Syncope (passing out)
Overview
When to see a cardiologist
Associated symptoms
Causes
Treatment
Overview
Syncope is the medical term for passing out, or losing consciousness, generally due to lack of blood flow to the brain. It is the most common cause of temporary loss of consciousness. Other causes of loss of consciousness include epileptic seizures, non-epileptic attack disorder and dissociative seizures. These are neurological problems, rather than problems with the heart or blood vessels. Syncope, on the other hand, is by definition, a problem with blood flow.
Generally, lack of blood flow in the brain is caused by a drop in blood pressure. Blood pressure is usually maintained by the heart pumping blood against resistance supplied by blood vessels. If either the rate of blood flow, or the “squeeze” supplied by blood vessels, drops, then this causes a drop in blood pressure. If both flow and resistance drop together, then the drop in blood pressure is usually very fast and severe. It is common to pass out in that situation. The body then goes limp and unless it is held up artificially, the person will usually fall to the floor. Most causes of syncope are very transient -ie. they recover quickly - so the person will regain consciousness rapidly after falling.
It is common during syncope for people to jerk or shake. This does not necessarily mean they are suffering a seizure, but these movements do mean that syncope is often confused for epilepsy. Epilepsy is not a cause of syncope - the two conditions have very different causes and treatments.
When to See a Cardiologist
Passing out is alarming and can be dangerous, depending on when it happens and how much warning you get. It is only natural to want to seek medical attention if you start to experience this problem. It may not always be clear what sort of doctor you need to see to help, however.
A cardiologist can help you confirm the diagnosis and investigate for the cause of syncope. Most cases will have a cardiovascular cause, and in this case a cardiologist may be able to advise on treatments to reduce the chance of it happening again.
A cardiologist can also advise on whether you need to inform the DVLA or other bodies. The rules around driving if you suffer from syncope can be complex, and in certain circumstances you may be advised against driving until a diagnosis is made and treatment has been effective for a period of time. Ignoring these rules can be a criminal offence and may invalidate your insurance. A cardiologist can help you understand the rules in this area.
Almost all of the serious causes of syncope have their roots in heart disease. A cardiologist is the right doctor to diagnose and treat heart diseases causing syncope.
Associated Symptoms
Some cases of syncope are preceded by a long period, or “prodrome” of other symptoms, which may include:
Lightheadedness
Nausea and / or vomiting
Ringing or pulsation heard in the ears
Feeling hot, clammy or sweaty
Feeling anxious
“Tunnel vision” - the visual field becoming restricted and seeming to darken at the edges
The pre-syncope prodrome can last up to hours in some people. In general, syncope with a long prodrome is much less likely to be due to an arrhythmia (heart rhythm problem) than syncope with no prodrome at all. Syncope without a prodrome is sometimes called “unheralded syncope”.
Causes
Syncope is caused by either a sudden drop in cardiac output (the volume of blood pumped by the heart) or by a drop in vascular resistance (the “squeeze” applied by blood vessels to maintain blood pressure).
Causes of transient decreased cardiac output leading to syncope include:
Tachyarrhythmias - the heart flipping into an abnormal fast rhythm. The rate has to be extremely high to cause a drop in blood pressure and this usually implies a serious heart rhythm abnormality such as ventricular tachycardia. This is uncommon.
Bradyarrhythmias - the heart rate drops suddenly. Bradyarrhythmias are a very common cause of syncope; in young patients this is usually part of a reflex syncope complex, but in older patients bradyarrhythmias are usually caused by conduction disease.
Cardioversion pauses - this is when there is a temporary pause in the heart rate as the heart reverts from a tachyarrhythmia such as atrial fibrillation, back into normal “sinus” rhythm. The sinoatrial node, which drives the heart rate during sinus rhythm, can sometimes take a few seconds to wake up after a period of tachyarrhythmia. This pause can sometimes be enough to cause syncope.
Causes of a drop in vascular resistance include:
Orthostatic hypotension - this occurs when blood vessels fail to tighten sufficiently on moving from a sitting or lying position to standing up, leading to a drop in blood pressure. This is a very common cause of syncope and presyncope with changes in position. Most people will suffer very brief episodes of mild orthostatic hypotension under the right circumstances, for example the on standing up after bending over to tie shoelaces. Only in severe cases will orthostatic hypotension cause full syncope.
Reflex syncope - this complex condition is the cause of classic “fainting” for example on the sight of blood, or in a warm room after a large meal. The “reflex” involved causes a sudden drop in heart rate, blood pressure, or both, leading to sometimes prolonged and repeated syncopes. The key to diagnosing this condition is to recognising the usually classic triggers.
Cardiovascular autonomic dysfunction - this is a spectrum of disorders affecting the regulation of heart rate and /or blood vessel tone. Sufferers commonly complain of dizziness and presyncope, sometimes progression to syncope. The most widely recognised disorder in this cluster of related conditions is Postural Tachycardia Syndrome (PoTS) which can cause a racing heart beat and lightheadedness on position change. It is uncommon to experience complete syncope with isolated PoTS but is may be more common in other forms of autonomic dysfunction.
Treatment
Treatment of syncope depends on the cause. Clearly syncope caused by an arrhythmia will only improve with treatment of the arrhythmia. For tachycardias and cardioversion pauses this may involve drugs and ablations to suppress rapid heart rhythms. For bradycardias a pacemaker may be recommended.
Syncope related to changes in blood vessel tone may be harder to control than arrhythmic syncope. A range of treatments will be used to boost blood pressure and to reduce the drive to initiate unhelpful reflexes.