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Because the use of absolute rate alone to distinguish sinus tachycardia (ST) from ventricular tachycardia (VT) lacks precision, rate variation algorithms including sudden onset have been proposed to improve the detection of pathological tachycardias by implantable antitachycardia devices. In this study, a median filtering algorithm was designed, tested, and compared to these established algorithms using identical data. Onset of ST during exercise and during VT was analyzed for 50 cases each. Fixed-interval change and percent change of cardiac cycles were compared as criteria for sudden onset. Optimal performance of the five-cycle median filter was achieved using a threshold of 25% change in median ventricular rate. It successfully differentiated ST from paroxysmal VT with a sensitivity of 92% and specificity of 96%. Median filtering appears to yield better performance when compared to previously proposed onset algorithms for VT identification. >

The authors assess the effect of position of the catheter electrodes on morphology analysis is both unipolar and bipolar configuration. Unfiltered bipolar and unipolar intraventricular electrograms were recorded from an electrode catheter initially positioned in the right ventricular (RV) apex (site 1) of 13 patients during sinus rhythm and induced monomorphic ventricular tachycardia (VT). Sinus rhythm and the identical VT were recorded a second time after repositioning the same electrode catheter within the RV apex (site 2) 0.2-4.4 cm from its original site. Analysis of unipolar electrograms detected 10/10 VTs at both sites, whereas analysis of bipolar electrograms detected 8/10 VTs at site 1 and 9/10 VTs at site 2, but was successful in all ten using a choice of either site 1 or 2. Thus, unipolar electrogram analysis for VT detection is less affected than bipolar electrogram analysis by a change in electrode catheter position but bipolar electrograms can be equally effective with a careful and judicious choice of electrode placement. >