Understanding bradycardia and a slow heart rate

Bradycardia is the medical word for a slow heart rate. In practice it usually means a heart that beats fewer than 60 times a minute at rest. On its own, that number is often nothing to worry about. Many fit people have a resting rate below 60, and the heart naturally slows during sleep.

What matters is whether the slow rate is the body working as it should or a sign that the heart's electrical system is struggling. A slow pulse that comes with dizziness, fainting, breathlessness or unusual tiredness needs to be looked at. A slow pulse found by a smartwatch in a fit person who feels completely well usually does not. This article explains how to tell the difference, what causes a slow heart rate and how it is treated.

How the Heart Sets Its Own Pace

Every heartbeat starts with an electrical signal from the sinus node, a small cluster of cells in the upper right chamber that acts as the heart's natural pacemaker. The signal crosses the top chambers, passes through a junction called the AV node and travels down into the main pumping chambers, which contract.

A slow heart rate can come from either end of that system. The sinus node can fire too slowly, or the signal can be delayed or blocked on its way down. Doctors call the first a sinus node problem and the second heart block, and the distinction matters because they are managed differently.

When a Slow Heart Rate Is Normal

The British Heart Foundation describes sinus bradycardia as a regular heartbeat that is slower than 60 beats a minute, and is clear that having it does not mean there is something wrong with your heart. The commonest reasons for a healthy slow rate are fitness and sleep. A heart that has been trained by regular exercise pumps more blood with each beat, so it needs fewer beats at rest, and a low heart rate can be a sign of being very fit.

That is why your own baseline, and whether it has changed, tells a cardiologist more than any single number. We explain why in our article on why your resting heart rate matters.

When It Is a Sign of Something Else

A slow rate becomes significant when the heart is no longer pumping enough blood for what the body needs. The causes fall into a few broad groups.

• Wear and tear in the electrical system. The sinus node can become sluggish with age, a condition called sick sinus syndrome. Some people swing between slow and fast rhythms, which is tachy brady syndrome.
• Heart block. The NHS notes that heart block is most often caused by a heart condition such as coronary heart disease or a heart attack. It ranges from first degree heart block, which rarely needs treatment, through second degree to third degree heart block, where the signal does not get through at all.
• Medicines. Beta blockers work by slowing the heartbeat, and they and some other heart medicines, digoxin included, can slow it more than intended.
• Other conditions. An underactive thyroid, an imbalance in the body's salts, inflammation of the heart muscle and a complication of heart surgery are all recognised causes of a slow heart rate.

When a medicine or another condition is responsible, treating that cause often brings the heart rate back up with no heart procedure needed.

Symptoms Worth Paying Attention To

Many people with a slow heart rate have no symptoms and only find out during tests for something else. When symptoms appear, they come from the brain and muscles getting less blood than they need. The NHS lists the symptoms of heart block as dizziness, fainting or feeling like you are about to faint, chest pain, tiredness and shortness of breath. Others notice they cannot manage a walk or a flight of stairs the way they used to.

Our pages on dizziness, blackouts and fatigue explain how a cardiologist thinks about each of these.

Some situations cannot wait for an appointment. The NHS advises calling 999 if someone has been diagnosed with heart block and has chest pain, has severe difficulty breathing, or feels sweaty, sick or lightheaded, and if someone faints and is not breathing or cannot be woken within one minute. Do not drive yourself to A&E. If you have fainted but recovered, or you feel dizzy all the time or it keeps coming back, the NHS advice is to get help from NHS 111.

How a Slow Heart Rate Is Investigated

The aim of the tests is to answer two questions. Is the slow rate coming from the heart's electrical system or from something outside it, and does it line up with the symptoms?

A 12 lead ECG is the starting point. It shows the rate and rhythm at that moment, and it often shows the signature of heart block or a slow sinus node. Because a slow rhythm can come and go, a single ECG can be normal on the day. That is where ambulatory ECG monitoring helps, by recording every beat over a day or longer so that pauses and slow spells can be matched against what you felt. Our article on the Holter monitor explains what wearing one is like.

Blood tests check thyroid function and the body's salts. An echocardiogram looks at the structure and pumping of the heart, because a slow rhythm sometimes travels with another heart condition. An exercise tolerance test shows whether the heart rate rises as it should when you exert yourself, which helps when tiredness or breathlessness comes on with effort.

A slow rate can turn out to be the effect of a tablet started for blood pressure, angina or a fast rhythm, and adjusting the dose can be the whole answer.

Treatment, From Nothing at All to a Pacemaker

Treatment follows the cause and the symptoms, not the number. The NHS is clear that heart block that is not causing any symptoms will not usually need any treatment, and the same is true of a healthy sinus bradycardia.

Where a medicine is responsible, the dose can be lowered or the medicine changed. Where a thyroid or salt problem is responsible, treating it usually corrects the heart rate.

Where the electrical system itself is failing and causing symptoms, the treatment is a pacemaker. It is a small device placed under the skin of the chest, and the British Heart Foundation explains that most pacemakers work just when they are needed, sending a signal that tells the heart to beat when its own rate drops too low. According to the NHS, fitting a pacemaker usually takes about an hour under local anaesthetic, and for some people with a slow heartbeat a leadless pacemaker can be placed through a vein with no wires and no cut to the chest. There are rules to follow while it settles, including no driving for at least the first week and no heavy lifting for four to six weeks, and the battery usually lasts six to seven years. Our article on how pacemakers help control heart rhythm covers living with one.

Because the device stops the heart dropping below a safe rate, people with a pacemaker can lead normal, active lives, although that also depends on the condition behind the slow rhythm.

Practical Points if You Have Been Told Your Heart Rate Is Slow

• Look at the whole picture. A reading in the 50s in somebody who exercises and feels well is very different from the same reading in somebody who has started to feel faint.
• Keep a note of symptoms. Write down when you feel dizzy, breathless or exhausted, what you were doing and how long it lasted. It makes any monitoring far more useful.
• Bring a list of your medicines. Include anything bought over the counter and any recent change of dose.
• Do not stop a prescribed medicine on your own. If you think a tablet is slowing your heart, speak to the doctor who prescribed it first.

Seeing a Heart Rhythm Specialist in Kingston

Heart rhythm disorders are Dr Jogiya's main specialist interest, covering electrophysiology and complex pacing, and he holds the British Heart Rhythm Society examination in electrophysiology and devices. He is part of the cardiology teams at Kingston Hospital and Guy's and St Thomas'. Our article on what a heart rhythm specialist in Kingston does explains how a rhythm assessment works, and the wider range of rhythm problems we see is set out on our arrhythmias page.

We see patients at private clinics in Kingston upon Thames and central London, and a consultation can be followed by any of the tests above. Investigations can often be coordinated alongside or following that first appointment.

Conclusion

A slow heart rate is common and very often healthy. The real question is whether the heart is keeping up with what the body needs.

A fit person with a resting rate in the 50s and no symptoms usually needs no tests at all. Dizziness, blackouts, breathlessness or new tiredness alongside a slow pulse deserve a proper look, and the answer is often simple, whether that is a change of medicine, a treated thyroid or, where the heart's wiring is the problem, a pacemaker that restores a safe rhythm.

If you have been told your heart rate is slow, or you have symptoms that might fit, you can contact us at Kingston Cardiologist to arrange a heart rhythm consultation in Kingston upon Thames or central London.