ECG, Medical, Reentry Supraventricular Tachycardia

[Sahrish Dar]

What is Reentry Supraventricular Tachycardia?

Its also called as reentrant supraventricular tachycardia. Reentry supraventricular tachycardias (SVT) occurs due to the reentrant pathways above the bifurcation of the bundle of His. The mechanism of action is simple. Reentry is nothing but the circular propagation of an electrical impulse by 2 interconnected pathways which have different characteristics, conduction speed and refractory periods. If conduction over the first pathway is slow enough, a premature impulse may continue retrograde all the way up the second pathway. This by now has past its refractory period. If the first pathway has also past its refractory period, the impulse may reenter it and may start recycle. This sends an impulse each cycle to the ventricle and also backward to the atrium. Thus a  reentrant tachycardia begins.  Reentry Supraventricular tachycardia may be Atrioventricular nodal type in about 50%, Accessory bypass tract in 40% and sinoatrial nodal type in rest 10%.

Source: https://www.msdmanuals.com

Atrioventricular nodal type of reentry tachycardia (AVNRT) is often synonymously called Supra Ventricular Tachycardia. When the onset and offset is sudden, it is called Paroxysmal Supraventricular Tachycardia.

Signs and Symptoms:

Common presenting symptoms are breathlessness, palpitation, chest tightness, discomfort, chest pain, numbness, weakness, giddiness, unconsciousness. Duration of symptoms are variable, sudden on onset and offset. The rapid ventricular rate reduces the filling time significantly. This results in a drop in cardiac output & leads to hypotension and giddiness. Symptoms are marked when heart rate is more than 150 pm.

Diagnosis:

Paroxysmal Supra Ventricular Tachycardia is a regular tachycardia  ~140-280 bpm. It has a narrow QRS complex  (< 120 ms) and regular in rhythm. Retrograde p waves sometimes appear as inverted Q waves just after the QRS complex (common in leads II, III, aVF).

Example of Reentry Supraventricular Tachycardia ECG 

 

Management:

1. Vagal Maneuver  with carotid massage, valsalva maneuver
2. Adenosine, Beta blockers, CCBs or amiodarone on case to case basis
3. Unstable patients with persistent SVT : DC cardioversion with  50-100 J.
4. Catheter ablation in recurrent episodes not responding to medical treatment.