Identify the views, anatomy, displayed catheter, type of map, and interpretation of the following 3D image.
Answer
Both images display the right and left atrium acquired by the Rhythmia mapping system by Boston Scientific. The first image is in the LAO view, notice that you are visualizing through the AV valves and the shadow of the CS catheter is displayed traveling on the posterior aspect of the LA. The second image is a modified PA view displaying the posterior wall of the LA, a portion of the posterior RA is also observed.
This is an LAT, or local activation time, map. The color scale on the top indicates the timing of activation compared to a reference point on the proximal CS. The earliest activation site is colored red and the latest purple, with the rest of the colors representing the time in-between. The gray on the map represents low voltage tissue.
Notice on the right atrial map that there is no red or early activation. The posterior RA displays a little orange and yellow (where it is nearest to the LA), but nothing early. The rest of the RA is all late activation. The RA displays activation from the posteroseptal aspect traveling to the right side of the heart and depolarizing the inferior aspect near the cavotricuspid isthmus last. This shows that the RA is passively being activated and the tachycardia is originating in the LA.
The earliest activation (compared to the reference) is seen on the posterior wall of the left atrium. Here, the entire circuit is seen on the posterior wall from red to orange, yellow, green, teal, blue, and lastly purple. The circuit then repeats. This is a left atrial flutter circling around an area of scar on the posterior wall, the rest of the LA and RA are passively activated.
Where would you suggest the physician to ablate?
To terminate an atrial flutter, whether typical or atypical, a complete line of block must be created from a non-conductive area to another non-conductive area. Here, the physician performed an RF ablation from the LIPV to the RIPV. The area of termination was marked with a blue lesion.
Are we done? What is the next step?
After a line of block is created, it should be tested for completeness. If there is a gap in the line, then the tachycardia may continue. The line was tested for block by pacing the heart below the ablation line. Here, this was performed by pacing the coronary sinus. The impulse traveled from the coronary sinus up both the posterior and anterior wall. When it traveled up to the posterior wall it reached the line of block created by RF ablation and was unable to continue. Notice the red near the ablation site followed by orange, and then the impulse could not continue.
The activation can not travel from orange to purple (seen on the opposite side of the line) therefore block is observed. The wave of depolarization traveled up the anterior wall, over the roof, and down the posterior wall until it reached the line of block created.
This ablation line was successful in treating the patient’s atypical atrial flutter. There is still activation and voltage in the pulmonary veins. If the patient has a history of or at risk for atrial fibrillation, a PVI (pulmonary vein isolation) ablation may be performed next.
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For more information: EP Essentials – Understanding EP: A Comprehensive Approach
