Fu, Qi

Sinus tachycardia (ST) is ubiquitous, but its presence outside of normal physiological triggers in otherwise healthy individuals remains a commonly encountered phenomenon in medical practice. In many cases, ST can be readily explained by a current medical condition that precipitates an increase in the sinus rate, but ST at rest without physiological triggers may also represent a spectrum of normal. In other cases, ST may not have an easily explainable cause but may represent serious underlying pathology and can be associated with intolerable symptoms. The classification of ST, consideration of possible etiologies, as well as the decisions of when and how to intervene can be difficult. ST can be classified as secondary to a specific, usually treatable, medical condition (eg, pulmonary embolism, anemia, infection, or hyperthyroidism) or be related to several incompletely defined conditions (eg, inappropriate ST, postural tachycardia syndrome, mast cell disorder, or post-COVID syndrome). While cardiologists and cardiac electrophysiologists often evaluate patients with symptoms associated with persistent or paroxysmal ST, an optimal approach remains uncertain. Due to the many possible conditions associated with ST, and an overlap in medical specialists who see these patients, the inclusion of experts in different fields is essential for a more comprehensive understanding. This article is unique in that it was composed by international experts in Neurology, Psychology, Autonomic Medicine, Allergy and Immunology, Exercise Physiology, Pulmonology and Critical Care Medicine, Endocrinology, Cardiology, and Cardiac Electrophysiology in the hope that it will facilitate a more complete understanding and thereby result in the better care of patients with ST.

Some studies report an increase of resting muscle sympathetic nerve activity (MSNA) during the midluteal (ML) phase of the menstrual cycle when compared to the early follicular phase (EF), while others do not. The inconsistent findings may be due, in part, to variable surges in estradiol and progesterone. We tested the hypothesis that the degree of sympathoexcitation during the ML phase (ΔMSNA) is associated with changes in estradiol (ΔE 2 ) and progesterone (ΔP). Retrospective analysis of previous studies with recordings of mean arterial pressure (MAP), MSNA, E 2 , and P during both EF and ML phases yielded 30 eumenorrheic women (age, 18–51 yrs). ML phase increased E 2 (37±2 to 117±9 pg/ml; p<.001), P (1±0 to 11±1 ng/ml; p<.001), and MSNA (12±1 to 15±1 bursts/min; p=.02), but did not alter MAP (83±2 to 83±2 mmHg; p=.91). ΔMSNA was correlated to ΔE 2 (r=−.50, p=.005) and ΔE 2 /ΔP (r=−.52, p=.004), but not ΔP (r=.21, p=.26). There was no association between ΔMAP and ΔE 2 (r=−.13, p=.49), ΔP (r=−.04, p=.83), or ΔE 2 /ΔP (r<.01, p=.98). In conclusion, sympathoexcitatory responses to the ML phase appear to be associated with the degree of sex steroid surges. While E 2 had a stronger influence on MSNA than P, it is worthy to note that a strong association with ΔMSNA persisted when both ΔE 2 and ΔP were considered. This dynamic interaction between E 2 , P, and MSNA likely explains previously reported inconsistencies in the field. Supported by NIH.

The relationship between mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), and total peripheral resistance (TPR) is altered in young women versus men and postmenopausal women due to endogenous sex hormone differences. Exogenous sex hormones in the form of oral contraceptive pills (OCPs) may further affect this relationship. We performed a retrospective review of 136 premenopausal women in whom MSNA and arterial pressure were measured, including 78 women with natural menstrual cycles in the early follicular phase (26±1 yr) and 58 women in the placebo phase of OCPs (24±1 yr). TPR and cardiac output (CO) were measured in a subset of women in whom continuous intra‐arterial blood pressure was recorded. Compared to those with natural menstrual cycles, women on OCPs had greater MAP (89±1 vs. 84±1 mmHg, p<0.01) and tended to have lower MSNA (15±1 vs. 18±1 bursts/100 heart beats, p=0.06). MAP and MSNA were positively correlated (r=0.22, p<0.05), TPR and MSNA were positively associated (r=0.41, p<0.05) and CO and MSNA (r=‐0.44, p<0.05) were inversely associated in naturally cycling women (n=26) but not in women on OCPs (r=0.15, r=0.11, r=‐0.01, respectively; p>0.05; n=38). In contrast to naturally cycling women, there appears to be no relationship between MSNA and hemodynamics in women on OCPs, suggesting that these women may regulate their blood pressure differently than women. Grant Funding Source : Supported by NIH

Endogenous female sex hormones influence muscle sympathetic nerve activity (MSNA), a regulator of arterial blood pressure and important factor in hypertension development. Although ≈80% of American women report using hormonal contraceptives sometime during their life, the influence of combined oral contraceptives (OCs) on MSNA and systemic hemodynamics remains equivocal. The goal of this study was to determine whether women taking OCs have altered MSNA and hemodynamics (cardiac output and total peripheral resistance) at rest during the placebo phase of OC use compared with women with natural menstrual cycles during the early follicular phase. We retrospectively analyzed data from studies in which healthy, premenopausal women (aged 18–35 years) participated. We collected MSNA values at rest and hemodynamic measurements in women taking OCs (n=53; 25±4 years) and women with natural menstrual cycles (n=74; 25±4 years). Blood pressure was higher in women taking OCs versus those with natural menstrual cycles (mean arterial pressure, 89±1 versus 85±1 mm Hg, respectively; P =0.01), although MSNA was similar in both groups (MSNA burst incidence, 16±1 versus 18±1 bursts/100 heartbeats, respectively; P =0.19). In a subset of women in which detailed hemodynamic data were available, those taking OCs (n=33) had similar cardiac output (4.9±0.2 versus 4.7±0.2 L/min, respectively; P =0.47) and total peripheral resistance (19.2±0.8 versus 20.0±0.9 U, respectively; P =0.51) as women with natural menstrual cycles (n=22). In conclusion, women taking OCs have higher resting blood pressure and similar MSNA and hemodynamics during the placebo phase of OC use when compared with naturally menstruating women in the early follicular phase.

The influence of the ovarian cycle on muscle sympathetic nerve activity (MSNA) remains controversial. Some studies report an increase of resting MSNA during the mid luteal (ML) phase of the ovarian cycle compared with the early follicular phase, whereas other studies do not. These inconsistent findings may be attributable, in part, to the variable surges in estradiol and progesterone. We tested the hypothesis that the degree of sympathoexcitation during the ML phase (ΔMSNA) is associated with changes in estradiol (ΔE 2 ) and progesterone (ΔP). Multiple regression analysis of data from previous studies with complete recordings of mean arterial pressure, MSNA, E 2 , and P during both early follicular and ML phases were available from 30 eumenorrheic women (age, 28±1 years; body mass index, 23±0 kg/m 2 ). ML phase increased E 2 (37±2 to 117±9 pg/mL; P <0.001), P (1±0 to 11±1 ng/mL; P <0.001), and MSNA (12±1 to 15±1 bursts/min; P =0.02), but did not alter mean arterial pressure (83±2 to 83±2 mm Hg; P =0.91). ΔMSNA was correlated with ΔE 2 ( r =−0.50, P =0.003) and ΔE 2 /ΔP ( r =−0.52, P =0.002) but not ΔP ( r =0.21, P =0.13). There was no association between Δmean arterial pressure and ΔE 2 ( r =−0.13, P =0.49), ΔP ( r =−0.04, P =0.83), or ΔE 2 /ΔP ( r <0.01, P =0.98). In conclusion, sympathoexcitation during the ML phase of the ovarian cycle seems to be dependent, in part, on the degree of sex steroid surges. This dynamic interaction among E 2 , P, and MSNA likely explains previously reported inconsistencies in the field; it remains possible that other sex steroids, such as testosterone, might explain further variance.