Sinus Bradycardia on an ECG: What Does It Mean and Is It Normal?

Sinus bradycardia on an ECG means your heart rhythm is starting normally, from the sinus node, but the rate is slower than expected. In adults this usually means fewer than 60 beats per minute at rest. Many people with this finding have no symptoms and need no treatment.

The word "sinus" refers to the sinoatrial node, the heart's natural pacemaker. "Bradycardia" is the medical term for a slow heart rate. A typical adult resting rate is 60 to 100 beats per minute, so the report is describing a rate below that range, not a fault in the shape of the heartbeat.

On the tracing, each beat looks normal in shape; it simply comes less often. If the report lists sinus bradycardia and nothing else, the electrical signal is following its usual path. If it also mentions other findings, such as a heart block, a bundle branch block or changes in the T waves, ask what those mean separately, because they answer different questions.

This guide explains the label on an ECG report. It cannot tell you whether your own slow rate is normal for you; that depends on symptoms, medicines, other results and examination by a clinician.

Call your local emergency number or go to the nearest emergency department if a slow heart rate comes with chest pain, trouble breathing, fainting or loss of consciousness, or new confusion. NHS advice also says not to drive yourself to hospital with these symptoms.

Cleveland Clinic advises emergency care if your heart rate falls below 40 beats per minute and this is unusual for you, and describes a rate in the 30s as needing immediate medical attention. A normal earlier ECG does not make new symptoms safe to ignore.

Often, yes. Regular endurance training makes the heart pump more efficiently, so it can beat more slowly at rest. MedlinePlus lists 40 to 60 beats per minute as a typical resting pulse for well-trained athletes, and Healthdirect notes that rates of about 40 to 60 can be normal in young, healthy or very fit adults.

Heart rate also falls naturally during sleep and deep rest, and tends to slow with age. Cleveland Clinic notes that sinus bradycardia is most common in adults over 65. A slow rate found on a relaxed, resting ECG, or flagged by a watch overnight, is therefore common.

Being fit does not rule out other causes. If an athlete notices dizziness, fainting, unusual breathlessness or a drop in exercise ability, a clinician should still assess it.

Yes. Several medicines can slow the heart. Cleveland Clinic lists beta blockers, calcium channel blockers, antiarrhythmic medicines, digoxin, opioids, lithium and some antidepressants among them. NHLBI also notes that some medicines for high blood pressure, heart rhythm problems and mental health conditions can affect the heart's electrical system.

An underactive thyroid (hypothyroidism) can cause a slower heart rate; NIDDK lists it as a symptom. Other possible causes include low or high electrolytes such as potassium, obstructive sleep apnoea, infections such as Lyme disease, low body temperature and conditions affecting the heart's conduction system, such as sick sinus syndrome or heart block.

Do not stop or change a prescribed medicine because of an ECG report. Bring a full list of what you take, including non-prescription products, and ask the prescriber or pharmacist whether any of them could be contributing.

A slow rate is more likely to need assessment when it causes symptoms, is new or very low for you, appears alongside other ECG changes, or occurs with a medicine change, thyroid symptoms or a known heart condition. Possible symptoms include dizziness or light-headedness, tiredness or weakness, breathlessness on exertion, fainting, palpitations and confusion or poor concentration.

Because a standard ECG records for only a short time, MedlinePlus notes it can miss problems that come and go. Depending on the situation, tests a clinician may consider include:

• Blood tests, for example electrolytes and thyroid hormone levels.
• A wearable heart monitor that records the rhythm during daily life, or over longer periods.
• An exercise test to see whether the heart rate rises normally with effort.
• An echocardiogram (heart ultrasound) to look at the heart's structure and pumping.
• A sleep study if sleep apnoea is suspected.

Usually not, if you are healthy and have no symptoms. When treatment is needed, it depends on the cause. That might mean a clinician reviewing a medicine, treating an underactive thyroid or another underlying condition, or, for people whose heart rate is persistently too slow and causing symptoms, fitting a pacemaker.

Cleveland Clinic suggests that a heart rate of 40 to 60 beats per minute without symptoms is usually not a concern, but is still worth mentioning to your clinician so it can be seen in context.

If a medicine is the likely cause, the prescriber may weigh its benefits against the slower rate before deciding whether anything should change. That decision belongs with the person who knows why it was prescribed.

Take the ECG report, any earlier ECGs or watch recordings, and a list of your medicines. These questions can help:

• What was my heart rate on the ECG, and was anything else on the tracing unusual?
• Is this rate expected for my age, fitness and medicines?
• Could any of my medicines, my thyroid or my sleep be contributing?
• Do my symptoms, such as tiredness or dizziness, fit with a slow heart rate, or are they more likely to have another cause?
• Do I need blood tests, a heart monitor or any other follow-up, and who will tell me the results?
• Which symptoms should make me seek urgent care?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a slow heart rate on an ECG described their symptoms, medicines and follow-up can help you notice details worth mentioning and questions you had not thought to ask.

Every case is different. Similar cases cannot tell you whether your own heart rate is normal, and they are not a substitute for assessment. Use them to prepare for your appointment, and seek urgent care for any warning symptoms.