Most sudden cardiac cases are related to an underlying cardiac condition, most commonly ischemic heart disease “heart attack related” or myocardial and structural related conditions. Sudden cardiac death (SCD) has been estimated to be responsible for around one million deaths annually around the globe. A careful check by the doctor will usually reveal the underlying cause, as previously mentioned, most commonly ischemic and structural heart diseases. However, a rather significant number of cases found NO cause which makes genetically related cardiac conditions highly probable.

Most sudden cardiac cases are related to an underlying cardiac condition, most commonly ischemic heart disease “heart attack related” or myocardial and structural related conditions. Sudden cardiac death (SCD) has been estimated to be responsible for around one million deaths annually around the globe. A careful check by the doctor will usually reveal the underlying cause, as previously mentioned, most commonly ischemic and structural heart diseases. However, a rather significant number of cases found NO cause which makes genetically related cardiac conditions highly probable.

This group of genetically attributed cardiac diseases with no structural heart abnormality, is commonly known as channelopathies of the heart.

Ion channels are the integral membrane proteins that are genetically encoded by separate genes, which are vital to the function of the cardiac physiology. Naming a few types, Na+ (sodium), K+ (potassium) and Ca2+ (Calcium) ions. These ion channels play a major part in maintaining the integrity in the generation of cardiac action potential and thus the stability of the heart rhythm. Hence, any mutation that affects any of these ions will conceivably affect the normal cardiac rhythm and be a risk for electrical instability.

One of the most common condition is Brugada syndrome (BrS). It is a hereditary condition that affects the young with usually no structural heart condition. Patients with BrS are at risk of developing SCD due to ventricular fibrillation (over rapid electrical conduction). The mean age of onset is around 40 years old, particularly men are affected. This condition was said to be associated with the local term of “bangungot”, known in the Philippines, which means ‘to rise and to moan in sleep’, where men with unexplained death were identified.

This could also be analogous to the local term “Pokkuri” in Japan, which means ‘sudden and unexpected phenomenon’. Men with this condition commonly experience attacks of SCD during their sleep, many locals practice taboo where men may even go to sleep dressed up as women as so to avoid the disturbance of this ‘unexplained’ condition.

Genetically, this condition carries an autosomal dominant pattern with variable penetrance. The gene commonly identified to be responsible for this mutation is SCN5A, which encodes the α-subunit of the cardiac Na+ channel. However there are also other genes linked to this condition, but to a lesser degree.

Long QT syndrome (LQTS) is also another cardiac channelopathy of leading cause of death in the young. There are generally 12 different types of LQTS, most of them related to K+ (potassium) channel disorders. This disorder causes a delayed repolarisation of the heart and increases the risk of polymorphic ventricular tachycardia, which could potentially lead to sudden cardiac death. Patients with such condition usually present with seizures, or fainting episodes if the attacks are brief and not sustained.

Some of these syndromes are closely related to environmental triggers such as loud noises (alarm clock), swimming, or heavy exercise. They usually manifest at a younger age, related to their lifestyle and activities. Another subgroup of LQTS is the acquired form, which is not genetically inheritable. This is mainly caused by electrolyte imbalances and drugs, and usually reversible.

Another condition worth mentioning is Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) where patient exhibits normal structural heart and normal ECG at rest, but when fuelled by adrenergic stimulation (exercise, fear), it is then associated with polymorphic Ventricular Tachycardia, which is related to an increased risk of sudden cardiac death. The two main genes identified responsible for this condition are the RyR2 gene (encoding the ryanodine receptor), and the mutated gene in calsequestrin (CASQ2). Patients may experience syncope during running the marathon or unexplained faints during certain emotional stress or fright.

There are many more channelopathies related to sudden cardiac death, which is beyond the scope of this reading material. It is therefore vital to understand and identify this genetically related conditions. The treatment for this usually involves the placement of an Implantable Cardiac Defibrillator (ICD), which will reduce the risk of sudden cardiac death due to the tachyarrhythmia generated.

In a nutshell, an apparent healthy heart with no structural abnormality in a genetically susceptible person could mask the underlying abnormality and risks of a deadly arrhythmia. Consult your healthcare provider to learn more.

When should you call an Ambulance?

Experience heart attack/severe chest pain, experience breathing difficulty, paediatric & neonatal cases, experience severe abdominal pain, experience severe bleeding, loss of consciousness, strokes, fainting, convulsions/fits/seizure, trauma (injury)/road or motor vehicle accident, fractures/ dislocation/serious sprain