Non-arrhythmogenic Mechanisms of Syncope

Introduction

Syncope is the medical term for fainting. Syncope is loss of consciousness due to impaired blood flow to the brain. It can be a symptom or diagnosis. The onset of syncope is rapid with a short duration, and the recovery is spontaneous and complete. Syncope is a common occurrence and more common in elderly patients. It is not a disease. A brief loss of consciousness characterizes syncope. Postural tone followed by spontaneous and complete recovery. It excludes seizures, comas, shock, or other states of altered consciousness. The onset is rapid, the duration is brief, and recovery is complete. Syncope is also called atrial bradycardia (abnormal heart rhythm), benign faint, neurogenic, simple fainting, psychogenic syncope, vasodepressor syncope, and vasovagal syncope. Non arrhythmogenic syncope has no arrhythmic (improper heart beating due to irregular electrical conduction in the heart) cause.

What Are the Causes of Syncope?

In syncope, there is a gradual failure of blood flow to the brain with reduced oxygen availability. The oxygen supply is cut off for 8 to 10 seconds. Predisposing factors include anxiety, fright, emotional stress, sudden unexpected pain, the sight of blood, and life-threatening situations. Non Psychogenic causes include a change in posture, drug-induced postural hypotension, hunger, exhaustion, poor physical condition, and a hot, humid, or crowded environment.

Syncope can occur in conditions such as a sudden drop in blood pressure, a sudden drop in heart rate, and decreased blood and oxygen supply to the brain. The pathophysiology of syncope is decreased blood flow to the brain because of stress. In addition, due to stress, catecholamines are released into the body, decreasing the total blood volume and pressure. It also includes family history such as deafness, arrhythmias, congenital heart disease, seizures, metabolic disorders, and myocardial infarction at a young age.

The following are the causes of syncope:

1. Neurally Mediated - It is also called reflex syncope, vasovagal syncope, or neurocardiogenic syncope. It is due to transient changes in the reflexes responsible for cardiovascular homeostasis. Normally when someone stands up for a long time, gravity makes blood settle in the lower part of the body. In vasovagal syncope, the heart rate and blood pressure decrease inappropriately. This is a benign condition. Most of the common types are vasovagal syncope. For example, syncope occurs when the body overreacts to conditions like the sight of blood or extreme emotional distress. It is usually harmless and requires no treatment. Recovery begins in less than a minute. It is more common in young age and women.

2. Situational Syncope - It is a type of vasovagal syncope. Common triggers are stress, the sight of blood, and standing for a long time. It happens in certain situations that affect the nervous system, such as:

• Dehydration.

• Alcoholism.

• Anxiety.

• Fear.

• Pain.

• Hunger.

• Emotional stress.

• Breathing in too much oxygen and breathing out too much carbon dioxide too quickly.

• Micturition fainting.

3. Postural or Orthostatic Syncope (Also Called Postural Hypotension) - It is a condition of low blood pressure while standing up after long periods of sitting or lying. It can be due to dehydration or lengthy bed rest. People with this type of syncope have blood pressure changes that drop to 20 milliliters per mercury from the previous level.

4. Postural Orthostatic Tachycardia Syndrome (POTS) - In postural orthostatic tachycardia syndrome, someone may have tachycardia (a very fast heart rate) that happens when they stand suddenly.

5. Cardiac Syncope - Severe obstruction to cardiac output or rhythm disturbance can lead to syncope. The following are the conditions causing syncope-

• Abnormal heart rhythm (arrhythmia).

• Obstructed blood flow to the heart because of the heart’s structure.

• Blockage in the heart’s blood vessels (myocardial infarction).

• Valve disease.

• Aortic stenosis (narrowing of the blood vessel).

• Blood clot ( block in the blood vessels).

• Heart failure ( inability of the heart to pump blood sufficiently for the body’s needs).

6. Neurologic Syncope - It is also called vasovagal neurocardiogenic syncope. It happens when the body overreacts to certain triggers, such as extreme heat, pain, and dehydration. In addition, neurologic syncope can happen when a person has a neurological condition such as a transient ischemic attack. Other conditions include migraine.

7. Idiopathic Syncope - Sometimes, the cause of syncope is unknown.

What Is the Mechanism of Non Arrhythmogenic Syncope?

When the person stands too long, peripheral blood pooling (500 to 1000 milliliters) in the lower extremities occurs. As a result, there is decreased venous return (blood) to the heart and reduced ventricular filling (lower chamber of the heart). This results in diminished cardiac output and blood pressure. These hemodynamic changes provoke compensatory mechanisms. The reflex increases the peripheral resistance, venous return to the heart, and cardiac output, limiting blood flow and resulting in decreased blood flow to the brain. Ideally, the blood flow to the brain ranges from 50 to 60 milliliters per minute per 100-gram brain tissue and remains relatively constant over perfusion pressures ranging from 50 to 150 millimeters of mercury. Cessation of blood flow for 6 to 8 seconds will result in loss of consciousness. Blood flow decreases impairment of consciousness when to 25 milliliters per minute per 100-gram brain tissue.

What Are the Symptoms of Syncope?

The following are the symptoms of syncope-

• Skin becomes pale.

• Lightheadedness.

• Tunnel vision (the vision narrows down, and the person can see only to a limited level).

• Nausea or vomiting.

• Feeling of warmth.

• A cold, clammy sweat.

• Blurred vision.

During a vasovagal syncopal episode, the symptoms include-

• Jerky, abnormal movements.

• A slow, weak pulse.

• Dilated pupils.

• After a vasovagal episode, recovery generally begins in less than a minute. If the person stands up too soon after fainting (within about 15 to 30 minutes), there is a risk of fainting again.

What Are the Diagnostic Tests Done for the Examination of Syncope?

The following diagnostic tests for syncope-

• Laboratory Testing - A blood test to check for anemia or metabolic changes.

• Electrocardiogram (EKG) - A test that records the heart’s electrical activity.

• Echocardiogram - Uses sound waves to create an image of the heart’s structures.

• Autonomic Reflex Testing - A series of tests to monitor blood pressure, heart rate, skin temperature, blood flow, and sweating in response to certain stimuli. The measurements can help physicians determine if the nervous system is functioning normally or not.

• Ambulatory Monitoring - A monitor that uses electrodes to record heart rate and rhythm information.

Exercise-induced syncope is infrequent, but exercise should be avoided in patients with severe, symptomatic heart diseases. It is a diagnostic test if syncope occurs immediately after exercise. We can help find them by monitoring the abnormalities in the ECG.

Conclusion

Most syncopes are not dangerous but can be life-threatening if it has abnormal heart rhythms or a neurologic cause. People with heart or neurological diseases can consult a physician for help. The recurrence of syncope can be prevented by patient management and treatment. The patients must be educated properly to know the triggers causing the event. There is no definite procedure. The patient must be aware of triggers that may predispose them to syncopal events. Syncope can be diagnosed and the cause established only by using an electrocardiogram and laboratory testing.