Common causes of Sudden Cardiac Death

Over 70 % of sudden cardiac deaths (SCD) are due to underlying heart blockages.

• The frequency of heart blockages is much lower in sudden deaths occurring under the age of 30 (24 %)
• 10% of SCDs are due to underlying structural heart disease (congenital coronary artery anomalies, myocarditis, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy). The frequency is much higher in subjects under the age of 30 (35%)
• 5 to 10% of sudden cardiac deaths are arrhythmias occurring in the absence of underlying structural heart disease (long QT syndrome, Brugada syndrome, Wolff-Parkinson-White syndrome, catecholaminergic polymorphic VT, all abnormalities seen on ECG).
• 15-25% of cardiac arrests are noncardiac in origin. The causes include trauma, bleeding, drug intoxication, intracranial hemorrhage, pulmonary embolism, near-drowning, and central airway obstruction.
• SCDs accounts for 30 to 50 % of deaths in patients with heart failure
• Women are less vulnerable to sudden death than men and a higher fraction of sudden deaths in women occur in the absence of prior overt blockages
• 60% of deaths associated with acute heart attack occur within the first hour and were attributable to a ventricular arrhythmia, in particular ventricular fibrillation
• Sudden cardiac arrest (SCA) and SCD refer to the sudden cessation of cardiac activity with hemodynamic collapse, often due to sustained ventricular tachycardia/ventricular fibrillation. Other causes of SCA and SCD are asystole and pulseless electrical activity. These events most commonly occur in patients with structural heart disease (that may not have been previously diagnosed), particularly coronary heart disease.
• Silent angina is defined as the presence of objective evidence of myocardial ischemia in the absence of chest discomfort or another anginal equivalent symptom (eg, breathlessness, nausea, sweating etc). 
• nBetween 25 and 45 per cent of patients with coronary heart disease have myocardial ischemia during daily life, and most of these ischemic episodes are not associated with chest pain.
• nMost ‘silent’ ischemic episodes occur during minimal or no physical exertion
• nPatients with diabetes, elderly, and those with prior heart attack or prior bypass surgery are particularly susceptible to silent myocardial ischemia
• nIn a review of over 4,30,000 patients with confirmed acute heart attack from the National Registry of Myocardial Infarction 2, one-third had no chest pain on presentation to the hospital. These patients may present with breathlessness alone, nausea and/or vomiting, palpitations, syncope or transient loss of consciousness, or cardiac arrest. They are more likely to be older, diabetic, and women.
• n65% of out of hospital cardiac arrests occur at home. If not resuscitated fewer than 2% will be alive after one month.

— Courtesy Dr KK Aggarwal, president Heart Care Foundation of India