Physiology: E-cigarettes may affect normal heart function in mice

E-cigarette aerosols may temporarily disrupt normal cardiac functioning in mice, a study in Nature Communications reveals.

E-cigarettes deliver nicotine without combusting tobacco. As a result, e-cigarette aerosol contains far less carbon monoxide, tar and carcinogenic compounds than cigarette smoke, leading some to assert that e-cigarettes are less harmful. However, the impact of e-cigarettes aerosols on cardiac function and the roles of some of their constituents remain relatively unexamined.

In this study, Alex Carll and colleagues used mice to study the real-time effects of e-cigarette aerosols on the electrical properties of the heart. A series of experiments that exposed mice to 5 different e-cigarette aerosols, mainstream smoke from 2 distinct reference cigarettes, and acrolein (a gas produced by e-cigarettes and cigarettes) were performed by the authors with each experiment involving 6–8 mice. The mice were monitored, from a baseline, during inhalation exposure, early after exposure (4–9 minutes after each exposure), and late after exposure (9–28 minutes after final exposure). The inhalation of e-cigarette aerosols was found to induce cardiac arrhythmias, impair ventricular repolarization and alter heart rate in mice, all via modulation of the autonomic nervous system during exposure. The authors found that several of the effects, including increases in heart rate, remained late after exposure. However, others remained comparable to levels early after exposure. The authors note that effects were not monitored after 28 minutes following the final exposure.

The authors suggest that the nature and magnitude of these responses may depend on the chemicals in the e-liquids, such as nicotine, solvents and flavours. Menthol-flavoured e-liquids, for example, were shown to affect atrial conduction (the conduction of electrical impulses through the atria of the heart). In addition, e-cigarette solvents were found to disrupt cardiac rhythm more overtly in male mice than in females, hinting at a role for biological sex. However, only 4 female mice were used in these analyses and the authors note the need for caution when interpreting these findings.

The authors highlight that the responses observed in rodents may be distinct to those that may be seen in humans. They also note that repeated exposure to e-cigarette aerosols may lead to tolerance in humans, thereby decreasing cardiac responses, especially in adults with prior smoking history.