Impedance measurements in the human right ventricle using a new pacing system

A promising new pacemaker that provides on-line measurements of right ventricular (RV) impedance was evaluated in ten patients with symptomatic second- or third-degree atrioventricular (AV) block. We tested the assumption that if changes in RV impedance represented changes in RV stroke volume (SV), conditions known significantly to affect RV SV should be accompanied by significant changes in RV impedance. One week after pacemaker implantation, RV impedance was measured noninvasively during normal respiration in the supine (baseline), left lateral, right lateral, sitting, and standing positions. In addition, all patients performed a Valsalva maneuver test. The amplitude of the impedance signal was different during in- and expiration in every body position studied. At baseline, the amplitude of the signal was 18.80 +/- 2.24 mm; in the right lateral position 16.75 +/- 3.24 mm (P = 0.04) and 17.80 +/- 2.35 mm in the left lateral position (P = 0.04). The amplitude of the signal in the sitting position was 16.65 +/- 2.89 mm (P = 0.07) and in the standing position 16.95 +/- 3.44 mm (P = 0.11). The most impressive change in amplitude was noted during performance of the Valsalva maneuver. During this test the amplitude decreased to 13 +/- 2.81 mm and rose to 20 +/- 2.66 mm (P = 0.002) afterwards. These results strongly support the assumption that changes of RV impedance as measured by this catheter represent changes in RV SV. This new pacing system is the first pacemaker that reports on the hemodynamic response of every heartbeat by measuring RV impedance.