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How do doctors figure out what causes fainting (syncope)?

When a person faints the doctor ties to figure out what the problem is. Trying to figure out what causes the problem is a process in medicine called Differential Diagnosis.

Hardi Kardi, M.D.

Hardi Kardi, the son of Cheif Engineer, Mr. Kardi, is a heart doctor. He performs a very similar job to his father.

How does the Alert village water supply system differ from blood circulation?

First the pipes are different, in the Alert village the pipes are made from steel, not from elastic contracting tissue as the body arteries and veins in the heart. Therefore the diameter of the pipes can not change.

If the mayor in the brain house needs more water he may have to change to bigger pipes or add more of them. On the other hand, the arteries going to the brain in the heart can dilate (increase their diameter), if the brain needs more blood, or they constrict (decrease their diameter), if the brain needs less blood to flow to it.

Both the heart and the water pumps in the Alert Village have electric parts (wires and switches) and mechanical parts (valves and reservoirs).

What are the Causes of Syncope?

Any sequence of steps that leads to transient decrease in brain blood flow may result in dizziness, near fainting or fainting (syncope).

Mechanical Problems

Mechanical problems could be due to a blocked valve (valve stenosis), or failure of the pump to pump the blood.

Electrical Problems

Electrical problems are caused by changes in current:

  • No Current: The electricity failing to switch on and off (Cardiac Arrest) 
  • Slow Current: The electric current is coming very slow (slow heartbeat or bradycardia) 
  • Fast Current: The electric switch is switching on and off very fast giving no times for the pumps to fill with blood before they open their doors (tachycardia) 
  • Erratic Current: The electrical current can be interrupted back and forth, back and forth (Erratic heart beat)

Heart Rhythm Disorders

  • Arrhythmias 
  • Tachycardia - abnormally fast heart beat. They are named after their site of origin:
    • They are called atrial or supra-ventricular if they originate from atria which are the cardiac chambers sitting above the ventricles.
  • Supraventricular tachycardias (SVT) (fast heart beats that begin above the ventricles in the atria). 
  • Ventricular tachycardias (fast heart beats that begin in the ventricles).

When the heart beats too fast, there is not enough time between contractions for the ventricles to fill with blood and pumping becomes ineffective, leading to low blood pressure and hence low blood flow to the brain causing syncope.

Noncardiac Causes of Syncope

  • Neurologic 
  • Tonic-clonic Movements 
  • Convulsive Syncope. A true seizure disorder. Seizure is the more likely diagnosis if the syncopal event is preceded by an aura, if it occurs while recumbent, or most importantly, if is followed by a prolonged postictal period of disorientation and lethargy. Residual neurologic abnormality following the syncopal episode strongly suggests a primary neurologic diagnosis. Syncopal migraine has been described; it is usually preceded by an aura and followed by a severe occipital headache. It may also be associated with a residual neurological deficit similar to that observed in adults with transient ischemic attacks. 
  • Metabolic 
  • Hypoglycemia. Hypoglycemia is a rare cause of syncope in pediatric patients. Preceding symptoms include hunger, diaphoresis, dizziness, and agitation 
  • Hyperventilation 
  • Hysterical Heat-Related Illness. Common in athletes. Symptoms range from mild weakness, dizziness and fatigue in cases of heat edema, to syncope, exhaustion and multisystem complications, including coma and death, in cases of heat stroke. Milder heat-related symptoms can be treated with hydration, rest and removal from the hot environment. Heat stroke, a life-threatening problem, must be treated emergently. Prompt recognition is critical since rapid cooling is the cornerstone of treatment.

Four Main Disorders

All of the causes of a transient decrease in brain blood flow can be organized into four main disorders:

  1. Conditions affecting the heart's ability to provide enough blood flow to the brain.
  2. Conditions leading to reduction in blood pressure so it can not maintain adequate blood flow to the brain. 
  3. Conditions altering the content of the blood going to the brain. 
  4. Conditions narrowing the arteries supplying blood to the brain.

What factors favor that one of these conditions is more likely to be the cause of fainting in a particular individual?

  • Age 
  • Sex 
  • Descriptive details of the fainting episode
  • Known presence of a heart condition 
  • Family history of a certain disorder 
  • Medications or drugs

Conditions affecting the heart's ability to provide enough blood flow to the brain

This is also called cardiogenic syncope. The heart is what generates the blood pressure to secure normal blood flow to the brain. The heart may not be able to provide the brain with adequate blood flow due to any of the following conditions:

  • Pump failure due weak heart muscle, so the heart pumping function is impaired, these diseases are known as cardiomyopathy, they cause heart failure force needed to propel the blood to the brain.
  • Obstruction of the blood filling the heart such as what happens with Atrial Myxoma, which is a benign heart tumor, that looks like a little ball attached to the left side of the atrial septum by a fibrous thread. Myxoma is very mobile, intermittently blocks the opening of the mitral valve, and obstructs the flow from the left atrium to the left ventricle. The empty left ventricle cannot generate enough blood flow to the brain and fainting occurs. Myxoma should be removed by surgery.
  • Obstruction to the valves guarding the blood flow out of the heart.
  • Cardiac Arrhythmias: Normal heart rate is critical for the heart to sustain it's function.
    • Asystole: Failure of the heart to beat
    • Bradycardias: Slow heart rate
    • Tachycardias: very fast heart rate does not give the heart enough time to fill, and if it becomes to fast and irregular, the heart contraction will become so disorderly like a bag of warms, the no efficient pumping is achieved such as may happen in ventricular fibrillation.

Conditions narrowing the arteries supplying blood to the brain

Atherosclerosis may also reduce blood supply to the brain. In some persons, moving the neck or upper body may transiently aggravate the reduced flow through narrowed arteries of the neck. Regional disturbances in blood flow to the brain, especially the lower brain (brain stem), are a rare cause of syncope.

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