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Circulation on the Run

Dec 30, 2019

Dr Greg Hundley: Well listeners, this is Dr Greg Hundley from the VCU Pauley Heart Center in Richmond this week, who is sadly missing his dear friend, Dr Carolyn Lam, who is away for just a week or two. I hope you've experienced a wonderful holiday season and are able to embrace the new year with joy and hope.

In our feature article this week, Dr Marcelo Di Carli and colleagues are going to discuss the role of coronary microvascular dysfunction assessed with cardiac stress during PET, as well as left ventricular remodeling assessed with echocardiography and how both of those relate to clinical outcomes in patients with chronic kidney impairment. But first, let's have a coffee and chat about other articles in this issue.

We have four original manuscripts, two or more clinical papers, and two from the world of basic science. So let's go to the clinical papers first. And the first emanates from our own associate editor, Dr Sana Al-Khatib from Duke University. Her paper comes from the ARISTOTLE trial, a randomized study of 18,201 participants that compared apixaban with warfarin in patients with atrial fibrillation at increased risk of stroke. And so this sub study included 17,423 patients in ARISTOTLE without severe renal or liver disease. And the authors evaluated the risk of bleeding and major cardiovascular outcomes in patients with atrial fibrillation taking either NSAIDs with therapixaban or warfarin. The authors found that those with NSAID use at baseline, so before starting into the study or incident NSAID use, that is they began an NSAID after initiating this study were more likely, both groups were more likely to have a history of bleeding, nearly a quarter of the patients to a fifth of the patients versus only 15% that had never used NSAIDs either before or after entering the study.

In addition, the safety and efficacy of apixaban versus warfarin appeared not to significantly be altered by NSAID use. That is whether you were taking apixaban or whether you're taking warfarin, the impact of NSAID use was not different between either of those anticoagulants.

The second original clinical article comes from Dr Audrey Blewer, also from Duke University, and evaluates the variation in bystander cardiopulmonary resuscitation delivery and subsequent survival from out of hospital cardiac arrest based on neighborhood level ethnic characteristics.

As background for this research, bystander cardiopulmonary resuscitation delivery and survival from out of hospital cardiac arrest varies at the neighborhood level, was generally lower survival seen in neighborhoods predominantly with individuals from black race. Despite Hispanics being the fastest growing minority population in the United States, few studies have assessed whether the proportion of Hispanics in a neighborhood is also associated with delivery of bystander CPR or subsequent survival for an out of hospital cardiac arrest. Accordingly, the authors in this study assessed whether bystander CPR rates and survival buried by neighborhood level ethnicity. And they hypothesized that neighborhoods with a higher proportion of Hispanics would have lower bystander CPR rates and overall lower survival.

This study was a retrospective cohort and use data from the Resuscitations Outcome Consortium, or ROC Epistry across the United States. So in this study, the authors identified 18,900 cardiac arrests. And they excluded pediatric arrests, EMS witnessed arrests, or arrest occurring in a healthcare or an institutional facility. And they found overall that bystander CPR was administered in 37% of these out-of-hospital arrests. Among neighborhoods with less than 25% Hispanic residents, bystander CPR was administered in 39% of the events, while it was administered in only 27% of the events in those neighborhoods with greater than 75% Hispanic residents. Also, lower rates of survival occurred in neighborhoods with greater than 75% Hispanic residents. And so the authors conclude that these findings suggest there's an important need to understand the underlying disparities in CPR delivery and an unmet CPR training need among Hispanic communities.

Well now let's shift to our two original articles that come from the world of basic science. And the first is from Dr Ying Shen from Baylor College of Medicine and reports on the critical role of cytosolic DNA and its sensing adapters sting in aortic degeneration, dissection and rupture. So as some background for this study, recent evidence has indicated that cytosolic DNA and abnormal activation of the cytosolic DNA sensing it after sting, a stimulator of interferon genes, plays a critical role in vascular inflammation and destruction. And so in this paper, the authors examine the involvement of this mechanism in aortic degeneration and sporadic aortic aneurysm and dissections. Just like with our other basic science papers, the authors perform both studies in a small animal model, mice, and also in human subjects. So what did they find?

The authors found that in human sporadic aortic dissection tissues, they observe the presence of cytosolic DNA in smooth muscle cells and macrophages. And they had significant activation of this sting pathway. In a mouse model, sting deficient mice showed significant reduction in challenged induced aortic enlargement, dissection and rupture in both the thoracic and abdominal aortic regions. Additional single cell transcriptome analyses were performed and provided some mechanistic understanding for the author's findings.

So in summary, for this very interesting paper from the world of basic science, the author's findings indicate that the presence of cytosolic DNA and subsequent activation of cytosolic DNA sensing it after, or sting signaling, is a key mechanism in aortic degeneration. And therefore future studies, perhaps targeting sting, may be performed to see if they could prevent sporadic aortic aneurysm dissection development.

The second basic original article in this issue is entitled In Vivo CRISPR CAS9-mediated gene editing and how that ameliorates atherosclerosis in familial hypercholesterolemia. It comes to us from Dr Bin Zhou from the Chinese Academy of Sciences.

So as background for this study, mutations in the low-density lipoprotein receptor are one of the main causes of familial hypercholesterolemia. The clustered regularly interspace short palindromic repeats of CRISPR and caspase-9 system is an effective tool for gene editing to correct gene mutations and thus ameliorate the disease.

So these authors tested whether in vivo sematic cell gene editing through the CRISPR CAS based nine system delivered by adeno associated virus could treat familial hypercholesterolemia caused by the LDLr mutant in a mouse model. Well, the authors ... As Carolyn would ask, so what did they find, Greg? Well, the authors observed some really exciting results. They found that the LDLr mutation was corrected in a subset of hepatocytes after the CRISPR CAS based nine treatment with LDLr protein expression partially restored. Compared with control animals, the CRISPR CAS based nine targeted SGRNA group had significant reductions in total cholesterol, total triglyceride, and LDL cholesterol in the serum while the aorta had smaller atherosclerotic plaques and a lower degree of macrophage infiltration. So this study really implicates perhaps not only a mechanism of disease, but a potential treatment. But with the relatively small numbers in this study, more research is needed to confirm and substantiate the findings from this group.

So great original articles in this issue. What else is in the issue? And let's move to those. We have a global rounds feature. Remember, global rounds are investigating how cardiovascular disease is assessed and managed in countries from all over the world. Well, in this global rounds feature Professor Ali Oto from Memorial and Cairo Hospital provides a quick reference to the control and management of cardiovascular disease in Turkey. And the next article, an on my mind piece, Dr Milton Packer explorers whether the conditions of atrial fibrillation and heart failure with preserved ejection fraction are two separate diseases that occur frequently together in patients or alternatively, whether these two adverse clinical syndromes may be parallel manifestations of the same underlying myocardial disease with atrial fibrillation affecting the left atrium and heart failure preserved ejection fraction afflicting the left ventricle.

In our what's in the mailbag series, Professor Nicholas Mills from the University of Edinburgh shares in a research letter the relationship between exercise intensity and duration on cardiac troponin release in 10 physically active healthy volunteers averaging 34 years in age. A great read for our readership that is actively exercising. And it looks like in this letter, intensity of exercise matters when evaluating post-exercise serum troponin values. I really encourage everyone to take a look at that letter.

And then finally, there's a letter to the editors from Dr Abdallah Fayssoil from the Raymond Poincare Hospital in Garches, France regarding a prior publication related to nutrition and functional tricuspid regurgitation.

Well, listeners, that sums up our summary. And I hope you had a great coffee or if you're running on your treadmill, a great run. And let's now move on to our feature discussion with Dr Di Carli. Welcome everyone to our feature discussion and we have Dr Marcelo Di Carli from Brigham and Women's Hospital who's going to be discussing with us a manuscript relating to the measurements of coronary micro circulatory function and how they may impact patients with chronic kidney disease. Also discussing today, we have our own associate editor, Dr Victoria Delgado from Leiden in the Netherlands. Well, welcome Marcelo and Victoria. We're so glad to have the opportunity to speak with you. And Marcelo, could you tell us a little bit about what was the hypothesis and some of the background of why you wanted to perform this study?

Dr Marcelo Di Carli: Chronic kidney disease represents a relatively large segment of the population. In the US alone, it's estimated that around 50 million people have the diagnosis of chronic kidney disease. And it's a disease that we all know is associated with a high risk of cardiovascular events. Even in the absence of obstructive coronary disease, it's been shown that the incidents of cardiomyopathy and the absence of obstructive disease, of coronary disease, is pretty high and that associates with a high risk of heart failure and death.

The mechanisms related to cardiomyopathy in patients with chronic kidney disease have been debated for a long time. This has been associated with LVH incidents of non-transmittal or non-ST-elevation MIs, also with microvascular disease as a measure of ischemic heart disease, but there's no clear association with how do these features of chronic kidney disease link to each other. And so our objective was to look at the associations between LV remodeling, coronary microvascular disease and adverse events. And we hypothesized that coronary microvascular dysfunction as a more integrative marker of myocardial ischemia and injury would associate with changes in cardiac structure and function and with increased risk of adverse cardiovascular events.

Dr Greg Hundley: Very nice. So tell us a little bit, Marcelo, about your study population and your study design.

Dr Marcelo Di Carli: Well, this is a cross sectional analysis of a cohort that is well-characterized in our registries. And so it consisted of a consecutive group of patients who underwent both PET scanning for measuring coronary vascular function and echocardiography within 90 days of each other. Could it not have evidence of overt obstructive coronary disease as defined by a history of prior revascularization, prior AMI or an abnormal PET scan indicating presence of obstructive disease.

We also excluded patients with severe valvular disease, cancer, severe LV disfunction to try to avoid confounding elements in the associations where we're trying to study. We used echocardiography to assess quantitatively the changes in LV geometry, diastolic function and subclinical systolic dysfunction. Most of our patients have relatively preserved LV function, LV ejection fraction. And so we looked at peak longitudinal strain, global radial strain and circumferential strain as indicators of systolic dysfunction. And of course we also looked at changes in LV mass. Patients were followed a little over four years for the occurrence of death, hospitalization for heart failure or myocardial infarction. And all of these myocardial infarctions were non-ST-elevation MIs, or people might call it type two MIs.

Dr Greg Hundley: Tell us a little bit about the results. But before you get to that, how old were these patients and what was their breakdown in terms of race and gender?

Dr Marcelo Di Carli: Yeah, so we had a population of 352 patients. The mean age was mid-sixties. not surprisingly, 60% of the patients were female. And this is because we obviously excluded obstructive coronary disease that would be more prevalent in male. They have about a 40% incidence of diabetes, a high percentage of them had hypertension. These are all the features that would typically be associated with chronic kidney disease. The rate of obesity was actually lower in patients with CKD. And we call CKD here as a GFR less than 60. That's the population we're targeting here. And so that's essentially the cohort.

Dr Greg Hundley: And what did you find?

Dr Marcelo Di Carli: Well, there were essentially three or four main findings. Number one and not very surprisingly, patients with CKD had worse myocardial mechanics that is worse diastolic function and worse systolic strain. In multi-variable models, fully adjusted for a number of clinical covariates as well as ejection fraction, we found that these abnormalities in myocardial mechanics were relatively strongly associated with abnormal coronary microvascular function as defined by PET. So this sort of suggests that the variability that we see in diastolic and systolic function are explained largely by microvascular disease, but not necessarily directly linked to GFR as a mediator.

The second finding was that patients with CKD, again, not surprisingly, it showed a higher incidence of MACE, including especially death and heart failure, more than triple the rate of death and doubled the rate of heart failure compared to those without CKD. And in multi-variable analysis, again, MACE was associated with coronary flow reserve as a measure of microvascular dysfunction but not glomerular filtration rate. And there was no interaction between coronary flow reserve and GFR. Interestingly, when we looked at the adverse events subgroup by measures of LV remodeling and we picked three measures. One is changes in LV geometry, diastolic dysfunction, and impaired global longitudinal strain, we found that the incidence of both mace as well as heart failure and myocardial infarction were significantly higher when both abnormal LV mechanics or remodeling were present and the patients also had microvascular disease. So in the absence of either one, the rate of mace was relatively low, indicating that there is a clear interaction between abnormalities in cardiac structure and function and microvascular disease.

And then lastly, we looked at mediation analysis to try to investigate a plausible pathway between impaired renal function and events and we hypothesized that coronary microvascular dysfunction might actually mediate at least part of that relationship. And indeed we found that about a third of the relationship was explained by the presence of microvascular disease. Very nice,

Dr Greg Hundley: Very nice. Very important work. So now we'll turn to our own associate editor, Victoria Delgado. Victoria, help us put this into perspective for what we know about patients with chronic kidney disease. How does the results of this study really move the field forward?

Dr Victoria Delgado: I think that this article brings new evidence on phenotyping of these patients and the factors that influence the cardiac abnormalities that we may see. There are not many studies including patients with chronic kidney disease. These patients are usually underrepresented in randomized control trials. And we know that these patients are associated with an increased mortality and morbidity and mainly heart failure hospitalizations. And I think that this study is showing another piece in the person that can help us understand why these patients are associated with much higher cardiovascular morbidity and mortality. I think that relating the coronary microvascular dysfunction is an important piece and important knowledge because then we may think how to improve the microvascular dysfunction on these patients and see if by improving these microvascular dysfunction, these abnormalities that have been described in terms of a structure and function can be reversed and see how these impacts on the outcome of these patients.

Dr Greg Hundley: So Marcelo, just briefly, what do you think is the next study that needs to be performed in this area of science?

Dr Marcelo Di Carli: I think that obviously our study has some limitations and the causation. Cause and effect cannot be inferred from our study. So I think the next steps will be to try to demonstrate whether indeed modifying microvascular dysfunction leads to improved outcomes. And I think this will be best done by intervention studies that can be targeted towards improving microvascular dysfunction. We can think of novel therapies as well that have been initially associated with improved renal outcomes. I'm talking about for example, SGLT2 inhibitors that can be potentially of benefit not only on renal outcomes but potentially on cardiovascular outcomes as has been shown in populations largely without CKD.

Dr Greg Hundley: Victoria, anything to add in terms of how noninvasive imaging could play a role in some of those next future studies?

Dr Victoria Delgado: I think that the point that Marcelo raise on the use of SGLT2 inhibitors is very timely and very appealing because we know that for patients with diabetes who have renal dysfunction and you have EGFR below 35, they may not be eligible for these therapies. But as you can see in this study, the mean EGFR of the patients with renal dysfunction was 41. So there is a wide range of patients that could be eligible for these therapies. How imaging can help to see or to detect the patients that may benefit from these therapies and see how these therapies may improve the structure and the function of the heart.

Dr Greg Hundley: Well, listeners, we've had a great discussion today with Dr Marcelo Di Carli from Brigham and Women's Hospital and Dr Victoria Delgado from Leiden. And really trying to understand some noninvasive markers of both micro circulatory dysfunction as well as abnormal echocardiographic assessments of both diastolic function as well as systolic dysfunction and how they forecast adverse events in patients with chronic kidney disease.

I want to wish you all a great week and on behalf of Carolyn and myself, I hope to see you next week. Take care now.

This program is copyright the American Heart Association 2020.