New York, Jan 8 (IANS): The nicotine in certain types of e-cigarettes may be more harmful than others, increasing the risk for irregular heartbeat or heart arrhythmias, according to a study.

A popular claim is that nicotine in e-cigarettes is relatively harmless, whereas additives and combustion products largely account for the harms of traditional cigarettes.

The research, which tested the effects of e-cigarettes with various types and doses of nicotine in animal models, showed that the nicotine form contained in pod-based e-cigarettes, nicotine salts, led to heart arrhythmias, particularly at higher doses.

In the study, published in the journal Nicotine and Tobacco Research, researchers compared heart rate and heart rate variability in mice exposed to vape aerosols containing different types of nicotine.

The aerosols contained either freebase nicotine, used in older types of e-cigarettes; nicotine salts, used in Juul and other pod-based e-cigarettes; or racemic freebase nicotine, simulating the recently popularised synthetic nicotine; and their effects were compared to nicotine-free e-cigarette aerosols or air.

In addition, the research team delivered increasing concentrations of nicotine over time, from 1 per cent to 2.5 per cent to 5 per cent.

The nicotine salts induced cardiac arrhythmias more potently than freebase nicotine, and the cardiac arrhythmias increased with the higher concentrations of nicotine.

"This suggests that nicotine is harmful to the heart and counters popular claims that the nicotine itself is harmless," said Alex Carll, Assistant Professor in Department of Physiology, at University of Louisville (UofL).

"Our findings provide new evidence that nicotine type and concentration modify the adverse cardiovascular effects of e-cigarette aerosols, which may have important regulatory implications," he added.

The study also revealed that the higher levels of nicotine salts increased sympathetic nervous system activity, also known as the fight-or-flight response, by stimulating the same receptor that is inhibited by beta-blockers, heart medications which are prescribed to treat cardiac arrhythmias.

In the autonomic nervous system, sympathetic dominance increases the fight-or-flight response in bodily functions, including heart rate.

"The nicotine in e-cigarettes causes irregular heartbeats (arrhythmias) in a dose-dependent manner by stimulating the very receptor that many heart medications are designed to inhibit," Carll said.

The findings conclude that inhalation of e-cig aerosols from nicotine-salt-containing e-liquids could increase cardiovascular risks by inducing sympathetic dominance and cardiac arrhythmias.

The researchers concluded that if these results are confirmed in humans, regulating nicotine salts through minimum pH standards or limits on acid additives in e-liquids may mitigate the public health risks of vaping.

Even without regulatory changes, however, the research suggests that users may reduce potential harm by opting for e-cigarettes with freebase nicotine instead of nicotine salts or using e-cigarettes with a lower nicotine content.