Inappropriate Tachycardia Syndrome: A Complex Arrhythmia Syndrome Not
Limited to the Sino-Atrial Node
Abstract
Introduction: Inappropriate sinus tachycardia (IST), a clinical syndrome
with distressing symptoms, is characterized by paroxysmal or persistent
sinus tachycardia in the absence of any identifiable primary etiology.
Sinus node modification is not first line therapy given frequent
recurrence and high complication rates. While medical therapy may be
effective, symptoms frequently persist. Our objective is to describe the
range of arrhythmias encountered during ablation in a cohort of IST
patients refractory to medical therapy and to further the understanding
of the etiology and mechanism of IST. Methods: We present a
retrospective review of 33 patients who underwent sinus node
modification for the treatment of therapy-refractory IST. Results:
Arrhythmias included IST in 33 patients (100%), atrial tachycardia or
frequent premature atrial contractions in 16 patients (48%), atrial
fibrillation in 7 patients (21%), typical and atypical atrial flutter
in 13 (39%) and 2 patients (6%), respectively, Wolff-Parkinson-White
syndrome in 3 patients (9%), AV nodal reentry tachycardia in 3 patients
(9%), and ventricular tachycardia or premature ventricular contractions
in 4 patients (12%). Accelerated atrioventricular junctional (AVJ)
tachycardia was present in 7/33 patients (21%), was refractory to
medical therapy and caused disabling symptoms in all seven patients.
Patients with AVJ tachycardia required extensive ablation at multiple
sites, and 3/7 patients became pacemaker dependent. Conclusion: In
patients undergoing SAN modification for IST, multiple arrhythmias were
encountered. Accelerated AVJ tachycardia was frequently encountered and
required extensive ablation of up-regulated tissue in the AVJ to improve
symptoms. Thus, the pathologic process underlying IST may not be limited
to the sinus node.