It is widely known that people who smoke have a higher risk of myocardial infarction (MI) than those who do not but the contributions to heart attacks from nicotine itself or from its delivery systems are still debatable. It has been well documented that nicotine increases blood pressure, which contributes to the risk of heart attacks but nicotine alone does not account for all increased risk. After all, people who switch to over-the-counter nicotine replacements dramatically decrease  their risk of heart attack rather quickly. And further, the use of traditional nicotine replacements such as nicotine gum is not related  to increased hospitalization for cardiovascular conditions nor are adverse cardiac events in people using the nicotine patch increased compared to those using a placebo.
This is because the main risk for cardiovascular disease and cardiac events is the carbon monoxide, toxins and particulate matters present in tobacco smoke. Although there are low levels of particulate matter and some toxins (although at concentrations far lower  than combustible cigarettes) present in e-cigarettes, there is no strong evidence to suggest that the levels present in e-cigarettes pose a risk of myocardial infarction. And further, levels actually present are below recommended safety thresholds.
Despite such available data, a recently published study, “Association Between Electronic Cigarette Use and Myocardial Infarction ,” found that daily e-cigarette users are almost twice as likely as non-users to have a heart attack.
Unfortunately, however, the study’s methodology poses major concerns:
- Its basic premise—that the increased odds of MI are independent of and in addition to the risks associated with combustible use simply cannot be supported by the data presented. This is because the authors did not account for the temporality of events (e.g., that e-cigarette use preceded the MI). Since e-cigarettes only entered the U.S. market roughly 10 years ago, it is likely that many current, daily e-cigarette users became e-cigarette users after their MI rather than before—perhaps as an attempt to prevent future cardiac events. This oversight increases the potential for differential misclassification bias. If it is true that current, daily e-cigarette users had experienced MI before switching from combustibles, the study’s results will likely overestimate the true risks associated with e-cigarette use rather than underestimate them, as the authors state.
- The authors have not provided sufficient evidence that both cigarette smoking and e-cigarette use do not interact to affect the rate of MI. Although they briefly mention that the effect of e-cigarette use did not interact with current smoking to influence the rate of MI (which would indicate that dual use has no effect), given the problems outlined above, it is entirely possible that an interaction between the two exposures exists. Although not statistically significant in this model, it is possible that the misclassification of MI occurrence based on current e-cigarette and/or combustible cigarettes eliminated the association between MI and dual use. The authors go on to describe how to estimate MI risk from combinations of behaviors using their model, which is contingent upon there being no interaction between smoking and e-cigarette use. Nevertheless, the authors emphasize this attribute.
Despite such flaws, the study does include one particularly interesting finding: namely, in its population, 51.5 percent of daily e-cigarette users are former smokers (and 95 percent of daily e-cigarette users are former, occasional or daily smokers), 2.8 percent are daily dual users (meaning that they use both traditional and electronic cigarettes). However, only 0.01 percent of never-smokers are daily e-cigarette users. This confirms other studies  showing that the overwhelming majority of e-cigarette users are experienced smokers in some form. It also highlights the relationship between traditional tobacco use and e-cigarette use. Put simply, a person who has never used the more dangerous method is almost entirely unlikely to pick up a brand new habit. This suggests that for most people who smoke e-cigarettes, the decision to use them is likely an attempt to choose a safer alternative.
Combustible cigarette smoking continues to kill over 400,000 people every year in the United States alone. For this reason, the wide availability of safer alternatives is key to improving health outcomes. It is therefore concerning that any research on this topic claiming to be conducted in the interests of public health would include such flaws. What is even more concerning, however, is that such research will almost certainly lead to headlines and conclusions that will unnecessarily deter current smokers from switching to these less-risky products. Interventions and responses to decrease the devastation that results from smoking must be based on properly conducted research. Accordingly, public health advocates must vociferously discourage the propagation of this kind of misinformation.
- “dramatically decrease”: https://www.rcplondon.ac.uk/projects/outputs/nicotine-without-smoke-tobacco-harm-reduction-0
- “is not related”: https://www.nejm.org/doi/full/10.1056/NEJM199612123352402
- “far lower”: https://tobaccocontrol.bmj.com/content/23/2/133
- “Association Between Electronic Cigarette Use and Myocardial Infarction”: https://www.ajpmonline.org/article/S0749-3797(18)31871-3/fulltext
- “other studies”: https://harmreductionjournal.biomedcentral.com/articles/10.1186/s12954-018-0238-6