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Now we're gonna talk about, uh,

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scanning protocols in tavr and specifically the role of CT in tavr. Um,

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CT is used for accurate valve sizing and selection,

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and this requires E C g gated CT of the aortic valve and the surrounding

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structures. And then CT is also used for vascular access assessment.

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Um, and this is, uh, obtained through a CT angiogram of the chest, abdomen,

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and pelvis. Um, and from the CT angiogram, uh,

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the radiologist, uh,

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imager is going to help decide on what are the best potential access routes, um,

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the ileal femoral route, which is preferred, uh, subclavian. Um,

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and then if those two are not available, uh,

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other possibilities include transaortic, transapical, uh,

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even carotid or or radial are available.

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So when you're putting together your TAVR protocol, uh,

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what are the components of a TAVR CT exam? Well, there are three. Um,

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the first is a calcium scoring examination.

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So this is a standard non-contrast calcium score. You see the asterisk,

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it's optional. Um, you don't have to do the calcium score. And I'd say, um, for,

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for many years we never obtained the calcium score at my institution,

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but more recently we've begun doing it. Um,

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we'll talk about how that's used in the calcium video. But um, basically, uh,

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the main use for the calcium scoring CT is to decide on these borderline

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patients, um, who may be in the low flow IIC stenosis category.

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And you're not completely sure whether they have severe IIC stenosis or moderate

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AIC stenosis. The calcium can help, uh, point you in one direction or the other.

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Um, the two other components which are absolutely needed are the E C G G cardiac

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imaging and the C T A of the chest ab and pelvis. Um, one note,

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we don't give medications for TAVR CT examinations.

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Unlike our coronary CT exams,

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generally beta blockers and nitroglycerin are contraindicated in patients, uh,

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with severe IIC stenosis. Um, one other note, um,

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that's important to recognize is that, um,

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the key thing that we want to do with the TAVR examination is measure the

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annulus.

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The annulus determines the size of the device that can be placed and the annulus

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actually changes in size during the cardiac cycle. Um,

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and here's a graph from a publication, uh,

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back in 2015 where they went ahead and measured the annulus and many patients

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across the cardiac cycle to try to determine which part of the cardiac cycle was

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the annulus the largest. And it actually turns out around the 20% phase,

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the annulus, uh, is the biggest. We always want to get the biggest annular size,

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um, for our sizing, um,

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because that helps reduce the chance of the device being too small, uh,

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relative to a large annulus. And when that happens,

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you can have the risk of leakage around the device, which we don't want.

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So what is the standard TAVR protocol that we use? Um,

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we use a fair amount of contrast material, 120 ccs of contrast. Um,

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and that's because not for the actual E C G gated cardiac CT portion of the

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exam, looking at the annulus, but rather because of the runoff. Um, and it

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Just makes your timing easier when you're doing, uh, two phases. Um,

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we always use a, a saline flush, um, 40 ccs,

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and we inject at a rapid rate five to seven ccs per second. Um,

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first you're gonna obtain the cardiac ct.

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You can limit your field of view just to cover the heart. Um,

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you do your injection and trigger to the ace and aorta. Uh,

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we generally do an E C G G retrospective acquisition. Um,

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we use dose modulation,

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so we put the full dose window in systole and then reduce the

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m a s, uh, for the remaining part of the cardiac cycle,

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somewhere around 20% of the full dose so that we can get, um, imaging, uh,

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and look at structures, um, but we're not, uh, maximizing the radiation dose.

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Um, and then at the end we're gonna do a full cardiac cycle, uh,

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multi-phase reconstruction at, you know, depending on your own preference,

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you can do five or 10% intervals. Um, and this gives us multiple phases. Uh,

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it turns out sometimes, particularly in these older patients, you may have, um,

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a little respiratory, uh, artifacts, um, or you may have some gating artifacts.

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And having that full cardiac cycle reconstruction helps you choose the best

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phase in case the 20% phase, uh, is limited by artifacts. Um,

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the other thing is having the retrospective acquisition also allows you the

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flexibility to do some E C G editing. Um, if you have some, uh,

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abnormal rhythms or say for instance A P V C, uh, during the acquisition,

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you can often rescue it with E C G editing. What we tend to do is, um,

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immediately, um, following the cardiac ct, um,

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do the c t a chest ab and pelvis.

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So the cardiac CT finishes and then the table moves immediately to the top of

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the chest and then the patient goes right down through for a chest,

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ab and pelvis. If you have a scanner with high pitch,

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then absolutely use that for your C T H chest, ab and pelvis. That helps a lot.

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Um, one note, um, for slower scanners,

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so I'm talking about 64 slice scanners or uh, below, um,

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you may need to split the bolus with two acquisitions. Um, so in that case,

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a lot of times people will do a gated chest at around seven or 80 ccs of

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contrast and then followed by a non gated abdomen pelvis,

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C T a with around 50 ccs of contrast. This is just a,

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a slide showing you the importance of the saline flush. Uh,

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the image on the left does not have a saline flush,

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whereas the image on the right does.

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And the key thing that you see here is this brightness in the right subclavian

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artery in the SS V C.

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This makes it really hard to evaluate the adjacent subclavian arteries.

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So we wanna make sure to have a saline flush to get a good look at those

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vessels. Some other protocol modifications, um,

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that you can consider.

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You can certainly do a low radiation dose protocol and we use the same type of

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injection, but instead of doing a retrospective acquisition,

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now we do a prospective acquisition and we're gonna get to systole again to get

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that maximal annular size that we talked about. Um,

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and then you can get as many multi-phase reconstructions as you like in that

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window. Um, and then no change with the chest ab pelvis ct. Um,

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this may become more important as the patients that

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Are getting the TAVR screening get younger and younger and younger. Um,

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we may wanna, uh, modify, um, you know,

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some of these protocols to minimize radiation dose.

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It's not uncommon to have patients coming for, um,

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TAVR who have atrial fibrillation or other irregular heart rhythms.

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There is a different modification you can make from that. In this case,

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we tend to use a prospective acquisition,

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but instead of making our window to a percentage of the cardiac cycle,

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we make it to a set time interval after the R wave,

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generally 200 500 milliseconds works and then you reconstruct it 50 millisecond

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intervals and look for your best, um, systolic phase, uh,

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with the least artifact. Um, and then no changes in the chest and pelvis, C T A.

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And then finally there is a low contrast dose protocol that we use.

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Um, and this comes up a lot.

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A lot of times patients who are being evaluated for TAVR have a lot of other

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comorbidities including, uh, renal dysfunction. Um,

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so not infrequently we need to give low contrast dose.

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What we do is we use 40 ccs of contrast and then dilu it up to 60 ccs with

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saline and then basically proceed as normal. Um,

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and that tends to give you a diagnostic imaging of the cardiac CT portion of

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the exam.

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You can see here we get really nice imaging in this particular patient with 40

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ccs of contrast. Where you really start to lose quality is in the c t a chest,

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abdomen, pelvis.

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It's often kind of washed out or venous because you just don't have quite enough

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contrast. Um, nonetheless,

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it's usually good enough to route any significant stenosis. Um,

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you may just run into problems using it with your three D software.

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And then finally, just last bit about reconstructions. Um,

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we do three thin slice reconstructions, uh, using an overlap with,

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with all these, um, acquisitions, both the cardiac CT and the, um,

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chest and pelvis, C t A, um,

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our typical 0.75 millimeters by 0.5,

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but certainly you can go a little bit thinner, uh, if you like. Um, and then,

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um, it's important to reconstruct the cardiac phases using a small field of view

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focused on the heart. Um, use a large,

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larger field of view for the chest head and pelvis, c t a. Um, and again,

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like I mentioned before, based on previous research,

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we wanna use the 20% phase for measurements by default, um,

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and only really use the other phases if the uh, 20% is non-diagnostic.

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And I talked about the E C G editing,

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that can be helpful in patients with irregular rhythms.