Sudden cardiac death

Sudden cardiac death (SCD) is defined as unexpected death either:

Within 1 hour of cardiac symptom onset or:
Within 24 hours of having been observed alive and symptom free

It is suspected that all cases of SCD occur due to ventricular arrhythmias, but the underlying cause of the arrhythmia can vary. SCD is due to an underlying coronary artery disease (CAD) in 80% of cases. It occurs most commonly due to:

Acute myocardial infarction (leading to acute heart failure or ventricular arrhythmia)
Chronic ischaemic heart disease (scars leading to ventricular arrhythmia)
Dilated cardiomyopathy
Hypertrophic cardiomyopathy
Arrhythmogenic right ventricular cardiomyopathy (ARVC)

In people with structurally normal hearts, rare conditions like Brugada syndrome and long QT syndrome are common causes of SCD.

Prevention

Primary prevention of SCD in people without heart disease is the same as primary prevention of CAD.

Primary prevention of SCD in people with heart disease (CAD, heart failure, cardiomyopathy) is important. The following are all class I recommendations:

Optimal medical therapy (ACEi/ARB, beta blockers, MRAs) reduces risk for SCD in all patients with left ventricular dysfunction (< 40%), and dilated cardiomyopathy
ICD implantation reduces risk for SCD in all patients who are at high risk for it, especially:
- Structural heart disease patients who are on optimal medical therapy and are expected to live > 1 year with good functional status
People with hypertrophic cardiomyopathy or ARVC should avoid participating in competitive sports
If the patient has a heart condition with high risk for SCD where ablation can be performed (like WPW, certain VTs), ablation reduces risk for SCD

Secondary prevention of SCD refers to prevention in those who’ve already experiences ventricular arrhythmias and is very important. The following are all class I recommendations:

ICD implantation reduces risk for SCD in people who have survived cardiac arrest
- (In cases where the cardiac arrest was not due to a clearly reversible cause)
ICD implantation reduces risk for SCD in people who have experienced syncope due to ventricular arrhythmia

However, ICDs are expensive and therefore not implanted in all cases where it is recommended, only the extra high-risk ones.