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Discussion

    Open ArchivePublished:February 04, 2018DOI:https://doi.org/10.1016/j.jtcvs.2017.10.156
        Dr T. Reece (Denver, Colo). I would like to thank the AATS for the opportunity to discuss this paper and for the manuscript well in advance. It was very well presented, and the manuscript is very well done. You study a simplified method for evaluating the relative aortic size in patients, particularly without defining the BSA. I have a few questions.
        First of all, how can we use this to utilize an ability to say that patients are not going to need anything in the future? So when we get a 3.5-cm aneurysm in the clinic, can we say there is no risk of this patient moving forward, we don't need to do any follow-up, or do we still need to continue to follow-up these patients?
        Dr Mohammad A. Zafar (New Haven, Conn). Thank you very much for your question, sir. We haven't studied the smallest aneurysm group in great detail, but we don't call back patients for follow-up into clinic unless the aorta is greater than or equal to 3.8 cm. Having said that, we don't usually see patients with such small aortas in the 3.5-cm size range unless something is going on, for example, if they have a family history of dissection, a connective tissue disorder, or symptoms, for that matter.
        Dr Reece. In my clinic, all that has to be said is they have a big aorta on their radiology report and they get to come see me, so that's why that question is there.
        The risk subsets are defined as a percent risk of any of the complications per year, at 4%, 7%, 12%, and 18%. How do you define those set points, and how can we justify either operating or not operating on somebody that has a 7% risk of having a problem per year? And your suggestion on those patients is that we should follow them up “closely.” So what does that mean, “closely,” and why can't we do a low risk hemiarch on those patients if the risk of them having a complication of their aorta is 7%?
        Dr Zafar. Thank you for your question, sir. We wholeheartedly agree with you about the safety of aortic surgery in the present era. In addition to what you have said, alluding to the safety of aortic surgery, there are also several other points that lend credence to a slight “leftward shift” in the criteria for intervention: In a recent study by our institution, we discovered that aortic size increases by approximately 7 mm instantaneously at the time of dissection. Therefore, on an immediate postdissection computed tomography (CT) scan, the size of the aorta may actually be overestimated, and the size at dissection is in fact smaller.
        Another point regarding the leftward shift in the intervention criteria is that our investigations have found that the new centerline CT method used by radiologists to image aortas and report aortic size actually underestimates aortic size by about 5 mm or so. Furthermore, as displayed on the hinge point graph that we showed, we have been able to zero in on the 5–6 cm aortic size range because of the increased patient numbers that we have at our disposal for analysis, and we found that there is an earlier hinge point at a diameter of 5.25 cm, where the risk increases.
        Therefore, we agree that a slight left shift in intervention criteria should be considered.
        Dr Reece. And my last question is that we are using most of the indexing or whatever we are going to call relative sizing of this in the smaller patients. Do you feel like your numbers of patients in these ranges are large enough for us to actually use these criteria for us to intervene on Turner's patients, et cetera, or smaller patients with relatively small aortas?
        Dr Zafar. Based on aortic size and the patient's height, if the patient is in a significantly high-risk category, then we feel that intervention is warranted. However, with respect to the extremes of sizes, height follows a bell-curve distribution, and therefore, at the tail end of the bell curve, there are very few patients. But, yes, if they do fall into high-risk categories, we do recommend surgical intervention.
        Dr Reece. I just worry when we apply the R2 to a whole list of sizes about patients and aortas that we are losing focus on the smaller patients with smaller aortas that we need to intervene upon and how we can validate that.
        Dr Zafar. We agree with this concern.
        Dr M. Borger (Leipzig, Germany). Once you have published your data and corresponding nomograms, there are going to be some people that are going to operate on a 160-cm person with a 4.9-cm aneurysm, and I'm still confused as to why that should be done. We know that the risk of dissection and rupture are directly related to wall tension. According to Laplace's law, wall tension has nothing to do with the size of the container on the outside of the tube that's containing the pressurized fluid. So why does the aorta care how big the body is outside of the aorta?
        Dr Zafar. Thank you very much for your question, sir. In our opinion, a confluence of factors may influence the risk of aortic rupture and dissection. Since aortic size is likely genetically predetermined, and height is also genetically predetermined, a taller individual would most likely have a larger aorta (which would be normal for that patient size) than a shorter individual. Thus, we believe that the risk of rupture and dissection can be effectively predicted based on the patient's height.
        Dr Borger. So you are saying there are other things than wall tension that are determining the risk of rupture or dissection. That is the only logical explanation, right?
        Dr Zafar. Yes, sir. If you are alluding to smaller sized aortas rupturing and dissecting, a large portion of the population has aortas in that smaller size range. So, although dissections are occurring at smaller sizes, the denominator, that is, the patients at risk in that size range, is quite large as well.
        Dr Borger. The aorta size paradox, yes. I am still waiting for a good answer to that question, and if somebody knows the answer to it, please tell me what it is.
        Unidentified Speaker. Does anyone know if aortic wall thickness varies with height?
        Dr Borger. That could certainly be the answer, but nobody has demonstrated it yet.
        Dr C. Miller (Stanford, Calif). Nice presentation. I know you have the blessing of great statistical resources at Yale, but I'm troubled by a linear R2 correlation for goodness of fit comparing your 2 curves; seems overly simplistic. Furthermore, both R2 values were in the noise level, which means the comparison does not convey any meaningful or useful information. Why didn't you do a proper sensitivity analysis with an AUC?
        Dr Zafar. Thank you very much for your question, sir. The statistical analyses were done by a dedicated statistical team; Drs Rizzo and Li are statistical experts and have worked with us on this project from the beginning. Thank you very much for your valuable suggestion; we will certainly take it into account and will include the sensitivity analysis with an AUC in the revised manuscript.