Identification ofventricular tachycardia with use of themorphology oftheendocardial electrogram

Currently available antitachycardia devices relyprimarily on timing information to define abnormal rhythms. Itwouldbeuseful tohave more specific means ofautomatically identifying pathologic tachycardias. Usingunfiltered (0.04 to500Hzbandpass) recordings madeduring electro- physiologic testing in10patients withventricular tachycardia (VT), we studied thedifferences in electrogram morphology during sinus rhythm andVT.Signals weredigitized at1kHz.Atemplate ofa normal sinus rhythm electrogram was created foreachpatient byaveraging five sinus complexes from thebeginning ofeachstudy. Tensinus electrograms just before theonsetofVT and10electrograms during stable monomorphic VT were compared withthis template. Thedifference inmorphology between agiven electrogram andits template was quantitated bysuperimposing thetwosignals and measuring theareabetween thecurves.There was no overlap intherangesofthese "area ofthe difference" measurements between sinus andVTelectrograms from any ofthe10patients studied, including four with intraventricular conduction disturbances. Incontrast, discrete features ofthesignal, including peakamplitude andmaximumdV/dt, didnotreliably differentiate sinus fromVTelectro- grams.Bandpass filtering, sample windowsize, anddigitizing rate weremanipulated todetermine the minimal signal content necessaryfortheareaofdifference method toreliably identify VT.These interventions suggest that thelow-frequency far-field portion ofthesignal isprimarily responsible for themorphologic differences between sinus andVTelectrograms. Inconclusion, themorphology ofVT electrograms inman isconsistently anddistinctly different fromthemorphology ofsinus electrograms. Morphologic analysis may bea useful adjunct fortheautomatic detection ofVT byimplanted antitachycardia devices. Circulation 77,No.6,1363-1369, 1988.