Cover Story

Utility of Ultra High-Density Mapping and Conduction System Pacing to Limit Lifelong Morbidity in a Young Patient

Kanwar Singh, MD, FHRS and Richard Abben, MD, FACC

Cardiac Arrhythmia Service, Cardiovascular Institute of the South, Houma, Louisiana

Kanwar Singh, MD, FHRS and Richard Abben, MD, FACC

Cardiac Arrhythmia Service, Cardiovascular Institute of the South, Houma, Louisiana


High-density (HD) 3D mapping has increasingly become an important tool in localization and ablation of complex atrial arrhythmias. In addition, conduction system pacing (CSP), including His bundle pacing (HBP) and left bundle pacing (LBP), has emerged as a significant technique in minimizing potential adverse effects of myocardial pacing. This case presentation demonstrates the importance of both high-density 3D mapping and CSP in the management of a complex young patient who required treatment for a resistant atrial arrhythmia while also requiring long-term ventricular pacing. 

Case Description 

A 42-year-old Caucasian female with a past medical history of recurrent palpitations, weakness, and anxiety, presented to our electrophysiology (EP) clinic to establish care. Her past cardiac history included a diagnosis of supraventricular tachycardia (SVT) established two years previously when she was living in a different state. She had undergone prior EP study and radiofrequency ablation for SVT by operative report; common atrioventricular nodal reentry tachycardia (AVNRT) was identified, requiring ablation at the inferior and gradually until the superior part of triangle of Koch, slow pathway region, and left side of the interatrial septum. Unfortunately, as a result of the procedure, the patient developed transient complete heart block that evolved to AV Wenckebach conduction and a baseline prolonged PR interval at rest up to 330 msec (Figure 1). She subsequently underwent right-sided dual-chamber pacemaker implant a few weeks post procedure for symptomatic bradycardia and began an antiarrhythmic Class 1C drug (flecainide). Over the course of the next several months, she continued to note disabling, episodic palpitations; thus, a second ablation procedure was performed. During the second procedure, atrial lead dislodgement occurred, and atrial tachycardia from the AV nodal area was also identified. Because of concern about the complete heart block, repeat ablation was deferred, and she was placed on nebivolol (20 mg PO q day) and flecainide was increased (150 mg PO BID). Atrial electrode revision was also performed, with additional antibiotic therapy required for post-operative wound infection.

Over the next six months, she continued to have episodic palpitations and orthostatic symptoms while on medical therapy; she also developed moderate dyspnea on exertion and intermittent chest sensations that she related to a paced rhythm. She was re-evaluated at our center, and device interrogation demonstrated complete heart block with pacemaker dependency and periodic noise with oversensing observed on the atrial sensing channel. This latter phenomenon resulted in intermittent symptoms of palpitations, and at times, initiated episodes of atrial tachycardia. Episodes of atrial tachycardia were well-documented in the device telemetry data (Figure 2). After extensive discussion of treatment options with the patient and her spouse, we decided to reattempt ablation of atrial tachycardia and consider extraction of the pacemaker electrodes with a planned upgrade to a His bundle pacing system via the contralateral side. 

Her medications were weaned off, and noninvasive EP study via pacemaker resulted in inducing sustained atrial tachycardia. P-wave morphology on 12-lead EKG was suggestive of inferior septal location. The tachycardia was then carefully mapped using a high-density multipolar catheter in the right atrium. The earliest local activation time (LAT) was noted to be below the proximal His bundle location in front of the coronary sinus (CS) os. A fast pathway was annotated anatomically posterosuperior to the CS os. Irrigated RF catheter with contact force and Agilis (Abbott) sheath support was used for ablation. RF ablation at 25W with titration to 30W terminated the tachycardia. Two additional prolonged (90-sec) RF lesions were delivered in the region of earliest LAT, which rendered the tachycardia non-inducible thereafter (Figures 3 and 4). The procedure was completed after isoproterenol challenge failed to induce tachycardia. The patient was discharged home on midodrine 5 mg BID to help with vasovagal symptoms, with plans for pacemaker electrode extraction and a new implant a few weeks post procedure. 

Two weeks after the ablation procedure, the patient was reassessed; she continued to be symptomatic related to the inadvertent atrial and ventricular pacing. Without flecainide therapy, complete heart block improved to Mobitz type I second-degree AV block with baseline prolongation of PR interval measuring 300-320 msec. She was brought back to the EP lab for pacemaker extraction and re-implant. A right-sided pacemaker system was extracted without significant difficulty using Cook Medical extraction tools, and the pocket was closed. Left-sided pacemaker implantation was then performed utilizing the Model 3830 lead and C315 Catheter (Medtronic). Selective and non-selective His bundle pacing was achieved, with excellent threshold at 0.75V@0.5ms. At a paced cycle length (CL) of 400 msec, 1:1 capture and conduction was observed. Post-device programming included an AV delay of 100 ms to allow normal PR interval with non-selective His bundle pacing utilized initially (Figures 5 and 6). The patient tolerated the procedure well and was discharged the next morning.

At discharge, the patient reported resolution of her constant awareness of pacing, despite 100% His bundle pacing. On follow-up, the patient noted no more symptoms and felt significantly better as compared to the two previous years. Four months after implantation, threshold testing demonstrated stability with non-selective HBP threshold at 1.5V@0.5ms, and selective HBP capture lost at 0.5V@0.5ms. With continued follow-up, the patient still required therapy for vasovagal symptoms, mostly with lifestyle changes and low-dose propranolol, but denies any palpitations, weakness, or dyspnea on exertion; she remains NYHA Class I from a cardiovascular standpoint. 


This case presentation highlights the importance of utilizing detailed diagnostic testing during the baseline EP study, high-density mapping to safely ablate complex arrhythmias, and His bundle pacing in a younger patient who requires long-term, high-burden right ventricular (RV) pacing. It underscores the importance of delineating the specific mechanism of SVT, and not to inadvertently consider a common AVNRT to be a simple tachycardia ablation. Differentiation of this from an atrial tachycardia with origin described can be challenging, as activation sequence and conduction times may be similar. In the patient presented, this issue resulted in fast pathway injury, with significant associated morbidity. Though uncommon, atrial tachycardias have been described originating from the slow pathway region in the triangle of Koch or CS os. Kistler et al1 described atrial tachycardias originating from the coronary sinus os, with a reported incidence of around 6%. We utilized general anesthesia and controlled respirations to allow minimal catheter movement, thus ensuring safe ablation in this region without further jeopardizing the compact AV node. The availability of HD mapping with a high-resolution catheter helped identify electrograms in the previously ablated region without much difficulty. High-density mapping is not a necessity for safe ablation techniques in general, but in problematic cases such as the one described here, the technique adds a level of ease and confidence in accurately delineating the appropriate arrhythmia mechanism while potentially reducing procedure time. 

CSP including His bundle pacing is an emerging physiologic pacing tool at the disposal of present-day electrophysiologists. There is a growing body of evidence that CSP (with selective and non-selective His bundle pacing) is superior to RV pacing and associated outcomes may be comparable to cardiac resynchronization therapy. This was described by Abdelrahman et al,2 who demonstrated feasibility and associated superiority of HBP when compared to RV pacing. The benefits were clearly present in our patient, who had experienced immediate resolution of her constant sensation of ventricular pacing after His bundle pacing was instituted. Currently, CSP is an emerging technique with a present Class IIb3 recommendation in patients with AV block at the level of the AV node as an alternative to RV pacing. Although its specific indications have not yet been clearly defined, observational data suggest improved hemodynamic outcomes4 in patients requiring a high frequency of ventricular pacing, as was the case in our patient. With improved implantation techniques and tools as well as rigorous comparative trials, it is anticipated that CSP will become a reliable approach to achieve physiologic pacing and improve long-term outcomes. 


Our case highlights the importance of utilizing all available EP tools at hand, including basic SVT diagnostic maneuvers, high-density 3D mapping, and novel conduction system pacing, in order to achieve excellent outcomes for our patients while avoiding potential complications and long-term morbidity. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein.  

  1. Kistler PM, Fynn SP, Kalman JM. Focal atrial tachycardia from the ostium of the coronary sinus: electrographic and electrophysiological characterization and radiofrequency ablation. J Am Coll Cardiol. 2005;45(9):1488-1493. doi: 10.1016/j.jacc.2005.01.042.
  2. Abdelrahman M, Subzposh FA, Beer D, et al. Clinical outcomes of His bundle pacing compared to right ventricular pacing. J Am Coll Cardiol. 2018;71(20):2319-2330. doi: 10.1016/j.jacc.2018.02.048.
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