Utilizing High-Density Mapping for Complex Arrhythmias in the EP Lab

In this feature interview, EP Lab Digest speaks with Drs. Sahil Attawala and Ibrahim Hanna about their experience using the Advisor^™ HD Grid Mapping Catheter, Sensor Enabled^™ (Abbott) at Princeton Baptist Medical Center in Birmingham, Alabama.

Can you give us an overview of your EP program?

Hanna: Princeton Baptist Medical Center is a 505-bed community hospital that has been serving the city of Birmingham and surrounding counties for over 95 years. Since the EP program’s inception 15 years ago, we have performed more than 8000 procedures. Three years ago, our program expanded to include two EP labs and two operators. We are currently supported by an anesthesia team, four nurses, and four EP techs. Reflecting the high burden of cardiovascular disease in the southeastern U.S., our case volume has steadily increased from around 600 annual procedures with one operator, to about 1100 procedures for two operators in 2018. I’m beginning to see that our mix of cases has shifted, and the complexity of ablations has escalated. More recently, we have added left atrial appendage occlusion, subcutaneous ICD implantations, and leadless pacing device implantations to our case load.

What has been your experience with high-density activation mapping?

Hanna: When we started in 2006, activation mapping of complex arrhythmias was primarily done using point-by-point movement of an ablation catheter. This was a rather lengthy exercise that was prone to errors, low resolution, and long procedure times. Therefore, early on in our experience, as we were using basket catheters for pulmonary vein mapping during atrial fibrillation (AFib) ablations, we started experimenting with the technology for the creation of high-resolution and high-density maps of difficult atrial flutters. The technology proved to be vastly superior to the conventional approach, and it became quite clear that the electrode resolution was particularly powerful compared to conventional ablation electrode designs. Since then, we’ve completed a large number of procedures using the technology, mostly targeting atypical flutters, atrial tachycardias, and PVCs, and found that the catheter design is primarily useful for the mapping of infrequent PACs and PVCs, as it enhances the ease of bracketing in the arrhythmia’s site of origin. However, we realized the catheter presented challenges of its own — such as limited steerability, resulting electrical noise, and highly complex chambers due to spline bumping. Therefore, we recently introduced the Advisor HD Grid into our lab.

What can you tell us about the role of the Advisor HD Grid for high-density mapping?

Attawala: The Advisor HD Grid is a unique mapping catheter that is designed for high-density mapping. It has a paddle-shaped design with four splines, and 3-mm electrode spacing with four electrodes that are on each spline, for a total of 16 electrodes. The paddle is on an 8 French shaft and built on the FlexAbility platform that provides bidirectional maneuverability. In addition, the four splines are connected, giving the catheter its unique shape, and allowing them to move in unison to map the area of interest. When this electrode arrangement is used along with the EnSite AutoMap Module (Abbott), it becomes a powerful tool to quickly and reliably map any type of arrhythmia. The electrodes on the shaft of the catheter are sensor enabled, having the added benefit of incorporating magnetic data to create a more reliable 3D geometry of the structure or chamber that we’re mapping. When we first started using the Advisor HD Grid about a year ago, my initial impression was that it was only going to be used to treat complex arrhythmias, and in fact, that is how I started using it. However, I realized how versatile it is, and it quickly went from a niche catheter to our workhouse catheter for all mapping. For me, it has replaced circular mapping catheters for all cases and linear mapping catheters for most cases.    

You’ve submitted some images and a video highlighting a variety of challenging cases where the Advisor HD Grid was used. One case is an atypical atrial flutter; can you share more information about this case?

Attawala: We have shared three cases that highlight different capabilities of the Advisor HD Grid, and how we leverage these unique properties. The first is an atypical atrial flutter case that highlights the ability of the Advisor HD Grid to record low-amplitude electrograms in the area of the scar. The patient is an 80-year-old female with persistent AFib that had recurred despite antiarrhythmic therapy, so she was referred for ablation. I initially performed a pulmonary vein isolation, and following this, we induced an atrial flutter with a cycle length of 350 milliseconds. Despite this being her first ablation procedure, we found areas of patchy scar throughout the left atrium (left image in Figure 1). We made an activation map of the atrial flutter using the Advisor HD Grid and AutoMap feature, which allowed us to quickly define the flutter circuit (right image in Figure 1, as well as Video 1). The critical isthmus of the flutter circuit was located along the anterior left atrium on an island of patchy scar. Figure 2 shows the signal at the site of termination with the first ablation lead, and that was applied. The signal on the Advisor HD Grid is much easier to discern, likely due to electrode spacing and the configuration compared to the ablation catheter. I believe that without high-density mapping, the flutter circuit may have been mistaken for a peri-mitral flutter, and based on the confidence that we had in the activation map, this particular case didn’t require any entrainment so as to not disturb the flutter circuit before we started doing the ablation.

What has been your most memorable case using the Advisor HD Grid?

Attawala: We’ve done several epicardial ventricular tachycardia (VT) cases with the Advisor HD Grid, and in fact, one of the first cases that we did with this catheter was an epicardial VT. For these cases in particular, I’ve been very impressed with the unique shape and the electrode configuration of the catheter. When used in the epicardial space, other multielectrode catheters can somewhat bang up against each other during mapping and create electrical noise, and can be difficult to maneuver, especially since some of them do not have a steerable handle. In my opinion, the Advisor HD Grid has been able to overcome this. The second case that we have shared here is a 72-year-old male with a history of non-ischemic cardiomyopathy; he had a secondary prevention ICD implanted, and was referred for VT ablation after he presented with VT storm with multiple ICD shocks despite being on two antiarrhythmic drugs. We initially started the case with the patient under conscious sedation, during which we were able to induce the clinical VT (Figure 4). RV pacing during the VT showed progressive fusion, which confirmed that the arrhythmia mechanism was reentrant and not focal. Also, given that the morphology of the VT, I thought that it was likely of epicardial origin, so epicardial access was obtained up front, and a voltage map with the Advisor HD Grid was created (Figure 3). Unfortunately, under general anesthesia, VT could not be induced again despite multiple attempts, so we employed a substrate modification and exit site pacemapping strategy. The voltage map with the Advisor HD Grid showed that there was no endocardial scar, and that there was dense epicardial scar along the lateral and the anterolateral LV. What was unique for this case was that for pacemapping, we were able to select different pacing configurations using the 16 electrodes of the catheter in different locations to rapidly identify areas of interest for ablation within the scar. With scar homogenization (top right image of Figure 3), the lesion set decided on was selected to avoid the phrenic nerve and a large obtuse marginal artery that was coursing through the scar. The patient has remained arrhythmia-free over the past year since the ablation.

What has been your experience using the Advisor HD Grid for PVC ablation?

Attawala: I think one of the best features of the Advisor HD Grid is that its splines are very pliable, and with appropriate orientation with ICE guidance, it can very nicely conform to the shape of any chamber that is being mapped, whether that is along the posterior wall of the left atrium, the aortic cusp, or the coronary sinus. Where I’ve found it to be very remarkable is during papillary muscle mapping for PVC ablation. It does not create a lot of false geometry, and allows you to create a very reliable three-dimensional model. I’ve also noticed that it reduces catheter-induced ectopy due to its pliable shape. This feature was highlighted nicely during several papillary muscle cases. The case that we shared here is of a 52-year-old male with a PVC-induced cardiomyopathy and a 38% PVC burden from the posteromedial papillary muscle, who had a previously unsuccessful ablation at another facility. With ICE guidance, the Advisor HD Grid was positioned at different areas along the posteromedial papillary muscle, and an activation map was created using the AutoMap settings (Figure 5). We were able to create an excellent 3D map of the papillary muscle using high-density mapping to rapidly identify the earliest activation site near the mid portion of the papillary muscle. Although we did perform a fair bit of ablation to get effective PVC suppression, on follow-up, the patient’s PVC burden is now less than 5% and he has had normalization of his LV function. 

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