VISUALIZING THE FAT STRIPE
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This illustrates the typical annular fat stripe in a 45 year-old female about to undergo an EP study for PSVT. The projection is 45o RAO. The fat stripe is the slightly fuzzy whitish, linear density roughly in the center of the fluoroscopic image. You can appreciate that it is more vertically oriented with its superior end slanted anteriorly (toward the right of the screen). It can also be appreciated that it is slightly crescent shaped with the concave side to the right. The fat stripe oscillates back and forth during the cardiac cycle, moving rightward on the screen during ventricular systole and back to the left during diastole. Arrows delineate the inferior and superior ends of the fat stripe.
VISUALIZING THE FAT STRIPE
This is another example of the fat stripe, this time in a 60 year-old male using the 40o RAO projection and without the arrows. Important anatomic correlates include the CS os, region of the compact AV node and the region corresponding to the triangle of Koch -whose contents include the slow AV nodal pathway.
The bottom end (inferior aspect) is where you will usually find the CS os. The middle third corresponds to the region of the compact AV node (see AV JUNCTIONAL ABLATION movie). The area of stripe between the middle third and the bottom end corresponds to Koch’s triangle and the area that can be used to target the slow AV nodal pathway.
CORONARY ANGIOGRAM SHOWING ARTERIAL AND VENOUS PHASES
This movie shows a left coronary angiogram in the 40o RAO projection so you can appreciate the appearance of the left circumflex artery, the coronary sinus and their relations to the fat stripe. Notice that, in this example, the fat stripe appears sandwiched between the artery and the vein; i.e. the coronary sinus runs parallel to but slightly on the atrial side of the fat stripe. The coronary sinus is usually found within or bordering the atrial side of the fat stripe as this example illustrates.
Also notice the slightly posterior angulation of the proximal coronary sinus as you move from the os to the proximal 2-3 cm of the coronary sinus. Watch the movie several times and note where the os is located with respect to the fat stripe.
THE FAT STRIPE WITH A FULL COMPLEMENT OF EP CATHETERS
This movie shows the relationship of the five primary catheters to the fat stripe. Note the following:
1. RA appendage catheter tip points to the upper end of the stripe
2. RA catheter, His catheter and mapping catheter situated just outside os all roughly line up on the stripe
3. Compact node roughly identified where His or RV catheter cross the stripe
4. CS catheter lying within the stripe. And you can appreciate that there is a slight angulation of the tip of the CS catheter toward the ventricular side of the CS -just what it takes to get hung up in a vein branch. Counterclockwise rotation would be advised to assure the CS catheter would continue to track the main body of the CS if you were trying to advance it out further.
GETTING THE CS CATHETER TIP INTO THE OS
In this movie, we’re trying to illustrate the technique of locating the CS os and getting the coronary sinus catheter tip to go there. The problem with the LAO view is that you never know whether the tip is advancing anterior to (going into the RV) or posterior to (going into the fossa ovale) the os. It ends up being a matter of luck when you see it dive into the CS. However, by watching in the RAO view and targeting the base of the fat stripe, you will always maximize the chance of getting the tip in the os since you can see where you are going. It is important to remember that your catheter tip must be oriented septally (not laterally) and you may need to glance at LAO to verify this. Another way to know is that counterclockwise torque on the catheter will bring the CS tip from the anterior to the posterior direction if the catheter is oriented septally (if it were inadvertently laterally oriented, counterclockwise torque would move the tip from the posterior to the anterior direction). The idea is to provide the right amount of torque (along with very slight in and out movement) to get the tip to come to rest at the base of the fat stripe.
In this movie, it only takes three such “passes” to get the tip to go into the os. You’re seeing real time without any gaps. The catheter is advanced down toward the RV, counterclockwise is applied and, as the catheter tip is drawn across the septum, it bounces too far posteriorly; second attempt: ditto; third attempt: the tip is drawn back anteriorly by clockwise rotation and lands in the os.
In other words, one attempts a “back and forth” movement of the CS catheter tip through counterclockwise and clockwise torque -along with slight “in and out” movement (no more than 1-2 cm) to transmit the torque to the tip. The base of the fat stripe is being targeted. Once in the os, the catheter will begin to “bounce with the annulus”. You now have the opportunity to advance the catheter to the more distal CS. But, as the next movie will show, the fat stripe will help you avoid the hang-ups of the atrial and ventricular side branches during subsequent CS catheter advancement.
GETTING THE CS CATHETER OUT TO THE DISTAL CORONARY SINUS
This movie shows how you can take advantage of the fat stripe to guide the advancing catheter to the more distal portions of the CS. The principle is to keep the CS catheter tip oriented parallel to the fat stripe. If the catheter tip is allowed to deviate too posteriorly (as it wants to do in nearly every case), it will have a tendency to hang up on atrial branches. If it is allowed to deviate too anteriorly, the tip will have a tendency to hang up on a ventricular branch. Getting stuck in side branches is more likely on the ventricular side simply because of their larger size.
In this example, the CS catheter tip starting position is slightly above and anterior to the level of the os (base of fat stripe). The catheter tip is oriented anteriorly (tip is pointing toward the RV). Counterclockwise torque is applied and the tip begins to be drawn across the septum with the plan to stop it at the base of the fat stripe. Instead, it jumps too posteriorly. The second pass is gentler and engages the os. Now we’re in and ready to advance distally.
Using the orientation of the fat stripe to guide the tip as parallel to the stripe as possible, you begin to advance the catheter. However, it becomes evident that the stripe is tilted anteriorly. In order for the catheter to remain parallel to the stripe, clockwise rotation now needs to be applied to the catheter so it remains within the body of the CS and avoids atrial side branches. This is the action being applied to the catheter after engaging the os to get it to advance distally. Thus, during catheter advancement to the more distal segments of the CS, clockwise torque will direct the tip more anteriorly toward the ventricular side of the annulus, while counterclockwise torque will direct the tip more posteriorly toward the atrial side. Go the direction the fat stripe tells you to.
GUIDING CATHETERS FOR BiV PACING AND THE FAT STRIPE
This is a patient undergoing an upgrade from a dual chamber ICD to a BiV dual ICD. As the movie begins, the guiding catheter tip has just been brought from a more anterior orientation toward the os by applying counterclockwise torque. As the tip is brought closer to the os, the amount of torque is lessened and the guiding catheter is advanced with the intention of aiming for the base of the fat stripe. Os engagement occurs followed by the application of clockwise torque to redirect the tip from a posterior orientation to one that more parallels the stripe. As this is being done, the guide is advanced and nicely moves distally. Two additional movies are provided. The second shows the contrast injection in the RAO view and the third shows the LAO view of the guiding catheter.
POSITIONING THE ABLATION CATHETER FOR AN AV JUNCTIONAL ABLATION
This is a patient undergoing AV junctional ablation and is at the moment complete AV block takes place. She has a dual chamber pacemaker in place (implanted about 15 minutes earlier). Note the position of the ablation catheter tip: roughly in the middle third of the fat stripe. The ablation is started just on the ventricular side of the fat stripe and the catheter is slowly withdrawn to the atrial side. Block is usually evident when the tip is still “inside the stripe”. If the position shown fails, I usually move down the stripe by a few millimeters.
USING THE FAT STRIPE AS A GUIDE TO THE ANNULUS DURING RIGHT FREEWALL AP ABLATION
This patient is undergoing ablation of a right freewall accessory pathway. The first movie shows intracardiac catheters (RA, His, CS, RV and TA mapping) in the RAO view. Notice the mapping catheter (2-5-2 with 5 mm tip) tip is riding on the annulus. From this view, you don’t know where on the tricuspid annulus but it would be either the 9 o’clock or 3 o’clock position. The important thing is that the fat stripe is your marker for the annular location. The catheter tip movement “bouncing with the annulus” further confirms reasonable contact (although in this particular example there may be a little bit of tip vibration suggesting less than perfect contact). You have to go to the LAO view to verify whether the annular position described above is septal or lateral. It confirms a lateral position. Now, it’s up to your accessory pathway potential electrogram recorded on the distal electrode pair of the ablation catheter to tell you to step on the throttle.
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