Syncope, Part 1 - First, let's make sure you don't die
By DrRich
Syncope is a sudden and temporary loss of consciousness. It is a common
symptom - most people pass out at least once in their lives - and often does not
indicate a serious medical problem. However, sometimes syncope idicates a
dangerous or even life-threatening condition, so when syncope occurs it is
important to figure out the cause.
The causes of syncope can be grouped into four major categories.
The four major categories of syncope
|
Categories of Syncope |
Common causes of syncope within these categories |
|
Neurologic |
Vertebrobasilar TIAs |
|
Metabolic |
Hypoxia |
|
Vasomotor |
Orthostatic Hypotension |
|
Cardiac |
Obstructive Lesions |
The causes of syncope listed on this table will be explained below.
Cardiac syncope – when does syncope predict sudden death?
We will deal first with the cardiac causes of syncope, since these are the causes of syncope that can be fatal. There are two major varieties of cardiac syncope: obstructive cardiac lesions, and cardiac arrhythmias.
Obstructive cardiac lesions: Several heart disorders can result in an obstruction of blood flow through the heart. These include obstructed heart valves (aortic stenosis and mitral stenosis are the most common examples); obstructed blood vessels (such as a massive pulmonary embolus); and cardiac tumors (such as an atrial myxoma, a benign tumor that can obstruct the mitral valve). Most of these lesions are readily apparent to a physician taking a careful medical history and doing a careful cardiac examination. And for the most part, they are readily confirmed by performing a simple echocardiogram. (Click here for a quick and easy review of the heart chambers and valves.)
Far more common as a cause of syncope – and especially as a cause of sudden death – are the cardiac arrhythmias. Again, there are two major categories of life-threatening, syncope-producing cardiac arrhythmias: the bradycardias and the tachycardias. (Click here for an quick and easy review of cardiac arrhythmias.)
Bradycardias, or slow heart rhythms, are treated effectively by inserting a cardiac pacemaker.
There are two varieties of tachycardia – ventricular tachycardias and supraventricular tachycardias (SVT). With rare exceptions, SVT does not cause syncope nor does it cause sudden death. (The most common exception to this rule is in patients with Wolff-Parkinson-White syndrome (W-P-W), in which, rarely, SVT can degenerate into the much more dangerous ventricular variety of tachycardia.)
Ventricular tachycardia, on the other hand, commonly causes sudden death. And unfortunately, ventricular tachycardia is common in people who have underlying heart disease, and is commonly overlooked by doctors. If it is missed once, neither the doctor nor the patient are likely to get a second chance to undo the error.
The key to diagnosing ventricular tachycardia is to understand that this arrhythmia is extremely rare in individuals with completely normal hearts, while it is very common in patients who have heart disease. Thus, a major consideration in evaluating a patient with syncope of unknown cause is to decide whether a patient has underlying heart disease (especially ventricular muscle damage due to coronary artery disease, or to a viral infection of the heart muscle). If the ventricular muscle is normal, then the possibility of ventricular tachycardia as a cause of syncope can be largely dismissed. (While there are exceptions to this “rule,” they are rare.)
On the other hand, if the ventricles are abnormal, the doctor’s focus must shift immediately from merely preventing syncope to preventing sudden death. The patient should be immediately hospitalized and placed on a cardiac monitor, and must remain monitored until either ventricular tachycardia is ruled out, or definitive therapy to protect against ventricular tachycardia is instituted. In general, an electrophysiology study is done to assess the heart’s electrical system, and evaluate the patient’s propensity for developing ventricular tachycardia. If the electrophysiology study documents ventricular tachycardia, the patient should receive an implantable defibrillator (an pacemaker-like device that monitors the heart rhythm continuously, and delivers therapy automatically if a dangerous heart rhythm occurs).
Because of the high price that may be paid if ventricular tachycardia is missed, the doctor’s index of suspicion for this diagnosis must be high. Thus, for instance, any patient with a history of coronary artery disease, or even with significant risk factors for coronary artery disease, needs to be evaluated. Indeed, if a careful medical history and physical examination do not reveal any other likely cause of syncope, a cardiac evaluation should be undertaken.
Fortunately, the great majority of patients with syncope have causes that do not represent an increased risk of sudden death. That, of course, does not diminish the frightening and disruptive nature of the syncope itself.
Click here for Syncope, Part 2.
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