HETEROGENEOUS EFFECT OF QUINIDINE ON THE VENTRICULAR DEPOLARIZATION PROCESS ASSESSED BY THE SPATIAL VELOCITY ELECTROCARDIOGRAM OF THE QRS COMPLEX - PRELIMINARY-REPORT OF A NEW INVESTIGATIVE METHOD

The negative conduction effect of quinidine on each of the successive phases of the ventricular depolarization was investigated using an ori ginal noninvasive method: the spatial velocity electrocardiogram of th e QRS complex (SVECG-QRS). We performed a randomized placebo-controlle d trial in 10 healthy subjects with a single oral dose of quinidine (3 30 mg) or placebo, Electrocardiographic acquisition and processing (22 0 recordings for the complete trial) were performed using the Lyon vec torcardiographic program, For each SVECG-QRS curve, the position of se ven specific points from A (onset of QRS) to G (end of QRS) were deter mined precisely. The six successive time intervals between these point s (AB-FG) and five velocity values (B-F) were then calculated, The QRS complex was longer under quinidine than placebo (102.4 +/- 1.6 vs, 10 0.3 +/- 1.5 ms), The difference was at the periphery of statistical si gnificance (p = 0.05), and this lack of statistical difference may be mainly due to the low serum levels of quinidine obtained at the peak o f the concentration (1.46 +/- 0.4 mg/l). All six QRS time intervals we re longer under quinidine, but only the BC interval was significantly different (9.3 +/- 1.1 vs. 18.8 +/- 1.1 ms; p < 0.05) suggesting a mor e pronounced negative conduction effect at the onset of ventricular de polarization. No significant modifications were observed for the veloc ity values. We conclude that (1) the negative conduction effect of qui nidine is heterogeneous, but a further study with a higher dose of qui nidine (concentration-dependent effect) is required to confirm this hy pothesis and (2) the spatial velocity electrocardiogram of the QRS com plex allows a detailed analysis of the ventricular conduction phases, The results of the measurement were found to be reproducible. This non invasive tool could be used in clinical practice to assess effects of antiarrhythmic drugs on successive ventricular depolarization phases.