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)
