Tachycardia-Induced J-Wave Changes in Patients With and Without Idiopathic Ventricular Fibrillation

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.