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c_svt_paed

paediatric supraventricular tachycardias (SVT)

introduction

  • 70-90% of SVT in infants is AVRT and many infant SVTs are due to presence of accessory pathways which close after age 2 yrs as the heart develops
  • 5% of infant SVT are broad complex - BBB or accessory pathways such as WPW
  • 95% of broad complex tachycardias in infants are SVT not ventricular tachycardia (VT)
  • most have structurally normal hearts
  • infants with SVT are at risk of cardiac failure: 20% risk if 24-36hrs duration, >50% risk if longer than 48 hrs duration

Mx of the infant with presumed SVT

  • remember >95% of broad complex tachy in infants is SVT so adenosine is generally a safer option than attempting sedation and DC reversion even if broad complex unless ECG is strongly suggestive of VT or child requires ventilatory support or is in shock
  • be ready for hypotension, hypoxia, and rarely asystole or VF
  • verapamil (Isoptin) is C/I in infants as case reports of deaths
  • move to resus area
  • cardiac monitor, ECG consider placing R arm lead next to V1
  • BP and SaO2 monitoring
  • if stable, attempt physiologic reversion via increased venous return:
    • lie with head down and legs up
    • 10degC ice water mask or bag applied to face for 30secs
    • older kids can blow on sphymomanometer tubing aiming for 40mmHg for 15secs
  • IV or IO access
  • if shocked then immediate DC reversion 1J/kg sync and sedate if possible awareness:
    • iv midazolam or diazepam
  • if stable, rapid iv bolus adenosine followed by flush
    • should be given only by experienced doctors
    • only 35% revert at 0.1mg/kg so many prefer starting at 0.2mg/kg iv or perhaps 0.4mg/kg if via i/o or a foot vein
    • hold arm with iv above head for higher efficacy
    • use 3-way tap and rapid bolus followed rapidly by 10mL saline flush
    • possible outcomes of iv adenosine
      • Reversion and well
      • no response - check the 5 D's:
        • dose - increase dose to max. O.5mg/kg or 18mg whichever is lower
        • delivery - ensure rapid delivery to heart
        • diagnosis - not SVT
      • reversion but reverts back to SVT:
        • check for atrial focus
        • might be incessant re-entry tachycardia (usually HR 180)
        • repeating adenosine won't be useful
        • change drug to either reduce automaticity or rate control:
      • unmasks an atrial tachycardia such as atrial flutter or atrial focus as evidenced by presence of non-conducting P waves on the transient rhythm strip:
      • reversion but unmasks CCF with fall in BP and SaO2:
        • may need ventilatory support plus inotropes such as dobutamine
      • asystole, VF or VT (rare but need to be prepared for it)
  • ECG post reversion
c_svt_paed.txt · Last modified: 2014/04/13 22:01 (external edit)