Initial Experience with the Advisor HD Grid Mapping Catheter: Case from Arkansas Heart Hospital

Case Description

A 67-year-old female with hyperlipidemia was referred for palpitations. Two years prior to referral, she was diagnosed with paroxysmal supraventricular tachycardia. Initial management was conservative; however, over the next several months, she noted palpitations of worsening frequency and severity, which generally terminated spontaneously or with vagal maneuvers. One week prior to evaluation, she presented to an outside emergency room with chest pain and presyncope during an episode of supraventricular tachycardia, with a ventricular rate of 180 beats per minute. Adenosine administration failed to terminate the arrhythmia, and she ultimately underwent electrical cardioversion to restore normal sinus rhythm. 

Her echocardiogram was unremarkable, with normal chamber sizes and normal left ventricular systolic function. The exercise stress echocardiogram demonstrated premature atrial complexes and short bursts of ectopic atrial tachycardia, but otherwise, there was no evidence of ischemia. She underwent an initial electrophysiology study. Atrial tachycardia (tachycardia cycle length 380 ms) was induced with delivery of an extrastimulus pacing at the proximal coronary sinus. The arrhythmia did not sustain long enough for mapping despite isoproterenol infusion. Antiarrhythmic therapy with dofetilide was initiated.

Despite dofetilide, she continued to have palpitations. Her electrocardiogram showed sinus rhythm with frequent premature atrial complexes (Figure 1). P wave morphology was used to localize the origin of the focal atrial tachycardia as follows. The P wave in lead V1 was positive, which means that the activation front travels toward this lead. Since V1 is located anterior and to the right of the atria, this suggests that the arrhythmia originated from a left atrial focus. Since the P wave was narrow, a more septal origin was expected.

The patient was brought back to the electrophysiology lab with a planned transseptal approach and mapping of the premature atrial complexes and ectopic atrial tachycardia. The Advisor HD Grid Mapping Catheter, Sensor Enabled^™ (Abbott) was used for high-density mapping. With two “breakout” sites on the septum and demonstration of an “R” wave on the unipolar electrogram, mapping in the right atrium confirmed that the origin was from the left atrium.

Using the Advisor HD Grid, the left atrial geometry and electroanatomical 3D mapping were collected (Figure 2). The earliest activation was located at the anteroseptal wall of the left atrium, near the mitral annulus (Figure 3). The activation was -17 ms ahead of the P wave. The unipolar electrogram demonstrated a QS morphology. Ablation at this site using the saline-irrigated FlexAbility^™ Ablation Catheter, Sensor Enabled^™ (Abbott) successfully eliminated the left atrial premature atrial complex/focal atrial tachycardia (Figure 4). The patient was taken off of dofetilide, with no further recurrence of atrial arrhythmias.

Discussion

Arkansas Heart Hospital was the first center in the state to use the Advisor HD Grid, a high-density mapping catheter with 16 electrodes on a paddle-shaped catheter (Figure 5). In addition to fast data collection (>8000 points in the case detailed above), the catheter allows for bipole recording both along and across the splines to account for directionality and prevent “bipolar blindness”. Typically, a signal is only visualized when the activation wavefront is propagating parallel to a catheter. The Advisor HD Grid design allows for the visualization of wavefronts approaching perpendicularly. The system analyzes both wavefronts and records the best signal of the two. The pliability of the catheter also reduces arrhythmogenicity and allows for more accurate mapping and less incidence of catheter-induced premature atrial or ventricular complexes. The catheter is flexible and bends when it makes contact against a structure. This allows mapping of all cardiac chambers accurately and atraumatically with a high degree of confidence.

High-density mapping has been described most commonly for scar-related ventricular tachycardia (VT) in the setting of ischemic cardiomyopathy. Via high-density mapping, the abnormal electrograms and channels that are responsible for induction and maintenance of VT are identified and localized. These important channels are often located in a dense scar and exhibit slower conduction velocities and longer conduction times. A substrate modification approach is then used to ablate in the location of these channels, thus eliminating the VT. 

The Advisor HD Grid eliminates “bipolar blindness” by visualizing wavefronts approaching the catheter from different directions, as detailed above. This heightens visualization of scar-related channels and improves accuracy of substrate mapping. Figure 6 delineates an ischemic VT ablation performed at Arkansas Heart Hospital, demonstrating analysis down the splines and capturing only wavefronts propagating parallel to the catheter. This contrasts with Figure 7, where the signals were analyzed both down and across the splines.

This case report demonstrates that the Advisor HD Grid catheter is helpful in both atrial and ventricular arrhythmias. Focal atrial tachycardia is characterized by atrial activation originating from a small focus and spreading out centrifugally. Focal atrial tachycardia can be caused by automaticity, triggered activity, or microreentry. Sometimes it is difficult to clinically describe the exact mechanism between triggered activity and microreentry. Most focal atrial tachycardias arise from the right atrium, and are usually distributed along the crista terminalis related to the anisotropy in the region. Most LA tachycardias are iatrogenic, and happen after left atrial surgery or ablation.

Although this patient did not have structural heart disease and had not undergone a prior left atrial procedure, her atrial tachycardia originated from the left atrium. The fractionated electrograms seen at the successful ablation site marked the anisotropic substrate. The Advisor HD Grid catheter is helpful in identifying areas of interest by establishing good contact to the tissue and by not missing important electrograms.

Disclosure: Dr. Lo has no conflicts of interest to report regarding the content herein. Outside the submitted work, she reports training honorarium from Abbott.

References

1. Kistler PM, Roberts-Thomson KC, Haqqani HM, et al. P-wave morphology in focal atrial tachycardia: development of an algorithm to predict the anatomic site of origin. J Am Coll Cardiol. 2006;48:1010-1017.
2. Nayyar SN, Wilson L, Ganesan AN, et al. High-density mapping of ventricular scar: a comparison of ventricular tachycardia (VT) supporting channels with channels that do not support VT. Circ Arrhythm Electrophysiol. 2014;7:90-98.