POSTURAL TACHYCARDIA SYNDROME - TIME-FREQUENCY MAPPING

Orthostatic tachycardia is common but its specificity remains uncertai n. Our preliminary work suggested that using autonomic function testin g in conjunction with time-frequency mapping (TFM), it might be possib le to characterize a subset of the postural tachycardia syndrome (POTS ), that is due to a restricted autonomic neuropathy. We describe 20 pa tients (17 women and 3 men, aged 14-43 years) with florid POTS and 20 controls (14 women and 6 men, aged 20-41 years). Autonomic failure was quantified by its distribution (cardiovagal, adrenergic and sudomotor ) and severity. a symptom profile was generated, and spectral indices, based on modified Wigner distribution during rest and head-up tilt (8 0 degrees), were evaluated. During tilt-up POTS patients differed from controls by an excessive heart rate (> 130 bpm) (P < 0.001), and high er diastolic pressure (P < 0.01). During rest, cardiovagal oscillation s (at respiratory frequencies [RF]) and slow rhythms at nonrespiratory frequencies (NONRF) (from 0.01 to 0.07 Hz) in R-R intervals (RRI) (P < 0.01) were reduced. Both RF and NONRF rhythms in RRI were further bl unted with tilt-up (P < 0.001). Slow adrenergic vasomotor rhythms in b lood (NONRF-Systolic BP (SBP)/RF-RRI) was dramatically increased in PO TS (P < 0.001). Distal postganglionic sudomotor failure was observed, and impairment of the BP responses to the Valsalva maneuver (phase II) suggested peripheral adrenergic dysfunction. Persistent orthostatic d izziness, tiredness, gastrointestinal symptoms and palpitations were c ommon in POTS patients. It is possible to identify a subset of POTS pa tients who have a length-dependent autonomic neuropathy, affecting the peripheral adrenergic and cardiovagal fibers, with relative preservat ion of cardiac adrenergic fibers.