Pediatric emergency medicine trisk 1730 1730
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Adenosine is absolutely contraindicated in patients with WPW syndrome
presenting in atrial fibrillation (i.e., wide complex, irregular rhythm). Blocking
the AV node may then cause atrial fibrillation to be conducted rapidly to the
ventricle via the accessory connection leading to VF and possibly death.
Adenosine is relatively contraindicated in heart transplant recipients due to
prolonged sinus pauses in the transplanted heart, which is denervated from the
autonomic nervous system. Besides prolonged asystole, the heart is vulnerable to
malignant escape rhythms. Starting with one-third the recommended dose, and
increasing if necessary may mitigate the effect of adenosine on the transplanted
heart. Finally, there are rare reports of adenosine causing bronchospasm in
asthmatics.
Wide Complex Regular Tachycardia. A wide complex regular tachycardia may be
VT, SVT with aberrancy, antidromic WPW, or sinus tachycardia with
aberrancy/bundle branch block. A quick history including symptoms, previous
tachycardia, baseline EKG, and any cardiac surgery or CHD will guide treatment.
The EKG and rhythm strip should be scrutinized to identify P waves and establish
the mechanism of tachycardia. Assess for hemodynamic stability and proceed
according to the PALS algorithms. Adenosine may be given with continuous
rhythm strip recording in a nonsinus regular tachycardia. Cardiology should be
consulted early to guide therapy.
While VT in adults is commonly due to ischemia secondary to coronary artery
disease, in children, ischemic VT is usually due to congenital coronary anomalies
or postoperative complications. Nonischemic VT may be due to scars in
postoperative CHD, ion channelopathies (LQTS, catecholaminergic polymorphic
ventricular tachycardia [CPVT] or Brugada syndrome), cardiomyopathies
(myocarditis, DCM, HCM, and arrhythmogenic right ventricular dysplasia
[ARVD]), cardiac tumors, or drugs. Idiopathic VF is diagnosed after cardiac
arrest when no cause for VF is identified in spite of a complete workup.
There are two types of monomorphic VT commonly encountered in the normal
heart. One is VT arising from the RVOT (LBBB, inferior axis) and the other is
Belhassen VT a left fascicular tachycardia (RBBB and left axis). Both are
relatively benign and may be treated with medication or cured by catheter
ablation. Belhassen VT usually responds to verapamil. Scars in the heart from
CHD surgery may provide a more malignant substrate for VT as can electrolyte
and metabolic disturbances (acidosis).
When wide complex tachycardia is only 15% to 20% faster than the underlying
sinus rhythm, it is called idioventricular tachycardia. This is generally a benign
