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Fainting (syncope) can present a challenge for the diagnosing physician. There are a wide range of conditions that can cause fainting, ranging from life-threatening heart disease to poor physical conditioning to adrenal disease and neuropathy. In addition, a number of conditions can closely resemble syncope, including anxiety attacks and hysterical fainting.
Finally, minor strokes and transient ischemic attacks can sometimes produce syncope-like symptoms, but are not actually true syncope. In this case, it is very important to see a physician and obtain a correct diagnosis because transient ischemic attacks and minor strokes are highly predictive of future, more devastating strokes.
A close medical history and physical examination are indispensable tools to help a physician diagnose the underlying cause of fainting. During the history, patients should be detailed about the syncope episode and include information about any other episodes of fainting. It is also very important to let the physician know about any existing heart disease, as heart disease and syncope are closely linked.
This information will help the physician decide what further tests should be ordered. Whatever the cause, the physician will diagnose it as soon as possible so that any potentially life-threatening conditions, such as ventricular tachycardia, can be treated or avoided.
To make a diagnosis, the physician may order a number of tests, which include:
- Tilt table test. There are a number of different factors that may cause fainting spells, and the tilt table test is used to assess one in particular – a sudden drop in blood pressure caused by a widening of the blood vessels. Fainting that results from this change in blood pressure and blood vessels is called neurocardiogenic syncope. It accounts for about half of all cases of syncope and is not associated with increased mortality. The tilt table test is conducted on a pivoting table. By securing the patient on his or her back to the tilt table, and then tilting the table upright, the factors leading to neurocardiogenic syncope may be simulated.
- Echocardiogram. This test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. It may reveal structural heart disease, such as hypertrophic cardiomyopathy, that is causing the patient to faint.
- Electrocardiogram (EKG). This test uses sensors attached to the chest wall to monitor the heart's electrical activity. Although this test is used to diagnose heart disease, it may be recommended for almost all patients who suffer a fainting episode, whether or not there is a history of heart disease or heart disease is suspected. This is because the test is common and relatively inexpensive, and considering the dangers of cardiac syncope, it is better to rule it out. It is worth noting, however, that an EKG will rarely result in a definitive diagnose of the cause of syncope. Instead, an abnormal EKG will likely result in further testing.
- Holter monitor. This is an EKG that is temporarily attached to a patient for 24 hours. The Holter monitor continuously records the heart’s electrical activity as the patient goes about his or her daily routine. The idea behind Holter monitoring is to match episodes of syncope to arrhythmias, which may be relatively rare and unlikely to occur in the examination room.
- Event monitor. If a patient only rarely experiences symptoms, the Holter monitor may not pick up the pattern and thus may not alert the physician to the problem. Therefore, the physician may ask the patient to carry a different type of portable device called an event recorder or event monitor. Rather than monitoring the heart’s electrical activity continuously (as the Holter monitor does), an event recorder is only used when the patient is feeling symptoms. When symptoms occur, the patient activates the event recorder by pressing a button. Because these devices are “on demand” rather than continuous, these recorders may be used for weeks or months. In certain cases, they may better reveal the exact pattern of specific symptoms.
- Electrophysiologic study. A procedure in which a thin tube (catheter) is inserted into a vein or artery (e.g., in the groin) and guided to the heart, where it can perform specific, essential measurements of the heart’s electrical activity and pathways. These measurements are particularly helpful in the diagnosis of heart rhythms that are particularly fast (tachycardias) or slow (bradycardias).
In addition to cardiovascular causes, loss of consciousness can be due to neurologic diseases. For example, sometimes it may be very difficult to distinguish between syncope (fainting spells) and a seizure disorder such as epilepsy. Some tests that may be ordered to evaluate neurologic causes of fainting include:
- Computed axial tomography (CAT) scan. A test that uses multiple x-ray sensors to generate a three-dimensional image of the target organ. During a CAT scan, the patient is positioned so that multiple sensors (up to 64) can detect x-ray scans. A computer is used to reassemble the individual pictures into clear, cross-sectional images. It is unique because it can provide clearer, more detailed information than single x-rays and can be used on a variety of different tissues, including soft tissue, bone and blood vessels.
- Magnetic resonance imaging (MRI) scan. A procedure that uses magnetic fields and a computer to produce high-resolution cross-sectional or three-dimensional images of the brain. Images from an MRI scan are similar in many ways to those of a CAT scan, but MRI generally provides much greater contrast between normal and abnormal tissues. It is done without x-rays or other forms of radiation.
- Electroencephalogram (EEG). A test that measures the brain’s electrical activity. It may be used to diagnose epilepsy, head injuries, infections, sleep disorders and other problems.
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