These electronic devices used as a substitute for conventional tobacco contain substances that can temporarily disrupt normal cardiac function in rodents, a study published in Nature Communications reveals.
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E-cigarettes deliver nicotine without burning tobacco. As a result, the aerosol from these devices contains far less carbon monoxide, tar and carcinogenic compounds than cigarette smoke, which has led some to claim that they are less harmful.
However, the impact of e-cigarette aerosols on heart function and the role of some of their components remains largely unknown.
Now, work by researchers at the University of Louisville’s Christina Lee Brown Envirome Institute (USA) has found that exposure to e-cigarette aerosols promotes arrhythmias and cardiac electrical dysfunction in mice. The results are published in the journal Nature Communications.
According to Alex Carll, a researcher at the US university’s Department of Physiology and leader of the study, “short-term exposure of mice to e-cigarette aerosols altered their heart rhythm, causing cardiac arrhythmias in the form of skipped beats and premature beats”.
Carll notes that “most of the aerosols used slowed the heart rate during inhalations and accelerated it immediately afterwards, while altering the electrical conduction measured on electrocardiograms”.
Human responses may differ
The researcher qualifies that, “although this is not a direct test of cardiac injury, and human responses may differ from those of mice, the study demonstrates that the use of e-cigarettes, with certain flavours or substances used as a solvent vehicle, may increase the risk of atrial or ventricular fibrillation and sudden cardiac arrest”.
The authors analysed the cardiac impact of inhaling aerosols used in these devices and coming only from the two main ingredients of the liquids (propylene glycol and nicotine-free vegetable glycerin) or nicotine-flavoured liquids.
They found that, with all aerosols, the mice’s heart rate slowed during inhalation exposure and accelerated afterwards, while heart rate variability decreased, suggesting fight-or-flight stress responses. In addition, exposure to menthol or propylene glycol-flavoured liquid caused ventricular arrhythmias and other heart conduction irregularities.
More studies are needed on the effects on the heart
Carll says they decided to conduct this study because “there remains a great deal of uncertainty about the effects of e-cigarettes on the heart. It was already known that exposure to many of the compounds in the aerosols used, such as nicotine, gases and particulate matter, could alter cardiac function in a dose-related manner; however, the immediate impacts of e-cigarettes on the electrical function of the heart were largely unstudied.
Asked whether the results obtained in this work in mice can be extrapolated to humans, the researcher points out that “studies in humans have shown that e-cigarettes can acutely increase the heart rate and alter the conduction of the heart so that arrhythmias occur”.
Our results are consistent with and build on these observations,” he adds, “as they also show that e-cigarettes can acutely induce arrhythmias, albeit in mice. Although there are some important differences between the cardiopulmonary systems of mice and humans, the effects we observed are more likely to reflect the impacts in new or young users of vaping, as the mice in the experiment were not exposed to long-term tobacco smoke prior to exposure to e-cigarettes.
Our findings show that the ingredients in e-cigarette liquids promote arrhythmias. Therefore, more research is needed on the cardiac effects of these components in both animals and humans.
Carll stresses that his team’s findings “showing that specific ingredients in e-cigarette liquids promote arrhythmias indicate that there is an urgent need for more research on the cardiac effects of these compounds in both animals and humans”.
The authors of the paper also note that responses in rodents may differ from those in humans. In addition, they point out that repeated exposure to e-cigarette aerosols may lead to tolerance in humans, thereby decreasing cardiac responses, especially in adults with a history of smoking.