Inappropriate Sinus Tachycardia

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Contents 1 Introduction 2 Diagnosis 3 Activation Mapping and Ablation 4 References

Introduction

Inappropriate Sinus Tachycardia is a clinical syndrome with a relative or absolute increase of heart rate at rest or an exaggerated heart rate response inappropriate to the degree of physical or emotional stress. The clinical diagnosis is usually made after documentation of an inappropriately rapid heart rate in the absence of any cardiovascular or systemic disease. It is important to exclude secondary causes of sinus tachycardia such as hyperthyroidism, pheochromocytoma, decompensated cardiac or pulmonary disease, malignancy, chronic infection, and Postural Orthostatic Tachycardia Syndrome. Patients are primarily young women,and clinical symptoms range from intermittent palpitations to multiple complaints.

Diagnosis

1. Surface P-wave morphology similar to that observed during sinus rhythm
2. Symptoms of palpitations and/or presyncope clearly documented to be related to resting or easily provoked tachycardia
3. Heart Rate Findings
   1. Mean 24-hour Holter monitor heart rate higher than 95 bpm
   2. Daytime resting heart rate higher than 95 bpm
   3. Increase in sinus rate from supine to upright position of more than 25–30 bpm

Activation Mapping and Ablation

An activation map is made during Isoproterenol infusion at a rate of 1 to 2 mg/min to maintain a cycle length of >500 ms. Ablation is performed at the site of the earliest bipolar electrogram relative to the surface P wave (mean of 29 +/- 14 ms). When the P waves are obscured by the preceding T waves, short bursts of ventricular pacing at a cycle length 10 to 20 ms can be delivered to unmask the P wave. Careful attention must be made to test for phrenic nerve stimulation at ablation sites by pacing at an output of 10 mA with the ablation catheter before delivery of radiofrequency energy. .The end points of the procedure are reduction of the baseline sinus rate to <90/min, or a 20% or greater reduction in the sinus rate during infusion of isoproterenol.

References

1. Modification and Ablation for Inappropriate Sinus Tachycardia: Current Status. Cardiac Electrophysiology Review 2002;6:349–355
2. Heart rate variability in inappropriate sinus tachycardia. Am J Cardiol 1998;82:531–534.
3. Radiofrequency catheter modification of the sinus node for “inappropriate” sinus tachycardia. Circulation 1995;92:2919–2928.
4. Radiofrequency catheter ablation of inappropriate sinus tachycardia guided by activation mapping. J Am Coll Cardiol 2000;35:451–457.
5. Is sinus node modification appropriate for inappropriatesinus tachycardia with features of postural orthostatic tachycardia syndrome? Pacing Clin Electrophysiol 2001;24:217–230.