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Slow-fast AVNRT 

Slow-fast AVNRT
Chapter:
Slow-fast AVNRT
Author(s):

Hein Heidbuchel

, Mattias Duytschaever

, and Haran Burri

DOI:
10.1093/med/9780198766377.003.0076
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Introduction to the case

Case 76 shows a 20-year-old woman with palpitations. Transition from a 2:1 narrow complex tachycardia to a 1:1 wide complex tachycardia is shown in Figure 76.1.

Figure 76.1 Transition from a 2:1 narrow complex tachycardia to a 1:1 wide complex tachycardia. Surface leads II and V1 and intracardiac recordings from the high right atrium (HRA), His bundle (HB), coronary sinus (CS), and right ventricular apex (RVA)

Figure 76.1
Transition from a 2:1 narrow complex tachycardia to a 1:1 wide complex tachycardia. Surface leads II and V1 and intracardiac recordings from the high right atrium (HRA), His bundle (HB), coronary sinus (CS), and right ventricular apex (RVA)

Question

What is the mechanism of transition?

  1. A SVT with a spontaneous PVC inducing VT

  2. B Atrial flutter inducing AVNRT

  3. C AVNRT with resumption of 1:1 infra-Hisian conduction after a PVC

  4. D AVNRT with resumption of 1:1 conduction over the LCP after a PVC

  5. E Atypical AVNRT inducing atrial flutter

Answer

C AVNRT with resumption of 1:1 infra-Hisian conduction after a PVC

Explanation

Slow/fast atrioventricular nodal re-entrant tachycardia and infra-Hisian block

Figure 76.1 (left): 2:1 tachycardia compatible with AVNRT or AT (cycle length of 286ms). Orthodromic AVRT and VT are excluded. There is 2:1 infra-Hisian AV block. A His bundle potential is recorded in the blocked complexes.

Figure 76.1 (middle): a spontaneous premature ventricular beat from the RV with early precocity advances His and atrial activation. Advancement of atrial activation by a PVC occurs in AVRT, but also in cases of early precocity in AVNRT and AT. The PVC unmasks the atrium at the His bundle electrogram (after the retrograde H deflection). The earliest A at the His bundle electrogram (anterior septum) suggests slow/fast AVNRT. In slow/fast AVNRT, 2:1 AV block is due to infra-Hisian block (absence of LCP) and maintained by long refractoriness at the proximal His–Purkinje system (prolonged refractoriness is explained by the 2-fold longer cycle length just distal from the site block).

Figure 76.1 (right): the PVC results in early retrograde activation of the His bundle. Together with delayed conduction over the slow pathway, this lengthens the H–H interval, enabling resumption of 1:1 AV conduction. Because of a prolonged A–H interval over the slow pathway, the cycle length is prolonged during the next AVNRT beats (cycle length of 298ms). This facilitates 1:1 infra-Hisian AV conduction (longer H–H interval), now with block in the right bundle (whereas before there was block in both bundles).

After ablation of the slow pathway, the tachycardia was rendered non-inducible.