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WHO definition : Death which occur within 24 hours of the onset of symptoms. But in Forensic sense , most sudden deaths occur within minutes or even seconds of the onset of symptoms.
It's important to remember that a sudden death is not necessary unexpected and unexpected death is not necessarily sudden, but these two factors are often combined.
A death occurring suddenly, in an individual in whom death was unexpected;
“
Sudden
” implies death usually within 24 hours of the first symptom, or those resuscitated from cardiac arrest and dying during the same hospital admission. Most such deaths occur over a few seconds or minutes. “ Unexpected ”, this refers to prior circumstances, particularly of someone who was believed to have been in good health or who had a stable chronic condition (e.g. hypertrophic or dilated cardiomyopathy, a neurological condition such as epilepsy, or a respiratory condition such as asthma), in whom sudden death was not expected. It also includes a sudden death occurring in the presence of an illness which would not be expected to cause death.
Sudden death may occur as a result of:-
1Trauma: e.g. head injuries, electric shock, burns.
2Poisoning: e.g. Co, insecticides, cyanide, or narcotics.
3Disease (natural death): Natural death means that the death was entirely by the disease and the trauma or poison did not plays any part in bringing the action
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(I)Diseases of the heart
Diseases of the cardiovascular system account for the majority of cases of sudden natural death worldwide, usually accounting for approximately 90% of such cases. Cardiovascular deaths include:
1Coronary artery disease (CAD):
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Account the majority of all sudden deaths, and about 25% die without any preceding history or signs. Coronary artery disease includes: Coronary artery atherosclerosis, coronary artery

نيدلا فرش باهولادبع ريبع م.د.أ thrombosis which usually associated with atheroma and coronary artery spasm.

CAD is narrowing of the coronary arteries caused by atheroma
(atherosclerosis) which is comprised of fatty deposits (plaque) which develop on the inner lining of the arteries. The plaques are made up of cholesterol, vascular smooth muscle cells and inflammatory cells.
Mechanism of death :
The simple stenosis and the complications of atheroma are both sufficient to cause death.
(a) Coronary stenosis: Having 75% or greater blockage in any of the coronary vessels is considered critical stenosis. It may lead to chronic ischemia of the muscle supplied by that coronary vessel and hypoxia of the myocardium. Hypoxic myocardium is electrically unstable and liable to arrhythmias and ventricular fibrillation. Thus the ischemia can lead to:
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Sudden death from fatal cardiac arrhythmias.
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Myocardial infarction: occurs when there is severe stenosis or complete occlusion of coronary arteries. The area of muscle damaged is further weakened by the process of cellular death and inflammatory response to these necrotic cells.
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Fate of myocardial infarction :
(1) The area of myocardial infarction is weakest and soft between 3 days and 1 week after the clinical onset of infarction and it's the time that the weakened area may rupture and cause sudden death from hemopericardium and cardiac tamponade .
(2) Healing by fibrosis: fibrotic area in the wall of the ventricle or septum may interfere with physical and electrical function. Cardiac aneurysms may form at the site of infarction; they may calcify and may rupture .
(b) Complications of atheroma:
(1) Bleeding into a plaque and this can be seen as a subintimal hemorrhage at autopsy.
(2) Rupture of atheromatous plaque: when it occurs, the extruded cholesterol, fat, fibrous debris will be washed downstream in the coronary arteries and impact distally causing many
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نيدلا فرش باهولادبع ريبع م.د.أ infarctions. Mural thrombus may be developed which will further reduce the vessel lumen.
2Hypertensive heart disease:
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This condition may lead to sudden death from left ventricular hypertrophy. At rest, when diastole is relatively long, the whole myocardium can be adequately perfused, but if the heart rate increases, diastolic time is reduced and the perfusion of endocardial cells is reduced. These cells become unstable and irritable and may produce arrhythmia and fibrillation.
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Sudden death in people with hypertensive heart disease may be due to an arrhythmia as mentioned before or one of the other complications of hypertensive cardiovascular disease, such as a rupture of the aorta or a hemorrhage in the brain.
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Atheroma is often associated with hypertension, so that the enlarged heart may also be deprived of a normal blood flow in the coronaries and become ischemic.
3Valvular disorder:
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Aortic stenosis: is a disorder of aging, and is characterized by hard calcification with associated stenosis causing left ventricular hypertrophy similar to hypertension. Sudden death is common in these patients.
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Mitral valve prolapse “floppy mitral valve syndrome”: is a myxomatous degeneration of the mitral valve characterized by a floppy, rubbery mitral valve, with redundant (excess) tissue, such that, on gross exam, the valve leaflets appear ballooned or prolapsed (into the left atrium). The disorder is actually common and is typically an incidental autopsy finding.
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Infective endocarditis or bacterial endocarditis, refers to a bacterial infection of the heart valves, The disorder may be subacute, and usually responds to antibiotic therapy, or acute, in which there is very rapid valve destruction with associated heart failure and systemic infection.
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Other valve disorders include rheumatic heart disease.
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4-Primary myocardial disease:
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Myocarditis: The term “myocarditis” specifically refers to inflammation of the heart occur in many infective diseases such as diphtheria and virus infections including influenza.
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Cardiomyopathies: this disease usually associated with areas of disordered myocardial fibers.
5Senile myocardial degeneration:
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The cause of death in these elderly individuals can be very difficult to determine.

Senile heart is small, the surface vessels are tortuous, and myocardium is soft and brown due to lipofuscin in the cells.
The most common lesions of the arteries themselves that is associated with sudden death include :
1Atheromatous aneurysm of the aorta.
2Dissecting aneurysm of the aorta.
3Syphilitic aneurysms.
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Very few disorders of the CNS cause sudden and unexpected death, for examples:
1Intracranial hemorrhage of varying etiologies (will be discussed in head injuries).
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Intracerebral hemorrhage.
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Subarachnoid hemorrhage.
2Brain tumors can cause sudden death, but patients usually present to a physician with signs and symptoms of their disease prior to death.
3Intracranial infections: e.g. Meningitis, encephalitis and brain abscess..
4Epilepsy: epileptics can die suddenly in a variety of circumstances, unconsciousness can leave the individual in a position that compromises the airway, a more common variation of this is the

نيدلا فرش باهولادبع ريبع م.د.أ epileptic who drowns as a result of having a seizure while taking a bath. Seizures may also lead to secondary trauma including falls, fires, and motor vehicle accidents.
Apart from these trauma-related deaths, status epilepticus is a recognized medical emergency that can cause death if the seizures are not brought under control.
The actual mechanism by which these deaths occur is not currently understood, but would appear to be related to some physiologic disruption of brainstem, cardiac and/or respiratory function.
Autonomic dysfunction has been also proposed as a mechanism.
5Cerebral thrombosis and infarction.
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1Pulmonary embolism: is very common and is the most clinically under-diagnosed cause of death. In almost every cause, the source of emboli is in the leg veins.
2Massive hymoptysis from cavitating pulmonary tuberculosis or from malignant tumors.
3Lobar pneumonia.
4Pneumocystis carinii pneumonia: Forensic pathologists must be aware of the numerous infections that can arise secondary to human immunodeficiency virus (HIV) infection and attempt to confirm the diagnosis with postmortem serology. Public health officers must be notified of either a possible or a confirmed diagnosis of HIV infection so that follow-up of close contacts of the decedent can be undertaken.
5Rapid (but not sudden) deaths can also occur from fulminating chest infections.
6Bronchial asthma is also associated with rare unexplained and unexpected deaths even there is no evidence of status asthmaticus.
Diseases of the gastrointestinal system tend not to present as sudden death. In some cases, however, avoidance of physicians, ignoring of symptoms, or vagueness of symptoms can create situations where the death was sudden.

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1Severe bleeding from a gastric or duodenal peptic ulcer.
2Ruptured esophageal varices most commonly encountered in patients with portal hypertension.
3Mesenteric thrombosis and embolism may result in infarction of the gut. Rapid but not sudden death is expected if the infarction remains undiagnosed.
4Pancreatitis: A variety of conditions can induce pancreatitis, including chronic alcoholism, various toxins, severe body trauma, and elevated blood fat levels.
5Intestinal infarction due to strangulated hernia.
6Peritonitis arising from perforated carcinoma.
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1A natural complication of pregnancy as rupture ectopic pregnancy or an induced complication as an abortion.
2Eclampsia.
The diagnosis of sudden unexpected death may be one of exclusion. Aims of investigation of sudden death victims are:
1Establishing the cause, mechanism and manner of death.
2Excluding an unnatural death, violence and poisoning.
3Proofing that the death is due to natural causes.
The diagnosis depends on:
1Circumstances: including clinical and family history and witness.
2All cases of sudden unexpected death in young people should have an autopsy.
3Complete autopsy: all body cavities are to be opened and organs examined very carefully.
4Obtain blood and urine for complete toxicological analysis.