Sudden Cardiac Death

Regarding Sudden Cardiac Death answer the following questions:

1. What kind of heart disease is seen most commonly in adults who die suddenly? In young athletes?
2. Which types of arrhythmias are associated with cardiac arrest and sudden cardiac death (SCD)?
3. Which patients are at highest risk for SCD?
4. What is the cause of SCD in the long QT syndrome?

Answers:
1. What kind of heart disease is seen most commonly in adults who die suddenly? In young athletes?
Approximately 90% of cases of SCD are due to ventricular fibrillation in the setting of preexisting structural heart disease; 5% to 10% occur in the absence of organic heart disease.
In individuals younger than 30 years and young athletes, SCD is very rare, but when it does occur it is usually due to hypertrophic cardiomyopathy. Arrhythmogenic right ventricular dysplasia and
acute myocarditis are other infrequent causes of SCD in the young adult.
After the age of 40, 65% to 70% of all SCDs are attributable to Coronary artery disease.

2. Which types of arrhythmias are associated with cardiac arrest and SCD?
In the field, paramedics most commonly record ventricular fibrillation or ventricular tachycardia during cardiac arrest. Less frequently seen, and associated w ith a poorer prognosis, are
bradyarrhythmias, asystole, and pulseless electrical activity (electrical–mechanical dissociation).
Cardiac arrest due to any arrhythmia results in rapid depletion of oxygen in vital organs. After 6 minutes, brain damage is expected to occur, except in cases of hypothermia. Therefore, early CPR and rapid advanced cardiac life support (ACLS), with defibrillation, are essential in improving survival and neurologic recovery.

3. Which patients are at highest risk for SCD?
Patients at highest risk for SCD are those who have previously survived an episode of SCD or have a history of rapid, sustained ventricular tachycardia especially in the setting of reduced left ventricular function. One of the best measures of risk of SCD is left ventricular function and the risk of SCD
increases as left ventricular function decreases. The incidence of SCD is greater in men than in women. This increased risk remains despite adjusting for the presence of comorbidities such as ischemic heart disease and age. The risk of SCD increases with age.

4. What is the cause of SCD in the long QT syndrome?
The long QT syndrome is a cause of syncope and SCD in patients with structurally normal hearts, but may also result in SCD in patients with structural heart disease. The long QT syndrome can be either acquired or inherited. Several genetic defects involving cardiac ion channels have been identified in families with inherited long QT syndrome.
In acquired long QT syndrome, several classes of drugs that affect cardiac ion channels and several medical conditions associated with electrolyte abnormalities have been identified. In both inherited and acquired forms, cardiac repolarization is prolonged, and reflected in a long QT interval on the ECG. Syncope and SCD in long QT syndrome are caused by a specific, polymorphic ventricular tachycardia called torsade de pointes (”twisting of the points”). Drugs that prolong the QT interval (e.g., phenothiazines, tricyclic antidepressants, and certain antiarrhythmics) are particularly likely to cause SCD in patients with another cause of prolonged QT interval or in patients with structural heart disease.