Time-frequency mapping of the magnitude squared-coherence for intra-QRS potentials detection

Intra-QRS potentials detected in the presence of heart disease represents unstable electrical conduction in damaged myocardium, probably due to dispersion in propagation time-constants. A one-dimensional linear model of continuous velocity waveform transmission is proposed, and a time-frequency magnitude squared-coherence (MSC) mapping of the ventricular activation (VA) of patients with ventricular tachycardia (VT) and normal volunteers was studied. Normal subjects shows high MSC estimates, mainly at the beginning and end of VA. Reduction of MSC estimate throughout VA was observed in VT, which reflects variation in the content of successive spectral estimates. This finding is indicative of fluctuation in propagation velocity of the ventricular activation in damaged myocardium.