| Separation of Ventricular Tachycardia
and Ventricular Fibrillation Using Two Unipolar Electrograms |
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| Stephanie A. Caswell, Julie Thompson, Lorenzo
DiCarlo, Janice M. Jenkins |
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| In third-generation implantable antitachycardia
devices (ATDs), immediate defibrillation is required for ventricular
fibrillation (VF) while lower-energy therapies can convert many ventricular
tachycardias (VTs). However, separation of these rhythms by rate measures
is not always feasible. This study employed a measurement to quantify
the coherence between two unipolar electrograms from the same catheter,
where incoherence between signals indicates VF. A normalized cross
correlation (CC) measured similarity between electrogram morphologies
and standard deviation (STD) and interquartile range (IQR) (Q3 minus
Q1) measured consistency over a passage. Two unipolar electograms
were derived from the distal and proximal electrodes of a catheter
located in the RVA (1 cm spacing). A wire located remotely in the
femoral vein was used as the reference electrode. Sinus rhythm (SR),
VT, and VF passages from 10 patients were recorded on FM tape at 3
3/4 ips (1-500 Hz) and digitized at 1000 Hz. The CC was computed for
a 150 point window spanning the depolarization with +/-10 point shift
and the peak CC value (PCC) was chosen. VF was separated from VT/SR
by the STD and the IQR of the PCC values for a passage where a large
STD or IQR indicates VF. \nRESULTS: Sensitivity (sens) and specificity
(spec) were derived for all patients where sensitivity is with respect
to VF only. The mean +/- std for PCC was 0.85+/-0.016 for SR, 0.79+/-0.046
for VT and 0.56+/-0.332 for VF. Patient-indepedent STD thresholds
of 0.15-0.25 provided 100% sens and 100% spec. The IQR mean was 0.017
for SR, 0.10 for VT, and 1.03 for VF, providing 100% sens and 100%
spec for IQR thresholds of 0.3-0.6.\nCONCLUSION: This method was able
to successfully separate incoherent (VF) from coherent rhythms (SR,
VT), improving upon ATD rate algorithms. Classification was achieved
with patient-independent thresholds. In addition, 'polymorphic', but
coherent rhythms (such premature ventricular depolarizations) would
not be misclassified as VF. Proper distinction of VT from VF would
allow defibrillation to be deferred for consideration of lower energy
therapies, providing significant energy savings. |
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| Winner of the Rosanna Degani Young Investigator
Competition. Published in Proceedings of Computers in Cardiology 1996
|
