Typical atrio-ventricular nodal reentrant tachycardia

ECG 16A: The rhythm is initially sinus; the tachycardia begins after an atrial extrasystole conducted to the ventricle with a sudden increase in PR interval; regular tachycardia with narrow QRS complexes, identical to the complexes of sinus origin; difficulty in differentiating atrial activity (during tachycardia, changes in the pattern of the portion preceding the QRS but also slight modification of the terminal portion of the QRS compared to the sinus complexes);

Tracing 16B: identical tachycardia;

ECG 16C:

ECG 16C: Interruption of the tachycardia after flash injection of an Adenosine ampule; recovery of sinus rhythm with slightly prolonged PR interval; the comparison of the QRS complex in tachycardia and in sinus rhythm shows a difference in the end of the QRS-beginning of the ST segment which is clearly visible in aVR and from V1 to V4 suggesting the presence of an atrial activity appended to the QRS during the tachycardia;

Comments: Certain elements of this pathway regarding the onset, maintenance and termination of the tachycardia (initiation on an atrial extrasystole with abrupt prolongation of the PR interval, regular tachycardia with narrow QRS, 1:1 atrial activity located at the end of the QRS, termination by injection of Adenosine) are typical of an intranodal reentry; this diagnosis was confirmed during an electrophysiological study.

Atrio-ventricular nodal reentrant tachycardia (AVNRT) is the most common type of junctional tachycardia and usually occurs in young patients without heart disease. They can occur at all ages, from infants to the elderly, clinical history often reporting a long history of palpitation episodes of varying durations, ceasing either spontaneously or by vagal maneuvers.

The clinical presentation of the episodes is relatively stereotyped (description corresponding to the tachycardias described by Bouveret): tachycardias are regular, of sudden onset (the patient knows precisely when the episodes began) and sudden end with often a sensation of well-being; the duration of the episodes varies from one patient to another from a few minutes to several hours; in the vast majority of cases, functional tolerance is good since these tachycardias occur predominantly in patients with a healthy heart. Depending on the degree of acceleration of the heart rate, the episodes may symptomatic with frequent description of palpitations, anxiety and/or dyspnea, and more rarely of chest pain, lightheadedness or syncope at very rapid heart rate.

Given that the episodes occur in the absence of underlying cardiac disease, they are considered benign even if the tachycardias can be disabling when they are frequent, very rapid and do not cease with the usual vagal maneuvers. The main evolving risk, aside from the number and duration of tachycardia episodes which tend to increase, is the appearance of atrial fibrillation, the incidence of which increases with age.

Termination of the tachycardia can be obtained by performing simple vagal maneuvers (valsalva, prolonged swallowing, sino-carotid compression; ocular compression is to be avoided since painful and traumatic) which are preferentially effective at the onset of the episode and for which the patient can perform on his or her own. If these maneuvers are ineffective, an injection of Adenosine or Verapamil may be administered under electrocardiographic monitoring, the presence of a potentially prolonged pause reduction being relatively frequent. Exceptionally, atrial pacing may be proposed when medical treatment is ineffective.

A long-term preventive treatment (Verapamil, beta-blockers, class IC anti-arrhythmic drugs) is only proposed when the palpitations are frequent and disabling. Ablation of the slow pathway may allow eliminating the symptoms at the cost of a small risk of the occurrence of a complete atrioventricular block.

Take-home message: The onset of a tachycardia by typical AVNRT (slow-fast) is generally characteristic: after an atrial extrasystole, the fast pathway is blocked, the impulse is then transmitted in anterograde manner with a conduction jump and a sudden prolongation of the PR interval. Atrial pacing easily triggers this type of tachycardia as opposed to ventricular pacing, where triggering is much more difficult.