Can a high or low heart rate make you feel dizzy?

Yes. A heart rate that is too fast or too slow can both make you feel dizzy, lightheaded or faint. Your brain needs a steady supply of blood, and your heart provides it by pumping a certain amount with each beat, a certain number of times a minute. When the rate climbs very high, the heart has too little time to fill between beats, so each beat pushes out less blood. When the rate drops very low, there are simply too few beats. Either way, the flow of blood to the brain can fall for a few seconds or longer, and dizziness is often the first sign.

That does not mean every fast or slow pulse is a problem. A normal resting heart rate for an adult is usually between 60 and 100 beats per minute, according to the British Heart Foundation, and many healthy people sit outside that range. What matters is the combination of an unusual rate with symptoms such as dizziness, breathlessness or fainting. Most dizziness turns out to have nothing to do with the heart, and the commonest episodes are due to low blood pressure or a simple faint. Even so, when dizziness comes with a racing or a very slow pulse, it is important to rule out a heart rhythm problem and to make sure a pacemaker is not needed.

Why your heart rate affects how your head feels

The amount of blood your heart pumps each minute depends on two things, how much it pushes out with each beat and how many times it beats. Your body is good at adjusting both. When you stand, exercise or get anxious, the rate rises to keep the blood flowing, and when you rest it falls again.

Problems start when the rate moves outside the range your body can make up for. A very fast rhythm leaves the heart's chambers too little time to refill, so the output can fall even though the heart is working harder. A very slow rhythm cannot make up the volume, especially when you get up or move about. Blood pressure then dips, the brain receives less blood for a moment, and you feel lightheaded, unsteady or as if you might pass out. If the flow falls far enough, you can faint.

Dizziness with a fast heart rate

A fast heart rate is called tachycardia, and it usually means a resting rate above 100 beats per minute. Often it is a normal response to something else. Exercise, anxiety, a fever, dehydration, caffeine and alcohol all push the rate up, and the dizziness that comes with them tends to settle once the trigger passes. A racing heartbeat of this kind needs the trigger dealt with rather than the heart treated.

Some fast rhythms come from the heart's electrical system itself. The ones that most often cause dizziness are these.

• Supraventricular tachycardia (SVT). The NHS describes SVT as the heart suddenly beating much faster than normal and then slowing down abruptly. Episodes usually last a few minutes but can go on for hours, and people often feel weak, breathless, lightheaded or dizzy during them. It is rarely life threatening.
• Atrial fibrillation. Here the rhythm is fast and irregular. Some people feel dizzy or tired, others notice nothing at all. The NHS atrial fibrillation page lists feeling lightheaded, dizzy or as if you might faint among its symptoms. It matters because treatment lowers the risk of blood clots and stroke, so it always needs proper assessment. I explain it more fully in what is the term AF.

These sit within the wider family of abnormal heart rhythms, and the right treatment depends on which one it is.

Dizziness with a slow heart rate

A slow heart rate is called bradycardia, usually a resting rate below 60 beats per minute. On its own this is often perfectly normal. The British Heart Foundation notes that a slow rate can be normal in people who are very fit, and most of us have a slower rate while we sleep. A slow pulse with no symptoms rarely needs anything doing.

A slow rate becomes a concern when it causes symptoms, and dizziness, fainting and tiredness are the main ones. The causes I look for include the following.

• Heart block. The electrical signal is delayed or blocked on its way through the heart. The NHS heart block page explains that first degree block does not usually need treatment, second degree sometimes does, and third degree (complete) heart block often does. Dizziness that keeps coming back is one of its symptoms. I explain the types in more detail in what is a heart block.
• Medicines. The British Heart Foundation lists medicines such as beta blockers among the causes of a slow heart rate, since slowing the heart is part of how they work. Digoxin, if too much builds up in the body, can cause a fast, slow or unsteady heartbeat with dizziness and feeling sick, according to the NHS guidance on digoxin. Never stop or change a heart medicine yourself. Speak to the doctor who prescribed it first.

When the heart rate is normal but you still feel dizzy

Many people who feel dizzy have a normal heart rate throughout. The NHS dizziness page lists the commoner causes, including a drop in blood pressure when you stand up, inner ear problems, low blood sugar, dehydration and the side effects of a new medicine. A spinning sensation (vertigo) usually comes from the inner ear rather than the heart. I cover the full range of heart and non heart causes in could dizziness be a sign of a heart problem, and the symptom page on dizziness or blackouts sets out how it is investigated.

What is worth noting when it happens

If you feel dizzy and can safely do so, sit or lie down first. Then, if you can, check your pulse at your wrist or neck, which the British Heart Foundation explains how to do. A few details help a great deal when you are assessed later.

• Roughly how fast your pulse was, and whether it was regular or irregular.
• Whether the episode started and stopped suddenly or built up gradually.
• What you were doing at the time, such as standing up, exercising or resting.
• How long it lasted, and whether you felt breathless, had chest discomfort or passed out.
• Any medicines you had recently started or changed.

A home blood pressure monitor also shows your pulse, and I encourage patients to have their own machine and take regular readings at home.

How the cause is found

The key is to record the heart's rhythm while you feel dizzy. A 12 lead ECG is usually taken during the consultation. It can show a rhythm problem or signs of an underlying condition, but it records only a short moment, and a normal ECG does not rule out a heart problem.

That is why longer monitoring is so often the step that gives the answer. An ambulatory ECG monitor can be worn for up to 7 days while you keep a diary of symptoms, and a ZIO patch records the rhythm for up to 14 days and is waterproof, so it keeps recording during exercise and in the shower. The NICE guideline on blackouts advises choosing the type of monitor according to how often the episodes happen. I explain the longer monitors in more depth in what is a Holter monitor and when is it used.

An echocardiogram, an ultrasound scan of the heart, shows whether the heart muscle and valves are healthy. This matters because a rhythm problem in a structurally normal heart is treated quite differently from one in a heart that has been damaged. Blood tests can look for causes outside the heart, such as anaemia or an overactive thyroid, both of which the British Heart Foundation lists among the causes of a fast heart rate.

How it is treated

Treatment depends entirely on the cause, which is why the diagnosis comes first.

For a fast rhythm, the first step is often dealing with triggers such as caffeine, alcohol and poor sleep, sometimes alongside a medicine to slow the heart. SVT that keeps coming back can usually be cured with catheter ablation, which the NHS says permanently cures the problem in most people. For ablation I work closely with my colleague Dr Para Dhillon. Atrial fibrillation is managed by controlling the rate or the rhythm and, in most people, with a blood thinner to lower the risk of stroke.

For a slow rhythm, the first step is often reviewing medicines, since adjusting a dose can be enough. When the slow rate comes from the heart's own wiring and is causing symptoms, a pacemaker keeps the heart from beating too slowly. The NHS pacemaker page explains how one is fitted under local anaesthetic, and for some people with a slow heartbeat a leadless pacemaker is now an option.

When dizziness with an abnormal heart rate is an emergency

Call 999 if a fast heartbeat comes with shortness of breath, chest pain or feeling faint. The NHS also advises calling 999 if someone faints and has chest pain or a pounding, fluttering or irregular heartbeat, has not fully recovered, or has difficulty speaking or moving, and if someone faints and is not breathing or cannot be woken within a minute. These thresholds come from the NHS pages on SVT, heart block and fainting.

Use NHS 111 for urgent advice if you feel dizzy all the time or it keeps coming back with a slow heart rate. If you are fainting regularly, the NHS says you must tell the DVLA, and you must not drive while you are waiting to see a specialist your GP has referred you to. I also discuss when a blackout needs urgent attention in could fainting be a sign of a heart problem.

When to see a cardiologist

It is worth arranging an assessment if you have repeated dizzy spells with a pulse you can feel racing or slowing, if your resting heart rate is often below 60 or above 100 and you have symptoms with it, if dizziness started after a new heart medicine, or if you have fainted. The same applies if you have a heart condition already, or a family history of sudden death at a young age.

Conclusion

A heart rate that is too fast or too slow can make you feel dizzy, because it reduces the flow of blood to the brain. Often the cause is harmless, such as a normal response to a trigger or a naturally slow pulse in a fit person. Sometimes it is a rhythm problem such as SVT, atrial fibrillation or heart block, and these are worth finding because effective treatment exists, from medicine to ablation or a pacemaker. The way to tell them apart is to record the rhythm while the dizziness is happening.

If you have dizzy spells with a fast or slow heartbeat, you can contact me, Dr Arvind Vasudeva on 020 8977 4826 or book an appointment at Parkside Hospital in Wimbledon, The New Victoria Hospital in Kingston, Cleveland Clinic London or the Heartsure clinic.