Feasibility of Measuring Relative Right Ventricular Volumes and Ejection Fraction with Implantable Rhythm Control Devices

Abstract

Ejection fraction (EF), the ratio between stroke volume (SV) and end-diastolic volume (EDV), is a valuable contractility indicator. Unlike SV, the Frank-Starling effect is automatically compensated in the calculation of EF. It was the aim of this study to evaluate the physiological behavior of impedance derived measurements of relative right ventricular (RV) volumes and EF, obtained with standard pacing leads. Seven patients were evaluated at the time of pacemaker implant or replacement. Since no absolute standard of comparison was available for RV volumes, the value of the measurements was assessed by observing their behavior under cardio-circulatory challenges. A 2.5-kHz carrier was fed to the ring and tip electrodes of standard bipolar pacing leads and the resulting voltage was digitized and stored. The peak-to-peak voltage (PPV) of the carrier at the time of QRS was used as EDV, and the largest PPV as end-systolic volume (ESV). Relative SV was the difference between EDV and ESV, and EF = SV/EDV x 100. Pacing was used to reduce EDV, and the effect of contractility was tested with isometric hand grip, recumbent leg exercise, or isoproterenol drip. Only minimal changes in EF were noted during incremental pacing; relative SV and EDV decreased as expected; and EF increased significantly during contractility challenges. A high correlation coefficient was observed between EDV and SV changes induced by incremental pacing at rest (r values from 0.62 to 0.98, P from < 0.01 to 0.001). The study revealed that impedance volumetry, utilizing conventional bipolar pacing leads, yields useful hemodynamic data related to EDV, ESV, and EF. Given the simplicity of the method, it is reasonable to conclude on the feasibility of using said impedance derived hemodynamic parameters in implantable rhythm control devices.

Analysis of the O-wave in acute right ventricular apex impedance measurements with a standard pacing lead in animals

“…These calibration steps are necessary to obtain absolute values of ventricular volume. As this calibration is not possible in an implantable device, only relative measurements of volume are possible in a pacemaker system, and, although studies using stroke volume for closed-loop control of stimulation have been performed (SALO et at., 1984;CHIRIFE, 1991;CHIRIFE et at., 1993), no such pacemaker systems are commercially available at the present time. Absolute values of volume can be very difficult to measure, if possible at all, although some non-invasive instruments are available on the market.…”

Intracardiac Impedance as Hemodynamic Sensor: Feasibility Study

“…Several attempts have bccn rcported to achieve this goal using right ventricular impcdancc mcasurcinents [1][2][3][4][5]. One problem with these mcthods is thc complexity of the right ventricular geomctry, which Icads to an overemphasis on the local conditions in the close vicinity of the electrodes.…”

Algorithm for ventricular capture verification based on the mechanical evoked response

“…Intracaacdiac impedance measurement was initially developed as a volume measurement technique (RUSHMER, 1953;GEDDES et al, 1966;KUBIECK, 1966) and later as a haemodynamic sensor 1986;McKAY et al, 1984). Multiple studies have demonstrated the relationship between stroke volume and changes in impedance during systole and diastole of the ventricles (RUSHMER, 1953;GEDDES et al, 1966;KUBIECK, 1966;SALO et al, 1984;1986;MCKAY et al, 1984;CHIRIFE et al, 1993).…”