What is Sudden Cardiac Death?
Sudden Cardiac Death or SCD is a sudden, unexpected, natural death caused by a sudden loss of heart function heralded by abrupt loss of consciousness within 1 hour of the onset of an acute change in cardiovascular status. It can affect any individual with or without pre-existing heart disease.
What are the causes of SCD?
Most SCDs are caused by an erratic, disorganized firing of impulses from the ventricles (the lower chamber of the heart which pumps the blood for circulation). When this occurs, the heart is unable to pump blood resulting in death within minutes, if not intervened.
Although SCD accounts for only 1-2 per 1000 natural deaths, its incidence is >20 times higher in patients with advanced cardiovascular disease. Worldwide SCD occurs most commonly between 45 to 75 years of age, affecting men thrice as often as women. It is rare in children and adolescents. However, in our country, the proportion of SCD cases in the younger age are relatively high, which is directly attributable to the higher prevalence of Coronary Atherosclerotic Disease (CAD) among the young in India.
How is SCD different from Myocardial Infarction (MI)?
Myocardial Infarction (MI), commonly known as Heart Attack, occurs as a result of the blockade in one or more of the coronary arteries, thereby preventing the heart from receiving oxygen-rich blood. As a result, the heart muscle starts to die because of lack of oxygen and the left ventricle starts becoming weak and may acutely fail.
In Sudden Cardiac Death the electrical system of the heart malfunctions and suddenly becomes very irregular. The heart starts beating dangerously fast. The ventricles may flutter or quiver (known as Ventricular Fibrillation or VF) and the blood is not delivered to the body. Death results within 4-6 minutes if circulation is not restored.
Although heart attack is a very common cause of SCD (perhaps the most common cause) there are a lot of other diseases which can result in SCD.
What are the causes and risk factors for SCD?
Worldwide, up to 80% of SCDs are related to Coronary Atherosclerotic Disease (CAD). It causes heart attacks and is probably the most common cause of SCD among adults. Of this, 70% of males with SCD have evidence of an old healed Myocardial Infarction (MI) in their heart.
Cardiomyopathies (heart muscle diseases) account for another 10-15 % of SCDs which involves:
- Dilated Cardiomyopathy – characterized by the dilatation of the ventricles
- Hypertrophic Cardiomyopathy – characterized by the enlargement of the ventricles
- Hypertrophy – increased wall thickness of the ventricles
All the remaining 5-10% of SCDs are caused by a long list of rare diseases. These causes are more common in young individuals and many of these are the cause of SCD among athletes. These include certain inherited disorders like Long QT, Brugada’s Syndrome and Arrhythmogenic Right Ventricular Dysplasias. Anomalies of Coronary Artery origin and course can rarely affect young individuals and present as SCD. Sarcoidosis, Severe Aortic Stenosis and Acute Myocarditis can also cause SCD.
How does Coronary Atherosclerotic Disease (CAD) cause SCD?
Coronary Atherosclerosis is characterized by deposition of cholesterol and inflammatory cells in the vessel walls (Plaques) of the arteries supplying blood to the heart. Due to acute changes in the plaques, there is clotting and abrupt occlusion of the artery, thereby, stopping the supply of blood and oxygen to the heart muscle. This event may, in some patients, cause electrical instability in the heart causing Ventricular Fibrillation (VF) and SCD. Although the treatment of heart attack has reduced the risk of death in hospital, the one-month death rate after Myocardial Infarction (MI) is still as high as 30%. More than half of these patients die before reaching the hospital due to SCD or out-of-hospital cardiac arrests. The first hour following a heart attack has the highest incidence of SCD and is the most lethal because these patients are not able to reach the hospital in time. SCD is the first manifestation of CAD in many of these patients, but the majority have a past history of CAD. Therefore, both primary and secondary prevention of CAD is important to reduce SCD.
What is the treatment for SCD?
When it comes to treatment, time is critical and the key factor when we consider the chances of survival of an SCD victim. Defibrillation (delivering shock or electrical energy by placing external paddles on the patient’s chest) reverts the heart rhythm to normal and should be performed within 3-5 min of SCA. Considering the fact that even people living in urban India cannot reach the hospital within this time frame, it is evident that the bystander stands the best chance of helping out these victims. However, most of us do not know how to respond when someone collapses suddenly. The knowledge of Cardiopulmonary Resuscitation or CPR techniques should not remain confined to the medics and paramedics. The basics of CPR should be a part of all Senior Secondary and Graduation/Training programs so that we are all better equipped to recognize and handle such an emergency situation.
The use of Automated External Defibrillators (or AEDs) in communities has been proven to nearly double the chances of survival after an out-of-the-hospital cardiac arrest. Though it involves cost issues the installation of AEDs at places with large population densities, such as railway stations, airports, large housing colonies, office complexes, and shopping malls can, over time, prove to be cost effective. Studies have shown that majority of SCDs occur at home and/or are witnessed. That is why the bystanders stand the best chance of improving the chances of survival of these victims and therefore educating everyone regarding this entity is crucial.
Is there any specific medical technology to abort this lethal heart rhythm?
An Intra-Cardiac Defibrillator (ICD) is a device like a cardiac pacemaker which can be implanted after a small surgical procedure in patients who are at high risk for SCD. Studies have conclusively demonstrated the life-saving advantages of this therapy in both the secondary and primary prevention of SCD among patients at high risk. The device can effectively detect this abnormal and lethal rhythm and deliver therapy to revert it to normal. The major barrier against the use of this therapy at least in the Indian context is the cost of this treatment.
How can we prevent SCD?
Since our country has an alarmingly high prevalence of CAD, Hypertension, Diabetes, and Dyslipidemia, the incidence of SCD is on the rise. The hospital treatment of heart attack incidences has improved and reduced the in-hospital death rates of this disease. However, the out-of-the-hospital SCD still remains a major killer. Community education about healthy lifestyle, prevention and adequate treatment of the above-mentioned diseases form the cornerstone for prevention of SCD. Regular medical checks are essential for all so as to detect and treat CAD and its risk factors. Patients who are high-risk candidates, especially those with a decreased Left Ventricular Ejection Fraction (LVEF) less than 35%, should be counseled and educated about the risk of SCD. Drug treatment and ICDs should be offered to all these patients.
To conclude, the treatment and prevention of SCD is akin to preventing fatal car accidents. Adopting a healthy lifestyle (like following road safety rules), getting regular health checkups to keep the risk factors under control (like the periodic car maintenance), drug treatment for established CAD and ICDs for those at very high risk (like the presence of air-bags in case of fatal accidents) are the means to reduce SCD (like avoiding fatal accidents).
Mass education to empower the bystanders to recognize and respond early to this situation and government initiatives to install AEDs at high population density areas can achieve higher survival rates from this mounting threat to mankind.
The author is Dr. Dheeraj Garg, Senior Consultant – Cardiology at Dharamshila Narayana Superspeciality Hospital, Delhi