Abnormal heart rhythms and health

by Dr. Yanushi Dullewe Wijeyeratne

The heart has an electrical conduction system which makes the heart muscle work in a coordinated way to pump blood around the body. The normal heart rhythm is called sinus rhythm. It is regular, with a rate of between 60 and 100 beats per minute at rest. An abnormal heart rhythm (also called an arrhythmia) occurs when this normal conduction system in the heart is damaged or overridden by an abnormal electrical system, which causes the heart to beat either abnormally slowly, abnormally fast, or in an irregular way. Some arrhythmias are more serious than others.

There are many reasons why a person may develop a heart rhythm problem. Most rhythm abnormalities develop with age or associated with other medical problems. Arrhythmias are most common in older people, and in people with abnormal heart structure or following a heart attack. However, some people may be born with an abnormality in the electrical conduction system in the heart that predisposes them to arrhythmias at a young age.

How can it be recognised?

Symptoms will depend on the type of rhythm problem, and how it affects the functioning of the heart. Some people may be completely unaware that they have an abnormal heart rhythm. The most common symptoms include palpitations, breathlessness, dizziness or recurrent fainting. Dizziness that comes on suddenly without any warning, sudden collapse, or loss of consciousness may be the only symptom of a serious heart rhythm problem. Palpitations are when a person becomes aware of their own heartbeat or feel 'extra beats' or 'missed beats'.

It is sometimes described as a fluttering in the chest, or feeling like the heart is pounding. It can feel unpleasant and may cause distress, although palpitations may not always be due to a serious rhythm problem of the heart. For example, occasional extra heart beats can be normal, but it is important that anyone having these symptoms are properly investigated as they can also indicate serious heart rhythm disorders.

There are many types of abnormal heart rhythms that may be associated with either fast or slow heart rates. On the other hand, slow or fast heart rates may not necessarily always be abnormal. Highly athletic or very active individuals often have very slow heart rates at rest.

This is part of the normal physiological response of the heart to long-term physical training. Brisk exercise, pain and emotional stress are associated with fast heart rates as part of the body's normal response to these situations. Although the heart rhythm should normally be regular, there can be normal variation in the beating of the heart with breathing, known as 'sinus arrhythmia'. Inspiration is associated with a slight speeding up of the heart rate, which then slows down with breathing out. This is completely normal and is not associated with any harmful effects on the body. In some people, particularly in children, this variation may be more obvious than in adults.

It is possible for anyone to find out if they have a normal heart rhythm. By feeling your pulse, you can not only count the heart rate, but also feel the rhythm of your pulse to see if it is regular or irregular. It is important to note though that abnormal heart rhythms are often intermittent. In between episodes, the heart rate and rhythm can be completely normal even if there is a serious underlying problem. If you think either yourself or someone you know sometimes has an abnormal pulse, or if you're concerned about your pulse, it is important seek medical attention promptly to rule out any serious heart rhythm disorders.

Diagnosis

An ECG (also called an electrocardiogram) is used to record the electrical activity of the heart. It is a painless test that usually takes about five minutes to carry out. Small electrodes are placed on the chest, arms and legs and are connected, by wires, to a recording machine. It can show an arrhythmia, but only if it is happening at the time that the ECG is being taken. Sometimes an ECG can show features that could suggest if a person might be at risk of a heart rhythm disorder.

If a standard ECG doesn't pick up an arrhythmia but if someone is getting symptoms that are suspicious, there are ways to monitor the rhythm over a longer period to try and capture the heart rhythm at the time that the person is getting symptoms. A 24 hour ECG recording, also known as Holter monitoring or ambulatory ECG monitoring, is where a small recording machine is worn around the waist for 24 hours (or longer if required), and connected to ECG leads taped to the chest. If symptoms only come on every few days or less frequently than that, a cardiac event recorder can record the heart rate and rhythm over a longer period. Alternatively if a person gets symptoms only very rarely but which raise the suspicion of a serious heart rhythm disorder, a cardiologist can place a device called an implantable loop recorder in the chest to record rare electrical disturbances in the heart. The cardiologist places the device just underneath the skin through a small surgical procedure. This small, slim device, which is about the size of a computer memory stick, can be left in the chest for up to 3 years to record potential abnormal rhythms.

Sometimes, problems with the heart muscle or heart valves can be the cause of the rhythm problem. Longstanding heart rhythm problems can also cause the heart muscle to weaken. An echocardiogram is a painless gel scan of the heart that can inform the cardiologist if the structure and function of the heart is normal.

Less commonly, the cardiologist may need to carry out a detailed heart study under sedation or general anaesthesia, called an electrophysiological study.

This helps to isolate electrical signals that originate in abnormal places within the heart, and to investigate abnormal electrical pathways. Once the problem is identified, it is often possible to treat the source of the arrhythmia during the same procedure, through a technique called radiofrequency catheter ablation.

The implications of an abnormal fast heart rhythm and its treatment can be very different depending on where it originates from in the heart. Some fast heart rhythms arise from the top chambers of the heart and are called supraventricular tachycardias (SVTs). SVTs may be due to one or more extra electrical pathways between the atria (top chambers of the heart) and the ventricles (bottom chambers of the heart). The extra electrical pathway can periodically make the heart beat very fast.

These are quite common, but rarely life threatening. They often present for the first time in early adulthood. The rhythm disturbance can be triggered by caffeine, alcohol, certain drugs, and hormone changes in adolescence or pregnancy. In most cases, there are no other heart problems. Simple manoeuvres like chewing on ice can make the abnormally fast heart rhythm revert back to a normal rhythm, whereas in other cases, specific treatment with medications, or electrical shock treatment for the heart (cardioversion) may be required. For some conditions, an invasive procedure called a catheter ablation may be required to permanently treat the underlying cause.

Sometimes electrical impulses circulate at a very fast rate around the top chambers of the heart to give rise to a condition called atrial flutter.

People who have atrial flutter usually have another underlying medical problem such as coronary artery disease, heart muscle disease, heart valve disease, lung disease or abnormal thyroid function. Atrial flutter may co-exist with another type of abnormal heart rhythm called atrial fibrillation (AF). AF is the most common type of abnormal heart rhythm, particularly in older people and affected people may not have any symptoms at all. Approximately 35 million people have atrial fibrillation worldwide, and its incidence is increasing. It occurs when different areas in the top chambers of the heart fire random electrical impulses in an uncoordinated way.

Both atrial flutter and atrial fibrillation increase the risk of developing a blood clot inside the heart because the top chambers of the heart contract less efficiently in the presence of the fast electrical activity. Consequently, there is stagnation of blood in the heart chambers, which can form clots. If a clot breaks off, it could block one of the blood vessels supplying the brain and cause a stroke.

Atrial fibrillation is a major cause of stroke, so it is extremely important that it is diagnosed and treated, even if there are no symptoms. In addition to treating the underlying rhythm problem, stroke risk is reduced through the use of blood thinning medications such as warfarin.Fast heart rhythms that originate from the main pumping chambers of the heart are called ventricular arrhythmias.

These are life-threatening rhythm disorders that can cause the blood pressure to fall rapidly and are medical emergencies that require immediate resuscitation and treatment.

If someone collapses and is found to have an absent pulse, it is important to immediately start resuscitation with chest compressions whilst awaiting an ambulance to improve chances of survival. These dangerously fast heart rhythms often come on suddenly and may occur in people with underlying heart muscle disease, or as a consequence of damage to the heart muscle in a heart attack. Young people may be at risk if they have an inherited heart condition for example, that predisposes to sudden death. Immediate treatment involves prompt resuscitation and reverting the rhythm back to a normal rhythm.

If the person survives, an implantable cardioverter defibrillator (ICD) may be implanted by a cardiologist to prevent future cardiac arrest from a similar rhythm disturbance.

The writer who holds BMedSci Hons(UK)BMBS(UK) MRCP(UK) is a Specialist Registrar in Cardiology at St George's Hospital and St George's University of London and has authored several articles published in international medical journals.