ConditionHeart & circulation
Inappropriate Sinus Tachycardia (IST)
Inappropriate sinus tachycardia (IST) is a condition in which the heart's natural pacemaker, the sinus node, fires too fast at rest and speeds up excessively with minimal activity, without an underlying cause such as fever, anemia, an overactive thyroid or dehydration. The resting heart rate is usually over 100 beats per minute, with an average over 90 across 24 hours. It mostly affects young women and causes palpitations, tiredness, dizziness and exercise intolerance. It is not dangerous for most people, and treatment focuses on symptoms.
Also called: IST, inappropriate sinus tach, chronic non-paroxysmal sinus tachycardia
At a glance
- What it is
- A persistently fast sinus heart rate without an identifiable cause.
- Typical findings
- Resting heart rate over 100, average over 90 bpm on 24-hour monitoring, normal ECG pattern.
- Who gets it
- Mostly women aged 15 to 50.
- Symptoms
- Palpitations, fatigue, dizziness, breathlessness, exercise intolerance, anxiety.
- Diagnosis
- Excluding other causes, ECG, Holter monitor, blood tests and echocardiogram.
- Treatment
- Lifestyle measures, beta-blockers, ivabradine. Ablation rarely.
When to get help
Call 911 or go to the ER
- Palpitations with fainting, chest pain, severe breathlessness or confusion
- A sudden, very fast heartbeat (over 150 bpm) that starts and stops abruptly, especially with dizziness
See a doctor within a day or two
- A fast heart rate with fever, vomiting, severe diarrhea or bleeding
- A new fast heart rate with weight loss, heat intolerance and tremor (possible overactive thyroid)
- Swollen ankles or breathlessness lying flat with a persistently fast pulse
Book a routine appointment
- A resting heart rate regularly above 100 bpm without an obvious reason
- Palpitations, fatigue or exercise intolerance lasting weeks
- Heart rate that jumps excessively with minor activity
What happens in IST
The sinus node in the right atrium sets the heart's rhythm. Normally it fires 60 to 100 times a minute at rest and speeds up appropriately with exercise, stress or fever. In IST, the rhythm itself is normal (sinus rhythm), but the rate is inappropriately high for the situation.
The exact cause is not known. Proposed mechanisms include:
- an overactive sinus node
- imbalance of the autonomic nervous system, with excess sympathetic ("fight or flight") activity or reduced vagal ("rest and digest") tone
- increased sensitivity to adrenaline
- autoimmune or post-viral changes; some cases follow viral infections, including COVID-19
Symptoms
- Palpitations: a racing or pounding heartbeat
- Fatigue and low energy
- Dizziness or light-headedness
- Breathlessness
- Chest discomfort
- Exercise intolerance: heart rate shoots up with mild exertion
- Anxiety, which can be both a result and a contributor
- Fainting (rare)
Symptoms can be persistent and significantly affect quality of life, even though the condition is usually not dangerous.
IST vs POTS and other causes of a fast heart rate
| Condition | Key difference |
|---|---|
| IST | Heart rate high at rest and in all positions |
| POTS | Heart rate rises by 30 bpm or more when standing, usually normal when lying down |
| Sinus tachycardia with a cause | Fast rate explained by fever, anemia, dehydration, pain, thyroid disease, caffeine or medicines |
| Supraventricular tachycardia | Sudden on and off episodes, often 150 to 250 bpm, abnormal circuit in the heart |
| Atrial tachycardia | Fast rhythm from outside the sinus node, different ECG P waves |
IST and POTS can overlap in the same person.
Diagnosis
IST is a diagnosis of exclusion: other causes must be ruled out first.
- History: symptoms, caffeine, alcohol, nicotine, stimulants and medicines (decongestants, asthma inhalers, ADHD medicines, thyroid medicine).
- ECG: confirms sinus rhythm.
- 24-hour Holter monitor: shows a mean heart rate over 90 bpm and an exaggerated rise with activity.
- Blood tests: thyroid function, full blood count (anemia), electrolytes, blood sugar, and sometimes urine metanephrines for adrenaline-producing tumors.
- Echocardiogram: checks heart structure and function.
- Exercise test and standing (orthostatic) test to distinguish from POTS.
- Electrophysiology study occasionally, to exclude atrial tachycardia.
Treatment
Treatment aims to ease symptoms, since IST rarely causes harm. Lowering the heart rate does not always relieve symptoms fully.
Lifestyle measures
- Reduce or avoid caffeine, alcohol, nicotine and stimulants
- Regular gradual aerobic exercise training to improve fitness and autonomic balance
- Adequate fluids and sleep
- Stress management, CBT or relaxation techniques
- Review medicines that raise heart rate
Medicines
- Ivabradine: slows the sinus node directly without lowering blood pressure. Often the most effective option, used off-label in IST. Not used in pregnancy.
- Beta-blockers: reduce heart rate and adrenaline effects but can cause tiredness and low blood pressure.
- Combination of ivabradine and a beta-blocker for resistant cases.
- Calcium channel blockers (non-dihydropyridine) as alternatives.
Procedures
Sinus node modification (catheter ablation) is reserved for severe symptoms that do not respond to medicines. Results are mixed: symptoms often return, and there is a risk of needing a pacemaker. It is generally a last resort.
Outlook
IST is usually benign and does not shorten life expectancy. Very rarely, a persistently high heart rate over many years can weaken the heart muscle (tachycardia-induced cardiomyopathy), so follow-up may include periodic heart scans. Symptoms often improve over time, and many people manage well with lifestyle changes and medicine.
Frequently asked questions
What is inappropriate sinus tachycardia?
It is a condition where the heart's natural pacemaker fires too fast at rest and with minimal activity, without a medical cause such as fever, anemia, dehydration or an overactive thyroid. The rhythm is normal but the rate is too high.
What are the symptoms of IST?
Common symptoms are palpitations, tiredness, dizziness, breathlessness, chest discomfort, anxiety and difficulty exercising because the heart rate rises quickly. Some people have few symptoms despite a fast rate.
What is the difference between IST and POTS?
In IST, the heart rate is high at rest in any position. In POTS, the heart rate is usually normal when lying down but rises by 30 beats per minute or more on standing. The two can overlap.
Is inappropriate sinus tachycardia dangerous?
For most people it is not dangerous and does not shorten life expectancy, although symptoms can be very bothersome. Rarely, years of very high rates may weaken the heart, so doctors monitor heart function.
How is IST treated?
Treatment starts with reducing caffeine, alcohol and stimulants, gradual exercise training and stress management. Medicines such as ivabradine or beta-blockers lower the heart rate. Catheter ablation is reserved for severe cases that do not respond.
Sources
This guide was written from current patient and clinical guidance, including:
- Heart Rhythm Society: 2015 Expert Consensus Statement on the Diagnosis and Treatment of Postural Tachycardia Syndrome, Inappropriate Sinus Tachycardia, and Vasovagal Syncope
- European Society of Cardiology: Guidelines for the management of patients with supraventricular tachycardia
- American Heart Association: Tachycardia, fast heart rate
- Cleveland Clinic: Inappropriate sinus tachycardia
- NHS: Heart palpitations