Initial Workup for Syncope in Children

From The Child's Doctor, Spring 2006

Sabrina Tsao, MD

Attending physician, Cardiology; Assistant Fellowship Director, Pediatric Cardiology, Ann & Robert H. Lurie Children's Hospital of Chicago; Assistant professor of Pediatrics, Northwestern University Feinberg School of Medicine

Disclosure: Dr. Tsao has no industry relationship to disclose and does not refer to products that are still investigational or not labeled for the use in discussion.

Other Disclosure Information

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Summary

Syncope is a relatively common, but complex presenting symptom, defined as "a sudden loss of consciousness associated with the inability to maintain postural tone, followed by spontaneous recovery."[1] The term syncope may have different meanings to different people, therefore specific questions should be asked to help differentiate cardiac causes of syncope from neuropsychogenic and metabolic conditions that can cause a similar symptom. The evaluation starts with a detailed history, physical examination and an electrocardiogram (ECG). Certain "red flags" in the history deserve a more urgent referral to cardiology for additional evaluation, whereas simple vasodepressor syncope can be managed in primary care.

History

While taking history, clarifying the following points should help pediatricians gather important details about the context and experience of "syncope."

• What does "black out" mean?
• Was the patient aware of what was going on?
• Could the patient hear people?
• What was the duration of the episode?
• Were there any witnesses?
• Did the patient sustain any injury?
• In what position was the patient when the vasodepressor syncope and oral fluid management episode occurred?
• What activity was the patient doing when it happened?

The "red flags" in the history that signal a need for an urgent pediatric cardiology referral are described in Table 1.

The history that suggests vasodepressor or benign syncope includes triggers such as positional changes, prolonged standing or sitting, or obnoxious stimuli (eg, pain, sight of blood). Patients may report seeing sparks, tunnel vision, or nausea. Vasodepressor syncope also may be associated with a feeling of fast heartbeat after the onset of these symptoms. Recovery of consciousness is prompt after the patient falls or lies down.

More information on the vasodepressor syncope is discussed in later sections.

Serious cardiac causes of syncope

During initial evaluation of syncope, pediatricians need to carefully consider the cardiac causes, and rule out the possible neuropsychogenic and metabolic explanations (see Table 2).

Below is a brief overview of the serious cardiac conditions that may involve syncope.

Tachyarrhythmia: Patients with syncope due to ventricular fibrillation may have long QT syndrome (Figure 1), Wolff-Parkinson-White (WPW) syndrome (Figure 2) with atrial fibrillation, or repaired congenital heart disease. The differential diagnosis for children exhibiting ventricular tachycardia is long QT syndrome, cardiomyopathy, or repaired congenital heart disease. Supraventricular tachycardia may present as syncope in children with a prolonged episode or in children with WPW who have rapid ventricular response during atrial fibrillation.

 

FIGURE 1: Patient with long QT syndrome; note abnormal broad tall T waves

 

FIGURE 2:  Note short PR interval and delta wave in a patient with WPW syndrome

 

Bradyarrhythmia: If it develops suddenly, bradyarrhythmia can significantly reduce cardiac output, and may result in syncope. Heart block may be due to congenitally corrected transposition of the great arteries (L-TGA), acute rheumatic fever, myocarditis, or Lyme disease. Sick sinus syndrome may be found in patients with a history of congenital heart surgeries. Sinus bradycardia or junctional bradycardia may develop before progressing to sick sinus syndrome.

Hypertrophic cardiomyopathy is the most common cause of sudden cardiac death in athletes. However, there are clues that point to the diagnosis on physical examination. On cardiac examination, the patient may have a forceful point of maximal impulse. The classic auscultatory finding is a crescendo-decrescendo systolic murmur along the left sternal border. The intensity of the murmur, unlike most other cardiac murmurs, increases with Valsalva maneuvers or with rising from squatting to standing. These maneuvers decrease preload resulting in reduced filling of the left ventricle, which results in increased obstruction and therefore, a louder murmur. The ECG usually shows left ventricular hypertrophy (LVH) with or without repolarization abnormalities.

Dilated cardiomyopathy patients may initially present with vague complaints of fever, vomiting, and abdominal pain. On physical examination, murmur of mitral regurgitation (holosystolic murmur at the apex radiation to the left axilla) with a displaced maximal point of impulse may be present prior to signs of congestive heart failure. These patients are at a risk of developing life threatening ventricular arrhythmias (Figure 3).

 

FIGURE 3: Spontaneous non-sustained monomorphic ventricular tachycardia in a patient with dilated cardiomyopathy

 

Severe aortic stenosis patients will have an abnormal cardiac examination. Bicuspid aortic valve has a systolic click, usually audible at the apex. However, with progressive stenosis, the click may become softer or inaudible. A thrill may be palpated in the upper right sternal border or in the suprasternal notch and the carotids. This becomes impalpable with increasing level of stenosis. A crescendo-decrescendo systolic murmur is heard loudest in the aortic area with radiation to the apex and the carotids. Depending on the degree of stenosis, the pulse pressure may be reduced. ECG shows LVH.

Congenital heart disease history discovered in a child presenting with syncope (Figures 4-6) requires referral to a pediatric cardiologist.

 

FIGURE 4:  Automated external defibrillator (AED) recording of a patient with tetralogy of Fallot successfully resuscitated from VF arrest

 

FIGURE 5: Atrial tachycardia with rapid ventricular response in an adult patient with D-TGA status post Mustard operation

 

FIGURE 6: Atrial tachycardia with variable AV conduction in an adult Fontan patient; note the subtle small negative P waves in II, III, aVF

 

Abnormal coronary artery accounts for the second most frequent cause of sudden cardiac death in athletes. The most common abnormality is the anomalous origin of the left main coronary artery from the right sinus of Valsalva.[2]

Primary pulmonary hypertension may present with exercise-induced syncope or may present as sudden death. On physical examination, patients have a loud P2 and ECG may show signs of right ventricular hypertrophy.

Cause of vasodepressor syncope

There are many synonyms for vasodepressor syncope, including vasovagal syncope, neurally mediated vasodepressor syncope, the simple faint, neurocardiogenic syncope, "church" syncope, "hair-grooming" syncope or benign syncope. Its pathophysiology is incompletely understood. The Bezold-Jarisch reflex with an exaggerated negative feedback loop has been commonly attributed to causing vasodepressor syncope.

Under normal circumstances, there is gravity-driven venous pooling during standing. This results in reduced ventricular filling pressures (preload), stroke volume and arterial blood pressure. The compensatory mechanisms of sympathetic stimulation and withdrawal of parasympathetic stimulation result in reflex tachycardia and vasoconstriction. The underfilled and hypercontractile left ventricle stimulates the mechanoreceptors, which transmit impulses via unmyelinated C-fibers from the ventricle to the central nervous system, causing vagally mediated bradycardia and vasodilatation.

In patients with vasodepressor syncope, this vagal response is thought to be exaggerated, leading to significant bradycardia (Figure 7), even transient asystole, thereby causing transient decrease in cerebral perfusion and possible loss of consciousness.[3]

 

FIGURE 7: Reflex sinus tachycardia with abrupt drop to sinus bradycardia in a patient during a positive tilt table test for vasodepressor syncope

 

Management of vasodepressor syncope

If vasodepressor syncope is suspected, a full dietary and fluid history should be obtained. A 2-week fluid diary may be helpful in documenting the overall fluid intake.

Oral fluid guidelines for managing vasodepressor syncope include a target daily fluid intake of 1 oz/kg. Additional fluid, in the form of water or sports drinks, is recommended with vigorous exercise. The patient should aim to drink 1⁄4 of the total daily fluid requirements with breakfast, 1⁄4 with lunch, 1⁄4 after school, and 1⁄4 in the evening. Most of the fluid intake should be during daytime when the patient is active.

The patient’s hydration status should be monitored by ensuring that the urine is dilute, either by using urine dipstick to check whether specific gravity is less than 1.010 specific-gravity unit or by observation. Dilute urine is either colorless or very light yellow in color. The patient needs to drink enough to abolish sensation of thirst and avoid caffeinated drinks.

Oral fluid therapy is an effective therapy in the majority of patients diagnosed with vasodepressor syncope.[4] If the patient feels onset of symptoms, the patient should either put his or her head down on the lap or even lie down horizontally in order to avoid a syncopal episode.

If, however, despite increasing salt and fluid intake, the patient continues to have symptoms, then it is appropriate to refer to pediatric cardiology for further evaluation. The pediatric cardiologist may determine the need for pharmacological therapy.

Further evaluations

Tilt table testing, echocardiography, trans-telephonic monitoring, and 24-hour ambulatory monitoring can be done more cost-effectively in conjunction with pediatric cardiology consultation. These are not always necessary in patients with simple vasodepressor syncope.

Conclusion

During initial evaluation of syncope, pediatricians need to differentiate between the serious cardiac causes of syncope and various other neuropsychogenic and metabolic possibilities. Syncope during exercise, exertion, or accompanied by intense emotion requires urgent referral to pediatric cardiology. Family history that may signal cardiac conditions includes early sudden death, long QT syndrome, cardiomyopathy, sensorineural deafness, drowning, single car accident. Pediatricians should also refer patients with an abnormal physical examination or ECG, and patients with vasodepressor syncope that is resistant to oral fluid management.

REFERENCES

[1.] Soteriades ES, Evans JC, Larson MG, Chen MH, Chen L, Benjamin EJ, Levy D Incidence and prognosis of syncope. N Engl J Med 2002;347:878-885.

[2.] Hosey RG, Armsey TD. Sudden cardiac death. Clin Sports Med 2003 Jan;22(1):51-66.

[3.] Grimm DR. Neurally mediated syncope: A review of cardiac and arterial receptors. J Clin Neurophysiol 1997 May;14(3):170-182.

[4.] Younoszai AK, Franklin WH, Chan DP, Cassidy SC, Allen HD. Oral fluid therapy. A promising treatment for vasodepressor syncope. Arch Pediatr Adolesc Med 1998 Feb;152(2):165-168.

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