Huiliang Qiu, Matt Springer, and colleagues’ paper “Increased vulnerability to atrial and ventricular arrhythmias caused by different types of inhaled tobacco or marijuana products” makes two important points: (1) even very short daily exposures to tobacco and marijuana products have serious cumulative effects on the heart, and (2) nicotine and THC, the psychoactive components of these products, are not necessary to produce these adverse effects.
They drew these conclusions based on experiments in which they had rats smoke Juul e-cigarettes, Marlboro cigarettes, IQOS heated tobacco products and marijuana, including products without nicotine or THC, once a day, 5 days a week for 8 weeks. They took care to ensure that the exposures represented actual smoking just 10 puffs of a single cigarette or a single vaping session over 5 minutes.
They found that all these products caused comparable pathophysiological changes, including development of high blood pressure, electrical, structural and neural changes that all increase the development of irregular heart beats (arrythmias). They also found that hearts enlarged (a bad thing), their ability to pump blood measured by ejection fraction (the fraction of blood in the heart pumped on each beat) was reduced, and there was also a reduction in heart rate variability, a measure of susceptibility to mortality after a heart attack and susceptibility to arrhythmias (the neural control part) among other bad things.
The structural changes they found were both at the level of the whole heart (it got bigger) and at the cellular level where the number of small blood vessels in the heart dropped and fibrosis increased.
While a study of rats – you could not ethically do this experiment on people – the rat is an accepted model relevant to understanding cardiac disease in humans.
This paper adds important information demonstrating that the adverse effects of using all these products occur quickly and at low doses. The similarity of effects across products is also evidence against the FDA’s assumption that small differences between products can have substantial effects on risk.
NBC Bay Area did a good story explaining the study, including an interview with Matt Springer, which is available here.
Here is the abstract:
Background. The emergence of a plethora of new tobacco products marketed as being less harmful than smoking, such as electronic cigarettes and heated tobacco products, and the increased popularity of recreational marijuana have raised concerns about the potential cardiovascular risk associated with their use.
Objective. The purpose of this study was to investigate whether the use of novel tobacco products or marijuana can cause the development of proarrhythmic substrate and eventually lead to arrhythmias.
Methods. Rats were exposed to smoke from tobacco, marijuana, or cannabinoid-depleted marijuana, to aerosol from electronic cigarettes or heated tobacco products, or to clean air once per day for 8 weeks, following by assays for blood pressure, cardiac function, ex vivo electrophysiology, and histochemistry.
Results. The rats exposed to tobacco or marijuana products exhibited progressively increased systolic blood pressure, decreased cardiac systolic function with chamber dilation, and reduced overall heart rate variability, relative to the clean air negative control group. Atrial fibrillation and ventricular tachycardia testing by ex vivo optical mapping revealed a significantly higher susceptibility to each, with a shortened effective refractory period and prolonged calcium transient duration. Histological analysis indicated that in all exposure conditions except for air, exposure to smoke or aerosol from tobacco or marijuana products caused severe fibrosis with decreased microvessel density and higher level of sympathetic nerve innervation.
Conclusion. These pathophysiological results indicate that tobacco and marijuana products can induce arrhythmogenic substrates involved in cardiac electrical, structural, and neural remodeling, facilitating the development of arrhythmias.
The UCSF press release for the study is here.
The full citation is: Huiliang Qiu, Hao Zhang, Daniel D. Han, Ronak Derakhshandeh, Xiaoyin Wang, Natasha Goyal, Mina Navabzadeh, Poonam Rao, Emily E. Wilson, Leila Mohammadi, Jeffrey E. Olgin, Matthew L. Springer. Increased vulnerability to atrial and ventricular arrhythmias caused by different types of inhaled tobacco or marijuana products. Heart Rhythm. 2022; https://doi.org/10.1016/j.hrthm.2022.09.021. It is available for free here.