AV nodal reentrant tachycardia, or atrioventricular nodal reentrant
tachycardia, is a type of tachycardia of the heart. It is a type of
supraventricular tachycardia, meaning that it originates from a location
within the heart above the bundle of His. AV nodal reentrant tachycardia is
the most common regular supraventricular tachycardia. It is more common in women
than men. The main symptom is palpitations. Treatment may be with
specific physical maneuvers, medication, or, rarely, synchronized cardioversion.
Frequent attacks may require radiofrequency ablation, in which the
abnormally conducting tissue in the heart is destroyed.
AVNRT occurs when a reentry circuit forms within or just next to the
atrioventricular node. The circuit usually involves two anatomical
pathways: the fast pathway and the slow pathway, which are both in the right
atrium. The slow pathway is located inferior and slightly posterior to the
AV node, often following the anterior margin of the coronary sinus. The fast
pathway is usually located just superior and posterior to the AV node. These
pathways are formed from tissue that behaves very much like the AV node, and
some authors regard them as part of the AV node.
The fast and slow pathways should not be confused with the accessory pathways
that give rise to Wolff-Parkinson-White syndrome or atrioventricular
reciprocating tachycardia. In AVNRT, the fast and slow pathways are located
within the right atrium close to or within the AV node and exhibit
electrophysiologic properties similar to AV nodal tissue. Accessory pathways that
give rise to WPW syndrome and AVRT are located in the atrioventricular valvular
rings. They provide a direct connection between the atria and ventricles, and
have electrophysiologic properties similar to ventricular myocardium.
Signs and symptoms The main symptom is the sudden
development of rapid regular palpitations. Often, no precipitant is
present, although some report development of symptoms in stressful
situations, consumption of alcohol or caffeine, or other factors.
In some cases, the onset of the tachycardia is associated with a brief
drop in blood pressure. When this happens, the patient may experience
dizziness or rarely syncope. If the heart rate is very fast, and the patient
has underlying coronary artery disease, chest pain similar to angina may be
experienced; this pain is band- or pressure-like around the chest and often
radiates to the left arm and angle of the left jaw. AVNRT is rarely
life-threatening. Diagnosis
If the symptoms are present while the patient is attending medical care, an
electrocardiogram may show typical changes that confirm the diagnosis. If
the palpitations are recurrent, a doctor may request a Holter monitor recording.
Again, this will show the diagnosis if the recorder is attached at the time of
the symptoms. Rarely, disabling but infrequent episodes of palpitations may
require the insertion of a small microchip-based device under the skin
that continuously record heart activity, and can be read through the skin after
an episode. All these ECG-based technologies also enable the distinction
between AVNRT and other tachycardias such as atrial fibrillation, atrial
flutter, sinus tachycardia, ventricular tachycardia and tachyarrhythmias related
to Wolff-Parkinson-White syndrome, all of which may have symptoms that are
similar to AVNRT. Blood tests commonly performed in people
with palpitations are: thyroid function tests - an overactive
thyroid increases the risk of AVNRT electrolytes - disturbances in
potassium, calcium and magnesium may predispose to AVNRT
cardiac markers - if there is a concern that myocardial infarction has occurred
either as a cause or as a result of the AVNRT; this is usually only the case if
the patient has experienced chest pain Classification
There are several types of AVNRT. The "common form" or "usual" AVNRT utilizes
the slow AV nodal pathway as the anterograde limb of the circuit and the
fast AV nodal pathway as the retrograde limb. The reentry circuit can be
reversed such that the fast AV nodal pathway is the anterograde limb and the
slow AV nodal pathway is the retrograde limb. This, not surprisingly, is
referred to as the "uncommon form" of AVNRT. However, there is also a third
type of AVNRT that utilizes the slow AV nodal pathway as the anterograde limb
and left atrial fibers that approach the AV node from the left side of the
inter-atrial septum as the retrograde limb. This is known as atypical, or
Slow-Slow AVNRT. = Common AVNRT=
In common AVNRT, the anterograde conduction is via the slow pathway and
the retrograde conduction is via the fast pathway.
Because the retrograde conduction is via the fast pathway, stimulation of the
atria will occur at the same time as stimulation of the ventricles. As a
result, the inverted P waves may not be seen on the surface ECG since they are
buried with the QRS complexes. Often the retrograde p-wave is visible, but also
in continuity with the QRS complex, appearing as a "pseudo R prime" wave in
lead V1 or a "pseudo S" wave in the inferior leads.
= Uncommon AVNRT= In uncommon AVNRT, the anterograde
conduction is via the fast pathway and the retrograde conduction is via the
slow pathway. Multiple slow pathways can exist so that
both anterograde and retrograde conduction are over slow pathways..
Because the retrograde conduction is via the slow pathway, stimulation of the
atria will be delayed by the slow conduction tissue and will typically
produce an inverted P wave that falls after the QRS complex on the surface
ECG. Treatment
An episode of supraventricular tachycardia due to AVNRT can be
terminated by any action that transiently blocks the AV node. Various
methods are possible. = Vagal maneuvers=
Some people with known AVNRT may be able to stop their attack by using various
tricks to activate the vagus nerve. This includes carotid sinus massage or the
Valsalva maneuver. = Medication=
Medical therapy can be initiated with AV nodal slowing drugs such as adenosine,
beta blockers or non-dihydropyridine calcium channel blockers. Numerous other
antiarrhythmic drugs may be effective if the more commonly used medications have
not worked; these include flecainide or amiodarone. Both adenosine and beta
blockers may cause tightening of the airways, and are therefore used with
caution in people who are known to have asthma.
= Cardioversion= In very rare instances, cardioversion is
needed in the treatment of AVNRT. This would normally only happen if all other
treatments have been ineffective, or if the fast heart rate is poorly tolerated.
= Electrophysiology= After being diagnosed with AVNRT,
patients can also undergo an Electrophysiology study to confirm the
diagnosis. Catheter ablation of the slow pathway, if successfully carried out,
can potentially cure the patient of AVNRT.
Pacemaker-mediated tachycardia A separate form of AV nodal reentrant
tachycardia is pacemaker-mediated tachycardia, a possible complication of
dual-chamber artificial pacemakers. In PMT, the artificial pacemaker forms the
anterograde limb of the circuit and the atrioventricular node forms the
retrograde limb of the circuit. Treatment of PMT typically involves
reprogramming the pacemaker. See also
List of circulatory system conditions Cardiac electrophysiology
Clinical cardiac electrophysiology References
External links AVNRT Clinical Cases from Life in the
Fast Lane Medical Blog Supraventricular Tachycardia: Diagnosis
and Management from Mayo Clinic Proceedings