Differences in cardiac autonomic function contributes to heart rate abnormalities in POTS and IST.

Our objective was to examine the differences in cardiac autonomic function in Postural Tachycardia Syndrome (POTS) versus inappropriate sinus tachycardia (IST). Subjects (IST, n = 8; POTS, n = 12) were studied using standard measurements of the autonomic reflex screen, baroreflex function and spectral analysis. Data was compared to age/gender-matched controls (n = 20). The components of the autonomic reflex screen did not differ between groups. The exception was the significant but expected difference in postural heart rate increment on head-up tilt in POTS (47.9 ± 13.8; n = 12) compared to IST (30.9 ± 9.7; n = 8; p = 0.008). Accordingly the Orthostatic Intolerance Scale showed significantly greater orthostatic symptoms in POTS (2.6 ± 0.5; n = 12) versus IST patients (0.4 ± 0.5; n = 8; p < 0.001). Conversely, IST patients had a significantly higher resting heart rate (96 ± 12; n = 8) when compared to POTS patients (73 ± 12; n = 12; p = 0.001). There was a significant difference in vagal baroreflex sensitivity (BRSv) in POTS (8.21 ± 2.3, n = 12) compared to IST patients (5.30 ± 2.94, n = 8, p = 0.036) during the Valsalva maneuver. Only POTS subjects showed a significant increase in sympathovagal balance (LF/HF) with tilt (FFT, 8.29 ± 6.38; AR, 7.84 ± 5.24) compared to the supine position (FFT, 2.25 ± 1.75; AR, 1.99 ± 1.38; p < 0.05) for both frequency domains. Differences in cardiac autonomic function contribute to changes in positional and non-positional heart rate in postural tachycardia syndrome versus inappropriate sinus tachycardia. These findings shed further light on the autonomic dysfunction underlying POTS and IST.

Corkal JC ，Palamarchuk I ，Kimpinski K 《-》

Autonomic nervous system dysfunction in adolescents with postural orthostatic tachycardia syndrome and chronic fatigue syndrome is characterized by attenuated vagal baroreflex and potentiated sympathetic vasomotion.

Stewart JM 《PEDIATRIC RESEARCH》

Postural tachycardia syndrome and inappropriate sinus tachycardia: role of autonomic modulation and sinus node automaticity.

Nwazue VC ，Paranjape SY ，Black BK ，Biaggioni I ，Diedrich A ，Dupont WD ，Robertson D ，Raj SR ... -  《Journal of the American Heart Association》

When Sinus Tachycardia Becomes Too Much: Negative Effects of Excessive Upright Tachycardia on Cardiac Output in Vasovagal Syncope, Postural Tachycardia Syndrome, and Inappropriate Sinus Tachycardia.

Stewart JM ，Medow MS ，Visintainer P ，Sutton R ... -  《-》

Noninvasive assessment of autonomic cardiovascular activity in patients with inappropriate sinus tachycardia.

Inappropriate sinus tachycardia (IST) is a clinical syndrome characterized by excessive resting heart rate (HR) or disproportional HR increase during exercise. The etiology of IST has not been fully elucidated and remains controversial. The aim of the present study was to assess autonomic function by means of noninvasive tests and commonly available electrocardiographic methods in a series of consecutive patients with symptomatic IST. Twenty-four patients (37 ± 12 years; 20 women) with IST were enrolled. Six cardiovascular reflex tests were performed: (1) HR variation during slow deep breathing, (2) 30-to-15 ratio during active standing, (3) blood pressure response to standing, (4) cold face test, (5) Valsalva maneuver, and (6) blood pressure response to sustained handgrip. Intrinsic HR was calculated and compared with HR after pharmacologic denervation. Additionally, spontaneous baroreflex sensitivity and 24-hour HR variability indices were analyzed. In IST patients, intrinsic HR was significantly higher compared with control subjects. Most cardiovascular autonomic tests revealed abnormal or borderline results, particularly those reflecting mainly parasympathetic function. The spontaneous baroreflex gain was significantly reduced in IST patients. After controlled orthostatic stress and during Valsalva maneuver, impaired baroreflex function was observed. The sympathovagal balance from HR variability was preserved, but altered activity in both bands of frequency domain analysis was recorded. In conclusion, IST is a heterogenic syndrome with enhanced sinus node automaticity modulated by complex alterations of autonomic tone.

Ptaszynski P ，Kaczmarek K ，Klingenheben T ，Cygankiewicz I ，Ruta J ，Wranicz JK ... -  《-》