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Circulation on the Run

Nov 27, 2017

Dr. Carolyn Lam:               Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr. Carolyn Lam, Associate Editor from the National Heart Center and Duke National University of Singapore.

                                                Our journal this week features novel data informing the choice between conscious sedation and general anesthesia for transcatheter aortic valve replacement. A very relevant discussion for those of us who see these patients. Stay tuned, that's coming right up after these summaries.

                                                Subclinical hyperthyroidism is known to be associated with an increased risk of atrial fibrillation, but the association with thyroid function in the normal range or subclinical hypothyroidism is unclear. That is, until today's study, which shows us that variation in thyroid function within the normal range is associated with atrial fibrillation.

                                                First author, Dr. Baumgartner, corresponding author, Dr. Rodondi and colleagues from University of Bern in Switzerland, conducted a systematic review and obtained individual participant data in more than 30,000 participants from 11 prospective cohort studies that measured thyroid function at baseline and assessed incident atrial fibrillation, which occurred in 8.6% of individuals.

                                                They found that in youth thyroid individuals, there was a significant increase in the risk of atrial fibrillation with increasing free T4 levels within the reference range. Risks did not differ significantly by age and sex.

                                                Conversely, there was no association between TSH levels within the reference range, or subclinical hypothyroidism and the risk of atrial fibrillation. Thus, free thyroxin levels might add to further assessment of atrial fibrillation risks. Further studies are needed to investigate whether these findings apply to thyroxine treated patients.

                                                The next study provides insight into how exercise promotes metabolic remodeling in the heart. First author, Dr. Gibb, corresponding author, Dr. Hill and colleagues from University of Louisville, use radiometric, immunologic, metabolomic and biochemical assays to measure changes in myocardial glucose metabolism in mice subjected to acute and chronic treadmill exercise.

                                                They found that in the heart, glucose utilization via glycolysis was reduced during exercise and in the early recovery period after exercise. Low rates of myocardial glycolysis were sufficient to activate gene programs that instigate physiologic cardiac growth. Metabolic inflexibility of the heart, such as occurs in heart failure and diabetes, was sufficient to diminish mitochondrial function.

                                                Phosphofructokinase mediated changes in metabolism appeared to regulate genes involved in processes critical for metabolic remodeling, transcription, cell division, differentiation, cell proliferation and contraction. Thus, this study provides important preclinical evidence, showing how exercise-induced changes in glucose metabolism may promote physiologic cardiac growth.

                                                The next study addresses the question of whether antiarrhythmic drugs are safe and effective when non-shockable rhythms evolved to shockable rhythms during resuscitation for out of hospital cardiac arrests. In this study from first and corresponding author, Dr. Kudenchuk of University of Washington and his colleagues, patients who initially presented with non-shockable out of hospital cardiac arrests were randomized upon subsequently developing shock refractory VF or VT to receive amiodarone, lidocaine or placebo by paramedics.

                                                The primary outcome was survival to hospital discharge, with secondary outcomes, including discharge functional status and adverse drug-related effects. The authors found that outcome from non-shockable turned shockable out of hospital cardiac arrest was poor, but not invariably fatal. Though not statistically significant, point estimates for survival showed a trend to greater survival after amiodarone or lidocaine than placebo without increased risk of adverse effects or disability. Together, these findings may signal a clinical benefit that invites further investigation.

                                                The final study provides experimental data supporting the importance of a novel Cardiokine governing the local environment in infarcted hearts and determining the fate of implanted cells. This novel Cardiokine is C1q/tumor necrosis factor-related protein-9, or CTRP9, which is a novel pro survival Cardiokine that is significantly down regulated after myocardial infarction.

                                                In today's study by co-first authors, Drs. Yan and Guo and co-corresponding authors Drs. Ma and Wang from Thomas Jefferson University in Philadelphia, mice were subjected to myocardial infarction and treated with adipose-derived mesenchymal stem cells, CTRP9 or their combination. The authors found that administration of adipose-derived mesenchymal stem cells alone failed to exert significant cardio protection.

                                                However, administration of these cells in addition to CTRP9 further enhanced the cardioprotective effect of CTRP9, suggesting a synergistic effect. CTRP9 promoted adipose-derived mesenchymal stem cell proliferation, survival, migration and attenuated cardio myocyte cell death by signaling mechanisms that included binding with N-cadherin, activation of ERK, MMP9, and ERK-Nrf2 signaling and upregulation or secretion of antioxidative proteins.

                                                In summary, these results suggest that CTRP9 is a Cardiokine critical in maintaining a healthy microenvironment facilitating stem cell engraftment in infarcted myocardial tissue. Well, that wraps it up for your summaries, now for our feature discussion.

                                                Conscious sedation is very frequently used during transcatheter aortic valve replacement, or TAVR, but with limited evidence as to the safety and efficacy of this practice. Well, that is until this week's journal and this feature paper. We're so lucky to have with us the corresponding author, Dr. Jay Giri from Hospital of University of Pennsylvania, to discuss his novel findings, as well as Dr. Dharam Kumbhani, Associate Editor from UT Southwestern.

                                                Jay, tell us your study findings and how this really helps us to characterize anesthesia choice and clinical outcomes of at least U.S. patients undergoing TAVR.

Dr. Jay Giri :                        We looked at 11,000 patients treated over a 15-month period in 2014 and 2015 with percutaneous transfemoral TAVR. Notably, this was a time period that was identified as the start of the era of conscious sedation for TAVR in the United States.

                                                Also, this five quarter period that we looked at represented a time of relative technological stability where only two valve types, the Sapien XT and original Medtronic CoreValve were being used in America.

                                                Looking at that 15-month period when conscious sedation was first being used in TAVR, we elected to compare those patients to a propensity matched group of patients who underwent TAVR by, what at that time was, the more traditional approach of general anesthesia.

                                                Our primary outcome within hospital mortality, because we had complete followup for this outcome. We also looked at 30-day outcomes for which we had about 90% followup. What we discovered was actually an associated reduction in mortality, an absolute reduction of about 1% in the patients who were treated with conscious sedation.

                                                We also noted that they had modest decreases in the hospital length of stay, as well as significant decreases in the rates of ICU length of stay and the rates of pressor or inotrope use during the procedure. Obviously, the most provocative of the findings was the fact that we seemed to discover, after propensity matching a slight improvement in in-hospital mortality that held true at 30 days, as well.

Dr. Carolyn Lam:               Thank you, Jay. What important findings ... I mean, mainly because, we really didn't have much data, did we? About conscious sedation and TAVR before this. Now, it's observational data, and I suppose the question always becomes what about bias by indication? More well patients get selected for conscious sedation versus general anesthesia, perhaps? Or even the other way around. Could you elaborate a little bit on how you think that may have impacted results and the measures you took to look at that?

Dr. Jay Giri :                        I think it was something that we were highly aware of and I also have to give credit to Dr. Kumbhani and the editorial staff at circulation for pushing us on that issue of selection bias for the two procedures. The obvious concern here, when you saw that there was a potential mortality reduction with conscious sedation patients, was that perhaps the conscious sedation patients actually represented a healthier cohort to start with, or they were perhaps treated at centers that were more highly experienced and by operators that were more highly experienced with TAVR in general.

                                                We tried to account for this in a number of different fashions. The first, as we mentioned, was with an inverse probability treatment weighted analysis that accounted for 51 co-variants that were balanced between the groups. Additionally, we did adjust for site characteristics and utilized a hierarchical method technique to take into account both the experience of sites and operators.

                                                Finally and most importantly, we performed what's called a falsification end point analysis in a postdoc fashion to verify that it looked like other outcomes outside of things, like mortality, length of stay, things we would expect to be influenced by sedation type, ended up being equal between the two groups. Falsification end point analysis represents, essentially, a negative control. You're supposed to theorize for potential outcomes that you would think would not be influenced by your intervention. In this case, those outcomes we theorized were vascular complications, major bleeding and pacemaker implantation, which we theorized would not be influenced by sedation type. In fact, we discovered that those outcomes were similar after adjustment, even though they had some differences before adjustment.

Dr. Dharam Kumbhani:  Jay, I want to congratulate you and your team on this paper. You guys really picked a very important topic to look at and then you jump ... as you outlined, you jumped through a lot of statistical hoops and try to really provide evidence for a field in which a randomized controlled trial is probably going to be just logistically probably hard to conduct, just given the sample size requirements, which also you've provided in your discussion.

                                                I think all the metrics that you looked at as far as utilization of therapies and length of stay, things like that, I think many people believe that and you were the first one to systematically evaluate and show that.

                                                As you alluded to, I think that mortality, and Carolyn mentioned that, as well. I think the mortality findings are very interesting. Again, it's always hard when you have observational data to really put a lot of stock into that and you guys, as you outline, looked at so many different ways of doing that.

                                                Again, I guess, observational data are always inherently going to have that limitation, no matter what statistical rigor we put them through. They were definitely very thought-provoking and, as you outlined, it's definitely come at the right time as the field is exploding and more and more centers are getting facile at it.

                                                The other thing that you mentioned, but which I want to make sure that people fully understand is that you also provided a very elegant analysis looking at site volumes, because traditionally the sites that are doing conscious sedation have done a number of TAVR's before and there is a very clear cumulative volume outcomes association, for TAVR.

                                                By accounting for the totality of experience, so you adjusted for the cumulative volume that sites have been doing this, so these are not just the high volume, high throughput centers, which have a lot of experience doing 150, 200 TAVR's a year, that thereby have really good outcomes by virtue of being expert, both as operators and as sites, but rather potentially something that is related to conscious sedation aspect itself. You guys really stepped up and provided a very elegant analysis to try to dissociate the two issues here.

Dr. Carolyn Lam:               Dharam, and you just provided a very elegant explanation of the thought processes that were going on with our editors about this paper. I join you in congratulating Jay. Just a question. This is the best available evidence now, what are we going to do about it? I mean, Dharam, you're an inventionist, what now?

Dr. Dharam Kumbhani:  The issues were not so much related to efficacy, initially. The initial concerns were related to safety, and Jay's paper clearly addresses that. Then, in addition to that, it says, "Well, it's not just that it's a safe procedure, but it's also effective with potential patient level and hospital level benefits from having a robust conscious sedation program."

                                                I guess the one question that I have about conscious sedation and, Jay, I would love to hear your thoughts on this, as well, is it is possible but it is usually not done, TEE's or transesophageal echos are typically not done when you're doing conscious sedation. It is possible, as I said. As you move towards lower risk patients, on the one hand, these would be ideal patients for conscious sedation because then it's almost like a day procedure, in some ways for them.

                                                But on the other hand, the fidelity of being able to look for even small paravalvular leaks, things like that, may be harder with a transthoracic echo. I don't know, as we expand towards the oldest populations, whether we'll see a greater adoption of conscious sedation, or whether there'll be some scaling back.

Dr. Jay Giri :                        Two points on that. The first is, I totally agree that it's relatively unusual for a transesophageal echo to be performed in the setting of conscious sedation. There's no question, secondly that transesophageal echo allows for the most rigorous evaluation of paravalvular leaks.

                                                It is striking, though, that the rates of paravalvular leaks, due to technological improvements to the valves, are significantly improving. Even since the time of our study two years ago, a new generation of valves is consistently coming out with leak rates in pretty well-conducted analyses that are in the low, single digit percentages for moderate leak or more.

                                                Part of I think the move towards conscious sedation, even initially and especially as we go forward, is predicated on the fact of continuing technological improvements that essentially almost solve the leak problem.

                                                I think it's true that there's always going to be a very small minority of patients that are stuck with concerns about paravalvular leak at the end of their TAVR procedure. For those who have moderate or greater leak, I think that the threshold for escalating care, even to intubation and TEE to evaluate that leak, I think should be relatively low in a lower risk population.

                                                However, I think the point that you bring up about the potential harm of trace or trivial leaks, or mild leaks, which may not be perfectly interpreted with transthoracic echo and aortograms and [inaudible 00:16:41] assessments at the time of the valve placement. It's something we're going to have to keep a close eye on.

                                                From a practical standpoint, I believe this train has left the station. Totally unscientific, but around the time they released the paper online. I just shot out a poll on Twitter and got about a couple of hundred responses from folks, what they're doing now.

                                                Now, Twitter certainly, probably doesn't represent the average transcatheter valve operator in the world, but I was surprised to see that over 70% of the respondents favored a conscious sedation approach at this point in time, which obviously is much higher than what we saw in our paper from two years ago.

Dr. Carolyn Lam:               Well, audience, I'm sure you enjoyed that. Thank you for joining us today. Don't forget to tune in again next week.