DOI: 10.7272/q66w98b3
title: Increased vulnerability to atrial and ventricular arrhythmias caused by different types of inhaled tobacco or marijuana products

description: 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 an increased popularity of recreational
 marijuana, has raised concerns about the potential cardiovascular risk
 associated with their use. Objective: The present study aimed to
 investigate whether the use of novel tobacco products or marijuana can
 cause the development of proarrhythmic substrate and eventually lead to
 arrhythmias. Methods and results: Rats exposed to smoke from tobacco,
 marijuana, or cannabinoid-depleted marijuana, or to aerosol from
 electronic cigarettes or heated tobacco products, once per day for 8 weeks
 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 a
 higher level of sympathetic nerve innervation. Conclusions: 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.
description: <strong>Animals</strong>.
 Sprague-Dawley rats, 8–10
 weeks old, of both genders, were used for this study. Rats were exposed to one of the following
 products: Marlboro Red tobacco cigarettes (CIG), HTPs (IQOS), e-cigs
 (JUUL, Virginia Tobacco flavor, 5% nicotine), marijuana (MJ, ~10%
 delta-9-tetrahydrocannabinol (THC)), or “Placebo marijuana” (pb-MJ,
 cannabinoid-depleted
 marijuana, &lt;.01% THC).
 All required federal, state, and institutional approvals for acquisition
 and possession of marijuana and exposure of rodents were obtained.
 Air exposure was used as
 control. Group size was 8–16. <strong>Pathophysiological
 assessments</strong>.
 Systolic blood pressure, echocardiography, ECG telemetry, arrhythmia
 inducibility testing, and optical mapping were assayed during or after
 exposure as described previously (see Supplemental Materials).
  We measured conscious SBP by
 tail cuff on the first exposure day and at the end of the 2nd, 4th, 6th,
 and 8th week to determine progressively chronic effects. On each
 measurement day, SBP was measured twice, both before and after that day’s
 single exposure, to determine that day’s acute effect. Eight weeks
 post-exposure, ex vivo heart optical mapping was performed as described
 previously to test the susceptibility to arrhythmias originating from left
 and right atria and ventricles and to evaluate their electrophysiological
 characteristics. The APD at
 80% repolarization and calcium transient duration at 80%
 repolarization were measured after a series of 20×S1 pacing trains at the
 pacing cycle lengths of 150, 130, 120, 110, 100, 90, 80, and 70 ms. The
 effective refractory period and the susceptibility to both AF and VT were
 tested via programmed stimulations including extra-stimuli and overdrive
 pacing. AF was diagnosed as fast and irregular beating lasting more than 2
 seconds, whereas VT was determined as at least 6 non-driven consecutive
 ventricular premature beats. For histological analysis, hearts were weighed,
 fixed, and embedded in O.C.T compound for the following histological
 analyses. Heart coronal
 or transverse cryosections
 were stained with Sirius red/fast green to assess fibrosis or
 fluorescently stained for the assessment of the intrinsic cardiac nervous
 system (ICNS) and cardiac microvessels. ICNS as the autonomic nerve system
 inside the heart is vital for cardiac function and maintenance of normal heart rhythm.
 To visualize ICNS, we
 performed immunofluorescence staining for sympathetic and
 parasympathetic nerves. In
 order to quantify microvessels including capillaries and small
 precapillary arterioles with a cross area of 10–314
 μm2, slides were incubated with biotinylated Griffonia
 simplicifolia I lectin and then labeled with Alexa Fluor 488 Streptavidin
 (Invitrogen) as we previously described. Microvessel density (count/mm2 tissue) and area
 percentage were calculated. Ten views were taken randomly from
 subepicardium, midmural, and subendocardium for each section to calculate
 mean optical area that represented the average intensity level using Fiji
 ImageJ. <strong>Statistics</strong>. Data are shown as mean ± SD. P&lt;.05 was
 required for significance.