Definitions and Epidemiology
Syncope can be defined as cerebral hypoperfusion sufficient to cause transient loss of consciousness. There are many potential causes, and most are benign. However, there are some life-threatening causes of syncope, and anyone who falls from syncope of any reason could injure themselves. Between 20% and 50% of people say they have had syncope at some point. It appears most commonly in females.
Abnormal circulatory control or cardiovascular volume can lead to situational syncope, vasovagal syncope, orthostatic hypotension, or reflex asystolic (pallid) syncope.
There are tachyarrhythmias, bradyarrhythmias, and structural heart defects that can lead to syncope. Toxic or metabolic abnormalities such as hypoglycemia, hypocalcemia, hypomagnesemia, hypoxia, and alcohol/medication overdose are associated with syncope. Addison disease can cause syncope through volume depletion.
A good history and physical examination are absolutely necessary if the cause of syncope is to be determined. Blood pressures should be checked lying, sitting, and standing. A drop in the systolic blood pressure of more then 20 mm Hg or a significant increase in pulse indicates probable volume loss or abnormal neurocardiac control. Check the pulse in all extremities. Check for a detectable mass in the abdomen. Listen for a heart murmur.
Check the mental status of the patient after the spell is over. An EKG to look for long QT syndrome, heart block, and ventricular hypertrophy should be performed. Cardiac monitoring for an arrhythmia may be indicated depending on the situation. A complete blood count to look for evidence of anemia and infection, electrolytes, glucose, calcium, magnesium, blood urea nitrogen, and creatinine should be checked. If appropriate, a pregnancy test, toxicology screen, or medication blood level should be done. If a seizure is suspected, an EEG should be ordered. An echocardiogram should be performed if there is a cardiac murmur, if the syncope occurred during exercise, or if there is a family history of cardiomyopathy or sudden death. Magnetic resonance imaging of the brain and cerebrovasculature is advised if any focal neurological signs were present at any time during the syncope. Tilt table testing is reasonable if there is suspicion of an inducible arrhythmia or hypotension. The most common finding on tilt table testing is hypotension and bradycardia or hypotension alone. Implanted loop recorders should be considered if syncope is recurrent and the workup is unrevealing. Repeated episodes of syncope that only occur when a certain parent or caregiver is present should raise the possibility of a factitious disorder.
Differential Diagnosis and Management
This is the most common cause of syncope in childhood. It is often triggered by pain, fear, or the sight of something unpleasant. Diaphoresis, light-headedness, and nausea are common before loss of consciousness but are often of short duration in children. It does not occur while supine, but may. The child will appear still while briefly unresponsive for usually under 1 minute. Occasionally, there may be brief jerks of the extremities for a second or two. The child may even have incontinence. These phenomena often raise the question of the possibility of a seizure. However, the patient with vasovagal syncope usually has no or only very limited jerking, little or no cyanosis, rarely bites the tongue, and usually awakens without much of a postictal state. Afterwards, there may be headache or fatigue.
Vasovagal syncope is caused by involuntary reflex activation of the vasovagal nervous system leading to bradycardia and vasodilation, resulting in a drop in blood pressure and cardiac output. Avoidance of the activity that triggers the response is sometimes helpful. Lying the person down flat is recommended. If a person is prone to vasovagal syncope they should pay particular attention to avoid becoming dehydrated. Fludrocortisone, midodrine, beta-blockers, serotonin reuptake inhibitors, and even pacemakers have been useful.6
A variety of activities can lead to an abnormal vasovagal response in some individuals, resulting in syncope. Coughing, micturation, defecation, and swallowing cold fluids or food have all lead to syncope in susceptible children. This is really just a form of vasovagal syncope caused by certain actions.
A healthy child who has breath-holding spells may become still and stop breathing after an episode of normal crying. It is often accompanied by cyanosis. The apnea usually occurs on expiration. If the apneic episode is long enough, hypoxia will occur. The child may lose consciousness and become limp. Further, the child may have short, limited muscle clonic jerks for a second or two after loss of consciousness. The episode usually lasts less than a minute and often ends with a deep inspiration. It usually starts between 6 and 24 months and disappears by 6 years. The breath holding is involuntary and scolding the child does not help. It is felt to be due to an immature autonomic nervous system. Parents or caregivers should be informed that the child has no control over these spells. Iron deficiency has been reported in some children with breath-holding spells. Treating these children with iron often helps reduce the number of spells.7 It seems reasonable to check the iron and ferritin level of any child with breath-holding spells. Iron deficiency states should be treated with iron supplementation. In a study by Daoud and colleagues,8 some children without iron deficiency responded to therapy and some with iron deficiency did not.
Reflex Asystolic (Pallid) Syncope
While reported between ages 3 months and 14 years, reflex asystolic syncope is usually seen in toddlers.9 These events were once called "pallid" breath-holding spells, but many of these children will not hold their breath during the episodes. The child will suddenly become pale or dizzy following a sudden painful or frightening event. As they lose consciousness and become limp, the child may or may not cry out. If the child is hypoxic long enough, there may be stiffening, twitching, and incontinence. The EEG shows no epileptiform activity during the spell and is usually attenuated. The EKG shows bradycardia or even asystole for several seconds immediately after the stimulus. It is felt to represent an abnormal vagal response to the painful or frightening event. To help the child regain consciousness, the child should be laid down flat and not carried around. Most children do not require any specific medical therapy. Atropine has been used successfully in some cases.
Orthostatic hypotension occurs when there is insufficient intravascular volume or autonomic nervous system dysfunction. The blood pressure drops when sitting up or standing, leading to cerebral hypoperfusion and syncope. Orthostatic intolerance can easily be tested by having the child stand still for 10 minutes while taking blood pressures every 2 minutes. A child with orthostatic intolerance will have a drop in blood pressure after standing still for a few minutes and will fall. It is recommended to do this test on a padded mat with someone ready to break the child's fall. Increasing the volume of fluids may help. Octreotide and midodrine have been shown to be effective.10
There are familial dominant (Romano-Ward syndrome), familial recessive (Jervell Lange-Nielsen syndrome which is associated with deafness), idiopathic nonfamilial, and medication-induced causes of long QT syndrome. Quinidine, procainimide, amiodarone, and cyclic antidepressants have each been associated with long QT syndrome. When terfenadine is taken with macrolide antibiotics (eg, erythromycin) there is an increased chance of developing long QT syndrome. An EKG can detect a long QT interval. There are normal people with a long QT interval and some people with long QT syndrome may have a normal QT interval. This can further complicate obtaining a diagnosis in some people. Genetic testing may help obtain the diagnosis in some. Epinephrine given during a stress test can help with diagnosis in others. Heart palpitations or an irregular heartbeat may occur in some people with long QT syndrome. People with long QT syndrome can develop syncope after an episode of sudden emotion, fright, or during vigorous exercise. Syncope in people with long QT syndrome may be due to a persistent burst of polymorphic ventricular tachycardia in a form called "torsades de pointes" or "twisting of the points" that can lead to ventricular fibrillation. Sudden death can occur if ventricular fibrillation is not treated. An implanted or automated external defibrillator (AED) may correct the abnormal fibrillation. Beta-blockers are sometimes recommended.
Sinus node disease can cause severe bradycardia, which decreases cardiac output and cerebral perfusion. It may be seen in children with atrial septal defects or Ebstein anomaly of the tricuspid valve. In children who have a complete heart block and have an escape rhythm that is slow, cardiac output will also be low and syncope can occur. These children may benefit from a pacemaker.
Tachycardias can occur that are so fast that diastolic filling and stroke volume are impaired. Syncope can occur with atrial tachycardias such as rapid atrial fibrillation due to the loss of "atrial kick." Occasionally, supraventricular tachycardia can last for a long time and may affect cardiac output. Wolff-Parkinson-White syndrome with atrial fibrillation or exercise-induced supraventricular tachycardia has caused syncope. Syncope occurs in ventricular tachycardia because of decreased stroke volume. When ventricular tachycardia persists and the myocardium becomes desynchronized, ventricular fibrillation can occur. Without cardioversion, persistent ventricular fibrillation will cause death within minutes. Seizures have been associated with atrial and ventricular fibrillation (Figure 5-1).
A. Baseline electrocardiogram recording of lead II in a 12-year-old boy with known sinus node dysfunction. He has an automatic implantable cardioverter/defibrillator (AICD). This recording shows an atrial paced rhythm, with normal atrioventricular node conduction at a rate of 85 bpm (25 mm/sec). B. Intracardiac electrograms from the AICD during a seizure in this 12-year-old boy. Simultaneous atrial and ventricular electrograms are demonstrated. Both atria and sentricles are fibrillating with rates greater than 300 bpm in all cardiac chambers. (Courtesy of Ann Dunnigan, M.D., Central Minnesota Heart Center, St. Cloud, MN.)