May 16, 2022
This week, please join author Andrew Stokes as he and Greg Hundley discuss the Research Letter "E-Cigarette Use and Risk of Cardiovascular Disease: A Longitudinal Analysis of the PATH Study (2013–2019)."
Dr. Greg Hundley:
Well, listeners, welcome to this May 17th issue of Circulation on the Run. And I am Dr. Greg Hundley, associate editor, director of the poly heart center at VCU Health in Richmond, Virginia. And this week, Carolyn is away out on vacation and we are going to go through the summaries together. We have a great feature today on e-cigarette use and the risk of cardiovascular disease. But before we get to that, how about we grab a cup of coffee and jump into some of the other articles in the issue? And the first one comes to us from the world of clinical science and Dr. Jiaqi Huang from the National Cancer Institute. Listeners, the objective of this study was to examine overall and cause-specific mortality in relation to dietary and serum cholesterol, as well as egg consumption through the prospective analysis of 27,000 men in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention or ATBC Study, and also a systematic review and meta-analysis of several other cohort studies.
Dr. Greg Hundley:
So, what did the investigators find? Well, first, based on 482,000 person-years of follow-up, the authors identified 22,000 deaths, including 9,110 deaths from cardiovascular disease. Now, greater dietary cholesterol and egg consumption were associated with increased risk of overall and cardiovascular disease mortality. Now, second, from the meta-analysis component of the study, overall consumption of one additional 50-gram egg per day was associated with an increased cardiovascular disease risk with a pooled relative risk of 1.04 with a higher risk of cardiovascular disease among those from us cohorts where their pooled relative risk ratio was 1.88, a borderline higher cardiovascular disease risk in European cohorts with a pooled relative risk of 1.05, but not an increased cardiovascular disease risk in the Asian cohorts. So, the results from this study, which includes an updated meta-analysis, suggest that there is support for restricted consumption of dietary cholesterol as really a means to improve long-term health and longevity.
Dr. Greg Hundley:
Well, let's go to our next article. So, in this next study, we are going to move from cholesterol risk now to salt substitution. And this article comes to us from Professor Maoyi Tian from the Harbin Medical University. Listeners, the Salt Substitute and Stroke Study, or SSaSS is a five-year cluster randomized controlled trial and demonstrated that replacing regular salt with a reduced sodium added or potassium salt substitute reduced the risk of stroke, major cardiovascular events, and premature death among individuals with prior stroke or uncontrolled high blood pressure that lived in rural China. So, this particular study, a substudy, assessed the cost-effectiveness profile of this particular intervention.
Dr. Greg Hundley:
So, listeners, what did the study find? Well, there was a mean follow-up of 20,995 participants that was conducted a little over four years, and over the period, replacing regular salt with salt substitute reduced the risk of stroke by 14% and the salt substitute group had on average 0.054 more quality-adjusted life years per person. The average costs were lower in the salt substitute group, and this intervention was dominant. That is better outcomes at a lower cost for prevention of stroke as well as for quality-adjusted life-years gained. Now, interestingly sensitivity analyses showed that these conclusions were robust except when the price of the salt substitute was increased to the median and highest market prices identified in China. The salt substitute intervention had a 95% probability of being cost-saving and a greater than 99.9% probability of being cost-effective. A really interesting article.
Dr. Greg Hundley:
Well, now, let's turn our attention to the world of population science. And in this study, these authors led by Dr. Steven Lubitz from Massachusetts General Hospital performed a Genome-Wide Association Study or GWAS of the QT corrected interval among 84,630 United Kingdom Biobank participants. And they created a polygenic risk score. Now, among 26,976 participants with whole-genome sequencing and electrocardiogram data in the Trans-Omics for Precision Medicine or TOPMed program, they identified 160 carriers of punitive pathogenic, rare variants in 10 genes known to be associated with the QT interval.
Dr. Greg Hundley:
So, the authors here examined the QTC corrected associations with the polygenic risk score and with rare variants from the TOPMed cohort. So, what did they find? They found 54 independent loci by GWAS in the UK Biobank. 21 loci were novel of which 12 were replicated in TOPMed. The polygenic risk score comprising over a million common variants was significantly associated with the QTC in TOPMed, and carriers of punitive pathogenic rare variants had longer QTC intervals than non-carriers. Now, 23.7% of individuals with a QT corrected of greater than 480 milliseconds carried either a monogenic rare variant or had a polygenic risk score in the top decile. 3.4% for monogenic and 21% for the top decile of the polygenic risk score.
Dr. Greg Hundley:
So, listeners, the findings of this study indicate that the QTC duration in the population is influenced by both rare variants in genes, underlying cardiac repolarization and polygenic risk, with a sizeable additional contribution from polygenic risk. And therefore, comprehensive assessment of the genetic determinants of QTC prolongation should include incorporation of both polygenic and monogenic risk.
Dr. Greg Hundley:
Well, listeners, let's turn our attention to the world of preclinical science. And this next article comes to us from Professor Junbo Ge from the Department of Cardiology in Zhongshan Hospital in Fudan University. Well, listeners, after myocardial infarction, cardiac resident macrophages, which are self-maintaining in that they originate from embryonic hematopoiesis are responsible for the efficient clearance and degradation of apoptotic cardiomyocytes. And that process is called efferocytosis. Now, efferocytosis is required for inflammation resolution and tissue repair. However, the underlying molecular mechanisms of this process really remain unknown.
Dr. Greg Hundley:
So, as such, listeners, these authors sought to identify the mechanisms of the continued clearance and degradation of phagolysosomal cargo by cardiac resident macrophages during myocardial infarction. Well, what did Dr. Ge and colleagues find? Several things. First, they identified legumine as a gene specifically expressed by cardiac resident macrophages, and legumine deficiency resulted in a considerable exacerbation in cardiac function, accompanied with the accumulation of apoptotic cardiomyocytes and a reduced index of in-vivo efferocytosis in the border area of infarcts. Furthermore, the formation of LC3 to dependent phagosome around secondary encountered apoptotic cardiomyocytes was disabled. In addition, legumine deficiency increased infiltration of MHC to high CCR2+ macrophages, and the enhancement of recruitment of MHC to low CCR2+ monocytes with downregulation of anti-inflammatory mediators, such as IL10 and TGF-beta, and upregulation of pro-inflammatory mediators, including interleukin-1-beta, Tumor Necrosis Factor alpha, IL6, and IFN-gamma.
Dr. Greg Hundley:
So, listeners, in summary, the results of this study directly link efferocytosis to wound healing in the heart and identify legumine as a significant link between acute inflammation resolution and cardiac function after infarction. Well, listeners, also in this issue, we have a wonderful On My Mind feature from Professor Camlet entitled “A Role for the Vascular Endothelium in Post-Acute COVID-19.” Well, next, we're going to head to our feature article on e-cigarette use and the risk of cardiovascular disease.
Dr. Greg Hundley:
Well, listeners, welcome to our feature discussion today. A very interesting topic. E-cigarette use and the risk of cardiovascular disease. And we have with us today the senior author of this particular manuscript, Dr. Andrew Stokes from the Boston University School of Public Health in Boston, Massachusetts. Welcome, Andrew. Andrew, to get started, can you describe some of the background information pertaining to your study and what was the hypothesis that you wanted to address?
Dr. Andrew Stokes:
Absolutely, and thank you for having me on the podcast. Despite the increasing popularity of electronic cigarettes, the long-term health effects of habitual e-cigarette use remain unclear. Most of the studies that have been conducted to date are either cross-sectional or they pertain to small clinical samples. The goal of the present study was to develop a longitudinal design to see if e-cigarette use at a point in time was linked to cardiovascular events over a multi-year follow-up period.
Dr. Greg Hundley:
Very nice. So, your specific hypothesis really pertained to e-cigarette use, correct?
Dr. Andrew Stokes:
That's right. As a novel product, information on e-cigarette use and its health effects is lacking, and so our goal was to see if e-cigarette use was associated with the incidence of clinical events.
Dr. Greg Hundley:
And so, can you describe for us your study population and your study design?
Dr. Andrew Stokes:
Absolutely. Data come from the Population Assessment of Tobacco and Health Study or the PATH Study, which is a nationally representative cohort study of the non-institutionalized population containing five annual waves of self-reported data collected between 2013 and 2019. The initial sample included over 30,000 US adults ages 18 years and older with oversampling of tobacco users. We excluded respondents who were lost to follow-up or who had a previous diagnosis of CVD or were missing baseline exposure information. Ultimately, we ended up with a sample of just over 20,000 individuals.
Dr. Greg Hundley:
Very nice. And so, what were your study results?
Dr. Andrew Stokes:
So, we had several key findings. One key finding was that, compared to people who only smoke cigarettes, people who smoke both traditional cigarettes and used e-cigarettes had no significant reduction in risk for heart attack, heart failure, or stroke, nor any cardiovascular disease outcome. This is significant because many e-cigarette users use both e-cigarettes and cigarettes in combination. Very few move to exclusive e-cigarette use. Additionally, we found that those who do move to e-cigarette use exclusively though, representing a very small fraction of the cohort, had some evidence of reduction in cardiovascular harm. However, these results for exclusive e-cigarette users were not statistically significant, indicating that additional studies with longer follow-up will be required before we can make any definitive conclusions about this group.
Dr. Greg Hundley:
Very nice. And did you notice any discrepancy in your results between either men versus women or between individuals that were younger in age versus those that may say be 50 years or older?
Dr. Andrew Stokes:
I think both sources of effect modification will be valuable directions for future research. Unfortunately, samples of e-cigarette users are quite small and incident events over follow-up are quite limited. Therefore, the present study did not pursue or explore these types of stratifications.
Dr. Greg Hundley:
Very good. So, sounds like more research to come forward. Well, Andrew, how do we put your results really in the context with other studies evaluating the harmful effects of e-cigarettes?
Dr. Andrew Stokes:
Of course. So, we know from toxicological studies that there are many constituents of e-cigarette aerosols that are concerning and have substantial toxicity. We know that the inhalation of e-cigarette aerosols among young healthy adults induce inflammation and oxidative stress. Population-based studies from cross-sectional data sources also suggest evidence of harm. What's needed are more longitudinal studies with longer follow-up periods and more incidence events so we can really parse this risk and identify the magnitude of these harms. Finally, we also need to understand better whether there's any harm reduction potential associated with e-cigarette use. E-cigarettes are currently not an FDA-approved cessation product. Therefore, we do not recommend their use despite preliminary evidence of potential harm reduction. We'll need further evidence before we can make any such conclusions.
Dr. Greg Hundley:
And Andrew, describe for us, and you've started to already, what series of studies are needed next to be performed in this sphere of research?
Dr. Andrew Stokes:
Right. So, it's difficult to really identify definitively the effects of e-cigarette use in the absence of randomized control trials. However, we can use observational data with target trial approaches to emulate the clinical trial that we would like to do if we were able to. So, the next step is really to look at transitions across products between cigarette and e-cigarette use and to associate those who switch products, such as from e-cigarettes to cigarettes or vice versa, to see if those switches are associated with any harm or harm reduction.
Dr. Greg Hundley:
Very good. Any specific racial or ethnic groups or even social determinants of health that may need to be targeted with some of these future studies?
Dr. Andrew Stokes:
That's a great question. So, what we know so far from preliminary research is that some groups are more likely to switch to e-cigarettes than other groups. Particularly among current combustible cigarette users, the rates of switching do vary by race and ethnicity. Thus, we need further research to understand why these patterns differ across subgroups and what their implications may be for health.
Dr. Greg Hundley:
Do you foresee any difficulty in trying to enroll participants from those other groups as you plan these studies moving forward?
Dr. Andrew Stokes:
The advantage of the current research design is that we're using a large secondary data set of survey participants who are enrolled in the Population Assessment of Tobacco and Health study. Therefore, we are not enrolling patients ourselves and the response rates are quite high in these surveys.
Dr. Greg Hundley:
Well, Andrew, we hear that some of the inhalants that are mixed with the inhaled nicotine can be flavors and perhaps have been approved by the FDA for consumption in the GI tract where, whatever these additives are, you would think might be broken down by the digestive system. But if they're inhaled and get into the lung tissue and the parenchyma, the alveoli, et cetera, do they perhaps have harmful effects that maybe we're not aware of?
Dr. Andrew Stokes:
Absolutely. E-cigarettes come in thousands of characterizing flavors including sweet flavors, tobacco flavors, and many other miscellaneous flavors. As we saw with the outbreak of lung injury associated with the use of e-cigarettes in 2019, inhaling flavors can have health effects that are unanticipated based on research in the GI tract, and therefore, as a next step in this research, we really need more work to investigate how different flavors are associated with the incidence of clinical events, whether cardiovascular or pulmonary conditions.
Dr. Greg Hundley:
Very nice. Well, listeners, we want to thank Dr. Andrew Stokes from the Boston University School of Health for bringing us this data from the PATH study, suggesting that combining smoking with e-cigarette use does not reduce cardiovascular events and that quitting both products is needed to ensure overall cardiovascular disease risk reduction.
Dr. Greg Hundley:
Well, on behalf of Carolyn and myself, we want to wish you a great week and we will catch you next week on the run. This program is copyright of the American Heart Association 2022. The opinions expressed by speakers in this podcast are their own and not necessarily those of the editors or of the American Heart Association. For more, please visit ahajournals.org.