Algorithms for SVT discriminators
Single chamber
Morphology
Stability
Onset
Dual chamber
Same as single chamber +
Chamber of onset
A:V ratio & relationship
Morphology
Compares sinus rhythm QRS morphology to VHR
Not suitable for
•has accessory pathway – fused baseline QRS
•Has rate related BBB
•VT with similar morphology to normal QRS
Stability
Helps discriminate from AF
Usually only available in VT zones
Not suitable for
•Polymorphic VT
•VF
Onset
Used to differentiate sinus tachycardia
•SVTs still have sudden onsets
Can be dangerous: VT may start slowly and become faster
•may cross from outside a zone into a zone and be classified as a STc – therapies withheld
Chamber onset
Used to differentiate atrial tachycardia
Issue: some SVTs can initiate in ventricle
A & V ratio
V>A
•Classified straight to VT
•Rare SVTs can have >Vs then As
A=V
•1:1 SVTs
•could be VT with retrograde A
A>V
•AF
•Can still have VTs during AF (dual tachycardia)
Manufacturer Summary of algorithms
V>A
•Classified straight to VT
•Rare SVTs can have >Vs then As
A=V
•1:1 SVTs
•could be VT with retrograde A
A>V
•AF
•Can still have VTs during AF (dual tachycardia)
