CARDIAC ARREST (1)

From the moment it starts beating in the 21 days embryo, to the day the individual dies, the heart never stops pumping. Well, this statement is not absolutely true; not with the invention of by-pass surgeries and definitely not in people who were fortunate to have survived an episode of cardiac arrest.

Ever heard “He just slumped and died!”? – This is most likely sudden cardiac arrest.

Cardiac arrest refers to a state in which the heart suddenly stops beating due to a lack of electrical activity in the heart muscles. When the heart is not pumping, blood is not being carried around the body to supply oxygen to tissues. Lack of oxygen to the brain almost immediately causes loss of consciousness and cessation of breathing. Within 4 to 6 minutes, permanent brain damage occurs and death quickly follows.

What causes the sudden black out?

The pumping activity of the heart is dependent on the electrical impulses generated by specialized fibers in the heart itself called the pacemaker or the SA node (sinoatrial node). The SA node is located in the wall of the right upper chamber of the heart called the right atrium. The muscle fibers of the heart are structurally different from muscle fibers in other parts of the body and are connected to each other in a special arrangement such that the impulses generated in that special spot in the right atrial wall are propagated and programmed to arrive at each of the other 3 heart chambers (left atrium, right ventricle and left ventricle) in perfect timing.

Electrical conduction pathway of the heart.
Original heart diagram illustrated by Patrick J. Lynch; illustrator; C. Carl Jaffe; MD; cardiologist Yale University Center for Advanced Instructional Media

The result is that the 2 atria receive electrical impulses at the same time and contract in unison, pushing blood out into the ventricles while the ventricles receive electrical impulses a bit later and are thus relaxed when the atria are contracting. By the time the ventricles finally begin to contract, the atria have emptied out, the building pressure in the ventricles cause the atrioventricular valves to close and blood is pushed out of both ventricles; from the right to the lungs and from the left to the aorta, the biggest artery in the body.

Many conditions including the following: low blood volume, hypoxia , acidosis, hyperkalaemia or hypokalaemia (High or low potassium), hypothermia (low body temperature), Low or high blood glucose, toxins, drugs, cardiac tamponade(compression of the heart by blood or other fluid building up around it e.g. following chest injury), tension pneumothorax (a collapsed lung), myocardial infarction (Heart attack), pulmonary embolism, electric shock and other forms of trauma, can ultimately disrupt the electrical activity of the heart muscles and lead to ineffective and  uncoordinated contractions (ventricular fibrillations) which cannot pump blood out of the heart. 

 Some people are also born with heart diseases such as Wolff Parkinson-White syndrome and Marfan syndrome which predispose them to cardiac arrest. However, the most common condition  underlying a cardiac arrest is ischemic heart disease,  which causes  heart muscle damage secondary to low oxygen supply.
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