Real-time continuous evaluation of left ventricular mechanics by single-beat estimation of arterial and ventricular elastance

LV mechanics are determined by the coupling of LV contractility, or end-systolic elastance (Ees), and arterial afterload, or arterial elastance (Ea). Clinical application of LV mechanics is hindered by difficulties associated with on-line determination of ventricular dimensions and the need to produce a significant and rapid LV preload reduction to generate Ees. Automated border detection (ADD) by TEE provides LV dimensions in real-time, on-line and continuously. Preload reduction may be obviated by a single beat estimate of Ees. We have developed a computer interface and software to bring continuous, real-time evaluation of Ea and Ees to the clinical setting. LV areas from ABD and pressure signals from an LV catheter are acquired simultaneously and digitized. Data from single cardiac cycles are used to generate pressure-area (P-A) loops. End-systole and end-diastole are automatically identified on the P-A loop. Peak isovolumic LV pressure is derived from the maximum of a sinusoidal curve fitted to the pressure tracing of a single cardiac cycle. The slopes of the lines connecting end-systole to end-diastole and to peak isovolumic pressure are used to determine Ea and Ees, respectively. The computer program was able to evaluate Ea and Ees continuously, in real-time, by repeating the acquisition and analysis on a beat-by-beat basis. Performance of this program was tested off-line, in 16 pts, by comparing Ea and Ees obtained by the single-beat algorithm with those from conventional methods of preload reduction by IVC occlusion. Comparison between the two methods yielded a good correlation for Ees (r=0.72; p < 0.01) and Ea (r=0.86; p <0.001). This algorithm allows continuous evaluation of Ees and Ea in real time, with results comparable to those obtained by conventional methods.