Definitions
Normal Heart Rate (‘Pulse’)
Normal resting heart rate ranges between 60 and 100 beats per minute for adolescents and adults.
Normal Heart Rhythm (Electrical Activity)
Sinus rhythm is the characteristic rhythm of the normal healthy heart.
Tachycardia and Bradycardia
‘Tachy-’ is a medical term that means fast.
‘Brady-’ means slow.
Tachycardia is when the heart rate (pulse) is above 100 beats per minute (bpm).
Bradycardia is when the heart rate is below 60 bpm.
Sinus Tachycardia
Simply means the heart rate is fast (above 100 bpm) and the rhythm (electrical activity) is normal (sinus rhythm)
This is a normal response to activities like exercise when the body requires more oxygen to the muscles and tissues.
It can also occur due to dehydration, anxiety, certain drugs or when we are unwell or have a fever.
It can also be as a result of certain medical conditions such as:
- anaemia (low haemoglobin levels or red blood cells)
or
- an overactive thyroid (hyperthyroidism)
What is Inappropriate Sinus Tachycardia?
Inappropriate sinus tachycardia (IST) is when you have an abnormally high resting heart rate with no clear reason.
One theory is that IST could be caused by a disturbance to the autonomic nervous system – the part of the nervous system responsible for ‘automatic’ functions such as heart rate and breathing.
Someone with IST will either:
- have a resting heart rate of 100 beats per minute or more
or
- their heart rate will suddenly increase to over 100 beats per minute for instance when moving from lying to sitting or sitting to standing.
When asleep or lying down, their heart rate often returns to normal.
Symptoms of IST:
Symptoms can range from mild to severe and often include:
- palpitations or ‘heart flutters’
- shortness of breath
- tiredness / fatigue
The symptoms can occur after even a small amount of exercise. Some people also feel weak, faint or dizzy when their heart is racing or beating fast.
Many people don’t have symptoms and IST is picked up incidentally.
In most people, these symptoms come and go so there are periods when normal day to day life is possible, but in others, the symptoms continue for a long time leading to reduced activity.
Treatment of IST:
Treatment is not always needed for IST, particularly if the episodes are fairly infrequent and not interfering with day to day life.
It is important to remain as active as possible to avoid becoming deconditioned, which can make the symptoms worse.
Medications used for IST aim to slow the heart rate down. Typical medications include
- Betablockers
- Calcium channel blockers
- Ivabradine
Talking therapies such as cognitive behavioural therapy (CBT) can be also be helpful.
Please ensure your doctor is aware of all the medications you are currently taking, both prescription and non-prescription.
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