Don’t Go Vaping My Heart: E-cigarette Exposure During Pregnancy Promotes Peripartum Ventricular Arrhythmias and Sympathetic Dominance

Abstract

Electronic cigarettes (E-cigs) are commonly presumed as a safer alternative to traditional cigarettes despite limited understanding of their health risks. This assumption may lead people, especially those in at-risk groups, to switch from traditional cigarettes to e-cigs, or to use e-cigs as their first form of nicotine consumption. Despite that pregnancy increases susceptibility to adverse cardiac events, a considerable fraction of pregnant women use e-cigs during gestation and postpartum. Pregnancy involves profound physiologic changes that increase risk for developing cardiac arrhythmias—disruptions in the normal rhythm of the heart that can promote ventricular fibrillation, cardiomyopathy, and sudden cardiac death. Additionally, studies have shown that e-cig aerosols can induce sympathetic nervous system dominance and evoke arrhythmias in mice. We posited that e-cig exposure during pregnancy destabilizes maternal cardiac autonomic modulation and induces ventricular arrhythmias. Using radiotelemetry, we found that gestational e-cig exposure accentuates pregnancy-associated sympathetic dominance and increases ventricular premature beats (VPBs) during the parturition period. Additionally, at three weeks postpartum (three weeks after exposure cessation), e-cig-exposed dams have more VPBs, shortened ventricular repolarization, and increased ejection fraction. Therefore, e-cig use during gestation promotes sympathetic dominance and ventricular arrhythmias during parturition. Importantly, these arrhythmias persist up to three weeks after cessation of exposure and parturition and are accompanied by accelerated repolarization and enhanced left ventricular systolic function consistent with sympathetic dominance. Thus, vaping during pregnancy may increase the incidence of peripartum arrhythmias, with these effects persisting well after e-cig cessation and accompanied by enhanced ventricular repolarization and systole.

New & Noteworthy

Although many women vape during pregnancy, the impacts on peripartum health remain largely unknown. We evaluated how e-cigarette exposures during pregnancy affect maternal autonomic balance and cardiac electrical and mechanical function. Gestational e-cigarette exposure accentuated sympathetic dominance in pregnant dams and increased ventricular premature beats during labor and at three weeks postpartum. Gestational e-cig exposures also shortened ventricular repolarization and increased ejection fraction and 3-methoxytyramine levels at 3 weeks after parturition and exposure cessation.

Introduction

E-cigarettes (e-cigs) are often presented as a safe alternative to smoking despite a poor understanding of their risks. Since their 2006 debut in the U.S., e-cigs have become increasingly popular among young adults.¹ Due to the limited information on the safety of vaping, scientific studies are urgently needed to rigorously test the health impacts of e-cigs, especially in vulnerable groups. Pregnancy is a state of exceptional cardiovascular vulnerability that could be adversely impacted by e-cig exposure. Furthermore, e-cig use prevalence has grown disproportionately for women of childbearing age relative to other ages,² with up to 15% of 19–30-year-old women reporting vaping in the past month from a survey in 2023.¹ Interestingly, the age of females most likely to use e-cigs coincides with the mean maternal age at first birth (27.4).³ Moreover, ~20% of smokers or ex-smokers who become pregnant use e-cigs during pregnancy rather than quitting inhaled nicotine products altogether.⁴ Given the prevalence of e-cig use during pregnancy, obstetricians urgently need more information on these products to advise their patients on the risks of e-cig use.⁵

Pregnancy is a major life event that elicits profound physiological adaptations, including hemodynamic and electrophysiologic changes.⁶ Importantly, even during normal healthy pregnancies, autonomic regulation shifts beginning at week 6 of gestation toward a state of sympathetic dominance.^7–9 Accordingly, heart rate (HR) increases during the first and second trimesters, while heart rate variability (HRV) indices, including the standard deviation of normal beat intervals (SDNN) and root mean squared of successive differences (RMSSD), decrease, implicating sympathetic dominance.^10,11 Notably, an imbalance in the autonomic nervous system toward enhanced sympathetic modulation is a significant cause of arrhythmias, yet it is a normal compensatory response to pregnancy.¹⁰ Additionally, multiple studies have found changes in ECG morphology during pregnancy, including shortened PR interval, prolonged QT interval and heart rate-corrected QT (QTc), and increased QT dispersion (QTd), with most reporting values within normal ranges.^12–16 These physiologic changes may contribute to ventricular premature beats (VPBs), which rank among the most common pregnancy-associated arrhythmias¹⁷ and occur in the majority of normal pregnancies.¹⁸

While pregnancy independently increases the risk for cardiac arrhythmias and cardiac arrest, observations in humans indicate vaping may also impair ventricular repolarization (increasing Tpe/QT, (T-peak-to-end/QT interval) Tp-e (T-peak-to-end), and Tp-e interval)^19,20 and promote sudden cardiac arrest.^21–23 Complemented by reports that e-cig exposures increase the inducibility of arrhythmias in male rodents,^24–27 we have repeatedly shown that acute e-cig exposure induces ventricular arrhythmias, and in some cases high-grade supraventricular block events, across both sexes of mice.^24,26,28 Longer-term (4-week) exposures in male mice transiently induced ventricular arrhythmias but consistently increased blood pressure, culminating after exposure in arrhythmia-, sympathetic-, and cardiomyopathy-associated changes in cardiac protein expression and phosphorylation, as well as persistent bradycardia and QTc prolongation.²⁸ Conversely, an 8-month (5 days/week) e-cig exposure of nulliparous female mice did not significantly alter HR or echocardiographic measures of left ventricular (LV) volumes or performance. ²⁹ Separately, a single-day exposure to PG:VG altered HR and HRV more markedly in males than in females.²⁴ Importantly, these studies did not investigate impacts on pregnant females. Because the impacts of vaping on cardiac rhythmicity during pregnancy remain largely unknown, we tested the hypothesis that e-cig exposure accentuates pregnancy-induced heart rate changes and evokes ventricular arrhythmias during pregnancy and postpartum. Here, we report that e-cig exposure in pregnant dams increases HR relative to air control, with effects sustained through gestational day (GD) 15 and accompanied by diminished RMSSD earlier in gestation. Interestingly, despite cessation of e-cig exposure, dams sustained increases in VPBs concurrent with accelerations in ventricular repolarization and increases in ejection fraction and 3-methoxytyramine (3MT) levels, demonstrating that gestational e-cig exposure has lasting cardiovascular effects.

Methods

Animal Studies

All animal procedures were in accordance with the institutional guidelines of the University of Louisville and were approved by the Institutional Animal Care and Use Committee. Before the study, mice were acclimated ≥1 week to the animal facility, which remained under controlled temperature (average: 21.8 °C) and humidity (average: 49.48%) with a 12h:12h light: dark cycle. Female and male, eight-week-old C57BL/6J mice (obtained from The Jackson Laboratory, Bar Harbor, Maine) were provided normal chow (Research Diets, #5010) and water ad libitum. After radio-transmitter implantation and recovery, females were assigned to either e-cig or filtered air groups by baseline HR and HRV prior to the study, ensuring no baseline differences between groups. All postpartum measurements were obtained three weeks following parturition to minimize maternal separation stress, as C57BL/6J mice can be weaned at 3 weeks old.³⁰ At the conclusion of the study, female mice were euthanized using pentobarbital (50 mg/kg) followed by whole blood collection via cardiac puncture in an EDTA-coated syringe (aliquoted in an EDTA tube, and centrifuged at 4°C and ≥ 4880 RPM for 5 minutes, and heart excision (as secondary euthanasia confirmation). All experimental procedures followed the ARRIVE guidelines.³¹

Radiotelemetry

Female mice were anesthetized with 2% isoflurane and subcutaneously implanted under aseptic conditions with radio-transmitters (ETA-F10, Data Sciences International, Inc., St. Paul, MN) equipped with ECG electrodes in a lead II position. Meloxicam (20mg/kg i.p.) was administered at the time of surgery and 24 hours post-operatively to reduce pain. All mice were allowed a minimum of 10 days for post-operative recovery before exposure initiation.

Timed Pregnancy

Nulliparous, single-housed mice were introduced to soiled bedding from age-matched males at approximately 10 weeks old to induce estrus, similar to other studies.³² Females were paired with age-matched males for 5 days, visually inspected daily for a copulatory plug during breeding, and weighed daily as a secondary measure to confirm pregnancy, as previously described.³² GD one is considered the day after identification of the copulatory plug. Once breeding was complete, mice were switched to breeder chow (Research Diets, #5012) purchased from Cincinnati Lab Supply INC. (Cincinnati, OH).

Air and E-cig Exposures

Telemetered female C57BL/6J mice were placed in SCIREQ inExpose whole body exposure chambers (inExpose, SCIREQ, Inc., Montreal, QC, Canada) for 165 min per exposure with dividers to avoid signal crosstalk. Mice were exposed to unflavored e-cig aerosols composed of 30% propylene glycol, 70% vegetable glycerin, and 5% nicotine benzoate salt administered via a mod device (10W, 1.5-Ohm coil SCIREQ, Inc., Montreal, QC, Canada). Unflavored e-cigs were used to avoid the compounding effects of flavorants observed in other studies.^24,27,28,33 Before the start of the exposures, every mouse underwent one day of acclimation to the chamber, followed by one day of HEPA-filtered air exposure for baseline ECG measurements. For both acclimation and air days, animals remained in the chamber for 165 minutes (duration of e-cig exposure). Each daily exposure involved 1 hour HEPA-filtered air followed by a 9-minute puffing phase (ten 4 second puffs every 30 seconds) and then a 9-minute washout phase involving HEPA-filtered air, repeated for a total of 5 cycles and then culminating with a 15-minute post-exposure period involving HEPA filtered air (Fig. 1A). Each female underwent daily exposure, beginning 5 days before breeding and continuing until parturition (Fig. 1A). E-cig aerosol levels within the exposure chamber were quantified using a Microdust pro (2958.86 ± 415.76 mg/m³ SEM). Additionally, changes in mod tank weights ( −0.72 ± 0.02 g) and filter weights (0.099 ± 0.004 g SEM; 1.10 ± 0.046 mg/puff SEM) were measured each day from before to after exposures to confirm and quantify e-cig aerosol production. Radiotelemetry monitoring was performed during exposures, in home cages overnight during pre-breeding and the parturition period (~24 hours), and at three weeks postpartum (~48 hours) over three days, allowing for continuous real-time ECG monitoring during exposures and, separately, within normal home cages.

Fig 1. Gestational e-cig exposure enhances sympathetic influence over chronotropy in early gestation and during the parturition period.

A, Gestational e-cig exposure regimen. Adult female C57BL/6J mice were exposed daily (90 puffs/day) to e-cig aerosols or filtered air (FA) beginning 5 days before breeding until birth of pups. B, E-cig exposure increases heart rate (HR) and decreases HRV during early gestation. Comparisons to pre-pregnancy air control (CTRL) exposure and concurrent filtered air, with values expressed as means during 15-min post-exposure phase. n=5 Air, n=4–5 E-cig. Significance at p<0.05 vs. CTRL (*) or vs. timematched filtered air (◆) by mixed effects analysis. Open circles indicate individual animal values. C: Gestational e-cig exposure decreases HRV during the parturition period. 1-hour means (± SEM) from home cage ECGs spanning 12:00–09:00. n=4 Air, n=4 E-cig. E-cig dams had significantly diminished SDNN from 05:00–08:00 and significantly diminished RMSSD from 01:00–02:00 and 04:00–08:00. Significance at p<0.05 vs. time-matched filtered air (*) by mixed effects analyses. One e-cig animal (CTRL) was excluded due to poorly defined QRS, and one e-cig dam was excluded on GD 16–18 due to dislodged electrode. D: Gestational e-cig exposure does notaffect HRV at three weeks postpartum. 3-hour means (± SEM; n=5 air, n=4) from home cage ECGs spanning ~48 hours over 3 days showed no effects on HR or HRV.

Electrocardiogram (ECG)

ECGs collected during the exposure protocol and in home cages were analyzed for HR, HRV, and arrhythmia in ECGauto 3.5 (emka Technologies, Paris, FR) while excluding signal artifacts, as previously described.²⁶ Following automated detection of QRS complexes, RR interval series were inspected, cleaned, and analyzed for time-domain HRV (root mean square of successive differences [RMSSD] and standard deviation of normal inter-beat intervals [SDNN]). Throughout each exposure, 1-minute averages were generated in a continuous series, as previously described.²⁶ Five-day HRV averages during the puffing, washout, and post-exposure phases were compared to prior filtered air exposure and between groups using mixed models. ECGs were additionally analyzed for ventricular premature beats, as previously described.²⁶ Ventricular premature beats (VPBs) that occurred within an episode of non-sustained ventricular tachycardia were quantified as individual arrhythmias. Mice were excluded from ECG measurements if signal quality was consistently inadequate for endpoint collection (e.g., dislodged electrode or poorly defined QRS). See figure legends for instances of exclusion. ECG morphology was quantified via automatic waveform detection with a library of ≥ 50 manually marked beats and visual inspection for fiducial point accuracy to derive intervals and waveform amplitudes.²⁴

Echocardiography

To determine whether e-cig use during pregnancy promotes persistent changes in cardiac structure and/or function, we performed transthoracic echocardiography on dams at three weeks postpartum (2% isoflurane induction, 1–1.5% maintenance) using a VisualSonics Vevo3100 preclinical imaging system, obtaining B-mode measurements as previously described.^34–36 The sonographer and image analyzer were blinded to treatment groups. ECGs were collected during this procedure for ECG morphology assessment using ECGauto 3.5 (see previous section).

Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) of plasma monoamines and their metabolites

For UPLC-MS/MS analysis, 60 μL of plasma samples were thawed on ice, vortexed, and diluted 1:5 with 0.2% formic acid in water containing isotopically labeled internal standards. The mixture was transferred to an Amicon Ultra-0.5 centrifugal filter device (3 kDa MWCO) and centrifuged at 14,000 g for 25 minutes at 4 °C. 10 μL of the resulting filtrate was analyzed using a UPLC-MS/MS system comprising an ACQUITY Premier I-Class binary solvent system coupled with a Xevo TQ Absolute Triple Quadrupole Mass Spectrometer (Waters Inc., MA). Separation was achieved on an ACQUITY UPLC HSS PFP column (150 mm × 2.1 mm, 1.8 μm; Waters Inc., MA) using a binary gradient of 0.2% formic acid in water (Solvent A) and methanol (Solvent B). For each analyte, three multiple reaction monitoring (MRM) transitions were monitored: one for quantification, one for confirmation, and one for the labeled internal standard. At least 12 data points were collected across each peak. Quantification was performed using peak area ratios against 9-point standard curves prepared before and after sample analysis.

Statistics

For HR and HRV, 1-minute averages measured throughout exposure were averaged into each exposure phase (acclimation, baseline, puffing, washout, and post-exposure). Mixed effect analyses (no repeated measures or Geisser-Greenhouse correction) were performed to test for differences between groups and back to the filtered air control day. Arrhythmia counts were normalized by sampling duration (VPBs per hour) and log-normalized, as previously described.²⁶ Unpaired t-tests were performed to test for statistical significance between groups in single average values of a given parameter over the entire gestational period, while mixed effect analyses were performed to test for differences between groups in home cage data spanning different phases of pregnancy (pre-breed, parturition, and postpartum. Any data that were deemed not normally distributed via a normality test were assessed via a Mann-Whitney test. All data are represented as mean ± SEM. ECG morphology and echocardiography data were analyzed via unpaired t-test for statistical significance between groups at three weeks postpartum. All data was screened for outliers using the ROUT outlier test (Q=1%). Only plasma catecholamine data yielded outliers that were then excluded; the remaining data were then assessed for correlations by combining e-cig and air dams for Pearson’s or Spearman’s coefficients, depending on normality. Statistical comparisons were made using GraphPad Prism 10 (GraphPad, San Diego, CA) with significance at P< 0.05.

Results

E-cig Exposure Increases Heart Rate and Diminishes HRV in Early Gestation.

Pregnant female mice exposed to either filtered air (FA) or e-cig aerosol throughout gestation (Fig. 1A) were assessed during exposures for changes in HR and HRV to determine the chronotropic and autonomic impacts of exposure during gestation. Comparisons were made between groups and pairwise relative to a single FA control day (CTRL) preceding all treatments. Compared to both the FA group and CTRL, e-cig exposure significantly increased maternal HR on gestational days (GD) 1–5, GD 6–10, and GD 11–15 during the post-exposure phase (Fig. 1B). Similarly, e-cig exposure also decreased the HRV indices SDNN and RMSSD on GD1–5 relative to CTRL and, for RMSSD only, relative to FA group (Fig. 1B). After GD 1–5, air-exposed dams also had diminished HRV compared to their CTRL, similar to e-cig exposed dams (Fig. 1B).

In home cages during the parturition period, e-cig-exposed dams had significantly diminished HRV at 01:00–02:00 (RMSSD only), 04:00 (RMSSD only), and 05:00–08:00 (RMSSD and SDNN) compared to the FA group (Fig. 1C), despite an unaltered HR. At three weeks postpartum, e-cig exposure did not affect maternal HR or HRV in home cages for 3-hour means (Fig. 1D) nor 1-hour means (data not shown). Thus, maternal e-cig exposure increases HR and decreases HRV earlier in gestation and diminishes HRV during the parturition period compared to a time-matched control group (CTRL).

Gestational e-cig exposure leads to fetal growth restriction.

E-cig exposure decreased the birth weight of offspring (1.14 g ± 0.09) compared to air exposure (1.29 g ± 0.08, p=0.02). However, e-cig exposure did not significantly change gestational length (Air: 20.1 ± 0.70 days; E-cig 18.7 ± 0.2 days p=0.20), gestational weight gain (Air: 14.49 ± 1.03, E-cig: 14.73 g ± 0.83 p=0.86), number of pups per litter (Air: 6.14 ± 0.91, E-cig: 6.67 ± 0.67 p=0.66), or the sex distribution of pups per litter (Air Males: 3.14 ± 0.59, E-cig Males 3.33 ± 0.67 (p=0.83)); Air Females: 3.00 ± 0.49, E-cig Females 3.33 ± 0.49 (p=0.64) [Air n=7 E-cig n=6 for all above parameters]. Thus, among common pregnancy-related outcomes, only birth weight was altered by gestational e-cig exposure.

Gestational E-cig Exposure Induces Ventricular Arrhythmias During Parturition and at Three Weeks Postpartum

To assess the arrhythmogenicity of e-cig exposure during pregnancy, VPBs were quantified from maternal ECGs during every daily exposure, one continuous ~24-hour period in home cages during pre-breeding and parturition, and ~48 hours over three days at three weeks postpartum. E-cig exposure did not significantly increase maternal VPBs during gestation (Fig. 2A); however, prior e-cig exposure significantly increased VPBs during the parturition period, and this effect persisted in home cages at three weeks after delivery and e-cig cessation (Fig. 2B). Thus, maternal e-cig exposure leads to increased incidence of VPBs during parturition and at three weeks postpartum.

Fig 2. Gestational e-cig aerosol inhalation induces spontaneous ventricular arrhythmias in dams during the parturition period and at three weeks after exposure cessation.

Ventricular premature beat (VPB) incidence rates (mean events/h/mouse) in pregnant mice during all gestational exposures (GD1-Labor), A, or in home-cages after exposures during prebreeding (pre-breed) and the parturition period, and at three weeks post-exposure and postpartum, B. Gestational data from 36 cumulative hours of mid-exposure ECGs sampled over 18 days, with significance at p<0.05 (*) in unpaired t-test. Post-exposure data from continuous home cage ECGs at pre-breed and parturition (~24h each), or at 3wk postpartum (3wk post, 48h) with significance at p<0.05 (*) by mixed effects analysis. n=4–6 Air, n=4–5 e-cig. Animals were excluded if they exhibited a poorly defined QRS. Circles indicate individual animal values.

Gestational E-cig Exposure Accelerates Ventricular Repolarization and Enhances Systolic Function at Three Weeks after Delivery and Exposure Cessation

At three weeks following parturition and cessation of exposure, dams were anesthetized for concurrent echocardiography and ECG acquisition and analysis. Relative to FA, prior gestational e-cig exposure decreased multiple indices of ventricular repolarization, including QT, QTc, JT, and JT/QT, without significantly affecting any other ECG parameters (Fig 3). Prior gestational e-cig exposure also increased ejection fraction and a trend for increased cardiac output compared to FA (Fig 4), but did not significantly alter heart rate, stroke volume, or end diastolic and systolic volumes. Thus, gestational e-cig exposure leads to a persistent increase in ejection fraction and acceleration of ventricular repolarization at three weeks postpartum (and three weeks post-e-cig exposure).

Fig 3. Gestational e-cig exposure expedites maternal ventricular repolarization three weeks after exposure cessation and delivery.

A: Representative averaged ECG tracings (each 1 sec, 7 beats) for e-cig and filtered air (FA) dams. B: Mean (± SEM) HR and intervals from ECGs collected during echocardiography at three weeks postpartum. n=7 Air n=6 E-cig. Circles indicate individual animal values. Significance at p<0.05 (*) and trend at p<0.10 (#) determined by unpaired t-test.

Fig 4. Gestational e-cig exposure increases maternal ejection fraction three weeks after exposure cessation and delivery of pups.

A: Representative B-mode echocardiography images from an air and e-cig exposed dam. B: Mean (± SEM) LV echocardiographic parameters from dams to air or e-cig aerosols daily (90 exposed puffs/day) during pregnancy and measured at 3 weeks post-cessation coinciding with 3 weeks postpartum. n=6 Air, n=6 E-cig. Significance at p<0.01 (**) and trend p<0.1 (#). SV, EDV, and ESV were assessed via unpaired t-test, and CO, EF, and HR were assessed via Mann-Whitney as they were not normally distributed. Abbreviations: CO, cardiac output; SV, stroke volume; HR, heart rate; EDV, end-diastolic volume; ESV, end-systolic volume; and EF, ejection fraction.

Gestational E-cig Exposure Increases 3-Methoxytyramine at Three Weeks after Delivery and Exposure Cessation.

Nicotine increases the release of dopamine, norepinephrine, and epinephrine, which are associated with increases in HR, blood pressure, and coronary vasoconstriction.^37,38 Thus plasma samples from three-week postpartum mice were assessed for changes in catecholamines. There were no statistically significant differences in epinephrine (Air: 3455 ± 1111 pg/ml n=5; E-cig: 9669 ± 4547 pg/ml n=5), norepinephrine (Air: 6633 ± 3549 pg/ml n=6; E-cig: 9742 ± 3907 pg/ml n=5), dopamine (Air: 197.8 ±79.14 pg/ml n=5; E-cig: 318 ± 57.33 pg/ml n=4), serotonin (Air: 89,668 ± 53,162 pg/ml n=5; E-cig: 325,954 ± 182,731 pg/ml n=5), metanephrine (Air: 640.5 ± 137.1 pg/ml n=6; E-cig: 626 ± 136.7pg/ml n=5), normetanephrine (Air: 1019 ± 114.5 pg/ml n=6; E-cig: 325,954 ± 182,731 pg/ml n=5), or 5-hydroxyindole-3-acetic acid (Air: 70,650 ± 6589 pg/ml n=6; E-cig: 77,139 ± 4598 pg/ml n=5; all p>0.05). Nonetheless, 3MT, a dopamine metabolite, was significantly increased in e-cig-exposed dams (562.8 ± 109.7 pg/ml) compared to FA-exposed dams (325.2 ± 18.72 pg/ml; p<0.05). We additionally tested whether catecholamines and their metabolites correlated with ECG morphology and ejection fraction. In collective analyses of all maternal samples, 3MT inversely correlated with QT, QTc, JT, and JT/QT (Pearson’s r’s: −0.6818, −0.6570, −0.7258, −0.8115, respectively, all p<0.05); however, it did not correlate with ejection fraction. Additional analyses of dopamine—which was not normally distributed—revealed a significant inverse correlation with PR (Spearman’s ranked r: −0.0368, p<0.05). Thus, gestational e-cig exposure leads to increased 3MT, which inversely correlates with shortened ventricular repolarization parameters (QT, QTc, JT, and JT/QT).

Discussion

Pregnancy is a unique condition that elicits a multitude of physiologic alterations impacting every organ system. The cardiovascular system undergoes many physiologic adaptations throughout pregnancy and postpartum, including elevated HR, diminished HRV, and prolonged ventricular repolarization.^{10–16,19,20} Pregnancy also corresponds with an increased likelihood of de novo arrhythmias.^15,39,40 Given the mounting evidence that e-cigarettes acutely disturb cardiac physiology, we sought to characterize the immediate and persistent impacts of gestational e-cig exposure on maternal cardiac electrical, autonomic, and mechanical function. Here, we demonstrated that exposure to e-cig aerosols throughout pregnancy accentuates gestational sympathetic dominance and elicits ventricular arrhythmias persisting from parturition until several weeks postpartum. Furthermore, e-cig aerosol exposure leads to shortened ventricular repolarization time as well as increased ejection fraction at three weeks following parturition and cessation of e-cig exposure.

The progression of pregnancy corresponds with gradual increases in HR and decreases in HRV,^7–11 as well as increases in muscle sympathetic nerve activity.^8,9,41,42 Likewise, e-cig aerosols evoke sympathetic dominance via nicotine^26,43,44 and β₁-adrenergic activation.²⁶ We recently demonstrated that nicotine correlates with—and β₁-adrenergic inhibition prevents—e-cig-induced VPBs, implicating nicotine’s sympathomimetic effects in this arrhythmogenesis.²⁸ Here, in pregnant dams, e-cig exposure diminished HRV at GD1–5 and increased HR from GD1–15 relative to air control, suggesting gestational e-cig exposure promotes sympathetic dominance throughout most of pregnancy.

At three weeks following parturition and cessation of exposures, e-cig-exposed dams had accelerated ventricular repolarization. Interestingly, multiple studies have demonstrated slight prolongation of QT and QTc during pregnancy,^12–16 which at late pregnancy in mice has been attributed to K_v4.3 downregulation, reduced total outward peak potassium current, and prolonged action potentials.⁴⁵ However, the state of these parameters during the postpartum period is largely unknown. Although it remains unclear whether the slight prolongation of repolarization during pregnancy is a salutary or adverse adaptation, reduced repolarization time, as seen in e-cig exposed dams, typically shortens ventricular myocyte action potential, which can decrease effective refractory periods (ERPs) in the atria and ventricles and thereby increase propensity for atrial and ventricular premature beats.⁴⁶ Such shortening in ERP and QT routinely stem from enhanced sympathetic tone⁴⁷, and could account at least partly for the increased VPBs seen in the parturition period and postpartum. Nonetheless, given that shortened QTc itself is associated with increased risk for cardiovascular mortality,⁴⁸ the impacts of gestational e-cig exposure on repolarization suggest that vaping during pregnancy may increase cardiovascular risk even several weeks after cessation. In addition, we noted a trend among e-cig dams toward shorter PR segment, which we found correlated inversely with circulating dopamine levels. These observations parallel our prior findings in a human cohort of smokers and non-smokers and further allude to autonomic mediation of the effects of tobacco products on atrioventricular conduction.⁴⁹

The concurrent increase in VPBs and decline in HRV during parturition hours after e-cig exposures contrast with our findings in male mice that VPBs dissipate in the initial days of a 20-day e-cig exposure and are not evident at post-exposure under basal conditions or after acute stress.²⁸ In that study, β₁-adrenergic inhibition prevented the acute arrhythmogenicity of e-cigs during an initial day of exposure. Accordingly, VPBs often result from sympathetic dominance.^50,51 Yet, these ventricular tachyarrhythmias can also activate vagal afferents and decrease parasympathetic efferent tone in the heart.⁵² Consequently, recurrent VPBs throughout the course of repeated e-cig exposures might durably enhance sympathetic tone to the heart. Although VPBs did not increase significantly during gestational e-cig exposures, this null finding might (due to underpowering) overlook biologically significant increases in arrhythmias that could alter autonomic modulation. Thus, we cannot exclude the reverse possibility of both sympathetic dominance and VPBs during the parturition period resulting from arrhythmias evoked earlier during exposures.

Regardless of the upstream mechanism, repeated exposure to e-cig aerosols in rodents can increase cardiac sympathetic innervation,²⁵ which has been tied to increased systolic function.^53,54 Of note, sympathetic stimulation evokes the release of norepinephrine from sympathetic nerves, thereby activating cardiac β-adrenergic receptors to modulate myocyte repolarization and contractility.⁵⁴ Importantly, sympathetic stimulation increases Ca²⁺ release from the sarcoplasmic reticulum, which activates cardiac myofilaments, augmenting myocyte contractility to meet elevated demand during sympathetic dominance, which in turn increases the risk for arrhythmias.⁵⁴ Additionally, increases in sympathetic nerve density can promote ventricular arrhythmias and may lead to sudden cardiac death.^54,55

Finally, the increase in 3MT among e-cig-exposed dams is consistent with our prior observations of sympathetic dominance in e-cig-exposed male mice.^24,26,28 3MT is a metabolite of dopamine, which increases the automaticity of Purkinje fibers and elicits atrial and ventricular arrhythmias in animals.⁵⁶ We saw an inverse relationship between 3MT and QT, QTc, JT, and JT/QT, which suggests gestational e-cig exposure may persistently accelerate ventricular repolarization via increased catecholamine secretion. As dopamine is also the parent compound for epinephrine and norepinephrine, these findings complement our findings in mice²⁸ and humans⁴⁹ that suggest use of nicotine-containing tobacco products alter cardiac electrophysiology secondary to sympathetic activation.

More investigations into the cardiovascular impacts of e-cig use during pregnancy are desperately needed to elucidate the arrhythmogenic impacts on mothers. While little is known about the effects of e-cig use during pregnancy, traditional cigarettes have been shown to increase maternal plasma norepinephrine and epinephrine levels, HR and blood pressure.^57,58 To our knowledge, only one prior study has addressed the implications of these effects, showing that inhaled nebulized nicotine vapor induces arrhythmias, including VPBs, in pregnant rats at GD16–20.⁵⁹ Our techniques allow for daily conscious ECG collection during exposures and at various timepoints in home cages to elucidate both real-time and post-exposure impacts. Thus, the current study provides novel insight into the potential impacts of e-cigs on maternal cardiovascular health during pregnancy and postpartum.

There are some important limitations to this study. First, humans do not typically use flavorless e-liquids. Although our prior work suggests nicotine salts²⁶ and menthol^24,28 exacerbate the autonomic and arrhythmogenic effects of e-cigs, our current work does not resolve the role of these constituents in the cardiotoxicity of e-cig exposures in pregnant dams. In addition, it is unclear how long the arrhythmogenic impacts may persist, given our endpoint was at three weeks postpartum. Future studies will test how flavorants and additives influence the effects of e-cig aerosols in pregnant dams, as studies have already suggested proarrhythmic effects of flavorants both in vivo and in vitro.^24,27,28,33 Because this study simulated direct exposure to primary e-cig aerosols, the cardiac impacts of exposures to secondary e-cig aerosols (typically at lower concentrations) during pregnancy remain unresolved. Likewise, our work does not address the potential influence of prior gestational e-cig use on cardiac responses to subsequent pregnancies, which correspond with greater gestational and postpartum increases in LV SV (stroke volume), CO (cardiac output), EDV (end diastolic volume), and systemic vascular resistance than initial pregnancies.⁶⁰ These changes are suspected to derive from hormonal stimuli with initial pregnancy imprinting the vasculature and altering cardiovascular responses to subsequent hormonal fluctuations.⁶⁰ Estrogen and progesterone modulate potassium channels to enhance slow delayed rectifier current (I_Ks) and diminish rapid delayed rectifier current (I_Kr).⁶¹ Meanwhile, relaxin which markedly increases through pregnancy, can upregulate cardiac sodium channel expression which may lead to arrhythmias.⁶¹ Furthermore, the rise in prolactin and oxytocin during the postpartum period has been shown to prolong cardiac repolarization and increase the propensity for arrhythmias in patients with Long QT Syndrome type 2.⁶² Hence, our findings warrant further work to assess how pregnancy-related fluctuations in sex hormones might underly the arrhythmogenic effects of e-cig use during pregnancy. Finally, assuming mothers typically do not stop vaping at childbirth, continuing e-cig exposures throughout the postpartum days 1–21 might enhance the generalizability of our findings; conversely, our choice to stop exposures at delivery provides compelling evidence for the persistence of gestational vaping-evoked cardiac electrical dysfunction. Nonetheless, the postpartum implications of e-cig use deserve further investigation, particularly to reveal how e-cigs can affect hormonal changes that likely underlie postpartum elevations in risk for arrhythmias.⁶³ For instance, lactation induces profound shifts in oxytocin and prolactin, which can exacerbate arrhythmia risk in susceptible women.⁶² Finally, more direct molecular experimentation could identify the mechanisms of gestational vaping-induced changes in cardiac electrical and mechanical performance to guide regulations and the development of treatment plans to reduce cardiac risk among women who vape during pregnancy.

Conclusions

These data provide a cornerstone for understanding the electrophysiologic changes imposed by vaping during pregnancy. Our findings suggest that vaping during pregnancy accentuates gestational sympathetic dominance and promotes ventricular arrhythmias and sympathetic regulation during the parturition period. Furthermore, these data indicate gestational vaping may increase arrhythmias while enhancing sympathetic regulation, ventricular systolic function, and ventricular repolarization during the postpartum period. Thus, e-cig use during pregnancy may induce long-term cardiac electrical dysfunction and autonomic imbalance well after termination of e-cig use. Collectively, this study demonstrates that gestational e-cig use can elicit a multitude of adverse cardiac electrophysiologic and autonomic changes in dams that can persist well after cessation of e-cig use and warrant further studies.