What is sudden cardiac death (SCD) ?
Sudden cardiac death is defined as natural death from cardiac causes, heralded by abrupt loss of consciousness within 1 hour of the onset of an
acute change in cardiovascular status. Related terms are sudden cardiac arrest and cardiovascular collapse. Sudden cardiac arrest means abrupt cessation of cardiac
mechanical function, which may be reversed by prompt intervention but will lead to death in its absence. Cardiovascular collapse means sudden loss of effective
blood flow due to cardiac and/or peripheral vascular such as cardiac arrest or syncope.
What is the relation to heart disease?
preexisting heart disease may or maynot have been known to be present. The mode of death is natural rapid and unexpected.
What are the symptoms?
Prodromes occuring weeks or months before an event are not very accurate to predict SCD. Sudden onset of chest pain, dyspnea, palpitation, lightheadedness
often precede the onset of cardiac arrest and eventual death.
How big is the problem?
For an adult population 35 years of age and older, the overall incidence of sudden cardiac death is 0.1% to 0.2% per year (that means in a country like India
12,00,000 to 24,00,000 people die suddenly from natural cardiac causes each year). Among people who have disease of coronary arteries of heart around 50% die
suddenly and unexpectedly. Even in developed countries where there is a decrease in total number of deaths due to coronary artery disease, the proportion of
deaths that are sudden and unexpected has remained same. These examples highlight the extent of the problem.
Who are at increased risk?
The conditions increasing the risk of sudden cardiac death are
- Coronary artery disease- Myocardial infarction, Angina etc
- Myocardial diseases and heart failure- e.g. dilated cardiomyopathy, ischemic cardiomyopathy etc
- Hypertrophy of ventricular myocardium – hypertrophic cardiomyopathy, left ventricular hypertrophy due to hypertension, etc
- Inflammatory diseases of heart- viral myocarditis, sarcoidosis, amyloidosis,
- Arrhythmogenic right ventricular dysplasia
- Diseases of cardiac valves- Aortic stenosis/insufficiency, mitral valve prolapse
- Electrical diseases of heart – long QT syndrome, Brugada syndrome, idiopathic ventricular fibrillation etc.
Mechanism of Sudden death
In 80% of cases sudden cardiac death is caused by ventricular tachycardia (VT) or ventricular fibrillation (VF) and in 20% of cases
SCD is caused by bradycardia. Patients having tachycardia have a relatively better outcome and chances of survival than those having bradycardia.
The acute management of cardiac arrest is cardiopulmonary resusitation. More information about latest guidelines of CPR can be found
Prevention of SCD is divided into two parts: Secondary prevention and Primary prevention. Secondary prevention means preventing further cardiac arrest
in people who have survived one cardiac arrest. Primary prevention means preventing cardiac arrest in people who have rish factors for cardiac arrest
but so far haven’t suffered a cardiac arrest.
Implantable cardioverter-defibrillator(ICD) is a device shown to be effective in secodary and primary prevention of SCD. This device is implanted like
a pacemaker and it gives an electrical shock from inside of the heart to abort an episode of VT or VF. It also has pacing function to support when the
heart rate falls.
Clinical trials like AVID, CASH, CIDS have shown effectiveness of ICD in secondary prevention of SCD. Clinical trials like MADIT, CABG-Patch, MUSTT, DEFINITE and
SCD-HeFT have shown benefit odf ICD in SCD.
Many modifications of the device has come like- subcutaneous ICD and wearable ICD.
EPS and radiofrequency ablation can be done in selected patients to prevent further episodes of cardiac arrest.