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Background: To know the underlying mechanisms of J waves, the response to atrial pacing was studied in patients with idiopathic ventricular fibrillation (IVF) and patients with non-IVF.Methods and Results: In 8 patients with IVF, the J-wave amplitude was measured before, during, and after atrial pacing. All patients had episodes of ventricular fibrillation without structural heart disease. The responses of J waves were compared with those of the 17 non-IVF control subjects who revealed J waves but no history of cardiac arrest and underwent electrophysiological study. The IVF patients were younger than the non-IVF patients (28±10 versus 52±14 years, respectively; P=0.002) and had larger J waves with more extensive distribution. J waves decreased from 0.35±0.26 to 0.22±0.23 mV (P=0.025) when the RR intervals were shortened from 782±88 to 573±162 ms (P=0.001). A decrease (≥0.05 mV) in the J-wave amplitude was observed in 6 of the 8 patients. In addition, 1 patient showed a distinct reduction of J waves in the unipolar epicardial leads. In contrast, J waves were augmented in the 17 non-IVF subjects from 0.27±0.09 to 0.38±0.10 mV (P<0.001): augmented in 9 and unchanged in the 8 subjects. The different response patterns of J waves to rapid pacing suggest different mechanisms: early repolarization in IVF patients and conduction delay in non-IVF patients.Conclusions: The response to atrial pacing was different between the IVF and non-IVF patients, which suggests the presence of different mechanisms for the genesis of J waves. [ABSTRACT FROM AUTHOR]

Background: The pacing lead system is electrically evaluated by a pacing system analyzer (PSA) during device implantation. However, it remains unknown whether measured data vary according to the PSA or the implantable device. We estimated differences in lead impedance measured by different PSAs and devices using a laboratory model. Methods: Five pacing and 3 defibrillation leads were used. We fixed the lead tip to a piece of meat immersed in physiologic saline and measured lead impedance using 4 PSA and 13 implantable device models. Results: The mean impedance of the 5 pacing leads as measured by PSAs was 735 to 611 ohms and the difference between the maximum and minimum values was 126 ohm. The maximum difference according to PSAs was 222 ohm. The mean impedance of the 5 pacing leads as measured by the implantable generators was 770 to 606 ohms, the difference was 175 ohms and the maximum difference was 309 ohms. The 3 defibrillation lead impedances varied from 427 to 1091 ohms and the mean impedance was 706 to 557 ohms. The differences were 149 ohm as measured by the PSAs and 157 ohms by the implantable cardioverter defibrillator (ICD) generators. The maximum differences were 241 ohms by the PSAs and 281 ohms by the ICD generators. Conclusion: Lead impedance varied according to analyzing systems. [ABSTRACT FROM AUTHOR]