Assessment of left atrial input impedance in normal subjects and in hypertensive patients

To assess left atrial (LA) input impedance in patients with signs and/or symptoms of heart failure and normal left ventricular ejection fraction, transesophageal Doppler pulmonary venous (PV) flow velocity and pulmonary capillary wedge pressure (PCWP) were studied in 20 patients and compared to 20 matched normal controls.

LA impedance was calculated as the ratio of harmonic terms of the PCWP (measured by right heart catheterization) to the corresponding harmonic terms of PV flow (measured by transesophageal Doppler echocardiography). Eight harmonics were analyzed.

Left ventricular mass index (LVMI, p<0.001), heart rate (p<0.05), systolic and diastolic blood pressure (p<0.001), isovolumic relaxation time (IVRT, p<0.001), peak A transmitral flow velocity (p<0.001), peak reversal atrial PV flow velocity (p<0.001) and LA diameter (p<0.001) were increased in patients compared to controls. Spectra of impedance moduli were displaced upwards and to the right. The increase in the impedance moduli was observed at all frequencies of the first to seventh harmonic components (p<0.001). In multivariate tests LVMI (p=0.003), IVRT (p=0.001), and LA diameter (p=0.007) had a significant effect on all harmonic components of the impedance moduli (adjusted R2=0.970 to 0.999, p<0.001).

LA input impedance derived from data obtained invasively and semi-invasively represents left ventricular diastolic function. Resistance to left ventricular filling is increased in hypertensive patients.