The discrimination between ventricular and supraventricular tachycardia and the evaluation of their hemodynamic impact are essential issues in the arrhythmia management. A new pacing device features a tachycardia diagnostic system relying on simultaneous recording of the transvalvular impedance (TVI) and the iECG, which is an integrated electric signal derived by the whole set of endocardial electrodes. The iECG waveform is sensitive to the pattern of ventricular activation, similarly to the surface ECG. The TVI increases in systole and decreases in diastole, and the amplitude of its cyclic fluctuation is an expression of the effectiveness of the pump function. In order to test the value of these signals in the analysis of a tachycardia, we have assessed the iECG and TVI modifications induced by different SVTs and tolerated and non-tolerated VTs, during electrophysiological studies.

In case of SVT, the ventricular component of the iECG maintained the same morphology as in sinus rhythm. The peak-peak amplitude of the TVI fluctuation was reduced to 66 ± 11 % of the individual sinus rhythm reference, but the signal was present at every beat and showed a remarkable stability (variation coefficient 0.19 ± 0.01). In case of a VT, the ventricular component of the iECG was strikingly different than in sinus rhythm. Regular TVI fluctuation was observed with tolerated VTs (peak-peak amplitude 74 ± 6 %; variation coefficient 0.21 ± 0.04). In contrast, with non-tolerated VTs the TVI amplitude was depressed below 40%, and the signal was virtually absent in the event of very fast VT or VF.

Our results confirm that the iECG is a reliable tool to quickly discriminate VTs from SVTs and that TVI can provide information on the severity of the hemodynamic impairment produced by a tachycardia, with potential clinical benefit in the follow-up of pacemaker patients. Furthermore, the application of these signals in automatic algorithms of arrhythmia recognition might improve the specificity of therapy administration by an ICD.