Syndrome of inappropriate sinus tachycardia refers to sinus node dysfunction causing rapid, physiologically inappropriate, heart rates. Symptoms are pronounced and include palpitations, orthostatic and exercise intolerance, weakness, fatigue, dyspnea, chest discomfort, and anxiety. Diagnosis is by electrocardiography. Treatment is augmentation of vagal tone, reduction of sympathetic tone, and reduction of sinus nodal rate.
(See also Overview of Arrhythmias.)
Syndrome of inappropriate sinus tachycardia is a defined as the persistent or paroxysmal presence of a sinus heart rate > 100 beats/minute with a mean 24-hour heart rate > 90 beats/minute in the absence of a physiologic or evident secondary cause associated with distressing symptoms (1) dominated by palpitations, orthostatic intolerance, and exercise intolerance.
Syndrome of inappropriate sinus tachycardia mainly affects females in their late second decade to mid fourth decade (2).
General references
1. Sheldon RS, Grubb BP 2nd, Olshansky B, et al: 2015 heart rhythm society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm 12(6):e41–e63, 2015. doi: 10.1016/j.hrthm.2015.03.029
2. Ahmed A, Pothineni NVK, Charate R, et al: Inappropriate Sinus Tachycardia: Etiology, Pathophysiology, and Management: JACC Review Topic of the Week. J Am Coll Cardiol 79(24):2450–2462, 2022. doi: 10.1016/j.jacc.2022.04.019
Etiology of Inappropriate Sinus Tachycardia
The etiology of the syndrome of inappropriate sinus tachycardia is unknown. Potential components include
Increased intrinsic sinus node automaticity
Decreased vagal sensitivity
Augmented beta-adrenergic sensitivity
Disturbed neurohumoral modulation
Symptoms and Signs of Inappropriate Sinus Tachycardia
Typically, patients with the syndrome of inappropriate sinus tachycardia are very symptomatic with palpitations, orthostatic intolerance, exercise intolerance, weakness, fatigue, dyspnea, chest discomfort, and anxiety. Physical findings are those of tachycardia aggravated by standing in the absence of orthostatic hypotension. The latter helps to distinguish the syndrome from postural orthostatic tachycardia syndrome (POTS).
Diagnosis of Syndrome of Inappropriate Sinus Tachycardia
ECG
24-hour ambulatory electrocardiographic monitoring
Measurement of thyroid stimulating hormone (TSH) to rule out hyperthyroidism
Inappropriate sinus tachycardia is a diagnosis of exclusion. All other secondary causes of sinus tachycardia are considered, including physiologic disorders (eg, cardiac conditions, infections, anemia, hypoxia), hormonal disorders (eg, hyperthyroidism, pheochromocytoma), anxiety, pain, medications and other stimulants (1).
Diagnosis reference
1. Sheldon RS, Grubb BP 2nd, Olshansky B, et al: 2015 heart rhythm society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm 12(6):e41–e63, 2015. doi: 10.1016/j.hrthm.2015.03.029
Treatment of Syndrome of Inappropriate Sinus Tachycardia
Avoidance of sympathomimetics, including caffeine
Down-regulation of beta-adrenergic activity through physical activity
Up-regulation of vagal activity (eg, with yoga, meditation, breathing exercises)
Nonselective beta-1 blocker medication or non-dihydropyridine calcium antagonist therapy
Treatment of symptomatic syndrome of inappropriate sinus tachycardia is difficult, and the condition is often inadequately treated (1, 21).
Transcatheter ablative modification of the sinus node has been proposed.
Treatment references
1. Sheldon RS, Grubb BP 2nd, Olshansky B, et al: 2015 heart rhythm society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm 12(6):e41–e63, 2015. doi: 10.1016/j.hrthm.2015.03.029
2. Ahmed A, Pothineni NVK, Charate R, et al: Inappropriate Sinus Tachycardia: Etiology, Pathophysiology, and Management: JACC Review Topic of the Week. J Am Coll Cardiol 79(24):2450–2462, 2022. doi: 10.1016/j.jacc.2022.04.019
Key Points
Syndrome of inappropriate tachycardia results in inappropriately fast heart rates.
Symptoms of palpitation, orthostatic intolerance, and exercise intolerance are usually pronounced.
The diagnosis is one of exclusion of secondary causes of sinus tachycardia.
