Sudden Cardiac Death
Encyclopedia
Sudden cardiac death is natural death from cardiac causes, heralded by abrupt loss of consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...

 within one hour of the onset of acute symptoms. Other forms of sudden death may be noncardiac in origin. Examples of this include respiratory arrest
Respiratory arrest
Respiratory arrest is the cessation of breathing. It is a medical emergency and it usually is related to or coincides with a cardiac arrest. Causes include opiate overdose, head injury, anaesthesia, tetanus, or drowning...

 (such as due to airway obstruction, which may be seen in cases of choking
Choking
Choking is the mechanical obstruction of the flow of air from the environment into the lungs. Choking prevents breathing, and can be partial or complete, with partial choking allowing some, although inadequate, flow of air into the lungs. Prolonged or complete choking results in asphyxia which...

 or asphyxiation), toxicity or poisoning, anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...

, or trauma.

It is important to make a distinction between this term and the related term cardiac arrest
Cardiac arrest
Cardiac arrest, is the cessation of normal circulation of the blood due to failure of the heart to contract effectively...

, which refers to cessation of cardiac pump function which may be reversible. The phrase sudden cardiac death is a public health
Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...

 concept incorporating the features of natural, rapid, and unexpected. It does not specifically refer to the mechanism or cause of death.

Causes

The most common cause of sudden cardiac death in adults over the age of 30 is coronary artery atheroma
Atheroma
In pathology, an atheroma is an accumulation and swelling in artery walls that is made up of macrophage cells, or debris, that contain lipids , calcium and a variable amount of fibrous connective tissue...

. The most common finding at postmortem examination is chronic high-grade stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....

 of at least one segment of a major coronary artery, the arteries which supply the heart muscle with its blood supply. A significant number of cases also have an identifiable thrombus
Thrombus
A thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...

 (clot) in a major coronary artery which causes transmural occlusion of that vessel. Death in these cases is thought to result from a period of transient or prolonged ischaemia (lack of blood supply) in the myocardium (muscle of the heart wall) which induces an arrhythmia (a conduction disturbance), usually a ventricular arrhythmia, which terminates into ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...

. As a consequence there may be no changes in the myocardium. The absence of the histological signs of acute necrosis and a healed infarct are a common finding. Chronic high-grade stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....

 may have caused previous episodes of ischaemia and areas of focal fibrosis may be seen histologically in the myocardium. Ventricular arrhythmias may arise from a myocardium which has been previously scarred by episodes of ischaemia.

Left ventricular hypertrophy is the second leading cause of sudden cardiac death in the adult population. This is most commonly the result of longstanding raised high blood pressure which has caused secondary damage to the wall of the main pumping chamber of the heart, the left ventricle. Once again, hypertrophy is associated with cardiac arrhythmias.

The mechanism of death in a the majority of patients dying of sudden cardiac death is ventricular fibrillation and as a consequence there may be no prodromal symptoms associated with the death. These patients may be going about their daily business and suddenly collapse without the typical features of myocardial infarction such as chest pain and shortness of breath. There are a number of cases in which patients feel the effect of myocardial ischaemia. Myocardial ischaemia is associated with referred pain, classically to the front of the chest, the left arm and the jaw. Patients may feel generally unwell, with nausea, dizziness and vomiting. These symptoms may precede the death for any length of time between a few minutes and several hours.

Cardiac rapid response units and the use of portable defibrillators have contributed to the survival of many people who have collapsed with ventricular fibrillation. However, in cases of sudden cardiac death, the heart appears to be resistant to attempts of resuscitation. Early defibrillation in these cases rarely results in survival. The mechanism underlying this resistance is currently being investigated.

Much attention in the press has been focused on young athletes who die suddenly whilst training as a consequence of sudden cardiac death. Though these cases are rare compared to the hundreds who die each year of coronary artery atheroma and left ventricular hypertrophy, they attract much more attention due to the sensational nature of young, otherwise healthy persons suddenly and unexpectedly dying. A great deal of time and money is being spent on researching these cases and implementing schemes to screen young athletes to prevent their occurrence.

Although the most frequent cause of sudden cardiac death is coronary artery disease, other causes include:
  • Non-atherosclerotic coronary artery abnormalities
  • Hypertrophy of ventricular myocardium
  • Myocardial diseases and heart failure, including
    • Arrhythmogenic right ventricular cardiomyopathy
    • Hypertrophic cardiomyopathy
      Hypertrophic cardiomyopathy
      Hypertrophic cardiomyopathy is a disease of the myocardium in which a portion of the myocardium is hypertrophied without any obvious cause...

    • Dilated cardiomyopathy
      Dilated cardiomyopathy
      Dilated cardiomyopathy or DCM is a condition in which the heart becomes weakened and enlarged and cannot pump blood efficiently. The decreased heart function can affect the lungs, liver, and other body systems....

    • Myocardial infarction
      Myocardial infarction
      Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

    • Noncompaction cardiomyopathy
      Noncompaction cardiomyopathy
      Non-compaction cardiomyopathy , also called spongiform cardiomyopathy, is a rare congenital cardiomyopathy that affects both children and adults. It results from the failure of myocardial development during embryogenesis....

  • Inflammatory, infiltrative, neoplastic, and degenerative processes
  • Diseases of the cardiac valves
  • Congenital heart disease
  • Primary electrophysiological abnormalities, such as
    • Long QT syndrome
      Long QT syndrome
      The long QT syndrome is a rare inborn heart condition in which delayed repolarization of the heart following a heartbeat increases the risk of episodes of torsade de pointes . These episodes may lead to palpitations, fainting and sudden death due to ventricular fibrillation...

      , both congenital and acquired
    • Sick sinus syndrome
      Sick sinus syndrome
      Sick sinus syndrome, also called sinus node dysfunction, is a group of abnormal heart rhythms presumably caused by a malfunction of the sinus node, the heart's primary pacemaker...

    • Brugada syndrome
      Brugada syndrome
      The Brugada syndrome is a genetic disease that is characterised by abnormal electrocardiogram findings and an increased risk of sudden cardiac death. It is named by the Spanish cardiologists Pedro Brugada and Josep Brugada...

    • Catecholaminergic polymorphic ventricular tachycardia
      Catecholaminergic polymorphic ventricular tachycardia
      Catecholaminergic Polymorphic Ventricular Tachycardia is an electrophysiological disorder of the heart that occurs in genetically predisposed individuals...

  • Magnesium deficiency
    Magnesium deficiency (medicine)
    Magnesium deficiency refers to an intake of dietary magnesium below minimal levels, which can result in numerous symptoms and diseases. These can generally be remedied by an increase of magnesium in diet or oral supplements...

  • Rhythm instability related to neurohumoral and central nervous system
    Central nervous system
    The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

     influences
  • Cystic tumour of the atrioventricular nodal region
    Cystic tumour of the atrioventricular nodal region
    Cystic tumour of the atrioventricular nodal region is a very rare tumour of the heart in the region of the atrioventricular node. It is also known as mesothelioma of the atrioventricular node.-Pathology:...

  • Commotio cordis
    Commotio cordis
    Commotio cordis is a disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart , at a critical time during the cycle of a heart beat. It is a form of ventricular fibrillation, not mechanical damage to the heart muscle or surrounding organs, and not the result...

  • Mechanical interference with venous return
  • Aortic dissection
    Aortic dissection
    Aortic dissection occurs when a tear in the inner wall of the aorta causes blood to flow between the layers of the wall of the aorta and force the layers apart. The dissection typically extends anterograde, but can extend retrograde from the site of the intimal tear. Aortic dissection is a medical...

  • Toxic/metabolic disturbances

See also

  • cardiac arrest
    Cardiac arrest
    Cardiac arrest, is the cessation of normal circulation of the blood due to failure of the heart to contract effectively...

  • clinical death
    Clinical death
    Clinical death is the medical term for cessation of blood circulation and breathing, the two necessary criteria to sustain life. It occurs when the heart stops beating in a regular rhythm, a condition called cardiac arrest. The term is also sometimes used in resuscitation research.Stopped blood...

  • ventricular fibrillation
    Ventricular fibrillation
    Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...

  • coronary thrombosis
    Coronary thrombosis
    Coronary thrombosis is a form of thrombosis affecting the coronary circulation. It is associated with stenosis subsequent to clotting. The condition is considered as a type of ischaemic heart disease.It can lead to a myocardial infarction...

  • myocardial infarction
    Myocardial infarction
    Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...


External links

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