Arrhythmias

How the heart works:

An electrical impulse is produced by your sinus node (SA node) which consists of a cluster of cells found in the upper part of the wall of the right atrium of your heart. The impulse is conducted to your atria, causing them to contract and push blood into the ventricles. The electrical signals pass to the atrioventricular node which is a cluster of cells found in between the atria and ventricles. After passing the AV node and after blood has passed into the ventricles, the electrical impulses are transmitted to the ventricles through special fibres embedded in the wall of the lower part of the heart, causing them to contract. This then pushes the blood around the body, out of the heart.

Normal Cardiac Conduction

Normal Cardiac Conduction

An arrhythmia is a disturbance of your heart’s usual electrical rhythm. It can be detected using an echocardiogram (ECG).

 Normal ECG Reading

Normal ECG Reading

Types of Arrhythmia:

Atrial Fibrillation

This is the most common form of arrhythmia and occurs when the electrical signals in your atria become disorganized, overriding your normal heart rate. This causes your atria to contract randomly and can cause an irregularly fast heart rate. A normal rate can be between 60 and 100 bpm (beats per minute) whereas in atrial fibrillation, it can be over 140 bpm. However, this is not always the case; your heart rate can be any speed. Attacks such as these can last from a few seconds up to a week.

ECG of Atrial Fibrillation showing tiny waves in between heartbeats.

ECG of Atrial Fibrillation showing tiny waves in between heartbeats.

 

Symptoms can include:

  • Palpitations
  • Breathlessness
  • Tiredness
  • Dizziness
  • Chest pain

Atrial Fibrillation can lead to a blood clot due to the irregular heartbeat which can potentially travel to the brain and cause a stroke.

Supraventricular Tachycardia

Also known as SVT, supraventricular tachycardia is caused by an extra electrical pathway in the heart, in between the atria and ventricles. This means that the impulses are able to re-enter the atria without passing through the ventricles, resulting in them travelling around your heart in a circle, producing a fast heart rate. This can be up to 250 bpm.

SVT ECG

SVT ECG

A vagal manoeuvre can sometimes be used to stop these attacks. Although these techniques work in less than 1 in 3 cases, they are simple ways in trying to stop it before more serious measures need to be taken. They stimulate the vagus nerve which can slow down the speed of the electrical impulses.

Ventricular Tachycardia

Electrical impulses are fired too quickly from your ventricles, resulting blood to be pumped out faster than usual. This could result in your ventricles not filling up with blood meaning that your heart could stop pumping blood around the body, resulting in cardiac arrest. This can lead to ventricular fibrillation.

Ventricular Tachycardia ECG

Ventricular Tachycardia ECG

Ventricular Fibrillation

Electrical impulses start firing from multiple sites in your ventricles, rapidly and in an irregular rhythm. Your heart is unable to beat properly and little to no blood is pumped around the body. This is a type of cardiac arrest which needs to be immediately treated with CPR (cardiopulmonary resuscitation) as it is fatal. Early defibrillation can reduce long-term disabilities.

Ventricular Fibrillation ECG

Ventricular Fibrillation ECG

It can be due to acute myocardial infarction.

Heart Block

This means that there is a problem with the electrical signal being transferred from the atria to the ventricles. This can occur in the Atrioventricular node; there are three different types of heart block (first, second and third degree).

Heart block can be congenital but it can also be caused by a number of different things:

  • Heart attacks
  • Infections such as diphtheria
  • Certain medicines
  • Open heart surgery
Heart Block Third Degree

Heart Block Third Degree

 

Arrhythmias can be caused by a number of things:

  • heart failure
  • heart valve disease
  • inflammation of your heart (myocarditis)
  • thyroid disease
  • diabetes
  • high blood pressure
  • heart attacks
  • coronary heart disease
  • chronic obstructive pulmonary disease (COPD)
  • Wolff-Parkinson-White syndrome (an electrical abnormality in the heart that can cause SVT and atrial fibrillation)

You are more at risk of developing an arrhythmia as you get older, if you are pregnant or if you have recently had heart surgery.