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Reductions in admissions for myocardial infarction (MI) have been reported in locales where smoke-free workplace laws have been implemented, but no study has assessed sudden cardiac death (SCD). In 2002, a smoke-free restaurant ordinance was implemented in Olmsted County, Minnesota, and in 2007, all workplaces including bars became smoke free.
To evaluate the population impact of smoke-free laws, we measured, through the Rochester Epidemiology Project, the incidence of MI and SCD in Olmsted County during the 18-month period before and after implementation of each smoke-free ordinance. All MIs were continuously abstracted and validated using rigorous standardized criteria relying on biomarkers, cardiac pain, and Minnesota coding of the electrocardiogram. SCD was defined as out-of-hospital deaths assigned to coronary disease.
Comparing the 18 months before the implementation of the smoke-free restaurant ordinance to the 18 months after the implementation of the smoke-free workplace law, the incidence of MI declined by 33% (P<0.01) from 150.8 to 100.7 per 100,000 population, and the incidence of SCD declined by 17% (P=0.13) from 109.1 to 92.0 per 100,000 population. During the same period, the prevalence of smoking declined while that of hypertension, diabetes, hypercholesterolemia, and obesity either remained constant or increased.
A substantial decline in the incidence of MI was observed after smoke-free laws were implemented, the magnitude of which is not explained by community co-interventions or changes in cardiovascular risk factors with the exception of smoking prevalence. As trends in other risk factors do not appear explanatory, smoke-free workplace laws seem ecologically related to these favorable trends. Secondhand smoke (SHS) exposure should be considered a modifiable risk factor for MI. All people should avoid SHS to the extent possible, and people with known coronary heart disease should have no exposure to SHS.
Secondhand smoke (SHS) exposure is associated with coronary heart disease (CHD) in nonsmokers, and a nonlinear dose relationship exists such that SHS exposure has a larger than expected adverse effect at low levels of exposure.1 Research suggests that the cardiovascular effects of SHS are nearly as large as active smoking.1 Indeed, the magnitude of endothelial dysfunction in nonsmokers approaches that noted in active smokers2 and may only be partially reversible.3 The 2006 U.S. Surgeon General’s Report underscored the negative impact of SHS stating that “exposure to SHS has immediate effects on the cardiovascular system.”4 An estimated 46,000 nonsmoking Americans die annually from cardiovascular events related to SHS.5 Eliminating smoking in public places holds potential for improving public health and reducing cardiovascular events beyond the expected impact of the reduction in active smoking.6 Finding additional scientific data in support of smoke-free policies will help ensure their continuation and encourage locales without such laws to consider them.
Several studies described a decline in admissions for myocardial infarction (MI) after implementation of smoke-free legislation,7–14 and a meta-analysis of 17 published studies reported a 10% reduction in admissions for MI after the implementation of such legislation.15 An expert committee from the Institute of Medicine concluded: “That there is a causal relationship between smoking bans and decreases in acute coronary events,” but the committee did not determine the magnitude of the decrease in relative risk.16 The 10-member committee concluded that none of the reports to date were of ideal design. In order to evaluate the population effect of the implementation of smoke-free laws on cardiovascular events, we examined data from the Rochester Epidemiology Project (REP) including individual patient data for MI cases validated using rigorous epidemiological criteria and sudden cardiac death (SCD) in Olmsted County, Minnesota, before and after implementation of smoke-free workplace laws.
Olmsted County, located in southeastern Minnesota, has a population of 144,248 (86% white, 51% female).17 Only a few providers (chiefly Mayo Clinic and Olmsted Medical Center) deliver nearly all medical care to county residents. Medical records used by each provider capture information for all encounters and can be retrieved from indices based on all diagnoses and procedures maintained by Mayo Clinic.18 This results in the linkage of medical records from all sources of care, providing a unique infrastructure to analyze disease occurrence and outcomes at the population level. Potential cases identified through the REP can then be validated by applying standardized methods appropriate for each disease entity. This process has been implemented for extensive cardiovascular disease epidemiology research.19–22
In Olmsted County. a smoke-free restaurant law which did not include bars or other workplaces (Ordinance 1) was implemented on January 1, 2002, and on October 1, 2007, all workplaces (including bars) became smoke-free (Ordinance 2).
Potential cases included patients admitted to Olmsted County hospitals who were assigned the International Classification of Disease, Ninth Revision code 410 (acute MI). Infarctions were validated after manual data collection of relevant information and using algorithms integrating cardiac pain, electrocardiographic (ECG) and biomarker data (creatine kinase [CK] and MB fraction of creatine kinase [CKMB]).23, 24 Biomarker values were recorded for up to three measurements on each of the first three days following admission or infarction onset, if the patient was already hospitalized.25, 26 All biomarkers were measured with a sandwich electrochemiluminescence immunoassay on the Elecsys 2010 (Roche Diagnostics Corporation; Indianapolis, IN), in the certified laboratories of the Department of Laboratory Medicine and Pathology at Mayo Clinic in Rochester, MN, with robust quality control in place. Three ECGs per episode were coded using the Minnesota Code Modular ECG Analysis System.27 Only first ever MIs were considered as incident. All MIs were continuously abstracted for the entire duration of this study. These methods have been used in our coronary disease surveillance work for more than a decade with excellent reliability.23, 25, 28
Our methods of ascertaining SCD have been previously published.22, 29 In brief, SCD was defined as out-of-hospital deaths with the primary cause of death classified as coronary heart disease on the death certificate (International Classification of Diseases, Ninth Revision codes 410–414).29
Baseline demographic and clinical characteristics were collected from the medical records by nurse abstractors at the time of MI diagnosis or SCD. Clinicians’ diagnoses were used to define hypertension, hyperlipidemia, diabetes, familial CHD, and smoking status. Body mass index (BMI) (kg/m2) was calculated using height and weight.
We utilized Behavioral Risk Factor Surveillance System (BRFSS) data from Minnesota adults for self-reported current smoking prevalence, hypercholesterolemia, diabetes, hypertension, and obesity (BMI ≥ 30).30 The BRFSS is a state-based system of health surveys collecting information on health risk behaviors, preventive health practices, and health care access primarily related to chronic disease and injury. Telephone interviews are conducted with more than 350,000 adults in all 50 states, the District of Columbia, and US territories.31 No Olmsted County-specific data for these risk factors exist.
Unadjusted and age- and sex-adjusted incidence rates of MI and SCD were calculated for the 18 months before and 18 months after the implementation of each smoking law. The counts of events were used as the numerators and the denominators were the Olmsted County population as determined by census data for the years 1990, 2000, and 2010 with linear interpolation for intercensal years. Adjusted rates were directly standardized to the age and sex distribution of the 2000 US population. Standard errors and 95% confidence intervals (CI) were calculated based on the Poisson error distribution. Differences in incidence in the 18 months before and after each law were assessed with Poisson regression adjusting for age and sex and using an indicator variable with a value of 0 or 1 for the 18 months before and after the law, respectively. Specific counts for each time period, age, and sex were used as the unit of observation with the time period-, age- and sex-specific Olmsted County population as the offset. Interactions between age and time period were assessed to determine whether changes in incidence rates were dependent on age, and in all cases, no significant interactions were detected.
Cause of death was missing for 128 (3.7%) of the 3480 persons who died out-of-hospital during the 18 months before and after each smoke-free ordinance. To account for these missing data, multiple imputation methodology was used to create 5 complete imputed datasets.32 Analyses were performed for each imputed dataset, and the results were combined using Rubin’s rules.33 Nonlinear trends over time were explored using data from all years from 1995 to 2009. For these analyses, Poisson regression models were generated with the use of generalized additive models34 with calendar year as a smoothed term.
Analyses were performed using SAS version 9.2 (SAS Institute Inc, Cary, NC) and R. All aspects of the study were approved by the Mayo Clinic Institutional Review Board.
During the 18 months before and after each smoke-free ordinance, there were a total of 717 incident cases of MI and 514 people who experienced SCD. Demographic and clinical characteristics for the MI and SCD patients are presented in Table 1. No characteristics were found to differ significantly between pre- and post-ordinance time periods except for hyperlipidemia in persons experiencing SCD before and after Ordinance 1 (36.4% versus 54.0%, respectively; P=0.004).
The age- and sex-adjusted rate of MI was 150.8 per 100,000 (95% CI, 129.0–172.6) for the 18 months prior to Ordinance 1 and 144.6 per 100,000 (95% CI, 123.6–165.5) for the 18 months after Ordinance 1 (Table 2). The incidence of MI did not significantly decline during this time period (age- and sex-adjusted RR 0.96; 95% CI, 0.78–1.18; P=0.71).
Conversely, for the time period surrounding Ordinance 2, the incidence of MI adjusted for age and sex declined from 152.3 per 100,000 (95% CI, 131.4–173.3) to 100.7 per 100,000 (95% CI, 83.8–117.5). This equated to a 34% decline over the 18 months before and after the implementation of Ordinance 2 (adjusted RR 0.66; 95% CI, 0.53–0.82; P<0.01).
Over the entire study period comparing 18 months before Ordinance 1 and 18 months after Ordinance 2, we observed a 33% decline in the incidence of MI (adjusted RR 0.67; 95% CI, 0.53–0.83; P<0.01).
The annual unadjusted MI incidence rates from 1995–2009 are presented in Figure 1. A smoothing spline with 95% CI is superimposed on the actual rates. The test for nonlinearity was significant (P<0.01), with an inflection point occurring around year 2005.
No decline in SCD was observed for the 18 months before and after Ordinance 1 (adjusted RR 1.01; 95% CI, 0.80–1.27; P=0.96), with the age- and sex-adjusted rates of SCD being 109.1 per 100,000 (95% CI, 91.0–127.2) and 112.7 per 100,000 (95% CI, 94.3–131.0), respectively (Table 2). Similarly, there was not a significant change in rates of SCD 18 months before Ordinance 2 compared to the 18 months after Ordinance 2 (adjusted RR 1.17; 95% CI, 0.91–1.51; P=0.22). The age- and sex-adjusted rate of SCD was 78.8 per 100,000 (95% CI, 64.0–93.5) 18 months before the ordinance and 92.0 per 100,000 (95% CI, 75.7–108.3) 18 months after the ordinance.
There was a 17% decline in the incidence of SCD for the overall study period comparing the 18 months before Ordinance 1 to the 18 months after Ordinance 2 (RR 0.83; 95%CI, 0.65–1.06; P=0.13).
The annual SCD rates from 1995–2009 are presented in Figure 1. A smoothing spline with 95% CI is superimposed on the unadjusted rates. The P value for the test for nonlinearity was 0.086.
Based on the Minnesota BRFSS data, the self-reported smoking prevalence among adults decreased from 19.8% in 2000 to 14.9% in 2010 while the prevalence of diabetes and obesity increased and the prevalence of hypertension and hypercholesterolemia remained flat30 (Figures 2 and and33).
We report a substantial decline in the incidence of MI from 18 months before the smoke-free restaurant law was implemented, to 18 months after the comprehensive smoke-free workplace law was implemented 5 years later. Our observed decrease in the incidence of MI is similar to the 40% decrease in the incidence of MI in the first report in Helena, Montana.7 In a large study which included biomarker confirmation, the decrease in the rate of admission to Scottish hospitals decreased by 19%.14 This study was limited by its inclusion of only 9 hospitals which accounted for 64% of the country’s hospital admissions; thus the rates were not true incidence rates, and the time frame was much shorter than ours.
The mechanisms of the deleterious effect of SHS are diverse. As little as five minutes of exposure to SHS in nonsmokers reduces aortic distensibility35 and abdominal aortic stiffness is increased with SHS exposure in children.36 In nonsmokers, thirty minutes of SHS exposure produces an abrupt and dramatic reduction in coronary artery flow velocity reserve.37 Thirty minutes of SHS exposure leads to vascular injury characterized by mobilization of dysfunctional endothelial progenitor cells with blocked nitric oxide production, which is essential to endothelial function as its release mediates vasodilatation.38 SHS exposure in nonsmokers has been associated with lower HDL levels, increased markers of inflammation, increased serum fibrinogen and homocysteine, decreased antioxidant levels, and increased insulin resistance.39–43
While not embodying the “ideal design” as described by the Institute of Medicine report,16 our study addresses some key limitations by reporting data from a defined community with a large sample size and a prolonged period of observation. As our data constitute before-after comparisons in the absence of a comparison geographic area in which no smoke-free law has been implemented, its interpretation should also explicitly consider alternative causes of changes in MI incidence. To this end, the new diagnostic criteria for MI were deployed in 2000, and we have reported that these new criteria increased the number of MIs25, 26 and thus could mask a decline in incidence. The present results, however, are not contaminated by the change in biomarkers as all MIs were confirmed with CK/CKMB. No concurrent intervention could explain the observed trends during the time period of the study. In particular, while automated external defibrillators have been increasingly used in the city of Rochester, MN, the concurrent incidence of ventricular fibrillation out-of-hospital cardiac arrest had begun to level off prior to the implementation of the first smoke-free law.44 Further, the prevalence of smoking declined (Figure 2) while the rate of hypertension and hypercholesterolemia remained essentially constant, whereas the rate of diabetes and obesity increased30 (Figure 3).
Finally, one important consideration is the interpretation of the trends reported herein in light of known secular trends. Although the incidence of SCD has been declining over the past thirty years, the decrease in the incidence of SCD and MI accelerated over the time period of the implementation of these smoke-free workplace laws. There were other tobacco control activities in Minnesota during the time frame of this study including a 2001 mass media campaign focused on helping smokers to stop smoking using a tobacco quitline or clinic services and a 2004–2007 mass media campaign focused on the hazards of SHS. A 2005 “Health Impact” fee of $0.75 per pack of cigarettes was imposed followed by a $0.62 per pack increase in Federal excise tax. In addition to a decrease in smoking prevalence, during the time period of 1999–2010 were: per capita cigarette sales in Minnesota declined by 40%, and smoke-free homes increased from 64.5% (1999) to 74.8% (2003) and from 83.2% (2007) to 87.2% (2010).45
While the determinants of the secular trend in the incidence of MI and SCD cannot be determined with certainty in ecological analysis, particularly with concomitant other tobacco control activities, the acceleration of the trends (nonlinearity of the smoothing spline analysis for MI), while all other cardiovascular risk factors (except smoking prevalence) were either stable or increasing, support the critical role of smoke-free workplace laws in tobacco control efforts. The impact of smoke-free legislation is multifold: reducing the intensity of smoking among smokers, increasing quit rates, reducing smoking startups by teenagers, and reducing exposure to SHS. Thus, the impact can be expected to occur over a period of time before and after implementation. Previous trends in MI in Olmsted County were stable between 1987 and 2006.26 Herein, we report that MI incidence did not change during the 18 months before and the 18 months after Ordinance 1 (July 2000 - June 2003) which is consistent with these previously published data. Thereafter, there was a substantial decline in MI incidence from the 18 months before compared to the 18 months after Ordinance 2 (April 2006-March 2009) pointing to a notable discontinuity of the MI trends, within a time period where no other obvious factor could have plausibly played a large role.
Some limitations should be discussed to aid in the interpretation of the data. We examine temporal trends in MI and SCD concomitant to the implementation of smoke-free laws. This design is consistent with a natural experiment with its well-known limitation regarding causal inference. We recognize that misclassification of deaths occurs in death certificates; however, the study focuses on temporal trends which are unlikely to be confounded by the classification of deaths. We do not have county-specific prevalence data for smoking or other risk factors; however, the trends in Olmsted County are usually consistent with those observed in the Minnesota data30 (Figures 2 and and3).3). The population of Olmsted County is primarily Caucasian, and further studies are needed in communities of more diverse racial and ethnic composition. Further, we do not have self-reported exposure to SHS nor biochemical markers of SHS exposure, though we expect similar results to the Scottish study where self-reported SHS exposure, confirmed by salivary cotinine, decreased after the smoke-free law was implemented.14
Our study has several major strengths. It was conducted under the auspices of the REP, which has a long track record of robust epidemiological studies for over 50 years. Our results reflect a complete enumeration of the cases of MI and SCD in a well-defined community; and in particular, all MI and SCD cases were validated using rigorous epidemiological criteria.25, 29 The time period over which this study was conducted is longer than reported in most published studies, thereby affording greater power to detect significant trends.
We believe that SHS could be considered a major risk factor for MI, joining family history, hypertension, hyperlipidemia, diabetes mellitus, and low physical activity. Hence, all clinicians should ascertain SHS exposure and promote the elimination of SHS exposure to their lifestyle recommendations.46 Further, all clinicians should be encouraged to become advocates for effective tobacco control policies such as increased taxes, graphic labeling, smoke-free workplaces, and marketing and advertising restrictions, as smoking and SHS exposure are responsible for 10% of all cardiovascular deaths globally.47
SCD represents 60% of all deaths from CHD, and the majority occur in people previously not diagnosed with CHD who do not meet high-risk criteria as defined by clinical trials and cohort studies.48 Thus, the prevention of SCD hinges upon public health interventions focused on the primary prevention of CHD or the wider availability of automated external defibrillators and implantable cardioverter-defibrillators. We observed a statistically nonsignificant decline in the incidence of SCD which may reflect the relatively smaller number of events in the SCD group. These findings suggest that SHS exposure could be a risk factor for SCD. As this risk factor is highly modifiable, the expansion of smoke-free workplace policies could have a major public health impact by reducing the incidence of SCD.
The implementation of smoke-free workplace ordinances was associated with a substantial decreases in MI, the magnitude of which is not explained by community co-interventions or changes in known cardiovascular risk factors with the exception of smoking prevalence. SHS exposure should be considered a modifiable risk factor for MI. All people should avoid SHS exposure, and people with known CHD should have no exposure to SHS.
This study was supported in part by ClearWay Minnesota (PI, RD Hurt); R01 HL59205 from NHLBI/NIH (PI, VL Roger); and R01 AG034676 from NIA/NIH (Rochester Epidemiology Project). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
The authors have no conflicts of interest to declare.
Presented in part at the Annual Meeting of the American Heart Association, Orlando, Florida, November 2011.
Dr. Hurt had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.