Case report: Para Hisian Atrial Tachycardia

Atrial tachycardia accounts for around 10% of supraventricular tachycardias (1). Atrial      tachycardia can either be focal or macrorenentrant. Focal AT usually start at a focal point and then spreads in a centrifugal fashion to initiate atrial activation. Electrophysiologic studies have demonstrated the propensity of these tachycardias to arise from right atrium in the majority of cases (60%) and rest from the left atrium. There is a great predilection for crista terminalis. On the left side most of these arise from around the pulmonary vein ostia (2). A small proportion of these have tendency for arising from the Para-Hisian region. Incessant focal atrial tachycardia can lead to tachycardia induced cardiomyopathy (3).        A 55year old woman known hypertensive and diabetic, presented to our outpatient department with complaint of palpitations for the last 7 years. Presentation ECGs were narrow complex regular long RP tachycardia and without pre-excitation in normal sinus rhythm. (Fig 1) Despite oral medications she had multiple ER admissions which required IV medications tom terminate tachycardia. Considering that she was significantly symptomatic and drug refractory, the patient was indicated for invasive electrophysiological study and RF ablation. Her pre-procedure workup was unremarkable for ischemia and structural heart disease. Fig 1. 12 Lead ECG showing Narrow complex Long RP Tachycardia  She had a 4 catheter EP study done using conventional system, St Jude’s EP Workmate with 3D mapping system Carto backup. Her intracardiac electrograms from high right atrium, His- bundle location, coronary sinus and right ventricular apex were simultaneously recorded and displayed using a surface ECG. The clinical tachycardia had a CL of 240ms. (Fig 2) This was induced spontaneously and with atrial burst pacing protocol. There was evidence of AV Wenckebach and AV disassociation. A diagnosis of focal right atrial tachycardia was made. for detailed mapping of ablation target site, the procedure was shifted 3D guided mapping and ablation procedure. Fig. 2 Intracardiac Electrogram: More As than Vs with VA dissociation. Electroanatomical mapping and ablation was performed using the CARTO 3 system with Navistar catheter. The electroanatomic activation mapping confirmed a focal right atrial tachycardia originating from the anterior interatrial septum in close proximity to the bundle of His (8mm). The intracardiac electrogram recorded from the right atrium recorded the earliest site which was 35ms earlier than the earliest atrial activation. It was then decided to map the aortic cusps in detail due to the close proximity to the interatrial septum. Relative safety of ablation that has been reported previously. Mapping in the non-coronary cusp of the aorta revealed an even earlier site of activation which was 38ms earlier than earliest atrial activation. RF Ablation was performed from the non-coronary cusp at this site at 30W. Additional lesions were given in close proximity to this site for 70 seconds in total. There was termination of tachycardia within 5 seconds of starting RF ablation. Atrial tachycardia was no longer inducible despite following aggressive stimulation protocols. Fig. 3 Fig. 3 Earliest atrial activation site from RA LAT -35ms. The distance of focal AT origin is 8mm from Bundle of His Fig. 4 Termination of Tachycardia. The patient remains on our follow up and has been asymptomatic since her procedure.   Discussion Para Hisian atrial tachycardia is a rare type of focal atrial tachycardia which is notorious due to its close proximity to the AV node. Various studies have been done to demonstrate the best way to approach ablation of these tachycardias. Literature review reveals that this was done traditionally from the right atrium. Using a transseptal approach to map the LA has also been used. In 2004 Tada et al (4) reported a case of atrial tachycardia originating near the AV node which was successfully ablated from the non-coronary cusp. Since then multiple studies have been published which demonstrate the success of adapting the retrograde route, although these studies are relatively small. Beukema et al in 2015 (5) published a case series of 7 patients with successful ablation of focal AT from non-coronary cusp. Our case report seems to be the first one from our region. Lyan et al in 2017 (6) demonstrated the success of various approaches for ablation of these tachycardias.   They found that ablation from right atrium resulted in success in 46.5% patients, LA=25% and NCC 88%. The recurrence rate was lowest with NCC- 4.4% and highest with those ablated from the RA. AV block was only present in just above 14% of patients and in only those who underwent RFA from RA. This is in contrast to Ju et al (7) who had previously published data in 2012 with 20 patients with the same focal atrial tachycardia, in which only 1/4th of the patients needed to have the retrograde aortic approach to map and ablate from the NCC successfully.  Conclusion Para Hisian atrial tachycardia is an uncommon focal atrial tachycardia. It can be ablated either anterograde (RA), anterograde transseptal (LA) or retrograde from aorta to the NCC. This can serve as an alternate site of ablation for high right atrium. The rate of AV block is lower with NCC ablation. It is always a good idea to map the NCC if the AT is found to originate in the Para Hisian region.