[Determination of the optimal atrioventricular timing by impedance plethysmography in patients with cardiac pacing; correlations with left ventricular filling].

The stroke volume (SV) was measured by the change in the impedance in thirteen patients with dual chamber pacemakers at different atrioventricular delay (AVD) intervals: 31 to 219 ms or 75 to 220 ms. The mitral inflow was also recorded by Doppler echocardiography at each AVD with measurement of the duration of mitral flow (MFD) and the velocity time integral (VTI). All thirteen patients were studied in the DDD mode; in addition, 5 patients were studied in the atrial sensing ventricular stimulation VDD mode. The SV measurement by impedance plethysmography was reproducible with an average variability of 3.5%: the optimal AVD was determined by this method in 11 patients with DDD and 4 patients with VDD pacing: in 3 patients (2 in DDD and 1 in VDD mode) 2 optimal AVD were obtained. The optimal AVD was 123 +/- 31 ms (63 to 156 ms) in DDD mode and 91 +/- 17 ms (63 to 110 ms) in VDD mode. The analysis of left ventricular filling showed that changes in AVD led to similar changes in mitral VTI. The MFD increased as the AVD was shortened to a constant value at the optimal AVD. In all patients, the optimal AVD was obtained when the MFD became maximal and constant. Measurement of MFD is a simple and rapid means of assessing optimal AVD at rest in patients with dual chamber pacing systems.