Sudden cardiac death refers to unexpected death from a cardiac cause in a short time period. Its possible underlying etiologies include acute coronary syndrome, aortic dissection, lethal ventricular tachyarrhythmia, atrioventricular block and so on. In modern countries, coronary event is an important cause of SCD. In young men, certain syndromes related ventricular tachyarrhythmia is a major cause.
In patients with coronary disease, an acute coronary syndrome may cause myocardial ischemia and lead to electrical instability. It is estimated that around 10% of patients with acute coronary event die outside hospitals. Ventricular arrhythmia typically occurs in the first 48 hours after an acute coronary event. On the other hand, patients with old myocardial infarction are also at risk of developing lethal ventricular arrhythmia but with a different mechanism. In these patients, scars in the ventricle form substrates for re-entry. In case of ventricular systolic dysfunction, elevated sympathetic tone may also contribute to the arrhythmogenecity. In patients with congestive heart failure due to dilated cardiomyopathy, similar mechanism might also results in lethal ventricular arrhythmia and SCD.
SCD may also occur in young and apparently health people. In the Western countries, hypertrophic cardiomyopathy with ventricular arrhythmia is the most common cause. This disease is also common in Taiwan and is a major cause of SCD in young people. Brudaga syndrome is a special syndrome cause by imbalance between myocardial sodium current and transient outward potassium current. This disease is endemic in the Southeastern Asia including Taiwan. Although it is rare in the USA but it is not uncommon in Taiwan. On the other hand, congenital long QT syndrome is more prevalent in the Western world than in Taiwan. Both Brudaga syndrome and congenital long QT syndrome are cardiac channelopathies. The primary cause of SCD is defect of cardiac ion channel function resulting in ventricular arrhythmias.
Nevertheless, there are other causes of SCD but with a lower incidence. By recognizing the causes of SCD can we prevent the tragic events by identifying the high risk patients and find a way of preventing SCD.
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