Tachycardia is a cardiovascular condition that is characterized by a faster than normal heart rate. Supraventricular tachycardia (also known as SVT) is a term that denotes the origin of the SVT i.e. above the level of ventricle. Supraventricular tachycardia can be further classified into atrial tachycardia, atrioventricular nodal reentry tachycardia (AVNRT) and atrioventricular reentry tachycardia (AVRT) on the basis of pathophysiology and site of origin. Most of the times, SVT is paroxysmal with frequent or infrequent episodes, and may last from minutes to months. This article will cover a precise introduction about what is reentry supraventricular tachycardia, while highlighting key symptoms and treatment options that should be considered to address this cardiovascular issue.
What Is Reentry Supraventricular Tachycardia?
Based on the mechanism and pathway of impulse conduction, there are two major types of reentry supraventricular tachycardia:
- AV-nodal reentry tachycardia (AVNRT): It involves the AV node and the AV nodal pathways; both can be fast and slow.
- Atrioventricular reentry tachycardia (AVRT): It involves the AV node, atrial myocardium, an accessory pathway and ventricular myocardium.
What Are the Symptoms of Reentry Supraventricular Tachycardia?
SVT is usually symptomatic; however, some patients may not experience recognizable episodes (in case of short paroxysms).
- The clinical history of patient is very important in all cases and is usually specific for discrete episodes of frequent palpitations that begin and end without any warning, randomly and suddenly.
- The sudden episodes are usually associated with symptoms of hemodynamic compromise such as light headedness, chest discomfort and dyspnea. The attacks may last from few seconds to up to several hours, rarely exceeding 12 hours. Clinical manifestation of infants with SVT includes precordial or rapid pulsation, feeding problems, lethargy and episodic breathlessness.
- Prolong tachycardia episode may also result in heart failure. Symptoms are more likely to appear on people between the ages of 15 to 35. SVT is more common on women as compared to men. At this point,patient is less likely to experience any symptoms during the episodes.And the cardiac investigation and examination appears to be normal.
- Doctor diagnoses reentry supraventricular tachycardia based on the patient's history which is further confirmed by an ECG obtained during the SVT episode. Heart rate usually ranges between 160-240 beats per minute whereas the ECG findings yield: narrow-complex tachycardia without any recognizable P wave; the P waves also do not appear in a 1:1 ratio with the QRS complex.
How to Treat Reentry Supraventricular Tachycardia
Treatment decisions must be made after conducting thorough clinical examination which is followed by investigations and radiological tests. It is common for some episodes to stop right prior to the initiation of treatment.
1. Vagotonic Maneuvers
Early use of vagotonic maneuvers may assist in terminating tachyarrhythmia. These include swallowing of ice cold water, ice water facial immersion, unilateral carotid sinus massage and valsalva maneuvers.
2. AV Node Blocker
In case these maneuvers fail to bring any effect and if the recorded ECG shows narrowed QRS complex (indicating orthodormic conduction), then AV node blockers should be used. These pharmacological agents help in blocking the AV node conduction to prevent the beat from interrupting the reentrant cycle. In all such cases, adenosine is usually the drug of choice and its dosage should be 6mg IV (rapid bolus) for adults and 0.05 to 0.1 mg/kg for children, along with 20 ml of saline bolus.
In case of failure of this treatment protocol,adenosine may be used. 2 subsequent doses of 12 mg q 5 minutes may be given. But it, at times, tends to cause cardiac standstill of a short period i.e. 2-3 seconds. Alternatively, verapamil in the dose of 5 mg IV may be used or Diltiazem in the dose of 0.25-0.35 mg/kg IV.
When the reentry supraventricular tachycardia episodes become bothersome and more frequent, the treatment options become narrow and they may include prolonged use of anti-arrhythmia and/or transvenous catheter radiofrequency ablation. Ablation is usually preferred; however, if it's unacceptable, then the prophylaxis is done with the drug called digoxin and proceeded to non-dihydropyridine calcium channel blockers, beta blockers or a combination of both based on patient's condition. It can be further proceeded to class Ia, class Ic or class III of anti-arrhythmic drugs.