HEART RHYTHM DISORDERS

What are cardiac arrhythmias?

Cardiac arrhythmias (also called dysrhythmias) are abnormal heart beats or heart rhythms that originate from sites other than the usual site (in the sinus node). The term “palpitations” refers to the sensation felt by the affected person with a cardiac arrhythmia. Such individuals may feel that their heartbeat is irregular, stronger than usual or too fast or slow. A normal heart rate ranges between 50 to 100 beats per minute for most people. Cardiac arrhythmias can occur with a normal heart rate, or with heart rates that are too slow (below 50 beats per minute) or too fast (greater than 100 beats per minute). In addition to feeling palpitations, patients with arrhythmias may also experience other symptoms, such as dizziness, lethargy, breathlessness and sudden blackouts.

What causes arrhythmias?

Arrhythmias may be caused by a variety of factors. These include:

• Coronary artery disease (CAD)
• Heart failure and valvular heart disease
• Healing process after heart surgery
• Electrolyte imbalances in your blood (e.g. abnormal potassium levels)
• Abnormal thyroid hormone levels
• Excessive alcohol or caffeine intake

Some patients with apparently “normal” hearts may also experience arrhythmias due to underlying electrical abnormalities in their hearts that cannot be detected with standard imaging tests. Patients with arrhythmias should therefore seek expert help from a cardiologist for accurate diagnosis and treatment.

What are the symptoms?

An arrhythmia may be silent and not cause any symptoms. This is particularly true of atrial fibrillation (AF), which may be picked up by your doctor during a routine medical check up. When symptoms do occur, they may include:

• Palpitations
• Chest discomfort
• Dizziness or light-headedness
• Breathlessness
• Weakness or fatigue
• Blackouts

What are the types of arrhythmias?

Ectopic Beats

These are extra heart beats that occur earlier than normal within the heart cycle. Ectopic beats (or extrasystoles) can come from either the atria (the two top chambers of the heart) or the ventricles (the two lower chambers of the heart). They can sometimes cause palpitations, which may feel like missed or extra heart beats. Ventricular ectopics (also known as premature ventricular contractions or PVCs) are very common and can occur in people with or without heart disease. Ectopic beats are not normally dangerous and only rarely cause damage the heart. However, people who experience a lot of ectopic beats and/ or have symptoms associated with them should seek expert assessment by a cardiologist.

Atrial Fibrillation (AF)

Atrial fibrillation is the most common, serious, heart rhythm abnormality and affects millions of people worldwide. The condition involves rapid, irregular activity in the atria and leads to symptoms such as palpitations, dizziness, blackouts, breathlessness and lethargy. Atrial fibrillation is also a common cause of stroke, which occurs in approximately 5% of people with atrial fibrillation per year. Although it may affect young people, it becomes more common with increasing age, and typically affects older patients of 65 and above.

Atrial Flutter

This is an arrhythmia caused by one or more rapid circuits in the atria (usually the right). The rhythm is more organized and regular than atrial fibrillation, although it can produce similar symptoms to atrial fibrillation and also increase the risk of stroke. Atrial flutter is more common in middle aged and elderly patients and usually occurs in patients with other heart conditions, such as high blood pressure or previous heart attack. It can also be associated with atrial fibrillation and some patients may have both atrial flutter and atrial fibrillation

Supraventricular Tachycardia (SVT)

This is a rapid heart rate, usually with a regular rhythm, that originates from above the ventricles. SVT begins and ends suddenly and can affect people of all ages, including children and older adults. It is not usually life-threatening, although the symptoms can be very unpleasant and occur unpredictably. Most SVT will recur and can be safely and very effectively treated with a procedure called catheter ablation. There are two main types of SVT:

AV nodal re-entrant tachycardia (AVNRT): This is due to more than one pathway through the AV node, which normally connects the atria and ventricles. This extra pathway allows a circuit to form within the AV node that can lead to very fast heart rates and symptoms of palpitations.

Accessory pathway tachycardias: These are due to an extra electrical pathway (accessory pathway) between the atria and ventricles that allows the electrical impulses to travel very quickly in a circuit around the heart, causing the heart to beat unusually fast. The accessory pathway is present from birth and may sometimes be seen on the normal resting ECG (in this case, the condition is termed Wolff-Parkinson-White syndrome or WPW).

Atrial Tachycardia (AT)

This is a rapid heart rate originating from an abnormal site in the atria that can lead to sudden onset palpitations. AT is less common than SVT and is often seen in diseased hearts, but may also occur in normal hearts.

Ventricular Tachycardia (VT)

VT is a rapid heart rhythm originating from the lower chambers of the heart (the ventricles) and may potentially be life-threatening. The rapid rate prevents the heart from filling adequately with blood- this decreases the amount of blood the heart can pump around the body and can result in dizziness, blackouts and sudden death. VT often occurs in patients with other forms of heart disease, such as a previous heart attack or heart failure, although it may also occur in patients with otherwise completely normal hearts. Patients with VT should seek expert assessment from a cardiologist.

Ventricular Fibrillation (VF)

This is an erratic, disorganized rhythm in the ventricles that results in the heart being unable to contract or pump blood to the head and body. The rhythm is a medical emergency and must be treated with cardiopulmonary resuscitation (CPR) and immediate defibrillation.

Bradyarrhythmias

These are abnormally slow heart rhythms that impair the ability of the heart to supply blood to the rest of the body leading to symptoms such as dizziness, lethargy, breathlessness and blackouts. These arrhythmias may be due to disease in the heart’s electrical conduction system at several points:

Sinus node dysfunction: due to an abnormal sinus node (the natural pacemaker of the heart). Significant sinus node dysfunction that causes symptoms is treated by insertion of a permanent pacemaker.

Heart block: Due to partial or complete block of electrical impulses travelling between the atria and ventricles. This may lead to the ventricular rate being too slow, despite the atrial rate being adequate. The heart may beat irregularly and too slowly. Some forms of heart block may require treatment with a permanent pacemaker.

How are arrhythmias diagnosed?

The following tests may be required to diagnose an arrhythmia:

• Electrocardiogram (ECG)
• 24 hour Holter monitor
• Event recorder
• Exercise Treadmill Test (ETT)
• Electrophysiological (EP) study