Sinus Tachycardia: Causes, Inappropriate Sinus Tachycardia, POTS, and What It Means for Athletes
Table of Contents
Key Takeaways: Sinus Tachycardia
- Sinus tachycardia means a sinus rhythm faster than 100 beats per minute (bpm). The impulse still comes from the sinus node, so the P waves on the ECG look like those of normal sinus rhythm.[1]
- It is often a response to something else, such as exercise, emotion, pain, fever, dehydration, anaemia, hyperthyroidism, medication, caffeine or alcohol, and guideline management of physiological sinus tachycardia centres on finding and removing that cause.[1]
- Inappropriate sinus tachycardia (IST) is a diagnosis of exclusion: a resting sinus rate above 100 bpm, a 24-hour average above 90 bpm without a primary cause, and distressing palpitations.[2]
- In a random sample of 604 middle-aged adults from one Finnish study, 1.16% met the diagnostic criteria for IST in use at the time, and follow-up of affected subjects suggested a benign prognosis.[3]
- Postural orthostatic tachycardia syndrome (POTS) is different: the heart rate rises by at least 30 bpm on standing without orthostatic hypotension, whereas IST is not tied to posture.[2][13]
- In athletes, international ECG recommendations describe sinus tachycardia as very rarely caused by intrinsic heart disease, but if the resting rate is above 120 bpm, a repeat ECG after rest should be considered, along with causes such as fever, dehydration, stimulants, anaemia or hyperthyroidism.[14]
- Short-term overload training raised resting heart rate only moderately in a meta-analysis of competitive athletes, and the authors noted that the change may fall within normal day-to-day variation.[11]
- Treatment evidence for IST is thin. The main randomised evidence for ivabradine comes from a small crossover trial of 21 patients.[5]
- In my clinical experience, a persistently raised resting heart rate often has a stressful life situation and what appears to be raised sympathetic tone behind it, but I do not attribute it to stress without at least one ECG and laboratory tests, as I have also found hyperthyroidism in this group; I also keep pulmonary embolism in mind whenever the patient’s background fits.
Introduction: Sinus Tachycardia
A heart rate above 100 bpm on an ECG, a blood pressure monitor or a smartwatch often prompts the same question: is something wrong with my heart? International recommendations for ECG interpretation in athletes describe sinus tachycardia as the most common atrial tachyarrhythmia and note that intrinsic cardiac disease is very rarely the cause.[14]
That does not mean sinus tachycardia is always harmless. The sinus node speeds up for a reason, and the reason can range from a cup of coffee to fever, anaemia, hyperthyroidism or a pulmonary embolism.[1] In a smaller group of people, the heart rate, at rest or on standing, rises without an identifiable secondary cause, which is when inappropriate sinus tachycardia and POTS enter the differential diagnosis.
This article explains what sinus tachycardia is, its most common causes, how IST and POTS differ, how the condition is usually evaluated, and what a fast resting heart rate may mean for athletes.
In my clinical experience, sinus tachycardia is a fairly common finding at the practice, and in my view the degree of tachycardia largely determines what kind of situation I am dealing with. A patient whose resting heart rate has crept up to around 70–80 bpm, which is still below the 100 bpm threshold, is a very different situation from one whose rate is well above 100 bpm, and how long it has lasted matters too. Some of the patients I see have an acute sinus tachycardia, while others have a resting heart rate that has simply stayed somewhat elevated for a longer period.
What Is Sinus Tachycardia?
The 2019 European Society of Cardiology (ESC) guidelines define sinus tachycardia as a sinus rate above 100 bpm. On a 12-lead ECG, the P wave is positive in leads I, II and aVF and biphasic or negative in lead V1, which is the same P-wave pattern as in normal sinus rhythm.[1] P-wave morphology helps separate sinus tachycardia from most other fast rhythms, such as atrial flutter or re-entrant supraventricular tachycardia, although focal atrial tachycardia arising near the sinus node and sinus node re-entrant tachycardia can produce similar P waves.[1]
In my experience, some supraventricular tachycardias can look like sinus tachycardia at first glance. In the cases I have seen, the ventricular rate has usually been in a very different range and has sometimes approached 200 bpm. Technically, these rhythms do not necessarily show the same sinus P wave, even though they arise above the ventricles. Symptoms vary a lot: some of the patients I see describe only a slight feeling of breathlessness, others have very strong symptoms, and some hardly notice the arrhythmia at all.
The ESC classifies sinus tachycardia into three main forms:[1]
- Physiological sinus tachycardia, which is driven by effort, stress, pregnancy or another medical condition or drug.
- Inappropriate sinus tachycardia (IST), in which the sinus rate is out of proportion to the physical, emotional, pathological or pharmacological stress present.
- Sinus node re-entrant tachycardia, an uncommon arrhythmia that, unlike IST, occurs in paroxysmal episodes.
The 100 bpm threshold is a convention. How the “normal” range was set, and why resting heart rate varies so much between individuals, is discussed in normal heart rate.
Common Causes of Physiological Sinus Tachycardia
The ESC guideline groups the causes of physiological sinus tachycardia into five categories:[1]
| Category | Examples listed in the 2019 ESC guideline |
|---|---|
| Physiological | Emotion, physical exercise, sexual intercourse, pain, pregnancy |
| Pathological | Anxiety, panic attack, anaemia, fever, dehydration, infection, malignancy, hyperthyroidism, hypoglycaemia, pheochromocytoma, Cushing’s disease, diabetes with autonomic dysfunction, pulmonary embolus, myocardial infarction, pericarditis, valve disease, congestive heart failure, shock |
| Drugs | Epinephrine, norepinephrine, dopamine, dobutamine, atropine, beta-2 agonists such as salbutamol, methylxanthines, doxorubicin, daunorubicin, withdrawal of beta-blockers |
| Illicit drugs | Amphetamines, cocaine, LSD, psilocybin, ecstasy |
| Other | Caffeine, alcohol |
The guideline states that physiological sinus tachycardia is managed by identifying and eliminating the underlying cause.[1] Several of these causes have been quantified in research.
Fever. In 27 young men with an acute febrile infection who underwent 24-hour ECG recordings, the mean heart rate was 84.0 bpm during the febrile period and 66.5 bpm after recovery. Heart rate rose by an average of 8.5 bpm for each 1 °C rise in temperature and stayed high even during sleep.[7] Training decisions during febrile illness are covered in fever and training.
Alcohol. In the MunichBREW study, 3,028 visitors to the 2015 Munich Oktoberfest had a 30-second smartphone ECG and a breath alcohol measurement. Sinus tachycardia was found in 25.9% of participants, and each 1 g/kg increase in breath alcohol concentration was associated with an odds ratio of 1.96 for sinus tachycardia. In a sensitivity analysis, 18.5% of participants with a breath alcohol concentration of 0 g/kg also had sinus tachycardia, which the authors suggested may reflect the festival setting.[8]
Intoxication and withdrawal. When I still worked many emergency shifts, I came across various intoxications every now and then, including stimulant users. In my experience, they typically had a tachycardic rhythm, were restless and often had wide pupils, although the picture varied somewhat. Some had also been using several substances at once, for example amphetamine or something similar together with a benzodiazepine as a kind of brake. I found that an unusual combination: the patient’s vital signs, including heart rate, are accelerated, while at the same time they are neurologically depressed.
Another group I saw in emergency work was patients who had been drinking for several days in a row and were shaky and tachycardic the following day. In my experience, these patients call for caution, because after a long drinking period they may be at risk of seizures or of developing delirium. When there is a clear risk of seizures or delirium, these patients often end up being treated with benzodiazepine loading.
Withdrawal symptoms in opioid-dependent patients are, in my experience, particularly difficult. These patients feel physically very unwell: they are tachycardic and sweaty, and they may itch all over. Unfortunately, at least in the emergency setting, they are generally offered only symptomatic treatment. As far as I know, opioid substitution treatment in Finland is centralised in dedicated substitution treatment clinics, and in the emergency departments where I have worked, giving substitution treatment in the emergency department has been explicitly prohibited; these patients are instead directed to the specialised clinics.
Pulmonary embolism. In a meta-analysis of 45 studies involving 8,209 patients with acute pulmonary embolism, tachycardia was among the most frequent ECG findings, present in 38% of patients. In the subset of studies with outcome data, a heart rate above 100 bpm was one of six ECG findings associated with an increased risk of circulatory shock and death.[10] By the same figure, tachycardia on the ECG was absent in most patients in that analysis.
Anaemia and hyperthyroidism. Both appear on the ESC list of pathological causes, and both are relatively easy to screen for with a complete blood count and thyroid function tests.[1][2] Hyperthyroidism is discussed in more detail in Graves’ disease.
A group I see quite often in my practice is patients who come in concerned about a raised resting heart rate, usually somewhere around 70 bpm or a little above, which has often been going on for a long time. In many of these patients, I find a stressful life situation in the background and what appears to be raised sympathetic tone from that load. Even so, in my view these patients deserve a careful differential diagnosis rather than a quick label of stress, because I have also come across other conditions in this group, including hyperthyroidism. In that case, my first thought was that the raised heart rate might simply reflect stress, but the work-up revealed a genuine disease, which reminded me how important the differential diagnosis is.
I also often see sinus tachycardia in patients with burnout. Many of them use a smart device, such as an Oura ring or a smartwatch, that also tracks heart rate variability, and in my experience the data often show reduced heart rate variability alongside the raised heart rate. The device may also report poor sleep and poor recovery, which in my view may make the patient’s symptoms even worse.
Inappropriate Sinus Tachycardia (IST)
The 2015 Heart Rhythm Society (HRS) expert consensus statement defines IST as a sinus heart rate above 100 bpm at rest, with a mean 24-hour heart rate above 90 bpm that is not due to primary causes, accompanied by distressing palpitations.[2] The ESC guideline adds that the tachycardia tends to be persistent and that most affected patients are young and female, although the disorder is not limited to that group.[1]
How common is it? One population-based estimate comes from Finland. In the OPERA study from Oulu, Still and colleagues screened a random sample of 604 middle-aged subjects and found that 7 (1.16%) fulfilled the diagnostic criteria for IST in use at the time.[3] This is a single study sample rather than a definitive population prevalence. The HRS statement notes that this 1.2% figure included both symptomatic and asymptomatic subjects.[2] Subjects with IST had higher ambulatory blood pressure than controls (systolic 147 vs 130 mmHg), but other laboratory and echocardiographic measurements did not differ.[3]
What causes it? The mechanisms are not fully understood. The HRS statement lists increased sinus node automaticity, beta-adrenergic hypersensitivity, reduced parasympathetic activity and impaired neurohumoral modulation, and notes that beta-adrenergic receptor antibodies may play a role in some patients.[2]
Is it dangerous? The available evidence is reassuring. In the Finnish study, IST subjects and previously diagnosed patients were followed for a mean of 6.0 years. None of the 11 who attended follow-up developed clinical or echocardiographic signs of structural heart disease despite ongoing palpitations, and the authors concluded that the prognosis was benign.[3] The ESC guideline states that IST has not been associated with tachycardia-induced cardiomyopathy, while the HRS statement describes that association as rare.[1][2] Benign prognosis does not mean a benign experience, though: the HRS statement notes that IST is frequently associated with a significant loss of quality of life.[2]
After infection. IST has also been described after COVID-19. In a prospective study of 200 patients attending a post-COVID-19 clinic, 40 (20%) met strict diagnostic criteria for IST after secondary causes such as anaemia, thyroid disease, pregnancy, infection and pulmonary embolism had been investigated. The affected patients had a mean age of 40.1 years, 85% were women, and 83% had had mild COVID-19. No structural heart disease, inflammatory state, myocardial injury or hypoxia was found, but heart rate variability was reduced, especially in measures related to vagal tone.[9] Return to sport after COVID-19 is covered in COVID in athletes.
Sinus Tachycardia vs. POTS
POTS and IST can look similar because both involve sinus tachycardia and similar symptoms, but the triggers differ. The HRS statement notes that IST is provoked by both physiological and emotional stress, whereas POTS is generally provoked only by orthostatic stress.[2]
A 2022 review in the Canadian Medical Association Journal summarises the diagnostic criteria for POTS:[13]
- A sustained heart rate increase of at least 30 bpm (at least 40 bpm in those aged 12–19 years) within 10 minutes of standing.
- No significant orthostatic hypotension (a fall of 20/10 mmHg or more).
- Frequent symptoms of orthostatic intolerance that improve rapidly when lying down.
- Symptoms lasting at least 3 months.
- No other condition that could explain the sinus tachycardia.
The same review notes that most patients with POTS have a normal or high-normal resting heart rate, and that a consistently raised heart rate regardless of body position points instead toward IST.[13] Its list of conditions that can mimic POTS includes acute hypovolaemia from dehydration or blood loss, anaemia, hyperthyroidism, adrenal insufficiency, medication effects, panic attacks and prolonged bed rest.[13]
The HRS statement puts the prevalence of POTS at about 0.2%, with most patients presenting between 15 and 25 years of age and more than 75% being female.[2] The CMAJ review gives a wider estimate of 0.1–1%.[13]
How Sinus Tachycardia Is Evaluated
Because sinus tachycardia often has an identifiable cause, evaluation focuses on finding the driver. For patients with supraventricular tachycardia, the standard initial evaluation in the ESC guideline includes a history, physical examination, 12-lead ECG, full blood count, biochemistry profile, thyroid function and transthoracic echocardiography, with 24-hour ECG monitoring listed as optional.[1]
For suspected IST, the HRS statement classifies a complete history, physical examination and 12-lead ECG as a class I recommendation, a complete blood count and thyroid function tests as class IIa, and 24-hour Holter monitoring and urine or serum drug screening as class IIb.[2] The ESC guideline describes the typical Holter finding in IST as a mean heart rate above 90 bpm with an exaggerated rise above 100 bpm during waking hours.[1]
For suspected POTS, the CMAJ review lists haemoglobin, electrolytes, renal function, ferritin, thyroid-stimulating hormone and morning cortisol as core laboratory tests to screen for secondary causes of orthostatic tachycardia.[13] Ferritin and iron status are discussed further in iron deficiency.
The ECG has one more important role: confirming that the rhythm really is sinus. The ESC guideline describes IST as a diagnosis made by excluding POTS, sinus node re-entrant tachycardia, and focal atrial tachycardia originating from the upper crista terminalis or the right superior pulmonary vein.[1]
When a patient’s resting heart rate is above 100 bpm, I find that concerning in its own right. At that point I usually check the patient’s haemodynamics and review their background, because in some situations a high heart rate could reflect a pulmonary embolism. The pre-test probability is often low, but pulmonary embolism is a serious condition and not something I want to miss, so in my practice excluding it is often an important step in these patients. I often check vital signs, including oxygen saturation, and take an ECG; when pulmonary embolism is suspected, I assess its clinical probability and choose further tests, such as a D-dimer, accordingly. If nothing specific turns up, blood tests, including thyroid tests, are then done at a less urgent pace. If no clear cause is found, I usually refer the patient for Holter monitoring or to a cardiologist, who often performs an echocardiogram followed by a Holter recording. If those are unremarkable, I find that reassuring, although these investigations do not exclude every possible cause, and in my practice the search then turns to other factors, such as psychological ones.
What the Evidence Shows About Treating Inappropriate Sinus Tachycardia
The guidelines take a cautious line. The ESC guideline states that, because the prognosis of IST is benign, treatment aims to reduce symptoms and may not be necessary, and it lists reassurance and lifestyle measures such as exercise training, volume expansion and avoiding cardiac stimulants as steps to try before drug treatment.[1] A 2013 review in the Journal of the American College of Cardiology reached a similar conclusion, noting that because the long-term outcome seems benign, treatment may be unnecessary or as simple as physical training, that beta-blockers often fail even at high doses, and that overtreatment is discouraged.[4] The HRS statement similarly notes that beta-blockers are usually not effective in IST and can cause adverse effects.[2]
Ivabradine. Ivabradine selectively blocks the pacemaker current (If) in sinoatrial cells and directly slows the heart rate.[1] In a randomised, double-blind, placebo-controlled crossover trial, 21 patients with IST received ivabradine (starting dose 5 mg twice daily) or placebo for 6 weeks each. On ivabradine, 14 of the 21 patients (67%) had at least 70% of their symptoms eliminated, and 9 patients had complete symptom elimination. Resting heart rate fell from 88 to 76 bpm and 24-hour heart rate from 88 to 77 bpm.[5] The HRS statement gives ivabradine a class IIa recommendation for IST, and the ESC guideline states that ivabradine alone or in combination with a beta-blocker should be considered in symptomatic patients.[1][2] The trial was small and short, so these results describe short-term symptom control rather than long-term outcomes.
Ablation. Both guidelines advise against sinus node modification or ablation as part of routine care for IST. The HRS statement cites high symptom recurrence and significant complications, including the need for permanent pacing and phrenic nerve paralysis.[1][2]
In my own practice, when a patient’s tachycardia has been found to be benign, I have usually prescribed propranolol. This reflects my experience with benign sinus tachycardia in general, not specifically the IST trials described above. In my experience, propranolol also eases the physical symptoms of anxiety for many patients, especially those whose anxiety symptoms come in episodes, and it is a medication many patients are already familiar with. Many patients also appreciate that it is not a sedative like a benzodiazepine, although propranolol has its own potential adverse effects and contraindications.
Sinus Tachycardia in Athletes
The international recommendations for ECG interpretation in athletes advise that if resting sinus tachycardia above 120 bpm is seen, a repeat ECG should be considered after a period of rest, because recent exercise or anxiety may explain it. If the rate stays high, the recommendations list fever, infection, dehydration, stimulant use, anaemia, hyperthyroidism and, rarely, underlying cardiac or pulmonary disease as causes to consider.[14]
Overreaching. Training load can shift resting heart rate. A meta-analysis of competitive athletes found that overload periods of 2 weeks or less produced a moderate rise in resting heart rate (standardised mean difference 0.55); in absolute terms, the 95% confidence interval for this rise was 2.2 to 6.8 bpm. There was also a moderate rise in the low-frequency/high-frequency ratio of heart rate variability. Overload periods longer than 2 weeks did not alter resting heart rate. The authors cautioned that these changes may fall within normal day-to-day variation, so they need to be interpreted alongside other signs of overreaching.[11] How resting heart rate behaves across the overtraining spectrum is covered in resting heart rate changes in overtrained athletes.
Dehydration and heat. During exercise, fluid loss and rising body temperature push heart rate up. In 15 endurance-trained cyclists exercising in the heat, a 1 °C rise in core temperature and a 4% loss of body weight each lowered stroke volume by 7–8% and raised heart rate enough to keep cardiac output stable. When the two were combined, stroke volume fell further and cardiac output dropped by 13%.[12] Fluid replacement strategies are discussed in rehydration after exercise.
Illness and recovery. Fever and infection appear both on the athlete ECG list and among the causes of physiological sinus tachycardia, and IST has been described after COVID-19, so they are reasonable to consider when an athlete’s resting heart rate rises without an obvious training explanation.[1][9][14]
Does a Persistently Fast Resting Heart Rate Matter Long-Term?
At the population level, higher resting heart rate is associated with higher mortality. A meta-analysis of 46 prospective cohort studies found that each 10 bpm increase in resting heart rate was associated with a relative risk of 1.09 for all-cause mortality, and a resting rate above 80 bpm was associated with a relative risk of 1.45 for all-cause mortality compared with the lowest category. Compared with 45 bpm, a significantly increased risk of cardiovascular mortality was seen at 90 bpm.[6]
These figures need caution. The authors detected substantial heterogeneity and publication bias, and after correction for publication bias the all-cause relative risk per 10 bpm fell to 1.04.[6] The data describe an association in the general population, not evidence that sinus tachycardia itself causes harm, and they sit alongside the benign long-term course reported for IST.[3]
Conclusion: Sinus Tachycardia
Sinus tachycardia is a sinus rhythm above 100 bpm, and it can reflect a normal response to exercise, stress, fever, dehydration, alcohol, stimulants or an underlying condition such as anaemia or hyperthyroidism.[1] For physiological sinus tachycardia, the guideline approach is to identify and eliminate the cause.[1]
This matches what I see in practice. In outpatient work, a stressful life situation is often in the background when a patient’s resting heart rate has stayed raised, while in my emergency work, stimulant use and withdrawal from alcohol or opioids have come up every now and then as causes of sinus tachycardia.
When no cause is found, IST and POTS come into consideration. In one Finnish study, 1.16% of middle-aged adults met the diagnostic criteria for IST in use at the time, and IST appears to have a benign long-term course, although symptoms can significantly impair quality of life.[2][3] POTS is defined by the heart rate response to standing rather than by the resting rate.[13] Treatment evidence for IST remains limited, with ivabradine supported by a small randomised trial and invasive procedures not recommended for routine care.[2][5]
For athletes, international recommendations advise considering a repeat ECG after rest when the resting sinus rate is above 120 bpm, and looking for causes such as fever, infection, dehydration, stimulants, anaemia or hyperthyroidism.[14] In a meta-analysis, short-term overload training raised resting heart rate by only a few beats per minute.[11] In my view, the most useful question is usually not whether a number is above 100 bpm, but what is driving it.
From a clinical perspective, the most important point for me is that sinus tachycardia is taken seriously and not immediately attributed to stress. In my practice, that means at least one ECG to make sure there is nothing unusual, and a careful background work-up including laboratory tests. I also keep the possibility of pulmonary embolism in mind whenever the patient’s background fits. I once saw a patient with sinus tachycardia who worked as a flight attendant, and therefore flew a lot, and who also had shortness of breath. Fortunately, she did not have a pulmonary embolism in the end, but her profile certainly raised the question. I have also seen pulmonary embolisms with very mild symptoms, which always keeps me on my toes as a clinician.
References
- https://doi.org/10.1093/eurheartj/ehz467
- https://doi.org/10.1016/j.hrthm.2015.03.029
- https://doi.org/10.1016/j.eupc.2004.12.007
- https://doi.org/10.1016/j.jacc.2012.07.074
- https://doi.org/10.1016/j.jacc.2012.06.031
- https://doi.org/10.1503/cmaj.150535
- https://pubmed.ncbi.nlm.nih.gov/2424378/
- https://doi.org/10.1093/eurheartj/ehx156
- https://doi.org/10.1038/s41598-021-03831-6
- https://doi.org/10.1111/acem.12769
- https://doi.org/10.1136/bjsm.2007.042200
- https://doi.org/10.1152/jappl.1997.82.4.1229
- https://doi.org/10.1503/cmaj.211373
- https://doi.org/10.1016/j.jacc.2017.01.015
