Sudden cardiac arrest (SCA) is the natural death from cardiac causes, heralded by abrupt loss of consciousness within one hour of the onset of acute symptoms.
SCA is one of the ways in which a heart attack presents. It is thought that in fact about half of heart attack victims present with SCA. The other victims present with the more familiar symptoms of chest pain, chest tightness, breathlessness, cold sweats, nausea etc.
SCA can be preceded by the more classical symptoms of a heart attack which then rapidly progress into abrupt collapse and loss of consciousness. However, premonitory symptoms may be absent or may be nonspecific.
About 80% of SCA is due to coronary heart disease (CHD). Since this is a condition whose incidence increases with age. SCA is more likely to be due to CHD in older patients. SCA is particularly likely to occur the more severe the CHD, the greater the number of coronary arteries affected and especially where the main trunk of the left coronary artery is obstructed (sometimes called the “widow maker’s disease). SCA risk also is higher in those who have previously had a heart attack resulting in extensive heart muscle damage and heart failure.
Since CHD is the commonest underlying cause of SCA the risk factors would be those which cause atherosclerosis, the disease process which results in CHD. These include age, smoking, high BP, high cholesterol, diabetes, obesity, sedentary lifestyle, stress as well as family history.
In younger patients in whom CHD is less frequent other causes which may have a genetic basis may be present. These conditions include abnormalities of the electrical system of the heart eg the “long QT interval syndromes”, Brugada syndrome ; abnormalities of the heart muscle eg hypertrophic cardiomyopathy, various forms of congenital heart disease (“hole-in-the-heart”, “blue babies”), various types of heart valve disease.
The risk of SCA can be reduced by reducing the risk of CHD, screening for CHD risk factors and effective control of these factors e.g. high BP, high cholesterol etc. In those with known CHD various types of tests can be conducted to identify those at higher risk of heart attack and sudden cardiac arrest. These tests include ECG, exercise or other types of stress tests, echocardiography, imaging techniques e.g. CT scans, isotope scans, coronary angiography.
Those at higher risk may be treated with medications, angioplasty, pacemakers or implantable defibrillators.
In younger individuals those with a family history of SCA or other types of heart disease affecting younger members of the family may be screened by a doctor and referred if there are suggestive signs e.g. an abnormal ECG.
Individuals planning to participate in strenuous exercise should have a medical examination which may include an ECG, a stress test (e.g. a treadmill test), and other types of cardiac examination.
The immediate cause of SCA is often a sudden development of an abnormal rhythm of the heart called ventricular fibrillation (VF) in which there is chaotic electrical activity without mechanical contraction so that there is rapid cessation of blood circulation. VF can be preceded by ventricular tachycardia (VT) where there is a rapid heart rate eg 200 beats per minute but blood pressure may be very low.
Since VF is usually present, the most effective treatment is the use of an electrical medical device called a defibrillator which delivers an electrical shock through the chest. However since a defibrillator may not be immediately available, CPR (cardiopulmonary resuscitation) should be immediately initiated to maintain circulation and ventilation until medical help arrives. Many ambulances now carry defibrillators and are manned by personnel trained in CPR and defibrillation.
All individuals especially those who are likely to witness SCA including family members of patients who have CHD or other types of heart disease with increased risk of SCA should be encouraged to learn CPR. Laypersons can also be trained to use a semi-automatic defibrillator. Many airlines now have these devices on board their aircraft. It would be advisable for those organising sports events to check whether the medical services on standby have this device.
SCA is often quite obvious because the victim collapses, rapidly loses consciousness, and eventually becomes pulseless when the heart stops. SCA can occur anywhere. Diagnosis cannot wait for a doctor to be called unless he or she is fortuitously present.
Resuscitation of SCA or any other form of cardiopulmonary arrest should be initiated within 4 minutes, as any delay beyond this period may result in permanent brain as well as cardiac damage. The chances of effective resuscitation also rapidly decrease the longer the delay before it is initiated.