Inappropriate sinus tachycardia

Inappropriate Sinus Tachycardia (IST) is a clinical syndrome characterized by a persistently elevated heart rate (HR) at rest, with minimal physical or emotional stress, and without a secondary cause. It is distinguished by an inappropriately high resting heart rate or disproportionate increase in heart rate with minimal exertion. The condition is diagnosed when the resting heart rate is consistently above 100 beats per minute (bpm) or there is a disproportionate heart rate response to minimal or moderate activity, in the absence of other causes of tachycardia such as heart failure, fever, or hyperthyroidism.

Etiology

The exact cause of IST is not well understood, but it is thought to involve dysregulation of the autonomic nervous system, which controls the heart rate. Some theories suggest an intrinsic abnormality in the sinus node (the heart's natural pacemaker), while others propose an exaggerated response to normal sympathetic stimulation. There is also evidence to suggest a genetic predisposition in some cases.

Clinical Presentation

Patients with IST may present with a variety of symptoms, including palpitations, dyspnea (difficulty breathing), fatigue, chest pain, lightheadedness, and occasionally, syncope (fainting). These symptoms can significantly impair the quality of life and mimic other cardiac conditions, making the diagnosis challenging.

Diagnosis

The diagnosis of IST is primarily clinical, based on the patient's history and physical examination. An electrocardiogram (ECG) is essential for observing the heart rate and rhythm. Additional tests may include a 24-hour Holter monitor, which records the heart's electrical activity for a full day, and an exercise stress test to evaluate the heart rate response to exercise. It is crucial to exclude secondary causes of tachycardia, which may require blood tests, imaging studies, or further cardiac evaluation.

Treatment

Treatment of IST focuses on symptom relief and may include lifestyle modifications, pharmacotherapy, and in some cases, invasive procedures. Lifestyle changes such as avoiding caffeine and alcohol, engaging in regular exercise, and stress management techniques can be beneficial. Pharmacological treatment may involve beta-blockers or calcium channel blockers to control the heart rate. In refractory cases, catheter ablation of the sinus node has been used, but its efficacy and safety are still under investigation.

Prognosis

The prognosis of IST varies. While it is not considered life-threatening, the symptoms can significantly affect the patient's quality of life. With appropriate management, many patients can achieve good symptom control and lead a normal life. However, some individuals may continue to experience symptoms despite treatment.

Epidemiology

IST is more common in young women, but it can affect individuals of any age and sex. The exact prevalence is unknown due to the variability in diagnostic criteria and the overlap with other conditions.

See Also

• Tachycardia
• Sinus Tachycardia
• Autonomic Nervous System
• Electrocardiogram

External Links

• American Heart Association
• Heart Rhythm Society

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