Treatment of SVT
-Vagal manoeuvres
=Look up the ‘REVERT’ manoeuvre/ carotid sinus massage
-Adenosine bolus (AVN block, not in asthma or verapamil/ CCB)
-Verapamil
-Beta blocker
-Amiodarone
-Flecainide (blocking accessory pathway tissue)
-DC cardioversion (haemodynamic instability)
-EP study and ablation= best
Prognosis and long-term care of SVT
-Prognosis is excellent with prompt diagnosis and treatment
-Ablation can be curative and life changing
-AVNRT rarely leads to serious complications
-AVRT can lead to 1:1 conduction which can rarely be fatal
