Atrioventricular nodal re-entrant tachycardia
Atrioventricular nodal re-entrant tachycardia constitutes 85% of all supraventricular arrhythmias, excluding of atrial fibrillation. In a population of patients suffering from this arrhythmia, the ratio between women and men is 3: 2. Atrioventricular nodal re-entrant tachycardia is propagated in all age groups. However, in most cases, clinical manifestations occur in age from 28 to 40 years. In a patient with atrioventricular nodal re-entrant tachycardia, as a rule, there are no signs of structural pathology of the myocardium. Disease (tachycardia) occurs in the form of bouts of frequent rhythmic heartbeat that starts and stops suddenly. Paroxysm of atrioventricular nodal re-entrant tachycardia lasts from several seconds to several hours, and their frequency of occurrence is from daily episodes of arrhythmia to 1-2 times a year. Symptomatology during an attack is dependent on the heart rate (typically from 140 to 250 beats per minute), the functionality of the cardiovascular system, the presence of comorbidity. During the paroxysm patients usually complain of weakness, dizziness, feeling of pulsation in the blood vessels of the neck, in the head. Sometimes the attack is accompanied by the development of syncope, hypotension. Today, radiofrequency catheter ablation (RFСA) is the most effective way of treatment of this arrhythmia, which allows the patient to completely stop taking anti-arrhythmic drugs. The effectiveness of RFСA is 98-99%. Complications in the form of AV block of high degrees occur in 1% (according to leading electrophysiology laboratories in the world). The essence of this method is destruction of fibers of the "slow" part in the bottom of the triangle of Koch. RFСA is an absolute indication for patients suffering from this arrhythmia. Contraindication for this operation is preference by the patient of a permanent anti-arrhythmic therapy.
Atrioventricular nodal re-entrant tachycardia is a stable impulse circulation (re-entry) in the AV node and the adjacent septal atrial myocardium. Atrioventricular nodal re-entrant tachycardia is based on the so-called "longitudinal dissociation" of AV node. This is the presence of two (rarely more than two) pathways of impulse conduction with different characteristics in AV node, which are structurally and functionally related to each other.
Depending on the nature of the impulse circulation in the AV node, there are three types of atrioventricular nodal re-entrant tachycardia:
- typical type is "slow-fast": impulse moves through the AV node anterograde (from the atria to the ventricles) via "slow" pathway, and from the ventricles to the atria (retrograde) via "fast" pathway;
- atypical type is "fast-slow": impulse moves through the AV node anterograde via "fast" pathway, and retrograde via "slow" pathway;
- another atypical type is “slow-slow”: impulse moves through the AV node anterograde and retrograde via two "slow" pathways.
Heart rate during atrioventricular nodal re-entrant tachycardia is typically 160-200 beats per minute, but often up to 250 or more beats per minute. Configuration of QRS complexes is generally not different from that during sinus rhythm. In some cases, it may develop a frequency-dependent block of one of the bundle branches (usually the right) with a corresponding deformation and broadening of the QRS complexes that require differential diagnosis with ventricular tachycardia.
It should be noted another feature of atrioventricular nodal re-entrant tachycardia. The use of so-called "vagal tests ": Valsalva maneuver (straining at the height of inspiration), Aschner (pressure on the eyeballs), massage the area of the carotid sinus, etc., usually accompanied by a deceleration of tachycardia rhythm and often cessation of it.
The high frequency of heart rate during a paroxysm of atrioventricular nodal re-entrant tachycardia can lead to an abrupt decrease in blood pressure, the development of collapse and even fainting. In people with impaired contractile function of the myocardium frequently observed phenomenon of acute left ventricular failure. Long persistence of atrioventricular nodal re-entrant tachycardia, that is extremely rare, can lead to dilatation of the heart chambers and the development of symptoms of chronic circulatory failure.