Vulnerability Caused by Arrhythmogenic Vulnerable Myocardium

Eighty-five percent of those older than 40 years of age dying from cardiac arrest have underlying coronary artery disease on autopsy studies. The most common underlying cause is ventricular fibrillation. Most victims of SCD have severe diffuse multivessel coronary artery disease. Healed myocardial infarctions are present in approximately 50% of victims of SCD. Two conditions appear to be important for the initiation of ventricular fibrillation: an abnormal myocardial substrate (e.g., abnormality of the myocardium, coronary arteries, or cell membrane ion channels) and a transient modulating event (e.g., ischemia). It is the effect of a transient disturbance on a susceptible substrate that is thought to lead to electrical instability.