Arrhythmia is a condition where the heart contracts irregularly, or at a faster or slower pace than normal. It is caused by an abnormality in the myocardial tissue, or in the electrical conduction system of the heart.
Arrhythmias that arise from ventricles (ventricular arrhythmias) can occur unexpectedly and can cause sudden death when insufficient blood is pumped out by the heart to sustain life.
Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation. In ventricular tachycardia, the ventricles beat faster than normal (at between 120 and 200 beats per minute).

In ventricular fibrillation, electrical impulses rapidly start firing from multiple sites in the ventricles, resulting in an uncoordinated, irregular rhythm.
Ventricular arrhythmias most commonly occur in people with underlying heart disease. Approximately 75–80% of the 70,000 sudden cardiac deaths could be attributed to ventricular arrhythmias.

The average chance of survival of adults after an out-of-hospital episode of ventricular arrhythmia has been reported to be as low as 7%. However, with appropriate treatment, recent studies have reported 5?year survival of 69-100% in people who had survived a cardiac arrest.

Many patients presenting with arrhythmias, with or without symptoms, are treated with antiarrhythmic drug therapy. However, anti arrhythmic drugs may not be optimally effective and need careful and frequent adjustment.
This can be confusing for patients and may lead to missed doses, taking the wrong dose or overdose. Many antiarrhythmic drugs result in tiredness, inability to perform day-to-day activities and dependence on carers, and consequently increase the risk of depression. Anti arrhythmic drugs also have many side effects on a range of organs including the thyroid, liver and lungs.

Chronic prophylactic antiarrhythmic drug therapy aims to suppress the development of arrhythmias, but does not stop an arrhythmia once it has started. People who survive a first episode of life-threatening ventricular arrhythmia are at high risk of further episodes.

For preventing further life-threatening events in survivors of previous serious ventricular arrhythmias, people are usually treated with implantable cardioverter defibrillators (ICDs).

Preventing sudden cardiac death in someone who has never had a cardiac arrest or ventricular arrhythmia is challenging because it requires identifying a person with substantial level of risk.
Many risk factors for sudden cardiac death have been reported such as age, hereditary factors, having a high risk for coronary artery disease, inflammatory markers, hypertension, left ventricular hypertrophy, conduction abnormalities (for example, left bundle branch block), obesity, diabetes and lifestyle factors.
There is currently no optimal strategy for risk stratification.

G Mohan.