Inappropriate atrial sinus tachycardia (IAST)

Inappropriate atrial sinus tachycardia (IAST)

• IAST is a clinical syndrome with a relative or absolute increase in sinus rate out of proportion to physiological need
  • general agreement among clinicians and investigators that a heart rate exceeding 90-100 beats per minute (bpm) at rest or with minimal physiologic challenge is "inappropriate" (1)
    • P-wave morphology during tachycardia is nearly identical to that during normal sinus rhythm (1)
    • on a 24-hour Holter monitor, the mean heart rate exceeds 95 bpm, a daytime resting heart rate exceeds 95 bpm, or an increase in sinus rate from supine to upright position of more than 25-30 bpm
  • clinical manifestations of this syndrome are diverse, and the epidemiology of this patient population is not well defined
    • patients are primarily young women (15-50 years of age)
    • association of IAST patients with health professional workers has been recognized (1)
    • common symptoms include palpitations, light-headedness, presyncope, syncope, exercise intolerance, easy fatigue, dyspnoea, chest pain, myalgia, headache, abdominal discomfort, anxiety, and depression
  • underlying mechanisms of IAST are not well defined
    • proposed mechanisms include:
      • enhanced automaticity of the sinus node, altered autonomic responses manifest as increased sympathetic tone, either directly or via sympathetic receptor hypersensitivity or blunted parasympathetic tone, and impairment of baroreflex sensitivity

Reference:

• 1. Pacing Clin Electrophysiol. 2005 Oct;28(10):1112-21.
• 2. Castellanos A et al. Heart rate variability in inappropriate sinus tachycardia. Am J Cardiol 1998; 82: 531–534.
• 3. Sgarbossa EB et al. Autonomic imbalance in patients with inappropriate sinus tachycardia. (abstract) Am Coll Cardiol 1995; 25: 193A.