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Inappropriate Sinus (IST) What is IST? Potentially related symptoms: Inappropriate Sinus Tachycardia (IST) is a n Drop in blood pressure upon standing condition in which an individual’s resting heart n Blurred vision rate is abnormally high – greater than 100 beats n Dizziness Inappropriate Sinus Tachycardia (IST) - Patient information per minute or rapidly accelerating to over 100 n Syncope beats per minute without an identifi able cause n Pre-syncope for the tachycardia, although small amounts n Sweating of exercise, emotional or physical stress are triggering factors. What causes IST? An ECG will not show any abnormalities (other Unfortunately, to date nobody knows. There than an abnormally fast heart rate), as IST arises is a belief that IST is a result of the sinus node within the sinus node where normal having an abnormal structure. There is another is generated i.e. the heart rhythm is arising from view that individuals with IST might be super- the normal location but at an inappropriately sensitive to adrenaline as the smallest amount of high rate. exertion can cause a pronounced rise in the heart rate. However, a number of informed medical It is a relatively new disorder (fi rst recognised professionals believe there are a number of in the late s) that is underappreciated factors and disorders which point to disturbance by many in the medical profession and with within the autonomic nervous system. It is for many doctors regarding it as a psychological this reason that it is a condition that can be condition. Individuals with this condition can mistaken for, or overlap with, postural tachycardia fi nd themselves increasingly disabled and syndrome (PoTS). Please contact Arrhythmia experiencing high levels of . Alliance for further information. Symptoms How is IST diagnosed? IST is primarily experienced by young women The following guidelines may help towards in their thirties, who may have been suff ering securing the correct diagnosis for an individual symptoms for a few years. The main symptoms presenting with IST symptoms. of IST include: 1. ECG for resting heart rate - a resting heart n rate generally must exceed 100bpm to be n Shortness of breath considered IST n Exercise intolerance n Fatigue 24hr ECG/ holter monitor - the average heart n Resting heart rate of greater than 100bpm rate during a 24 hr period is usually >95bpm. n Sleeping heart rate of 70 – 90bpm When lying down or sleeping there should be n Heart rate will rapidly reach 150bpm upon little reduction in heart rate minimal exertion Exercise/stress test - demonstrate an inappropriate heart rate response to exercise 2. Symptoms documented should indicate tachycardia 3. Other known causes of sinus tachycardia must

President: Prof. A John Camm Trustees: Mr Mark Bullock, Mr Nigel Farrell, endorsed by Dr Adam Fitzpatrick, Prof. Richard Schilling, Trudie Lobban MBE endorsed by

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be excluded - these include anaemia, hyper is deliberately created in an attempt to prevent thyroidism, phaeochromocytoma, diabetes the tachycardia. It is best to discuss this with an induced autonomic dysfunction, , Electrophysiologist who specialises in this form and of treatment. 4. Sometimes an EP Study will be performed to Self help exclude before an IST

diagnosis is fi nally made Inappropriate Sinus Tachycardia (IST) - Patient information Cognitive behavioral therapy (CBT) has had some 5. Echocardiogram – to rule out any structural success in helping patients come to terms with abnormality of the heart IST, and help manage their lives. It is very important to recognise that, however Treatment disabling symptoms may be, this is not a life IST doesn’t shorten life expectancy, therefore threatening disorder and lifespan is normal; with treatment is aimed at alleviating symptoms. no increased risk of strokes or heart attacks. The Patients can choose to do nothing, and live with number of people who develop any problems with the symptoms if they are not that severe or their heart function as a result of a long-term fast have little impact on their life. Or they can take heart rate is also very small. So, in some people, medications to try and slow the heart rate, have the best thing is to wait and see how things an ablation procedure to destroy the heart tissue develop – it may improve on its own, particularly responsible for the tachycardia, or have open once a person has been reassured that there is no heart surgery if symptoms are very severe and other sinister problem. Where there is an overlap other treatment options have failed. with autonomic dysfunction, increasing salt and Medication A variety of medications have been fl uid intake may help. tried and it is a matter of trial and error to see if a helpful medication can be found for each IMPORTANT POINTS individual. Beta blockers are often tried fi rst; Where sinus tachycardia is identifi ed it is calcium channel blockers (diltiazem or ) important to rule out other treatable conditions are an alternative. Where there is an overlap before making the diagnosis of IST – it may be with autonomic dysfunction, Fludrocortisone, that there is a curable cause. Midodrine, and serotonin-reuptake inhibitors IST is not a life threatening condition but have all been used. More recently drugs such symptoms can be very disabling. as Ivabradine have been tried, but with varying results. It is important not to make things worse A variety of therapies exist, but it is important not with side eff ects from the drugs, which may be to make things worse with any treatment. worse than the symptoms of IST itself. The opinion of a specialist, usually an Ablation Ablation of the sinus node (either Electrophysiologist, can be helpful. to modify the node or destroy it completely) has been used with some success, but this is Please contact Arrhythmia Alliance for further very variable and may not be long-lasting, information and advice regarding IST. and ablation carries its own risks. Ablation is a surgical procedure that uses either heat or freezing methods to destroy areas of the heart tissue via a catheter (thin, fl exible tubes passed Acknowledgements: Arrhythmia Alliance would like to thank through blood vessels to the heart). Scar tissue all those who helped in the development and review of this publication. In particular, thanks are given to Dr Kim Rajappan (Electrophysiologist) and Dr Charlotte D’Souza (Arrhythmia Alliance medical writer & reviewer).

President: Prof. A John Camm Trustees: Mr Mark Bullock, Mr Nigel Farrell, endorsed by Dr Adam Fitzpatrick, Prof. Richard Schilling, Trudie Lobban MBE endorsed by

© Arrhythmia Alliance Registered Charity No. 1107496 Published April 2010, Reviewed January 2017 Please remember that this publication provides general guidelines only. Individuals should always discuss their condition with a healthcare professional. 2 If you would like further details on the sources of our information or would like to provide feedback please contact Arrhythmia Alliance.