2014 Boston AF Symposium
How ECGI (Non-Invasive Electrocardiographic Imaging) Works
Report by Dr. Steve S. Ryan, PhD
Dr. Michel Haissaguerre of the LIRYC Institute in Bordeaux, France gave a presentation entitled “Mechanistic Insights From Noninvasive Mapping of AF—Implications for Catheter Ablation.”
Dr, Haissaguerre began by discussing the concept of voltage vs. noise in reading an ECG. High accuracy can be obtained with a EGM (electrogram signal) of >0.15mV. Body Filtering (ECGI) can miss small local A-Fib signals, but does not affect global patterns.
He found that when mapping Focal A-Fib signals from both inside and outside the heart, they may differ in location by 3.1mm. (This is a relatively small difference and isn’t enough to affect the overall accuracy of the mapping and ablation.)
How ECGI (Body Mapping) Works
He described how the ECGI system works. A patient lies down on his/her back and a technician places a vest-like device with 256 electrodes over his/her chest and stomach. These electrodes combine with rapid CT (Computed Tomography) scans to produce a very detailed 3D color map of the heart. (For a detailed description and discussion of the ECGI system, see 2013 BAFS: Non-Invasive Electrocardiographic Imaging [ECG])
The system automatically detects rotors and foci and computes them into a “Cumulative Map” or movie. These driver regions are ranked, based on statistical prevalence. Dr. Haissaguerre showed slides of these drivers originating from PVs in Paroxysmal A-Fib.
In persistent A-Fib he found multiple interplaying driver regions (median 4, 1 to 7) found in the Left Atrium, PVs and Right Atrium (“driver regions” include both focal sources and rotors). The rotors were temporally and spatially unstable. They were not sustained. Most had 2-3 rotations with a mean of 448ms. They required a statistical analysis of their core trajectory/density. Patients in Persistent Long-Lasting A-Fib for more than six months had the most driver regions and the least success in A-Fib termination after six months.
…ECGI ablation significantly reduced the amount of burns needed to terminate A-Fib.
Compared to the traditional Bordeaux step-wise ablation for persistent A-Fib, ECGI ablation significantly reduced the amount of burns needed to terminate A-Fib.
Dr. Haissaguerre uses a Multielectrode circular catheter not yet approved for use in the US. This catheter can more easily capture and isolate regional targets like rotors that do move a little.
Dr. Haissaguerre’s Conclusions
- Regional clusters of A-Fib drivers can be mapped non-invasively
- ECGI mapping before a procedure identifies critical regions to ablate. This reduces targeted atrial areas and RF delivery. The optimal timing is in the early months of persistent A-Fib.
- There is a need for appropriate ablation tools (such as circular or multielectrode catheters) as rotor targets are not so limited (they tend to move slightly).
Back in 2013 I predicted that “the ECGI system, barring unforeseen circumstances, will rapidly supersede all other mapping systems and will become the standard of care in the treatment of A-Fib patients.”
Not only does the ECGI system produce a complete, precise, 3D, color video of each spot in a patient’s heart producing A-Fib signals, but also an ECGI can be done by a technician before the procedure rather than by a doctor during an ablation. And the ECGI map is a better, more accurate, more complete map than an EP can produce by using a conventional mapping catheter inside the heart.
From a patient’s perspective, ECGI reduces both the time it takes to do an ablation and the number of burns a patient receives.
The only caveat that Dr. Haissaguerre found (which relate to all mapping strategies, not just to ECGI) is that rotors move slightly and are somewhat unstable. A computer has to be used to statistically analyze their core trajectory. But circular catheters can be used to contain and isolate them.
Addendum: April 2015
Jeffrey Patten asked, “I’ve heard that the new mapping and ablation vest system ECGI (CardioInsight), though very detailed with 256 electrodes, doesn’t directly map the septum area. Is that correct?”
It’s correct to say the ECGI does not directly map the septum area. But, that doesn’t mean the septal activity can’t be mapped with the ECGI.
I posed your question to the world-reknown cardiologist, Dr. Pierre Jais of the Bordeaux group. He explained that “the septal activity projects at the anterior and posterior attachments of the septum on both atria.” He added that mapping the septum with the ECGI system “…requires some experience, but is at the end easy.”
So don’t be reluctant to seek out the new mapping and ablation vest system ECGI (by CardioInsight). Just be sure you have a top-notch, experienced operator.
Return to Index of Articles: AF Symposium: Steve’s Summary Reports
Last updated: Wednesday, September 2, 2015