Tachydysrhythmias
The tachydysrhythmias can be classified broadly into those that originate
from loci above the AV node (supraventricular), those that originate from
the AV node (AV node re-entrant tachycardias), and those that are ventricular in origin. Although AV node re-entrant tachycardias are more
common in adults, the vast majority of tachycardias in children are supraventricular
in origin. It is important to record continuous ECG or rhythm
strips with the child in tachycardia, while medication is being pushed, and
when converted to sinus rhythm. On recognition of a tachycardia, stepwise
questioning can help clarify the ECG tracing. Is it regular or irregular? Is
the QRS complex narrow or wide? Does every P wave result in a single
QRS complex?
Sinus tachycardia can be differentiated from other tachycardias by a narrow
QRS complex and a P wave that precedes every QRS complex. Sinus
tachycardia is a normal rhythm with activity and exercise and can be a normal
physiologic response to stresses, such as fever, dehydration, volume
loss, anxiety, or pain. Sinus tachycardia that occurs at rest may be a sign
of sinus node dysfunction. It is important to keep in mind, however, that
the normal range for heart rate is higher in children (see Table 1).
Supraventricular tachycardia (SVT) is the most common symptomatic
dysrhythmia in infants and children, with a frequency of 1 in 250–1000 patients
[6]. The peak incidence of SVT is during the first 2 months of life.
Infants with SVT typically present with nonspecific complaints, such as fussiness,
poor feeding, pallor, or lethargy. Older children may complain of chest
pain, pounding in their chest, dizziness, shortness of breath, or may demonstrate
an altered level of consciousness. The diagnosis often begins in triage
with the nurse reporting that ‘‘The heart rate is too fast to count.’’
In newborns and infants with SVT, the heart rate is greater than 220 bpm
and can be as fast as 280 bpm, whereas in older children, SVT is defined as
a heart rate of more than 180 bpm [7]. On the ECG, supraventricular tachycardia
is evidenced by a narrow QRS complex tachycardia without discernible
P waves or beat-to-beat variability (Fig. 3). The initial ECG may be
normal, however, and a 24-hour rhythm recording (eg, Holter monitor) or
an event monitor may be necessary to document the dysrhythmia in cases
of intermittent episodes. In children younger than 12 years of age, the
most common cause of supraventricular tachycardia is an accessory atrioventricular
pathway, whereas in adolescents, AV node re-entry tachycardia
becomes more evident
SVT can be associated with Wolff Parkinson White (WPW) syndrome.
SVT in WPW syndrome generally is initiated by a premature atrial depolarization
that travels to the ventricles by way of the normal atrioventricular
pathway, travels retrograde through the accessory pathway, and re-enters
the AV node to start a re-entrant type of tachycardia [7,8]. Antegrade conduction
through the AV node followed by retrograde conduction through
the accessory pathway produces a narrow complex tachycardia (orthodromic
tachycardia) and is the most common form of SVT found inWPWsyndrome
Less commonly re-entry occurs with antegrade conduction through the
accessory pathway and retrograde conduction through the AV node (antidromic
tachycardia) to produce a wide complex tachycardia [9]. Typical
ECG findings of WPW are a short PR interval, wide QRS complex, and
a positive slurring in the upstroke of the QRS complex, known as a delta
wave (Fig. 4). The ECG in most WPW SVT does not show the delta wave,
because tachycardia is not conducted down through the accessory pathway.
Episodes of SVT in children who have WPW usually occur early in the first
year of life [9]. Episodes of SVT often resolve during infancy but may recur
later in life, usually from 6–8 years of age [9].
Atrial ectopic tachycardia may be differentiated from SVT by the presence
of different P-wave morphologies. Each P wave is conducted to the
This ECG was done shortly after adenosine was administered and the rhythm converted
to sinus. Note the abnormally short PR interval for age and the presence of a delta wave
(arrows) at the beginning of the QRS complex. The delta wave is not uniformly apparent in
all leads.
ventricle, and because the ectopic atrial focus is faster than the SA node, the
ectopic determines the ventricular rate (Fig. 5).
Although supraventricular tachycardias are more common than those of
ventricular origin, it is important to remember that the normal QRS complex
is shorter in duration in children than adults. As a result, a QRS complex
width of 0.09 sec may seem normal on the ECG but actually represents
an abnormal wide QRS complex tachycardia in an infant. The differential
diagnosis of wide complex tachycardia includes sinus/supraventricular
tachycardia with bundle branch block or aberrancy, antidromic AV re-entry
tachycardia, ventricular tachycardia (VT), or coarse ventricular fibrillation. ECG findings that support the presence of VT include AV dissociation
with the ventricular rate exceeding the atrial rate, significantly prolonged
QRS complex intervals, and the presence of fusion or capture beats. If there
is a right bundle branch block, the presence of VT is supported by a qR
complex in V1 and a deep S wave in V6. If there is a left bundle branch block
present, then the presence of VT is supported by a notched S wave and an
R-wave duration of O0.03 sec in V1 and V2 and a Q wave in V.
source:
Pediatric ECG
Ghazala Q. Sharieff, MDa,b,*, Sri O. Rao, MDc
aChildren’s Hospital and Health Center/University of California–San Diego,
3020 Children’s Way, San Diego, CA 92123
bPediatric Emergency Medicine, Palomar-Pomerado Hospitals/California
Emergency Physicians, 555 East Valley Parkway, Escondido, CA 92025, USA
cDivision of Pediatric Cardiology, Children’s Hospital and Health Center,
3020 Children’s Way, San Diego, CA 92123, USA
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