Spontaneous transformation of a concealed to manifest posteroseptal accessory pathway requiring epicardial ablation.

Concealed accessory pathways (APs) are considered benign as they can only sustain orthodromic atrioventricular re-entrant tachycardia (ORT). We describe a unique case of a concealed posteroseptal AP where longitudinal surveillance following repeated failed ablation attempts due to abnormal coronary sinus (CS) anatomy revealed spontaneous development of manifest pre-excitation. The pathway was ultimately ablated via the percutaneous epicardial approach. The potential for development of Wolff-Parkinson-White (WPW) syndrome in patients with concealed APs has implications for ongoing surveillance in these patients.

INTRODUCTION

Concealed accessory pathways (APs) are only capable of retrograde conduction and therefore do not manifest pre‐excitation or the WPW pattern on the surface electrocardiogram (ECG). The natural history of concealed APs is unknown as most are diagnosed and cured during the same index electrophysiology (EP) procedure performed for investigation of supraventricular tachycardia (SVT). We present a unique case where longitudinal follow‐up over a decade demonstrated the evolution from a concealed to a manifest posteroseptal AP. Complex anatomy which prevented successful ablation during this period was eventually overcome by epicardial ablation via the pericardial space.

CASE PRESENTATION

A now 23‐year‐old female presented 10 years earlier with recurrent palpitations, chest pains, and presyncope. Her resting ECG demonstrated normal conduction intervals without evidence of pre‐excitation (Figure 1A). Echocardiogram confirmed a structurally normal heart.

Figure 1

Panel A—Presenting ECG demonstrating the absence of pre‐excitation with a normal PR interval and septal Q waves (leads I, aVL, V6—arrows). Panel B—ECG prior to the 3rd EP study demonstrating manifest pre‐excitation with superior axis delta waves with V2 transition (arrows) consistent with a posteroseptal accessory pathway

During her initial EP study, ORT utilizing a concealed septal AP was induced. There was no evidence of pre‐excitation at baseline, during atrial incremental and extrastimuli testing with or without isoprenaline. Prior to ablation attempts, the operators had difficulty cannulating the CS from the femoral vein. They achieved limited proximal access to what was described as a “tight and narrow” CS via the right internal jugular approach; however, radiofrequency ablation (RFA) attempts here and on the left septum (via the retrograde aortic approach) were unsuccessful.

Soon after, she underwent a repeat EP study due to ongoing palpitations despite flecainide therapy. A preprocedural cardiac MRI demonstrated a small pit at the usual site of the CS os suggesting severe stenosis. There was no evidence of pre‐excitation. Coronary angiography with delayed venous phase contrast revealed CS drainage into the right atrium (RA) at a high septal site. RFA was attempted at this site and again at the left septum via the retrograde aortic route. Both approaches were unsuccessful.

At some time within the next 2‐4 years, pre‐excitation was noted on her ECG with a pattern consistent with anterograde conduction down the same posteroseptal AP (Figure 1B). She underwent a 3rd EP study due to ongoing symptoms despite medical therapy. A preprocedural CT venogram confirmed abnormal CS drainage with a vestigial tortuous 4‐ to 5‐mm‐diameter vessel draining from the confluence of the middle cardiac vein (MCV) and CS, both of which were significantly dilated, into the RA at the expected CS os site. The earliest ventricular electrograms were no more than 10 ms predelta on both sides of the septum (left side mapped transseptally). RFA was unsuccessful at these sites.

During her final EP study a year later, retrograde CS access was attempted via the left axillary vein. However, no persistent left superior vena cava was seen on venogram, and probing of the region with a 0.014” coronary wire was unsuccessful in locating a vestigial lumen. Percutaneous epicardial access was obtained, and earliest ventricular electrograms (15 ms predelta wave) were found over the posteroseptal region (Figure 2E). After confirming satisfactory distance from coronary artery branches with angiography, irrigated ablation at 30W was performed during atrial pacing (Tacticath™, St. Jude Medical, St. Paul, MN) resulting in loss of AP conduction within 6 seconds (Figure 2F). No recurrence was seen during the 40‐minutes waiting period.

Figure 2

Panel A—Contrast venography through the ablation catheter (Abl) lumen demonstrating a vestigial tributary (yellow arrow) draining into the right atrium (during 3rd EP study). Panel B—Three‐dimensional CT‐integrated anatomical map (EnSite™ NavX™, St. Jude Medical, St. Paul, MN) of the coronary sinus (CS) vasculature demonstrating the vestigial tributary draining the confluence of the dilated CS and middle cardiac vein (MCV) into the right atrium. Panels C/D—LAO 30° and RAO 30° views of ablation catheter (Abl) at the site of successful ablation which was confirmed to be distant (>5 mm) from the branches of the right coronary artery (RCA). Panel E—Intracardiac electrograms during atrial pacing demonstrated the earliest candidate potential to be 16 ms predelta wave (arrow) at the site of successful ablation. Panel F—Loss of pre‐excitation within 6 s (arrow) of radiofrequency ablation onset

DISCUSSION

Retrospective studies of patients with WPW syndrome have demonstrated that some patients did not have manifest pre‐excitation on ECGs predating their diagnosis.1 However, as none of these patients underwent EP studies prior to diagnosis, it is unclear whether this was due to intermittent pre‐excitation, inapparent pre‐excitation due to dominant AV node conduction, or a concealed AP that spontaneously developed anterograde conduction. The development of pre‐excitation is significant for the associated small but significant risk of sudden death.2

APs have dynamic conduction properties which can change over time. Spontaneous loss of pre‐excitation is well described.1, 3 Our case is the first description of a long‐standing concealed AP subsequently evolving to manifest pre‐excitation. Although adenosine was not administered, intermittent or inapparent pre‐excitation was excluded during the first two EP studies by demonstrating normal and fixed HV intervals at rest, during atrial incremental and extrastimuli testing and following isoprenaline. A case series has described manifest pre‐excitation arising following attempted RFA in patients with concealed APs; however, this tends to occur within 2 weeks of ablation4 suggesting a modulating effect of ablation on pathway conduction. This is an unlikely explanation for the phenomenon in our patient as serial ECGs performed up to 2 years following her second EP procedure revealed no evidence of pre‐excitation. However, we cannot exclude the possibility that intermittent pre‐excitation was present following the 2nd EP study and simply not caught on ECGs until 2 years later.

Ablation of posteroseptal APs in the absence of CS access can be challenging. Alternative approaches should be considered including the right posteroseptum and the left posteroseptum (via transseptal or retrograde aortic approaches). Retrograde mapping of the CS can be attempted via a persistent left superior vena cava if present. If these sites are unsuccessful, a percutaneous epicardial approach should be considered. As these APs can involve the coronary sinus vasculature, they can often be successfully ablated in the epicardial space.5

CONCLUSION

The natural history of concealed APs is unknown as most are cured at the time of diagnosis during an EP procedure performed for symptomatic SVT. Our case demonstrates the potential for concealed APs to develop manifest pre‐excitation. Given the small but significant risk associated with the latter, patients with paroxysmal SVT who choose not to undergo ablation should have ongoing surveillance if a concealed AP has not been excluded.

CONFLLICT OF INTEREST

None.