Blood Pressure See Low Blood Pressure Diagnosis 

Diagnosis

Doctors try to determine the cause of fainting because some causes are  more serious than others. Heart disease, such as an abnormal heart rhythm or narrowing (stenosis) of the aortic valve, can be fatal. Other causes are much less worrisome. 

Sometimes the nature of the symptoms suggests  a cause to the doctor. Descriptions from witnesses of the fainting episode may be helpful. Of concern is fainting that occurs without any warning symptoms (particularly during exertion), is accompanied by shortness of breath or chest pain, results  in injury, or occurs in a person with an abnormal finding during an examination of  the heart or nervous system. Doctors also need to know whether  the person has any disorders and whether the person is taking any prescription or over-the-counter drugs. 

If  the fainting occurs during emotionally stressful situations or  is preceded by symptoms of vasovagal syncope (such as nausea, sweating, cool  and clammy skin, and paleness), fainting usually is not serious, and extensive diagnostic procedures and treatment are rarely necessary. 

Doctors will often obtain an electrocardiogram (ECG), which records  the electrical activity of the heart and can detect an underlying heart disorder. Continuous ECG may be required to determine the cause of fainting. For this procedure, the  person wears a small battery-powered device (Holter monitor). It records  the heart's electrical activity for 24 hours or more as the person engages in normal daily activities (see Holter Monitor: Continuous ECG Readings ). If an irregular heart rhythm coincides  with a fainting episode, it is probably—but not necessarily—the cause. 

Other procedures, such as echocardiography, which uses ultrasound waves  to produce an image of  the heart (see Symptoms and Diagnosis of Heart and Blood Vessel Disorders: Echocardiography and Other Ultrasound Procedures), can detect whether the heart has  a structural or functional abnormality. Blood tests may show that the person has hypoglycemia or anemia. 

Loss of consciousness due  to a seizure (see Seizure Disorders) is distinguished from fainting because  the causes and treatment are different. To distinguish between  the two, doctors may use electroencephalography (EEG), which records  the brain's electrical activity (see Diagnosis of Brain, Spinal Cord, and Nerve Disorders: 

Electroencephalography). Also, after a seizure, recovery from unconsciousness is much slower, causing drowsiness that usually lasts for at least 10 minutes. 

To confirm a suspected cause, doctors may attempt to re-create a fainting episode under safe conditions. For example,  the person may be asked to breathe quickly  and deeply. Or, while monitoring  the heartbeat with ECG, a doctor may press gently over  the carotid sinus (a part  of the internal carotid artery containing sensors that monitor  blood pressure). This  pressure temporarily increases blood  pressure inside the carotid sinus, tricking  the body into thinking that  blood pressure has increased throughout the body. The sinus then sends signals to the brain to reduce  blood pressure, and faintness or fainting may result. 

Tilt table testing (see Symptoms and Diagnosis  of Heart and Blood Vessel Disorders: Tilt Table Testing)  is commonly done to determine the cause of fainting.  The person  is strapped to a motorized table. Then  the table tilts until the person  is almost standing. This position is held  for up to 45 minutes. Blood pressure  and heart rate are continuously monitored during the test. If  blood pressure does not decrease, the person is given isoproterenol Some Trade Names 

ISUPREL: (a drug that stimulates the heart),  and the test is repeated. Use of this drug makes the test more sensitive.