AF Symposium 2015
Critical Analysis of the FIRM Mapping System
By Steve s. Ryan, PhD
There was probably no more heated discussion at the 2015 AF Symposium than about the FIRM mapping system.
Dr. Ravi Mandapati of Loma Linda University in Loma Linda, CA, gave a presentation entitled “Lack of Evidence of Stable Rotors with Multipolar Mapping of Persistent AF.”
In his presentation Dr. Mandapati compared data from his study of FIRM ablations performed at UCLA Medical Center to the CONFIRM clinical trial data published by Dr. Sanjiv Narayan, one of the inventors of the FIRM mapping system.
Background: The FIRM mapping system uses a multipolar basket catheter (FIRMap™), a novel panoramic contact-mapping tool by Topera. FIRM stands for Focal Impulse and Rotor Modulation.
Dr. Mandapati echoed other 2015 AF Symposium speakers in stating that “the (FIRM) multipolar basket catheter provides inadequate coverage of the left atrium with half the surface area unsampled.” He showed slides where only 54% of the left atrium surface area was mapped by the FIRM system.
“The (FIRM) multipolar basket catheter provides inadequate coverage of the left atrium, with half the surface area unsampled.”
In an editorial in the Journal of Innovations in Cardiac Rhythm Management, Dr. John Day (Intermountain Health, Utah), echoed Dr. Mandapati’s concerns about the mapping basket catheter. The greatest limitation of rotor mapping is from the archaic Constellation basket mapping catheter developed nearly 20 years ago with few changes over the years.
Dr. Day wrote, “This contact mapping basket often does not fit the very enlarged left atria we typically see with ablation of the more persistent forms of atrial fibrillation.” Also, the base of the basket catheter doesn’t have any electrodes. Dr. Day added, “Thus, the left atrial septum is a blind spot with this catheter.”
[But Topera is working on developing its own line of mapping basket catheters to address these shortcomings.]
Sustained Rotors Not Found by Other Research
Dr. Mandapati discussed one of the early articles about CONFIRM trial results by FIRM inventor, Dr. Sanjiv Narayan, who observed “sustained sources in 47/49 patients, in the form of electrical rotors (N=57) and focal beats (N=11).”
Dr. Mandapati then described his own research. He and his colleagues looked at FIRM-guided ablation procedures performed at the UCLA Medical Center (n=24). (Dr. Narayan actually performed 11 of those cases while he was at UCLA and assisted in others.) A quantitative analysis was performed of EGMs (electrocardiograms) of FIRM rotors and non-rotor sites.
Dr. Mandapati’s own research looked at FIRM-guided ablation procedures performed at the UCLA Medical Center.
In contrast to the CONFIRM trial results, Dr. Mandapati’s analysis of UCLA FIRM results failed to demonstrate similar stable reentrant rotors.
Rotor Sites Don’t Show Distinct Electrophysiological Characteristics
Dr. Mandapati’s UCLA study showed that FIRM-identified rotor sites didn’t exhibit features distinguishing them from other atrial sites. He showed slides of disorganized activation patterns at rotor sites.
He used Frequency Domain and Shannon Entropy Analysis to show how rotors don’t appear where one would expect them to be found.
[Shannon Entropy is one of the most important metrics in information theory. It measures the uncertainty associated with a random variable, i.e. the expected value of the information in the message (in classical informatics it is measured in bits). The “entropy” of the message is its amount of uncertainty; it increases when the message is closer to random, and decreases when it is less than random.]
Quantitative Analysis of FIRM Rotor Sites and Ablation Results
Dr. Mandapati and his colleagues did a quantitative analysis of FIRM rotor sites and ablation results. They found a success rate of 50% (12/24) and the following:
― AF termination: 1/24 [how many patients were returned to sinus rhythm without resorting to shocks or drugs]
― AF organization: 3/24 [how many converted to an organized arrhythmia such as Flutter as compared to a more disorganized arrhythmia such as A-Fib.]
― AFCL (A-Fib cycle length) slowing of at least 10%: 8/24 [how many patients’ A-Fib frequency was slowed; a step in returning a patient to sinus rhythm.]
In addition, after approximately 500 days of follow-up, they found the following intermediate outcomes:
• Survival free from AF: 46%
• Survival free from Atrial Tachycardia (ATA): 38%
• Survival free from ATA and off Antiarrhythmic Drugs (AAD): 29%
In contrast, Dr. Sanjiv Narayan’s CONFIRM studies found:
• Survival free from AF: 82%
• Survival free from ATA: 71%
• Survival free from ATA and off AAD: 79%
Researchers found the following FIRM long-term clinical outcomes:
• Long term follow up results (from two centers):
– Single procedure freedom from AF: 37%
– Single procedure freedom from ATA: 30%
– Single procedure freedom from ATA off ADD: 21%
• No patient who underwent FIRM-guided ablation alone (n=5) was free from ATA off AADs.
Dr. Mandapati’s Conclusions:
1. The FIRM multipolar basket catheter provides inadequate coverage of the left atrium, with half the surface area unsampled, and decipherable atrial electrograms from only 48% of electrodes
2. FIRM identified rotor sites do not exhibit distinctive electrophysiological characteristics with regard to dominant frequency or Shannon entropy
The FIRM multipolar basket catheter provides inadequate coverage of the left atrium.
3. Rotational activation (>1 rotation) on electroanatomic mapping was not observed at FIRM-identified rotor sites
4. Ablation of rotor sites, even when accompanied by PVI, did not result in AF termination in the majority (20/24, 83%) of patients.
5. Long term follow up results (2 centers) were disappointing. Single procedure freedom from AF, all ATA and all ATA off AAD were 37%, 30% and 21%.
And he stated, “Rotor ablation should be validated scientifically to get a mechanistic understanding and subsequently should be assessed in prospective randomized trials.”
Further Research Questions
Dr. Mandapati raised the following questions that need to be addressed in further research:
1. If a rotor is deemed to be stable (mother rotor), what are the characteristics, the number of rotations, stability, etc.?
2. What percentage of the atrium should be mapped to deem a rotor the driver/mother?
3. Are these rotors functional or structural?
What Patients Need to Know
Up to this point in time, everyone seemed to be jumping on the FIRM/Topera ‘bandwagon’ with very little critical analysis or understanding of how it worked.
We are very indebted to Dr. Mandapati and his colleagues at UCLA Medical Center for what is probably the first in-depth critical analysis of the FIRM mapping system.
Be Skeptical of the FIRM Mapping System
As patients, we should now be skeptical of the FIRM system:
• It doesn’t map nearly ½ of the left atrium
• The FIRM mapping algorithms finds stable rotors that other research finds are not stable, and electrophysical characteristics that other research doesn’t confirm
• Results of ablating FIRM-identified rotor sites are relatively poor. (This is what should most concern us as patients.)
Patients seeking an ablation should be cautious of the FIRM system
Dr. Mandapati’s critical analysis of FIRM is co-authored by several leading Electrophysiologists (EPs) at the UCLA Medical Center (where both Dr. Mandapati and Dr. Narayan worked when this study was done).
The Bottom Line
At this point, as an A-Fib patient, you may ask: “Should I now stay away from doctors or centers using the FIRM system?”
My answer: No. Even though the FIRM-guided ablation system may have problems and inherent limitations, it may still work well for you and be better than regular mapping.
The FIRM-guided ablation procedure has great potential, but currently offers mixed or uneven results. A competing system, ECGI (Non-Invasive Electrocardiographic Imaging), has better clinical trial results but is only available in Europe at this time. (For more on ECGI, see my AF Symposium article, How ECGI [Non-Invasive Electrocardiographic Imaging] Works)
If choosing an ablation using the FIRM mapping system, discuss these limitations with your doctor before your ablation.
[FYI: The FIRM technology by Topera, developed by Dr. Sanjiv Narayan and others, was sold to Abbott Laboratories in December 2014 for $250 million; Dr. Narayan received around $10 million dollars from the sale.]
Additional Research Studies Support Similar Conclusions
Posted January 4, 2016: A recent three-center study (Texas Cardiac Arrhythmia Institute-Austin, TX, Heart Center Bad Neustadt-Germany, Baptist Health, Lexington, KY) using FIRM-guided only ablation in patients with persistent or long term persistent A-Fib also found poor results.
“Targeted ablation of FIRM-identified rotors is not effective in obtaining AF termination, organization or slowing (≥10%) during the procedure.”
Posted January 9, 2016 In a follow-up article by Dr. Gianni and colleagues, rotors-only ablation was performed in 65% of persistent (91%) and long term persistent (9%) patients. In the other 35%, rotors-only ablation was performed after conventional ablation.
The success rates were respectively 25% vs. 53%.
The authors again found that FIRM-guided ablation was not effective in obtaining A-Fib slowing/organization/termination during the procedure, “and in preventing mid-term AT/AF recurrences.”
FIRM (Focal Impulse and Rotor Modulation) for Catheter Ablation of A-Fib by Dr. Narayan of UC San Diego
by Steve S. Ryan, PhD
I have received several emails asking why I don’t write about Dr. Sanjiy M. Narayan’s studies. I must admit to not understanding some aspects of FIRM and was hoping further information would make things clearer.
Ablating focal beats and electrical rotors, or as Dr. Narayan describes them, “localized areas of electrical activity” is nothing new. (See 2011 Boston A-Fib Symposium, Using CFAEs in Ablating Persistent A-Fib, and 2009 Boston A-Fib Symposium, CFAEs vs. Dominant Frequency) Dr. Narayan’s FIRM procedure uses the largest 64-pole standard basket catheter to do the mapping and uses “monophasic action potentials” (MAPs) catheter mapping to physiologically identify the A-Fib generating spots in the heart.
Proprietary, Patented Algorithm
What is new is the proprietary, patented algorithm Dr. Narayan uses to display the optical images and movies of the activation. (A description of the signal processing Dr. Narayan uses is found in the article “Computational Mapping Identifies Localized Mechanisms for Ablation of Atrial Fibrillation.”) Topera Medical, which licensed this algorithmic-based mapping system, calls it RhythmView.
This author doesn’t understand how Dr. Narayan’s proprietary system differs from other non-proprietary systems using basket catheters to map focal beats and rotors, with the possible exception that he uses the largest basket catheter with a wide field of view to be able to map almost an entire atria at one time.
Targets Rotors and Focal Beats Before Any Other Ablation Sites
After ablating rotors and focal sources found by his FIRM mapping system, Dr. Narayan also ablates the pulmonary veins utilizing wide area circumferential ablation—similar to what is currently done in most A-Fib centers.
Dr. Narayan targets ablation at rotors and focal beats before any other ablation sites, including the pulmonary veins. “Ablation at only rotors and focal sources revealed by our mapping approach (without pulmonary vein isolation) terminated AF predominantly to sinus rhythm in seconds to minutes.”
According to Dr. Narayan, “patients undergoing this targeted ablation (FIRM) experienced a superior rate of AF elimination in the long-term compared to patients undergoing traditional ablation procedures focusing on trigger mechanisms near the pulmonary veins.” Yet, after ablating rotors and focal sources found by his FIRM mapping system, Dr. Narayan also ablates the pulmonary veins utilizing wide area circumferential ablation—similar to what is currently done in most A-Fib centers.
Others Start By Ablating the PVI First
Dr. Narayan’s approach differs from standard operating procedure in almost all centers which start with ablating or isolating the pulmonary vein openings first before moving to other areas.
To this author, Dr. Narayan’s approach doesn’t make intuitive sense. If the pulmonary veins are still firing when mapping is done of the rest of the atrium, wouldn’t these PV signals interfere with or confuse the mapping? In most paroxysmal A-Fib patients, isolating the pulmonary veins is often all that’s needed to eliminate A-Fib (these patients often don’t have any other sources of A-Fib signals outside of the pulmonary veins).
Dr. Narayan found that patients with persistent A-Fib had more sources than those with paroxysmal A-Fib, though these sources were few in number—only about 2 for both atria. This is in contrast to previous studies which have found a greater number of A-Fib producing spots, especially in persistent A-Fib patients.
Dr. Narayan found that almost one-quarter of A-Fib sources come from the right atrium.
Contrasts with Established Protocols
For persistent A-Fib patients Dr. Narayan makes a left atrial roof line ablation, and for those with typical atrial flutter he makes a cavotricuspid isthmus ablation. No other ablation is performed even for persistent A-Fib. This contrasts with established protocols for ablating persistent A-Fib. (See 2008 Boston A-Fib Symposium, Stepwise Approaches in Ablating Chronic A-Fib.)
PRECISE-PAF trial results of FIRM ablation for atrial fibrillation without pulmonary vein isolation (PVI). This was a multi-center trial performed at nine centers with 33 patients showed a 67% termination of A-Fib, with another 17% showing a greater than 10% slowing in their A-Fib.
This is a relatively few number of patients.
EDITOR’S COMMENTS: Perhaps the most important innovation of FIRM is the ability to map and ablate rotors and focal beats in “seconds to minutes.”
Right now doctors doing ablations on patients with persistent A-Fib spend a great deal of time and effort tracking down and ablating rotors and focal sources of A-Fib. If Dr. Narayan’s FIRM system makes this part of the ablation procedure easier, faster and more accurate, this would be a major medical breakthrough for A-Fib patients and doctors.
(The author admits to not understanding how the FIRM system works compared to other systems using basket mapping catheters.)
But one can question the validity and accuracy of the FIRM system, since it typically finds only about 2 A-Fib sources in each atria.
It’s hard to compare Dr. Narayan’s results or to say his approach is superior to standard Pulmonary Vein Isolation. Most experienced A-Fib centers achieve around a 67% success rate as Dr. Narayan does. Though Dr. Narayan first ablates rotors and focal sources in the left atrium, he does later ablate the Pulmonary Veins like almost all other centers.
(It probably makes more sense to first ablate the PVs, then use the FIRM system to track down any A-Fib
A second important innovation of Dr. Narayan’s FIRM mapping system is the finding that one-quarter of A-Fib signals come from the right atrium. If future trials confirm this finding, doctors might have to change their ablation procedures and direct more attention to the right atrium.
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Last updated: Wednesday, September 2, 2015