The patient is a 33-year-old female with a past medical history significant for inappropriate sinus tachycardia (IST). Over a one-year period of follow-up and medical management, the patient’s ejection fraction (EF) decreased from 60-65% to 40-45%. She was quite symptomatic with minimal exertion, complaining of palpitations, fatigue, lightheadedness, and shortness of breath (Figure 1). An implantable cardiac monitoring device (ICM) (Reveal LINQ™, Medtronic) was implanted to assess her heart rate at rest and with different degrees of exertion. The ICM revealed a resting average heart rate of 105-115 bpm, with an increase in heart rate to 150-170 bpm with normal daily activities (Figure 2). She was medically managed with beta blockers, calcium channel blockers, and fludrocortisone, as well as with behavioral changes such as frequent hydration, leg exercises, small frequent meals, and compression stockings. These changes failed to improve her symptoms, so we decided to electively perform a radiofrequency catheter ablation for IST.
Ultrasound-guided vascular access was obtained twice in the right femoral vein. The EnSite™ Array™ non-contact mapping catheter (St. Jude Medical) was used for mapping purposes. Utilizing a 9 French groin sheath and a 150 cm J-tip wire, the 64 unipolar multi-electrode array catheter was deployed in the high right atrium close to the crista terminalis and sinus node area. Once deployed, a Tegaderm dressing (3M) was placed at the groin site to help prevent further movement of the catheter. A heparin bolus was given based on the patient’s weight with a targeted ACT range of 250-300 seconds. Right atrial geometry was created around the EnSite™ Array™ catheter using the FlexAbility™ Ablation Catheter (St. Jude Medical). Because the EnSite® Array has no inherent orientation, fluoroscopic orientation was defined and correlated on the EnSite mapping system. The His recording was used as a spatial reference to define our EnSite™ Array™ catheter orientation. The EnSite™ Array™ catheter is capable of rapidly sampling unipolar voltage data at multiple (thousands) sites on the created endocardial geometry surface. Once geometry is created, a single beat of tachycardia can be played back as a dynamic wavefront of activation. Because the patient was in her clinical tachycardia (IST) at the time of procedure, isoproterenol infusion was not needed, so an initial recording of the clinical tachycardia was made (Figure 3).
Her initial IST rate was 510 msec (117 bpm) (Figure 3). Ablation delivery was complicated due to phrenic nerve (diaphragmatic) stimulation when pacing at 20 mA output all around the focus (brown lesions). Low-power ablation at 20W was attempted at this site. Immediately upon termination of our first ablation, two faster foci occurred higher up on the crista (Figure 4). These foci were also mapped and ablated, with the heart rate abruptly dropping from 150 to 76 at one point. Ablation at these sites was performed at 30-35W in a power-controlled mode. Once the more rapid foci were ablated, the clinical rate of tachycardia returned. More extensive mapping of the phrenic nerve was performed. Ablation lesions were delivered at locations where there was no diaphragm stimulation at 10 mA (small brown lesions), even if there was stimulation at 20 mA (larger brown lesion). Upon completion of lesion set delivery, the patient’s baseline heart rate was 84 bpm (Figure 5).
In many institutions, ablation of IST is not frequently attempted due to low efficacy rates and recurrence of the arrhythmia and patient’s symptoms. In this case study of a young patient with a documented decrease in EF and basal heart rate exceeding 100 bpm as documented by her ICM, the decision to attempt ablation resulted in symptomatic relief and an objective decrease in her baseline heart rate, as noted by her monthly ICM recordings (Figures 6 and 7). At 1-, 2-, 3-, and 4-month remote and/or in-person follow-up visits, the patient reports to be asymptomatic and has returned to work without experiencing any symptoms. She denies palpitations and is not taking any cardiac rate-modulating medications. Her ICM and post-ablation ECG (Figure 8) show a resting heart rate of 76 bpm with normal response to exercise and a normal heart rate histogram. In our practice, the Reveal LINQ ICM is used frequently for remote electrocardiographic monitoring as a diagnostic tool as well as to assess a patient’s arrhythmic burden or lack of arrhythmias after therapeutic interventions. In addition, the EnSite™ Array™ catheter has become our tool of choice to offer patients that have failed medical therapies for IST and other right-sided arrhythmias such as atrial tachycardias or RVOT-PVCs/VT.
Disclosures: Dr. Hong has no conflicts of interest to report regarding the content herein; outside the submitted work, he reports he is on St. Jude Medical’s speaker’s bureau. Ms. Carpenter reports she is employed by St. Jude Medical.
Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board.