Electronic cigarettes alter cardiac rhythm and heart rate variability hyperacutely in mice.

Aims: There has been an unprecedented rise in electronic cigarette (EC) usage likely because of its perception of being safer than smoking. Recent studies show that EC exposures impact heart rate (HR) and heart rate variability (HRV), but how they are affected by the timing and frequency of exposures remain unclear. We examined the electrocardiographic (EKG) effects induced by brief EC exposures over time, their relation to EC aerosol particle and mass concentrations, and potential to promote prooxidative effects in the lungs.

Methods & Results: Six 10-week-old C57BL/6J mice, implanted with telemetry devices to monitor EKG activity continuously, were exposed once per week for three weeks to two EC exposures, each lasting 15-min followed by 45-min post-exposure periods. Filtered air (primary) and PBS aerosol (secondary) were used as controls. After combining weeks, EC aerosol induced bradycardia and increased time domain parameters during EC exposures with significant reductions in the post-exposure periods. Log-transformed frequency domain parameters were significantly elevated during and after exposures (p < 0.001). HRV changes occurred within minutes with similar trends observed in particle number and mass concentrations of EC aerosol. HR and HRV varied by week and parameter, with Week 2 and 3 effects overshadowing those in Week 1. ECs induced prooxidative effects in the lungs as evidenced by elevated potential for hydroxyl radical generation in bronchoalveolar lavage fluid of exposed mice (p = 0.003).

Conclusion: Short-term EC exposures altered murine HR and HRV within minutes during and after exposures, effects that were modulated by the timing and frequency of EC exposures.