Introduction to sudden cardiac arrest
A natural disaster hits, the power goes off and the lights go out. It's a common scene that plays out during hurricane and tornado seasons, and it's very similar in trying to explain sudden cardiac arrest. The heart sustains an insult, the electricity is short circuited, the heart can't pump, and the body dies.
The heart is an electrical pump, where the electricity is generated in special pacemaker cells in the upper chamber, or atrium, of the heart. This electrical spark is carried through pathways in the heart so that all the muscle cells contract at once and produce a heart beat. This pumps blood through the heart valves and into all the organs of the body so that they can do their work.
This mechanism can break down in a variety of ways, but the final pathway in sudden death is the same: the electrical system is irritated and fails to produce electrical activity that causes the heart to beat. The heart muscle can't supply blood to the body, particularly the brain, and the body dies. Ventricular fibrillation (V Fib) is the most common reason for sudden death in patients. Without a coordinated electrical signal, the bottom chambers of the heart (ventricles) stop beating and instead, jiggle like Jello. Ventricular Fibrillation is treated with electrical shock, but for it to be effective, the shock usually needs to happen within less than four to six minutes, not only for it to be effective, but also to minimize brain damage from lack of blood and oxygen supply. Automatic external defibrillators (AEDs) are commonly available in public places to allow almost anybody to treat sudden death. Less commonly, the heart can just stop beating. The absence of a heart beat is known as asystole (asystole: a=no + systole=beat).
What are the causes of sudden cardiac arrest?
Sudden death is most often caused by heart disease. When blood vessels narrow, the heart muscle can become irritated because of lack of blood supply. In heart attack (acute myocardial infarction), a blood vessel becomes completely blocked by a blood clot, and there is enough irritability of the muscle to cause ventricular fibrillation. In fact, the reason many people with chest pain are admitted to the hospital is to monitor their heart rate and rhythm for signs that might lead to ventricular fibrillation. Sudden death may also be the first sign or symptom of heart disease.
Congestive heart failure and heart valve problems, like aortic stenosis (narrowing of the aortic valve) also increase the risk of sudden cardiac arrest.
Cardiomyopathy is a broad category of heart disease where the heart muscle does not contract properly for whatever reason. Often it is ischemic, where part of the heart muscle doesn't get an adequate blood supply for a prolonged period of time and no longer can efficiently pump blood. People whose ejection fractions (the amount of blood pumped out of the heart with each heart beat) is less than 30% are at greater risk for sudden death (a normal ejection fraction is above 50%). In some people, cardiomyopathy may develop in the absence of ischemic heart disease.
Inflammation of the heart muscle, known as myocarditis (myo=muscle + card=heart + itis= inflammation), can also cause rhythm disturbances. Diseases like sarcoidosis, amyloidosis, and infections can cause inflammation of the heart muscle.
Some people are born with electrical conducting systems that are faulty, which place them at higher risk for rhythm disturbances. Some are due to the wiring, or electrical conduction system, like Wolff-Parkinson-White syndrome, while others are due to the structural basic structural problems within the heart, like Marfan syndrome.
Pulmonary embolus or a blood clot to the lung, can also cause sudden death. Clots form in the leg or arm and may break off and flow to the lung where they decrease the lung's ability to get oxygen from the air to the body. Risk factors for blood clots include surgery, prolonged immobilization (for example, hospitalization, long car rides or plane trips), trauma, or certain diseases like cancer.
Blunt chest trauma, such is in a motor vehicle accident, may result in ventricular fibrillation. (please see commotio cordis below)