Sinus Tachycardia

How sinus tachycardia works

The sinus node, in the upper right chamber, sets the heartbeat. The nervous system speeds it up (adrenaline, sympathetic nerves) or slows it down (vagus nerve) to match the body's needs. In sinus tachycardia, the sinus node fires faster, but the electrical signal spreads through the heart normally. That is why the ECG shows a normal shape, just faster.

On an ECG

• regular rhythm
• rate above 100 beats per minute
• an upright, normal P wave before every QRS complex
• normal PR interval

At very fast rates, P waves can merge with the preceding T waves, making sinus tachycardia hard to distinguish from other rhythms such as atrial flutter or supraventricular tachycardia. Clues favoring sinus tachycardia are gradual speeding up and slowing down, rather than the abrupt switch of SVT.

Causes

Physiological (appropriate)

• exercise
• anxiety, excitement, pain
• fever: roughly 10 beats per minute per 1 °C rise
• pregnancy
• caffeine, nicotine, alcohol, energy drinks

Medical conditions

Inappropriate sinus tachycardia

Inappropriate sinus tachycardia (IST) is an uncommon condition, mostly in young women, in which the resting heart rate is persistently above 100 and the average 24-hour rate is above 90, with an exaggerated rise on minimal effort, and no other cause is found. Symptoms include palpitations, fatigue, dizziness and exercise intolerance. Its cause is unclear, possibly overactivity of the sinus node or its nerve control.

Postural tachycardia syndrome

In POTS, sinus tachycardia appears specifically on standing, with a rise of 30 beats per minute or more (40 in teenagers) within 10 minutes, along with dizziness and fatigue.

Symptoms

Many people feel nothing. Others notice:

• palpitations or a pounding heart
• shortness of breath
• dizziness or lightheadedness
• fatigue
• chest discomfort

Diagnosis

• ECG to confirm sinus rhythm.
• History and exam to identify triggers and medicines.
• Blood tests: blood count, thyroid function, electrolytes, blood sugar, and others based on symptoms.
• Holter or wearable monitoring to see the 24-hour pattern, especially for suspected IST.
• Echocardiogram if heart disease is suspected.
• Tilt table test for suspected POTS.

Treatment

• Treat the cause: fluids for dehydration, iron for anemia, antibiotics for infection, thyroid treatment, stopping triggering medicines.
• Lifestyle: reduce caffeine, alcohol and nicotine; manage stress; improve fitness gradually.
• For inappropriate sinus tachycardia: beta-blockers or ivabradine, which slows the sinus node specifically, may be used under a cardiologist's guidance. Catheter ablation of the sinus node is rarely considered because of high recurrence and risks.
• For POTS: increased fluids and salt, compression garments, graded exercise and sometimes medicines.

Beta-blockers are avoided when sinus tachycardia is a compensating response, such as in blood loss, sepsis or heart failure, because the fast rate helps maintain circulation.

Outlook

Sinus tachycardia from a temporary cause resolves when the cause is treated. Inappropriate sinus tachycardia is usually not dangerous but can affect quality of life; many people improve with treatment and time.

Frequently asked questions

What does sinus tachycardia mean on an ECG?

It means the heart's electrical signal starts normally in the sinus node, the rhythm is regular, and the rate is above 100 beats per minute. It is a normal rhythm that is simply fast, often responding to something like fever, exercise or anxiety.

Is sinus tachycardia dangerous?

Usually not. It is often the heart's normal response to stress, exercise or illness. It matters because of what is causing it, such as infection, blood loss, dehydration or a blood clot. A persistently fast rate without explanation should be checked.

What causes sinus tachycardia at rest?

Common causes include anxiety, caffeine, dehydration, fever, anemia, an overactive thyroid, poor fitness, medicines such as inhalers or decongestants, and alcohol. If no cause is found, inappropriate sinus tachycardia or POTS may be considered.

How is sinus tachycardia treated?

By treating the cause: rehydration, treating infection or anemia, adjusting medicines, or treating thyroid disease. Specific medicines such as beta-blockers or ivabradine are used for inappropriate sinus tachycardia that causes troublesome symptoms.