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Definition, Etiology, PathogenesisTop
Atrioventricular nodal reentrant tachycardia (AVNRT) is a paroxysmal tachycardia that occurs in patients with dual atrioventricular (AV) node physiology, as they have both a fast nodal pathway with a longer refractory period and a slow nodal pathway with a shorter refractory period. It is most commonly observed in individuals with no underlying structural heart disease.
Types of AVNRT:
1) Typical and most common type of AVNRT: Anterograde conduction (from the atrium to the ventricle) proceeds over the slow pathway and retrograde conduction (from the ventricle to the atrium) proceeds over the fast pathway (slow-fast AVNRT).
2) Atypical AVNRT: Anterograde conduction proceeds over the fast pathway and retrograde conduction proceeds over the slow pathway (fast-slow AVNRT).
Clinical Features and Natural HistoryTop
AVNRT usually occurs in young patients, causing paroxysmal palpitations that abruptly start and stop. The palpitations are usually relatively well tolerated, as no concomitant structural heart disease is found and the heart rates are usually ≤170 to 180 beats/min. Patients may describe a sensation of rapid regular pounding in the neck during tachycardia. The attacks may be frequent (up to several a day) and may require emergency care.
Electrocardiography (ECG): Typical AVNRT is characterized by the absence of evident P waves, which are hidden in or present immediately after the QRS complex (short RP interval) but may distort the terminal portion of the QRS by mimicking an S wave in the inferior leads or an r wave in lead V1. In atypical AVNRT the RP interval is long (RP interval > PR interval). In both typical and atypical AVNRTs the P waves are negative in the inferior leads.
Classification of antiarrhythmic drugs: Table. Vaughan Williams classification of antiarrhythmic….
Antiarrhythmic agents: Table. Antiarrhythmic agents.
1. Termination of an AVNRT attack:
1) Vagal maneuvers (eg, Valsalva,Evidence 1Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to imprecision. Smith GD, Fry MM, Taylor D, Morgans A, Cantwell K. Effectiveness of the Valsalva Manoeuvre for reversion of supraventricular tachycardia. Cochrane Database Syst Rev. 2015 Feb 18;(2):CD009502. doi: 10.1002/14651858.CD009502.pub3. Review. PubMed PMID: 25922864.carotid massage, and facial immersion in cold water) should be initiated to terminate the arrhythmia or to modify AV conduction.
2) IV adenosine as a bolus of 6 mg. If not effective, 12 or 18 mg can be given after 1 to 2 minutes.
3) IV beta-blockers, diltiazem, or verapamil are a reasonable option in stable patients.
4) Direct current cardioversion should be performed for acute treatment in hemodynamically unstable patients.
2. Recurrence prevention:
1) In patients with frequently recurring AVNRT attacks who prefer long-term oral treatment to ablation, use diltiazem, verapamil, or a beta–blocker.
2) In patients with no structural heart disease who do not respond to drugs that inhibit AV node conduction (see above), use flecainide or propafenone.
3) In minimally symptomatic patients with AVNRT, clinical follow-up without pharmacologic therapy or ablation is reasonable.
4) In patients with poorly tolerated AVNRT, recurrent attacks, and significant symptoms, as well as in those with mild and well-tolerated symptoms who wish to achieve a complete cure of AVNRT, catheter ablation of the slow pathway is indicated. This is the most successful treatment method, although associated with a low risk (0.5%-1%) of AV block requiring pacemaker implantation.