How should this patient’s ‘Fitbit’-recorded tachycardia be managed?

Clinical conundrum: In the next in our series, Professor Raj Thakkar considers how to manage a patient who presents with apparent tachycardia from a recording on her ‘Fitbit’ wearable device

A 32-year-old woman’s ‘Fitbit’ wearable device shows that she has a resting tachycardia (of around 104bpm) and that her heart rate goes ‘too high’ during exercise. She has no relevant cardiological symptoms and is a non-smoker with no family history. She has tried another device to confirm the readings and received much the same results. You arrange FBC and TFT and these come back normal.

1. How accurate and useful are Fitbit and other similar devices?
In the era of wearable smart technology, it is common for patients to present to primary care with health alerts from their devices. This trend is set to increase exponentially over time.

The European Society of Cardiology (ESC) working group on wearable devices recognises the potential value of such devices, particularly for people with infrequent symptoms, but also accepts there is a knowledge gap and various challenges in this rapidly evolving field of medicine.

Such challenges include cost effectiveness of widespread device use, lack of recommendations on how to manage results, workload challenges, and risk of overtreatment. The group is clear however, that unusual readings on a consumer heart rate device are insufficient for a diagnosis [of arrhythmia] and ECG confirmation is mandatory.

Of note, Fitbit wearable devices use photoplethysmography, not ECG technology. Photoplethysmography detects microvascular blood volume changes and is the technology used in pulse oximeters. It can display the heart rate and also reflect the rhythm, but it cannot offer an ECG. While Fitbit devices have FDA approval and is CE-marked to detect AF, with a positive predictive value (PPV) of 98% seen in the Fitbit AF study, an ECG should still be used to formally diagnose arrythmias.¹

In a situation like this case with the patient already in front of you, it is best to assume the Fitbit is indeed reflecting a true tachycardia, given it may be reflective of serious disease. Nevertheless, a formal ECG will still be needed whereas some devices such as some Apple watches have an ECG facility and AliveCor offer a dedicated 1 and 6-lead home device. If the patient does have a device that offers ECG, it would certainly be advisable to ask the patient to provide this information, as it may prove invaluable.

2. What is the potential significance of a resting tachycardia?

Resting tachycardia, that is, a rate >100bpm, has an association with adverse cardiovascular risk factors such as adverse lipid profiles and high blood pressure, poor fitness and lower life expectancy.²

Causes of tachycardia are many-fold and include stress, pregnancy, medication, infection, dehydration, ketoacidosis, Addisonian crisis, catecholamine excess, pain, anaemia, mast cell disorders, autonomic dysregulation disorders, respiratory diseases (acute hypoxia, eg, PE; chronic, eg, COPD) and cardiovascular causes.

It would be essential to exclude any acute cause, such as PE and to establish whether the patient has a sinus tachycardia or another rhythm. Any other rhythm except sinus rhythm is abnormal.

Key points to explore would be: general level of fitness; pregnancy status; the timeline and circumstances of the tachycardia (eg, posture related, infection); and whether they experience any constitutional or cardio-respiratory symptoms such as feeling unwell, fever, weight loss, sweats, tremor, diarrhoea, sleep apnoea, chest pain, palpitations, breathlessness, dizziness or collapse. Any of these symptoms, if present, will need exploration. In this case, the FBC and TFTs are normal, excluding anaemia and thyroid disease. Exertional cardiac symptoms, such as exertional palpitations, angina, breathlessness or syncope would be of concern.

Past medical history is essential to appreciate, such as known coronary disease, albeit less likely in this age group, or cardiomyopathy.

A careful drug and medication history should be taken. Caffeine overuse, alcohol and illicit drugs may be implicated. Many prescribed medications can influence cardiac rate or rhythm, for example, beta-agonists and amlodipine can cause a sinus tachycardia.³

Family history should be explored including inherited cardiac diseases and sudden cardiac death.

Both a general and cardiac examination would be advised, considering non-cardiac causes of tachycardia such as acute and sub-acute infections (eg, TB and endocarditis), lung diseases, malignancy and autonomic dysfunction. Blood pressure including checking for postural drop should be assessed. The heart should be auscultated to assess heart rate and regularity, and to appreciate any evidence of structural heart disease including murmurs and heart failure.

If the patient appears acutely unwell, including potential sepsis, breathlessness, chest pain or hypotension, they should be managed according to your local urgent care pathways.

The Primary Care Cardiovascular Society has useful information on the investigation of arrhythmias.⁴ In addition to standard blood tests, it may be useful to check CRP and magnesium and, if the patient has fatigue, breathlessness or oedema, an NT-proBNP. Low magnesium levels are pro-arrhythmogenic and heart failure is often underdiagnosed in primary care. An ECG is essential to assess the rate and cardiac rhythm.

Reversible causes for tachycardia should be managed, such as addressing lifestyle issues or replacing prescribed drugs. Risk factors for atherosclerotic cardiovascular disease should be reviewed and a lifetime QRISK should be used, not a 10-year QRISK.

Red flags, an abnormal examination such as murmur, or concerning investigations would justify referral to the appropriate specialty. Open access referral for ambulatory monitoring in patients with no associated symptoms or signs, and a normal resting ECG may be appropriate. Those with resting tachycardia with no clear reversible cause or in those who can’t be managed in primary care should be referred.

3. How should the pulse rate change with exercise and what is the significance of disproportionately fast rates?

Tachycardia on exertion may or may not be physiological. It would be essential to understand if the tachycardia is appropriate to the level of exertion, if it is sinus tachycardia or another rhythm, and if there are associated symptoms. It is not straightforward to define what a normal rate as there are several factors at play, including level of fitness. The American Heart Association, however, does have a useful chart to help.⁵ Non-sinus rhythm exertional tachycardias are always abnormal.

Associated red flags should be proactively looked for and managed including abnormal examination or ECG, concerning family history, exertional angina, exertional palpitations, unexpected breathlessness, dizziness or syncope. In addition to abnormal rhythms and red flags, disproportionally high exercise induced sinus tachycardias should be referred.

Professor Raj Thakkar is a GP and President and CKD lead of the Primary Care Cardiovascular Society, Honorary Visiting Professor at Cardiff University School of Medicine and NHS England National primary care workstream co-lead, Cardiac Transformation Programme

References

1. Lubitz S et al. Detection of Atrial Fibrillation in a Large Population Using Wearable Devices: The Fitbit Heart Study. Circulation 2022;146(19):1415-24
2. Jensen M et al. Resting heart rate is associated with cardiovascular and all-cause mortality after adjusting for inflammatory markers: the Copenhagen City Heart Study. Eur J Prev Cardiol 2012;19(1):102-8.
3. Tisdale J et al. Drug-induced arrhythmias: a scientific statement from the American Heart Association. Circulation 2020, 142:e214-33
4. Primary Care Cardiovascular Society: https://pccsuk.org/
5. American Heart Association. Target heart rates chart. Last reviewed August 2024