Smoking Hikes STEMI Risk, Especially in Young Women

Batya Swift Yasgur MA, LSW

June 27, 2019

Smoking increases the risk for acute segment elevation myocardial infarction (STEMI) in both men and women, but female smokers have a significantly higher increased risk, compared with male smokers, especially if they are younger than 50 years, a new study suggests.

Investigators studied more than 3300 STEMI events to assess smoking as an independent risk factor and determine the differences in risk between age groups and genders.

They found that smoking increases STEMI risk in patients of all ages and both genders, but the risk is higher in women than in men.

Although the largest relative risk (RR) difference between male and female smokers was found in those between 50 and 64 years of age, the highest risk increase was found in the youngest group (aged 18 to 49 years), with the risk for female smokers 13 times higher than the risk for their nonsmoking female counterparts, and eight times higher in young male smokers.

More positively, former smokers had a level of risk similar to those who had never smoked.

"Overall, I think the findings of this study go some way to more precisely define the increase in STEMI risk associated with smoking and I hope this sobering new awareness will encourage smokers to quit," senior author Ever Grech, MBBS, MD, told | Medscape Cardiology.

"The second message is a very positive one, in that this study found that those who did stop smoking were able to reduce their risk of a major heart attack to a level similar to a contemporary who had never smoked," said Grech, who is a consultant interventional cardiologist and TAVI lead, South Yorkshire Cardiothoracic Centre, Northern General Hospital, Sheffield Teaching Hospitals, NHF Foundation Trust, United Kingdom.

The study was published online June 24 in the Journal of the American College of Cardiology.

Reluctance to Recognize Risk

"As a senior interventional cardiologist working in a major UK heart attack center, I undertake emergency primary PCI [percutaneous coronary intervention] for those with major STEMI," Grech explained.

He observed that "a great many" of the younger patients who experienced acute STEMI were smokers.

"I often found they were reluctant to accept the association between smoking and STEMI because the actual increase in risk caused by smoking had not been defined," he continued.

"I therefore set up a research group with the involvement of the University of Sheffield and ScHARR [School of Health and Related Research] and our initial investigations revealed that around 50% of all STEMI patients were current smokers, but this increased to around 80% in those under 50 years," he recounted.

"I felt this striking increase warranted closer scrutiny, which led to a more extensive examination of data, both within our unit and across the South Yorkshire region."

To investigate the question, the researchers conducted a retrospective ecological cohort study, compiling data for all patients presenting with acute STEMI managed by primary PCI in the South Yorkshire region between January 4, 2009 and July 31, 2014. Data from these patients were combined with population data to generate incidence rates of STEMI.

Data collected included the patient's age, sex, smoking status, key cardiovascular risk factors, cardioprotective drugs taken prior to STEMI onset, and culprit artery of STEMI.

Exsmokers were considered to be abstinent for a minimum of 28 days prior to STEMI, although the duration of smoking cessation was omitted from patient case notes in more than a third (38%) of exsmokers.

The researchers used Poisson distribution to calculate age-standardized incidence rate ratios (IRRs) by comparing STEMI rates between smokers and nonsmokers stratified by sex and three age groups (18–49, 50–64, and >65 years).

The prevalence of most risk factors and all pre-STEMI cardiac medications were similar between the sexes, although hypertension, diabetes, and history of cerebrovascular accident were significantly more common in women, and a previous history of MI was more prevalent in men.

The proportion of STEMI patients who were current smokers was similar between women and men (46.8% vs 47.6%).

Silver Lining

During the 5-year study period (5,639,328 person-years), a total of 3343 patients presented with STEMI, 27.3% of whom were women,

The mean age at presentation in women was 5.8 years older than in men (66.6 vs 60.8 years; = .011).

Peak STEMI rate for current smokers differed between women and men (70–79 years old [235 per 100,000 patient-years] vs 50–59 years old [425 per 100,000 patient-years]).

Moreover, smoking was associated with a greater increase in STEMI rate for women than for men (IRR, 6.62 [95% CI, 5.98–7.31] vs 4.40 [95% CI, 4.15–4.67).

There were both age- and sex-related differences in STEMI-related culprit artery, with the right coronary artery (RCA) more likely and the circumflex less likely to be involved in women.

The RCA was also less frequently involved in those aged 18 to 49 years, whereas current smokers were more likely to have the RCA as their culprit lesion and less likely to have left anterior descending artery involvement.

In smokers, the highest rate of STEMI was in the 50- to 59-year age group, (286.3 per 100,000 patient-years; 95% CI, 262.1–312.2 per 100,000 patient years), in contrast to nonsmokers, where the highest rate was among those aged 70 to 79 years (95.1 per 100,000 patient-years; 95% CI, 82.7–108.9 per 100,000 patient years).

The researchers created an incidence rate graph showing the raw STEMI figures compared with the general population, which showed a similar risk between ex- and never-smokers for STEMI incidence, with CIs overlapping between the groups at every 10-year age group.

The highest RR of acute STEMI was found in female smokers age younger than 50 years — which is 13.22 (95% CI, 10.35–16.66) times greater than in their nonsmoking counterparts — a calculation that was significantly higher than in men of the same age group (smoking-associated risk, 8.60; 95% CI, 7.70–9.59).

Moreover, the largest RR difference in smoking-associated STEMI was found in the middle-aged group (50–64 years) — with female smokers at 9.66 (95% CI, 8.30–11.18) times increased risk for STEMI, compared with male smokers (4.47; 95% CI, 4.10–4.86) — "indicating that smoking is a more severe risk factor for women of this age group compared with men by a factor of 2.16," the authors explain.

"For the first time, this study provides a numerical hazard which specifically focuses on the cardiac risks of smoking in a way that is much easier to understand and I hope this will correct the perception by young smokers that heart attack risks arise much later in life," Grech commented.

"The reversibility [of STEMI risk in those who had stopped smoking] was a surprise, which I regard as a 'sliver lining' within the dark cloud of smoking outcomes," he continued.

"This will undoubtedly incentivize smokers who may have genuine concerns regarding their longer-term health and realize the massive benefits of abstaining," he said.

Dangers of Vaping

Commenting on the study for | Medscape Cardiology, Deepak L. Bhatt, MD, MPH, executive director of interventional cardiovascular programs, Brigham and Women's Hospital Heart and Vascular Center, Boston, who was not involved with the study, called it "very interesting, well-done, and important."

He suggested that "sometimes, physicians forget that there is still a lot of smoking out there and that it is still a very important risk factor; if anything, it is important not to take our eyes off the ball."

Bhatt, who is also professor of medicine at Harvard Medical School, said that although the "absolute numbers [of smokers at risk for STEMI] might differ between the US and the UK, where this study was conducted, the association between smoking and STEMI, which has been known for a while, remains true in any population."

He noted that in many places in the United States, smoking bans have been enacted and rates of smoking have stabilized, but vaping has "been growing in popularity in astronomical ways."

The risks associated with e-cigarettes "haven't been well characterized yet, but now reports are coming out focusing on the association with increased risk of heart attack," he observed.

He added that e-cigarettes "are being marketed by companies as being safer than conventional cigarettes, although there are no data to support that and the flavorings make them even more addictive [than conventional cigarettes], even if they don't contain quite as many harmful chemicals."

Thus, "even if the rates of smoking [conventional cigarettes] have gone down in the US, in past couple of years, vaping has more than made up for it," Bhatt said.

Tailored Lifestyle Counseling

Also commenting on the study for | Medscape Cardiology, Raffaele Bugiardini, MD, Department of Experimental, Diagnostic and Specialty Medicine – DIMES, Bologna, Italy, said he is "glad that new emphasis is given in the article to the higher risk for women than for men," although he is "not convinced about the manuscript's claims for novelty."

The authors should instead "consider claiming that this is the best study confirming differential smoking-related outcomes between sexes rather than the only study quantifying these outcomes."

He also wondered if there was sufficient adjustment for possible confounding cardiovascular risk factor, which tend to be "worse in women, which would actually lead to these results being an underestimate of the harm of smoking in men."

Additionally, he cautioned, the authors enrolled patients with and without previous cardiovascular events and, "consistent with the 'smoker's paradox,' smoking is an independent predictor of a more favorable postinfarction left ventricular remodeling, even after multivariable adjustment."

For this reason, "without evidence on the effects of smoking separately in patients with or without prior cardiovascular events, we fear that the whole modeling approach may need to be recalculated according to this method."

The study nevertheless has important take-home messages for practicing clinicians.

"Smokers should quit completely instead of cutting down in order to reduce the risk of MI, [which is] even more important for women, as their risk remains higher."

He advised that general lifestyle counseling "should be tailored to sex."

Grech added that the biological factors behind the increased female risk are "likely to be complex and multifactorial" and require further research.

"What is clear is that the protective effects of estrogens in young female smokers are overridden by the powerful impact of cigarette smoking, and although these reasons are interesting to know, what matters more is the result," he emphasized.

No source of funding listed. Grech and coauthors, Bhatt, and Bugiardini report no relevant conflicting interests.

J Am Coll Cardiol. Published online June 24, 2019. Abstract

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