NCS, or the simple faint, is the most common cause of loss of consciousness in childhood. It is characterized by inappropriate vasodilatation leading to neurally mediated systemic hypotension resulting in low cerebral perfusion pressure and cerebral blood flow. This systemic hypotension stems from vagal stimulation and often is precipitated by pain, fear, excitement, positional changes, and extended periods of standing, particularly in a warm environment. In this condition, an extended period in the upright position, dehydration, a vagal trigger, or external stimuli such as pain or emotional upset increases vagal tone leading to a decreased heart rate, peripheral vasodilatation, and systemic hypotension. The child with recurrent episodes is frequently referred for cardiovascular evaluation.

Evaluation includes a detailed history, cardiovascular examination, and a 12-lead electrocardiogram (ECG). Obtaining orthostatic vital signs can also be helpful in diagnosing this problem. With the patient in the supine position, blood pressure and heart rate are recorded. The patient is then asked to stand for 10 minutes and the measurements are repeated. A drop in systolic blood pressure of >15 mm Hg or a rise in heart rate of >20 beats per minute when standing is consistent with the diagnosis of neurally mediated hypotension that may result in NCS. An echocardiogram may be ordered if abnormalities are noted on the ECG or cardiovascular examination. Typically, this is sufficient to rule out a serious cardiac cause. Rarely, in cases where the mechanism of syncope is believed to be NCS but symptoms are atypical, a tilt-table test or graded exercise test may be ordered. In the tilt-table test, the child or adolescent is placed on a table and tilted to 70 degrees while being monitored by ECG and an automated blood pressure monitor. This creates an artificial orthostatic stress that often provokes a drop in heart rate and/or blood pressure, which is diagnostic. Exercise testing can elicit similar results. Following graded exercise, testing patients are asked to stand for 10 minutes and their blood pressure and heart rate are measured. This also creates an artificial orthostatic stress that often provokes a drop in heart rate and/or blood pressure, which is diagnostic. Patients with a positive tilt-table test or graded exercise test (e.g., those with NCS) are encouraged to increase their intake of fluids. If syncope persists, treatment with a mineralocorticoid may be initiated to help expand the intravascular blood volume.

Cardiac syncope is the result of a sudden decrease in cardiac output, leading to systemic hypotension, decreased cerebral perfusion, and a loss of consciousness. The differential diagnosis of cardiac syncope includes left ventricular outflow tract obstruction and arrhythmia.