Inappropriate sinus tachycardia (IST) is a syndrome in which the sinus heart rate is faster than expected without a good reason. A sinus tachycardia is defined as a:
fast heart rate of over 100 beats per minute (BPM) whilst at rest or
the AVERAGE resting heart rate is over 90 BPM or
the resting heart rate is normal but the heart rate will shoot up abnormally during the lightest physical effort
The heart’s electrical signal usually starts in the sino-atrial (SA) node, which is found in the heart’s right upper chamber. This area triggers the electrical signal that spreads throughout the heart and coordinates the heartbeat. The SA node receives signals from nerves. These nerves can cause the heart to beat more quickly or more slowly, depending on the body’s needs.
In this figure the SA node is called the Sinus Node. AV= atrioventricular node
Naturally our hearts beat faster with a fever, during exercise, or with anxiety or stress. As you can see this is why it is often, and inappropriately diagnosed, as an anxiety disorder. Especially as IST is generally more common in women.
Inappropriate Sinus Tachycardia is classed as a heart rhythm abnormality or arrhythmia.
Associated symptoms can also be present. These include:
Sensation of a rapid heartbeat (palpitations)
Shortness of breath
Decreased ability to exercise
Causes of Post Covid-19 Inappropriate Sinus Tachycardia
Persistent tachycardia / IST has been demonstrated in patients recovering from SARS, suggesting it may be seen in patients recovering from COVID-19 also. Mechanisms responsible for IST are not very well understood but it is thought to be likely multifactorial including:
Intrinsic sinus node hyperactivity - the area in the heart responsible for the heart beat is overactive so the heart beats too fast.
Autonomic dysfunction - IST results from inappropriate signaling of the nerves that increase the heart’s rate. The nerves that lower the heart’s rate may also not work as they should.
Hyperadrenergic state - basically means high adrenaline. Adrenaline and nor-adrenaline (epinephrine and nor-epinephrine) are natural stimulants within the body, the same ones released in the flight or fight response.
Inflammatory cytokines - released by patients with COVID-19 may affect the function of heart muscle ion channels and perpetuate arrhythmias including sinus tachycardia.
It is important to distinguish IST from so-called appropriate sinus tachycardia and from postural orthostatic tachycardia syndrome, with which overlap may occur.
Appropriate sinus tachycardia is seen when the heart rate elevates when we move positions such as from lying to standing, during stressful times, during exercise and if you have a fever.
Postural Orthostatic Tachycardia Syndrome has an inappropriate elevation of the heart rate when you move from lying to standing with many other associated symptoms.
Incidence of Post-Covid Inappropriate Sinus Tachycardia
In the paper “Management of Arrhythmias Associated with COVID-19” by Desai et al (New York) the authors felt the incidence of inappropriate sinus tachycardia in patients with COVID-19 was currently uncertain. By definition, IST is a diagnosis of exclusion. It is unlikely to be diagnosed during the acute Covid-19 infection as patients have low oxygen levels (hypoxemia) and or a high fever and this causes sinus tachycardia.
Dr Alexander Lyons at the Brompton, London found that of the patients he had seen with post- covid breathlessness 29 % had IST.
How is Post-Covid Inappropriate Sinus Tachycardia diagnosed?
Detailed medical history
A physical exam - including resting pulse, standing pulse, resting blood pressure and standing blood pressure, a NASA lean test
Electrocardiogram - to analyse the heart’s electrical rhythm and the type of tachycardia
Continuous monitoring of the heart rhythm (Holter monitor), to check the rhythm for a longer period of time. Minimally 24 hours ideally 7 days
Blood tests, to look for other causes of the fast heartbeat - anaemia, overactive thyroid, low blood pressure, ongoing fever
Echocardiogram, to check the size, structure, and pumping of the heart
Chest X-ray, to view the heart and lungs
Tests to exclude other causes of sinus tachycardia - pulmonary embolus, myocarditis etc.
Please make sure you get your 9 am cortisol levels checked too. Having all that adrenaline washing around our bodies constantly is not healthy to our adrenal glands.
How is Post-Covid Inappropriate Sinus Tachycardia treated?
Simple measures include:
Eliminate potential triggers/ heart stimulants in your diet such as caffeine, nicotine, and alcohol
Discuss pain management options with your doctor
Restricting exercise or gentle exercise within your energy envelope
Eating a heart-healthy diet and maintaining a healthy weight
Anxiety reduction/ meditation/ medication
I put myself on herbal medication to help protect my adrenal glands - Siberian Rhodiola
For patients with intolerable symptoms, therapeutic measures are needed. You may be started on a β-adrenergic blockers (beta blocker) the first-line therapy however even at high doses these are often found to be ineffective.
Many are started on Ivabradine, a more cardio-selective beta blocker, although treatment efficacy is unknown in patients with COVID-19.
Calcium channel blockers are also used. For patients in rare instances, catheter ablation of the right atrial or sinus node may be helpful, but even this is fraught with limited efficacy and potential complications.
Postural orthostatic tachycardia syndrome (POTS) is caused by autonomic dysfunction; the underlying mechanism of which may be related to peripheral neuropathy, increased serum norepinephrine, baroreceptor dysfunction, or hypovolemia. The syndrome has previously been reported to develop after viral illness and, therefore, may also develop in some patients recovering from COVID-19 . Nonpharmacologic management of POTS includes increasing salt and fluid intake, use of lower extremity compression garments to reduce venous pooling, and participation in regular exercise to prevent deconditioning as appropriate. However, patients with COVID-19 and evidence of myocardial injury or inflammation should abstain from competitive sports or aerobic activity until resolution of imaging findings or normalization of cardiac biomarkers.
I just though I would share with you my Garmin watch data. I have a Post-Covid Positional Orthostatic Tachycardia Syndrome diagnosis and am currently on 5 mg Ivabradine three times a day to try and control my heart rate.
I find my heart rate increases inappropriately still when I go from lying to standing (getting out of bed in the morning), when I go for a walk, when I talk too much, or if I am stressed.
Can you see any difference?!!
Me neither really - my resting pulse has dropped, when I stand for long periods my heart rate doesn't spike so high and I am not dizzy anymore and my brain fog has cleared a little. But I think its quite clear that my IST is far from being under control it's just softened somewhat. I think this really highlights the importance of medicine just helping the symptoms and not addressing the root cause.
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Yu CM, Wong RS, Wu EB, Kong SL, Wong J, Yip GW, Soo YO, Chiu ML, Chan YS, Hui D, Lee N, Wu A, Leung CB, Sung JJ. Cardiovascular complications of severe acute respiratory syndrome. Postgrad Med J. 2006;82(964):140–144. doi: 10.1136/pgmj.2005.037515.
Olshansky B, Sullivan RM. Inappropriate sinus tachycardia. J Am Coll Cardiol. 2013;61(8):793–801. doi: 10.1016/j.jacc.2012.07.074.