Apr 24, 2018
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 featured paper today is so important for cardiac surgeons and their patients. It answers a question of whether targeting a higher versus a lower blood pressure during cardiopulmonary bypass helps to prevent cerebral injury. Curious? Well, more soon right after these summaries.
In the first original paper this week, MicroRNA-22 is shown to be a novel mediator of vascular smooth muscle cell, phenotypic modulation, and neointima formation. Co-first authors, Drs. Yang and Chen, co-corresponding authors, Dr. Zhang from Zhejiang University and Dr. Xiao from Queen Mary University of London and their colleagues used wire injury mouse models to show that MicroRNA-22 controls vascular smooth muscle cell phenotype and injury-induced arterial remodeling by modulating multiple target genes, including methyl-CpG-binding protein 2, histone deacetylase 4, and ecotropic virus integration site 1 protein homolog.
The authors observed that MicroRNA-22 expression was suppressed in human femoral arteries with atherosclerotic plaques, and that there was an inverse relationship between MicroRNA-22 and its target genes in healthy and diseased arteries. Furthermore, local delivery of MicroRNA-2 in the injured arteries prevented adverse arterial remodeling, thus suggesting that site-specific delivery of MicroRNA-22 mimics may be a potential therapy for in-stent restenosis.
The next paper adds to our understanding of the pathobiology of pulmonary hypertension related to left-sided heart failure and importantly adds histomorphometric evidence from human lung specimens at autopsy or surgery.
First author Dr. Fayyaz, corresponding author Dr. Redfield, and colleagues from the Mayo Clinic studied patients with heart failure with preserved or reduced ejection fraction and pulmonary hypertension and compared these to normal controls, as well as patients with primary pulmonary veno-occlusive disease.
They found that patients with heart failure and pulmonary hypertension had global pulmonary vascular remodeling with thickening of the media and intima in arteries and thickening of the intima in veins and small pulmonary vessels compared to normal control subjects.
This venous and small-vessel intimal thickening was more severe than the arterial intimal thickening in heart failure with a pattern that was similar to patients with pulmonary veno-occlusive disease. In fact, the severity of pulmonary hypertension correlated most strongly with venous and small vessel remodeling rather than arterial remodeling.
These findings expand our understanding of the pathobiology of pulmonary hypertension in heart failure. It also suggests that pulmonary venous remodeling in heart failure may predispose to worsening alveolar edema with pulmonary vasodilators as in primary pulmonary veno-occlusive diseases.
Are there sex and race differences in the lifetime risk of HFpEF versus HFrEF? First author Dr. Pandey, corresponding author Dr. Berry from UT Southwestern Medical Center, and their colleagues used participant level data from two large respective cohort studies, the Cardiovascular Health Study, and the Multi-Ethnic Study of Atherosclerosis to determine remaining lifetime risk estimates for heart failure with preserved and reduced ejection fraction at different index ages.
They found that compared to women, men have a higher lifetime risk of HFrEF, heart failure reduced ejection fraction with a similar lifetime risk of HFpEF, or heart failure preserved ejection fraction. Compared with blacks, non-blacks have a similar lifetime risk of developing HFrEF but a higher risk of HFpEF.
Lifetime risks of HFpEF and HFrEF were similar and substantially higher in those with versus without antecedent myocardial infarction.
In summary, these findings provide novel insights on sex and race differences in the lifetime risks of HFpEF and HFrEF, and may help health policymakers in appropriate resource allocation for targeting HFpEF and HFrEF specific preventive therapies at the at-risk population.
What are evidence-based blood pressure targets during pediatric cardiopulmonary resuscitation? Well, first and corresponding author Dr. Berg from Children's Hospital of Philadelphia and his colleagues studied a multi-center population of children with invasive arterial blood pressure monitoring during in-hospital ICU cardiac arrest, and the Collaborative Pediatric Critical Care Research Network Intensive Care Units, between 2013 and 2016.
They found that a mean diastolic blood pressure greater or equal to 25 millimeters of mercury during cardiopulmonary resuscitation in infants, and greater or equal to 30 millimeters of mercury in children 1 year old or greater, was associated with a 70% greater likelihood of survival to hospital discharge, and a 60% higher likelihood of survival with a favorable neurologic outcome.
On the other hand, survival rates were markedly lower with mean diastolic pressures less than 20 in infants and less than 25 in children 1 year or older. Thus, clinicians should consider targeting diastolic blood pressure of 25 or greater in infants, and 30 or greater in children 1 year old or older during cardiopulmonary resuscitation when invasive arterial blood pressure is monitored.
That wraps up our summaries for this week. Now for our featured discussion.
Does a higher versus a lower blood pressure target during cardiopulmonary bypass surgery reduce the risk of cerebral injury? Well, the feature paper today provides some answers, and we have the first and corresponding author, Dr. Anne Vedel from University of Copenhagen with us today, as well as our associate editor, Dr. Timothy Gardner, who's a cardiac surgeon from University of Pennsylvania.
Thank you so much for being with us today and this was a terrific trial, a very difficult trial to carry out. Could you please tell us a bit more about it?
Dr Anne Vedel: Cerebral injury is an important complication after cardiac surgery with the use of cardiopulmonary bypass. Up to half of our patients suffer these perioperative silent strokes. Therefore, in Copenhagen we conducted a trial investigating the importance of two distinct blood pressure levels during cardiopulmonary bypass. Now, on this subject of optimal perfusion strategy during bypass, there are many opinions, but also a stunning lack of convincing evidence, for instance, when it comes to blood pressure management.
Now, the question is whether normal physiological principles, such as cerebral autoregulation therapy, whether they apply during bypass, or if perfusion pressure indeed does play a less important role when blood flow is mechanically provided in an uncomplicated and sufficient way by the heart and lung machine.
So, in a patient on the assessor-blinded randomized trial, we allocated patients to a higher or a lower MAP target, 70 to 80, or 40 to 50 millimeters of mercury, respectively, by titrating intravenous norepinephrine during bypass.
Pump flow levels were set at 2.4 liters per minute per square meter of body surface, and our primary outcome was the total volume of new ischemic cerebral lesions, expressed as a baseline MRI, and opposed to the difference between the baseline MRI and the postop MRI on day three to six. Secondary outcomes were a number of new ischemic lesions and newer psychological test evaluations.
Now among the 197 patients enrolled who were scheduled for coronary artery bypass, or heart valve repair surgery, or a combination of both, we found that 53% of patients in the low target group as opposed to 56 in the high target group had new cerebral lesions on their postop cerebral MRI.
The primary outcome of volume of new cerebral lesions was comparable between groups, and so was the total number of newer lesions. No significant difference was observed in stroke rates in frequencies of postoperative cognitive dysfunction, or in severe adverse event rate.
Therefore, we concluded that among patients undergoing on-pump cardiac surgery, targeting higher versus a lower mean arterial pressure did not seem to affect the volume or number of new infarcts.
Dr Carolyn Lam: Wow, thank you so much, Anne. Tim, you think about these issues a lot more than I do as a non-surgeon. Could you tell me what your insights were?
Dr Tim Gardner: You know, it's a very difficult study to do a randomized control trial in this environment, and they're really to be congratulated for doing it. As Anne acknowledges, this is not an area where randomized trials are very frequent.
The first thing about the trial, I think, is a growing awareness among all of us that there seems to be a lot of imaging evidence of what we call injury or changes based on diffusion-weighted imaging in patients after cardiopulmonary bypass. This is not the first study that shows that.
But the question is are these incidental, trivial lesions? I'd have to, again, ask Anne to clarify how many of the patients in either group, what percentage had what we would consider evidence of overt strokes?
Dr Anne Vedel: Well, overt strokes, as opposed to silent strokes, 1 patient in the lower target group had stroke and 6 patients in the high target group, which corresponds to 1 as opposed to 7%.
Dr Tim Gardner: That was not quite statistically significant difference but headed in that direction with the assumption that if you have a larger sample size there might be, in fact, some association with overt stroke using the high target vasopressor approach, is that right?
Dr Anne Vedel: We can only speculate. But as you do, yes, I agree.
Dr Tim Gardner: To go back to the original question, the significance of these, well, you were referring to as silent strokes. Can you comment on the clinical significance there? We hear of silent heart attack. What is a silent stroke and what are the implications of that long term for patients?
Dr Anne Vedel: In other fields of research on the silent strokes, it's been shown that they correlate to both frequency of postoperative cognitive dysfunction and also later development of mild cognitive impairment and dementia. But these kinds of results, there isn't enough research in the field of cardiac study for us to say the same. But those are the implications from other research fields.
Dr Tim Gardner: But you can understand from the perspective of a cardiac surgeon, and this concern has been expressed and talked about in the literature for 20 years or more, the possibility that even what seems to be, with no injury apparent and no overt stroke, there may be some neurological consequence to cardiopulmonary bypass.
So just to move on from that because I agree that we just don't have any reliable information that these silent strokes result in late or permanent injury, I think again the finding that manipulating the blood pressure, which seems to be intuitively beneficial in patients, especially elder patients, did not, in fact, show any benefit and, in fact, may have been associated with a slight increase in overt stroke. Is that a fair conclusion from your study? A summary of your study?
Dr Anne Vedel: I would say it is a fair conclusion, and surprisingly so. The question is whether it is the blood pressure or the means that we apply to have this increase in blood pressure that is the point of interest here.
Dr Tim Gardner: You mean whether, in fact, using the norepinephrine, the vasoconstrictor, to increase the blood pressure whether that itself, it certainly didn't benefit, it may have been a problem.
Dr Anne Vedel: Exactly. That's what I speculate might be the case. But I also think it's fair to say at this point that this is somewhat artificial physiological scenario, the cardiopulmonary bypass.
Dr Tim Gardner: I agree with that, that you're controlling blood flow and the patient is exposed to a lower hemoglobin and oxygen-carrying capacity and so on. But I think what struck me about your findings, or strikes me about your findings, is what appears to be in many of the patients, the low target patients, pretty effective autoregulation of the cerebral circulation, despite the artificiality of cardiopulmonary bypass.
I think that's, again, something that has been not well known or well accepted by many people, thinking that if you lower body temperature, you lower hemoglobin, autoregulation may not be enough to maintain good cerebral perfusion. It looks like this study shows that in these patients, autoregulation worked fine. Is that fair?
Dr Anne Vedel: Yes. Or sufficient blood flow was delivered. All in all, what's new in our study, I think, is that hypertension per se shouldn't necessarily be considered a proxy for hyperperfusion during bypass.
Dr Tim Gardner: Yeah, that's a very good qualification. So none of your patients, despite being in their mid to late 60s had evidence of carotid artery disease or whatever? Those patients were excluded from the trial, is that right?
Dr Anne Vedel: No, that's not correct. We didn't screen for carotid artery disease because we don't routinely do that in our institution. As we describe in our discussion, we included quite a heterogeneous study sample by enrolling the patients that came to us. We didn't screen and we didn't exclude these patients that you mention.
Dr Tim Gardner: Do you know how does your group handle a patient that is known to have carotid artery disease, comes in with a known either prior endarterectomy or established disease? Do those patients, are they treated any differently either as a result of the study or just in general?
Because that is a targeted group of patients, at least in my own experience, that we would be more concerned about allowing autoregulation to be the determinant, feeling that if there is a fixed stenosis in the carotid artery that we might need to increase the mean arterial pressure.
Dr Anne Vedel: I can certainly understand your point and, of course, it is a concern in our center, as well. But having said that, there were no patients in the PPCI trial that came to us with a history of carotid artery disease, so it wasn't a concern for us in this study.
Dr Tim Gardner: That would be one point that I would make that we probably should pay attention to patients who do come for surgery and have known significant obstructive extracranial disease, but I understand that you didn't specifically have those patients or were aware of those patients.
I think that this is a very useful study for us concerned about the possibility of inducing cerebral injury with cardiopulmonary bypass. To some people it's sort of counterintuitive that increasing perfusion pressure didn't improve the tolerance of patients to cardiopulmonary bypass but that's why you did the study. I think it's a very notable and important report that's going to be in circulation.
The significance of these "silent infarcts" is merely something that we have to sort of sort out. I know you said that silent infarcts, as I agree, are associated with or presumed to be predictive of later cognitive dysfunction, dementia and so on. It really is a concerning message if that's the main message that comes out of these imaging studies. Because these are patients that, obviously, didn't have heart surgery for no reason, there was obviously a compelling indication for patients to have it.
You would hate to re-ignite this concern as we had in and around year 2000 when the group at Duke was talking about writing about patients who had cognitive decline after cardiac surgery, were going to end up being demented five or 10 years down the line, so, that's from the perspective of a cardiac surgeon. Let's stick with the evidence but let's follow-up and see how predictive these silent infarcts are and what the consequences are long term. Do you think that's fair, Anne? Am I making a fair statement?
Dr Anne Vedel: I absolutely do think it's fair. And for a cardiac surgeon as yourself, I would find it very interesting to see that these kind of studies are also conducted in TAVR patients where you have sometimes a 200% incidence of these silent strokes.
I mean you have a good taste as a cardiac surgeon if you only see them in 50% of your patients, understand me correctly, but I don't necessarily think that this high incidence, it's high, yes, but compared to other patient groups, such as TAVR patients, it's not necessarily that bad.
Dr Tim Gardner: Right. Anne, I don't know whether you've seen the editorial that's going to accompany your paper, but it's very good. It's very supportive of your study and has some good comments. You'll be pleased with the editorial, I believe, if you haven't seen it.
Dr Anne Vedel: Thank you very much. I'm happy to hear that. I know we do things a bit controversially over here in Copenhagen, compared to many centers in the U.S.
Dr Tim Gardner: That is not what the editorialists think. An anesthesiologist from Stanford and a neurologist from Penn, they have a very good commentary on your study and the whole field, so you'll be pleased.
Anne Vedel: I'm very happy to hear that. Thank you.
Carolyn Lam: Well, listeners, I'm sure you learned a lot. Thank you for joining us today, and don't forget to tune in again next week.