Syncope–Part 1


Some of you will know about professional triathlete Joanna Zeiger’s recent troubles with syncope. Her trials and tribulations with race-related dizziness are summarized in a nice article at, “Zeiger sidelined by dizziness.” Her story is typical. This week and next week, we’ll talk about the causes, medical evaluation, and treatment options for syncope.

Syncope is the medical term used to describe a brief period of loss of consciousness (either partial or complete) that is due to insufficient blood flow to the brain. This process is temporary and is followed by spontaneous recovery. Patients often use different terms such as “dizziness”, “light-headedness”, “blacking out”, “passing out”, or “falling out” to describe this problem. This is a common medical condition that affects approximately 3% of the population at some point during life. It is increasingly common as we age, affecting 6% of individuals over the age of 75. It’s not surprising, then, that this is a fairly common problem among athletes.

Syncope may occur without warning or may be preceded by warning signs that are called premonitory symptoms. Typical premonitory symptoms might include palpitations, light-headedness, grogginess, feeling warm, or experiencing nausea.


There are many types or causes of syncope and it can be useful to categorize the types as: 1) cardiac (heart-related), 2) non-cardiac, or 3) unknown. This framework helps the physician sort out an individual’s cause among the many possibilities and then provide any needed treatment.

Cardiac syncope

A variety of cardiac disorders can produce syncope, but cardiac causes account for the explanation in only 10% of cases. As patients age, it is more likely that a cardiac cause is responsible for their syncope. Some of the cardiac causes are potentially life-threatening, but most are less serious; all can be treated.

Life-threatening cardiac causes. Acute myocardial infarction (“heart attack”) or aortic dissection (tearing apart of the layers of the aorta) can produce syncope or other changes in the level of consciousness. Both of these conditions are usually accompanied by chest or back pain and can also be associated with shortness of breath. In these situations, syncope is the result of decreased blood pressure and/or decreased blood flow to the brain. Both of these conditions can result in sudden death and affected individuals require urgent medical attention.

Arrhythmias. The most common cardiac cause of syncope, though, is an abnormal heartbeat, or arrhythmia—either atrial (from the upper heart chamber) or ventricular (from the pumping chamber of the heart). Syncope can be the result of an abnormally fast (tachy-) or slow (brady-) arrhythmia. Bradyarrhythmias are usually found in patients with known, pre-existing heart disease, but they sometimes occur because of unwanted side effects of medicines (eg, beta-blockers for high blood pressure). It’s important to remember that the well-trained athlete typically has a baseline slow heart rate and this can sometimes confuse the picture. Syncope is more common with atrial or ventricular tachyarrhythmias, though. The atrial tachyarrhythmias include atrial fibrillation (A-fib), atrial flutter (A-flutter), and supraventricular tachycardia (SVT). These arrhythmias may be accompanied by chest discomfort, palpitations, or shortness of breath. With persistent arrhythmias, syncope often occurs when moving from the sitting to standing position (postural) due to decreased blood pressure. Ventricular tachyarrhythmias include ventricular fibrillation (V-fib) and ventricular tachycardia (V-tach). These arrhythmias are usually associated with known, pre-existing heart disease. Syncope due to ventricular tachyarrhythmias is not usually related to posture.

Cardiac bloodflow obstruction. A third set of cardiac causes of syncope are due to obstruction to blood flow in the heart. This can be due to narrowing (stenosis) of the aortic, mitral, or pulmonary valves, hypertrophic obstructive cardiomyopathy (HOCM, one of the most common causes of sudden death in athletes), or to tumors of the heart. With these conditions, syncope is often sudden, without any preceding symptoms.

Low cardiac output. The last set of cardiac causes are those due to decreased pumping function, or cardiac output, from the heart. Long-standing congestive heart failure (CHF) or leaking (regurgitant) heart valves may lead to a low blood pressure that limits blood flow to the brain.

Non-cardiac syncope

Neurocardiogenic syncope. The most common type of syncope is termed neurocardiogenic, or vasovagal syncope. The term vasovagal conveys the association of “vaso,” for vasodilation of arterial system (leading to a decrease in blood pressure) and “vagal,” for the accompanying slow heart rate (sometimes produced by decreased activity in the vagal nerves). This type of syncope usually occurs in the standing position and is usually preceded by symptoms such as light-headedness, nausea, or sweating.

Situational syncope. A variety of precipitating factors, such as emotional stress, anxiety, pain, cough, urination, or defecation can lead to syncope. In this situation, the resulting syncope is thought to be due to a reflex, sudden decrease in heart rate that produces a transient reduction in blood flow to the brain.

Orthostatic syncope. Syncope can be caused by a sudden drop in the blood pressure as we rise from a sitting to standing position. The medical terms for this situation are orthostasis, or orthostatic hypotension (reduced blood pressure). Ordinarily, the body adjusts to this change in position by increasing the heart rate and increasing motor tone in the blood vessels to keep the blood pressure constant. When these mechanisms fail, the sudden (relative) drop in heart rate and blood pressure may produce syncope. This problem can be made worse by dehydration or medications that reduce the circulating blood volume or by medications that limit the blood pressure response (eg, beta-blockers).

Neurologic syncope. One last, unusual category of causes is termed neurologic. In this situation, the syncope is caused by a sudden decrease in blood flow to the brain in conditions such as stroke, transient ischemic attack (TIA, or “near-stroke”), or seizures. In one variant, syncope is due to a sudden decrease in blood flow to the posterior portion of the brain called the cerebellum. This is often due to pre-existing vascular disease in the vertebral arteries that supply this portion of the brain. Patients with neurologic syncope often experience other neurologic symptoms such as vertigo, visual changes, or muscle movement clumsiness immediately before the syncopal event.


Syncope can sometimes easily be explained by benign problems such as dehydration, but the majority of individuals with syncope should be evaluated carefully for an explanation. Because of the demands on the athlete’s cardiovascular system during exercise, it is particularly important for the athlete with syncope to be evaluated completely.


Next week, we’ll talk about the medical evaluation of patients with syncope and discuss the various treatment options.

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  1. says

    Hi, new to this site – very interesting> Ishare the concern, having been sent for ECG etc a few years ago by a concerned doctor (I was in my late 20’s!). Have you read Dr Kenneth Cooper’s “The Antioxidant revolution”? An interesting take on why intense and extreme exercise may cause a myriad of problems, including cardiovascular problems. I’d be interested in your thoughts.

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