Marijuana and e-cigarettes could be just as harmful to the heart as traditional cigarettes

Previous studies have already proved that smoking tobacco increases the chances of arrhythmias (abnormal heart rhythm) and is a major factor in developing cardiovascular disease. On the other hand, e-cigarettes and heated tobacco products gained popularity as a result of the public opinion that they are less harmful than smoking tobacco.

But according to a new study conducted by a team of researchers at the University of California, San Francisco, the harmful effects of e-cigarettes and marijuana on the heart are similar to those of tobacco cigarettes.

"We found that cigarettes, e-cigarettes, and marijuana greatly interfere with the electrical activity, structure, and neural regulation of the heart," said lead author Huiliang Qiu, MD, Ph.D., a postdoctoral scholar in the UCSF Division of Cardiology.

"Often, any single change can lead to arrhythmia disease. Unfortunately, these adverse effects on the heart are quite comprehensive."

Exposing rats to various smokes

The heart must pump blood efficiently with the correct timing to function properly. Thanks to the nerves that control it, the heart has its own electrical control system. Plus, it has the ability of electrical impulses to move through the heart muscle in a way that synchronizes the entire heart to time the pumping correctly.

When the heart can't handle the electrical signals correctly, it can result in life-threatening arrhythmias since different regions of the heart will act asynchronously — essentially fighting against each other rather than functioning as a single efficient pump.

In this study, the research team employed rats to conduct an eight-week trial during which they exposed rats to Marlboro Red cigarette smoke, "vapor" from the popular e-cigarette JUUL, aerosol from the heated tobacco product IQOS, marijuana smoke, and smoke from modified marijuana that lacks all cannabinoids, compared to just air.

The rats inhaled clean air in between the five-second bursts of smoke or aerosol for a total of five minutes. This process was done once a day and five days a week for eight weeks. Over that time, the rats exposed to the products but not to air developed lower cardiac function and higher blood pressure.

All the products have similar effects

After eight weeks, the team conducted various tests on rats to determine the electrical and physical properties of their hearts.

The final results revealed that all the tested products caused increased scarring in the hearts, a decrease in the number of blood vessels, a negative change in the type of nerves found in the heart, a reduction in the important ability to vary heart rate, and a higher likelihood of developing arrhythmias.

"It's notable that all of these tobacco and marijuana products had such similar effects," said senior author Matthew Springer, Ph.D., a UCSF professor of cardiology. "And what's really striking is that this was caused by a single realistic smoking/vaping session per day."

"While rats are a good model for many cardiovascular effects of humans, there are still differences and one can't draw firm conclusions about effects on humans from rat studies alone," he added to explain a limitation of the study.

The bottom line: E-cigarettes, IQOS, and marijuana cigarettes involve many of the potential harmful effects of smoking tobacco

But he also stated that the results align with various reports about heart rhythm disturbances in those who use e-cigarettes or marijuana. The current study's findings of various physical disturbances in the heart, such as scarring and nerve changes, suggest a similar explanation.

"The bottom line is that e-cigarettes, IQOS, and marijuana cigarettes still involve many of the potential harmful effects of smoking tobacco," Springer said. "None of these products should be assumed to be a harmless replacement for smoking. In other words, just breathe air."