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.”