Adenosine-sensitive decremental conduction over short non-decremental atrioventricular accessory pathways after radiofrequency ablation: case series

Abstract

Introduction: Decremental conduction in short anterograde atrioventricular accessory pathways (AV-APs) is rare.

Case presentation: We report on two cases with radiofrequency (RF) ablation of anterograde fast non-decremental AV-AP conduction. In Case 1, electrophysiological testing revealed fast non-decremental conduction over an anterograde short right posteroseptal AV-AP. During ablation, latent pre-excitation due to anterograde adenosine-sensitive slow decremental conduction over the same AV-AP manifested after eliminating its non-decremental conduction. Complete abolition of AP conduction was achieved by additional ablation. In Case 2, overt pre-excitation disappeared after the first ablation session for an anterograde short non-decremental right mid-septal AV-AP. However, latent pre-excitation due to markedly decremental conduction over the same AV-AP unmasked by intravenous adenosine and atrial pacing manoeuvers could be eliminated in a second session.

Discussion: This report describes unusual anterograde short non-decremental AV-APs, developing markedly slow adenosine-sensitive decremental conduction during ablation. Such AV-AP conduction properties due to RF injury may be overlooked and mask incomplete ablation and point-out careful testing including stimulation techniques and low and higher dose adenosine administration post-ablation.

Keywords: Atrioventricular accessory pathway; Case series; Decremental conduction; Latent pre-excitation; Radiofrequency ablation; Wolff-Parkinson-White syndrome.

Figure 1

Case 1: electrocardiogram with overt pre-excitation during sinus rhythm (A) and atrial pacing at a cycle length (S1S1) of 375 ms (B). Paper speed = 50 mm/s. (C) Bipolar electrogram (radiofrequency, RF) before ablation of fast accessory pathway conduction. Paper speed = 200 mm/s. A, atrial electrogram; V, ventricular electrogram; CSP, proximal coronary sinus; CSM, middle coronary sinus; CSD, distal coronary sinus; HBE, His-bundle electrogram; LRA, low right atrium; RV, right ventricle.

Figure 2

Case 1: radiofrequency ablation during sinus rhythm. Asterisk indicates block of fast accessory pathway conduction followed by non-preexcited sinus rhythm. Paper speed = 25 mm/s. Abbreviations as listed in Figure 1.

Figure 3

Case 1: bipolar electrogram (radiofrequency) recording (A) and electrocardiogram (B) during non-preexcited sinus rhythm after ablation of fast accessory pathway conduction. (C) Electrocardiogram during atrial pacing at a cycle length (S1S1) of 375 ms unmasking a nearly maximum ventricular pre-excitation. H, His-bundle potential. Abbreviations as listed in Figure 1.

Figure 4

Case 1: atrial extra-stimulation (S2) coupled with atrial driving (S1S1 400 ms) after ablation of fast accessory pathway conduction. With atrial prematurity (S1S2) shortening from 280 (A) to 250 ms (B), the local S2-Δ2 measured in the radiofrequency progressively lengthened along with a progressive pre-excitation pattern. Note a delayed local ventricular activation in the radiofrequency inscribed after non-preexcited QRS complexes during atrial driving. Paper speed = 150 ms. Abbreviations as listed in Figure 1.

Figure 5

Case 1: intravenous adenosine during non-preexcited sinus rhythm. (A) After 6 mg adenosine, three non-preexcited sinus beats with a progressive PR time prolongation are followed by sinus beats conducted with unmasked pre-excitation. (B) After 18 mg adenosine, two non-preexcited sinus beats are followed by one pre-excited sinus beat with a long PR interval, followed by transient complete atrioventricular block. Paper speed = 50 mm/s. Abbreviations as listed in Figure 1.

Figure 6

Case 1: radiofrequency ablation during atrial pacing. Single (*) and double (**) asterisks indicate transient and persistent accessory pathway block, respectively. Paper speed = 50 mm/s.

Figure 7

Case 2: electrocardiogram showing non-preexcited sinus rhythm (A, paper speed = 50 mm/s) and latent pre-excitation unmasked by intravenous adenosine (6 mg) (B, paper speed = 50 mm/s) and atrial pacing (C, paper speed = 25 mm/s). (D) Bipolar electrogram (radiofrequency) at the ablation site recorded during high right atrial pacing at a cycle length of 462 ms. Paper speed = 100 mm/s.