Usefulness of the impedance cardiogram to reflect left ventricular diastolic function

The impedance diastolic waveforms, early O wave (zO) and late A wave (zA), were evaluated, and their relation to diastolic mitral flow patterns under changes in loading conditions was assessed. Eight normal subjects and 9 patients with Doppler evidence of delayed ventricular relaxation were studied with simultaneous transmitral Doppler flow and computerized, ensemble-averaged, impedance cardiography in the supine position. Thirty-degree, head-down and head-up tilt were performed to alter preload. Peak Doppler early diastolic velocity (E) and E integral were preload-dependent in both normal and abnormal groups (p < 0.003), but were not significantly different between patients and normal subjects. Peak Doppler late diastolic velocity (A) and A integral, although significantly different between groups (p < 0.001), did not vary significantly with tilt. E/A ratio was significantly different between groups in all positions (p < 0.006). Impedance zA was preload-dependent (p < 0.001) in both groups and significantly different between groups (p < 0.05). Impedance zO was also preload-dependent (p < 0.003), but not significantly different between groups. Impedance zO correlated with Doppler peak E (r = 0.64; p = 0.001). Impedance zA did not correlate with Doppler A. Impedance cardiography diastolic waveforms can be altered by position and may reflect changes in vena caval or pulmonary vein volume flow, or both. This technique, in combination with Doppler mitral flow patterns, may be useful in evaluating diastolic function.