Table 1

Potential Mechanisms of Inappropriate Sinus Tachycardia

Intrinsic sinus node overactivity: channelopathy
Autonomic influence
 Decreased parasympathetic activity
  Hyposensitivity of muscarinic receptors
  Decreased efferent vagal activation
 Increased sympathetic activity
  β-receptor autoantibodies
 Combined
  Baroreceptor activity
Neurohormonal modulation
 Vasoactive intestinal polypeptide
 Histamine
 Norepinephrine
 Epinephrine
 Serotonin 1-A receptor activation
 Central GABA-nergic activation
 Substance P

GABA =gamma-aminobutyric acid.