Syncope: making sense of its various causes

Recently I was consulted on two patients who presented to the hospital after a syncopal episode. As syncope is relatively common, I thought that is what I should discuss in my next post.

So what is syncope? Well simply put a syncopal episode is nothing other than a fainting episode. It is characterized by momentary/ temporary loss of consciousness and posture. Patients may refer to it as I “fainted” or “passed out”.  Whenever a patient presents to the hospital after a syncopal episode we take pains to find out what led to the syncope.

So what are the different causes of syncope?  Syncope can come either from the heart or from the brain. Let me explain this further. If for some reason the heart suddenly malfunctions and stops pumping blood to the brain, you will pass out (lose consciousness). This is referred to as cardiogenic syncope. Among the various causes of cardiogenic syncope are included disorders of cardiac rhythm such as atrial and ventricular arrhythmias. Heart blocks and of course an acute myocardical infarction (heart attack) may present as a syncopal episode with the patient collapsing and passing out.

Syncope though can also come from the brain and this is referred to as neurogenic syncope or at times as neurocardiogenic syncope. This neurally mediated syncope is also at times referred to as vasovagal or vasodepressor syncope. Let me explain what vasovagal syncope is with a classical example. Lets assume you are walking on the street. A car hits a cyclist right in front of you. You rush to help the poor man. As you come near, you see him bleeding profusely, his skull cracked open. You go pale, the blood drains from your face and you pass out. There you just had a vasovagal syncopal episode. Why you may ask did you pass out?

Vasovagal syncopal episodes classically occur in the upright position meaning either you are sitting upright or standing (they usually do not occur when you are reclining). The episode is usually preceded by an unpleasant or painful episode such as the sight of blood, a medical procedure, an intense emotionally disturbing argument or news (sudden extreme emotions), standing in the hot sun or a hot shower for a long time especially if you are hungry and dehydrated at the same time.

Other less common triggers may include a bout of violent coughing (cough syncope), urination (micturition syncope) and abdominal straining as during defecation.

Usually prior to the onset of the syncope (prior to passing out), patients feel dizzy and light headed. They may complain of blurring of vision and feel as if they are about to faint. If at this stage the person sits down, they usually do not pass out or lose consciousness. This is referred to as pre-syncope (A syncopal episode was about to occur but since the patient sat down it was aborted midway).

During a vasovagal synope episode there is transient loss of the baroreflexes (this is the autonomic nervous system which helps to maintain our blood pressure). Pooling of blood occurs in the dependent calf muscles and there is lack of blood flow to the brain resulting in the patient passing out. Hence one of the simple things to do when a person has a vasovagal syncopal episode is to make them lie down flat on the ground on their back and to lift the legs above the plane of the heart. As the blood rushes back to the brain, the person quickly comes around and may look a little dazed wondering what happened.

As seizures too are associated with loss of consciousness, one always has to differentiate whether a patient had a seizure Vs a syncopal episode. As you can imagine it is important to make this differentiation as the two conditions are treated in very different ways. So how does one differentiate a seizure from a syncopal episode?

A seizure can occur with the patient in any position: sitting, standing or lying down. Syncope usually occurs in the erect posture.

Seizures are usually not preceded by the prodrome seen in syncope. Patients before they pass out in a syncopal episode complain of feeling light-headed, dizzy, room spinning and blurring of vision. Seizure patients on the other hand may give history of their aura prior to the seizure. Common auras include smelling of burning rubber, metallic taste in their mouth or a funny rising sensation in their tummy.

Patients who have a seizure and fall usually hit and hurt themselves. They fall hard and may come to the hospital with craniofacial injuries like broken teeth. Syncopal patients on the other hand do not fall hard, they rather ease themselves to the ground.

Some but not all seizures are associated with tongue biting and loss of bladder and bowel control (patient may pee on themselves and wet their pants). Most syncopal episodes are not associated with tongue biting or loss of bladder control.

Patients after a seizure are usually confused and disoriented, they may fall asleep. We call this a post-ictal state. Syncopal patients as they come out of their syncope are not confused. They know where their are and may be embrassed by the fact they fainted.

In my next post I shall discuss the diagnostic work-up and management of syncope.

Nitin Sethi, MD