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8.4 Discriminating VT/VF from SVT using Wavelet
Patients who are experiencing supraventricular tachycardia (SVT) may exhibit ventricular
rates in the VT/VF detection zone. If sustained and not correctly identified, such fast
ventricular rates may cause an inappropriate delivery of a VT/VF therapy. Identifying and
withholding detection for conducted SVT reduces the chance of delivering an inappropriate
therapy for high ventricular rates that are not ventricular in origin.
8.4.1 System solution: Wavelet
The Wavelet feature is designed to withhold inappropriate ventricular detection during
episodes of rapidly conducted SVT. Tachyarrhythmias of ventricular origin typically have
different QRS morphologies than rhythms of supraventricular origin. The Wavelet feature
compares the patient’s current QRS waveform to a collected and stored template of the
patient’s QRS waveform in sinus rhythm. VT/VF detection is withheld if the current waveform
sufficiently matches the template.
8.4.2 Operation of Wavelet
Figure 162. Using a Wavelet template to discriminate SVT from VT
Template
Rhythm matches template
SVT
VT
Rhythm does not match template
The device collects EGM data for sensed ventricular events and compares it to a stored
template using the programmed Match Threshold value (nominally 70%). A QRS complex
is classified as a “Match” if its match score is greater than or equal to the programmed Match
Threshold value. If at least 3 of the last 8 QRS complexes sufficiently match the stored
template, the device withholds detection. If fewer than 3 of the last 8 QRS complexes
sufficiently match the stored template, the device allows detection and therapy.
After VT detection is withheld, the ventricular rhythm is continuously evaluated until VT
detection occurs or the fast ventricular rate ends.
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