Abstract 14743: Analysis of Load, Rate, and Contractility Dependency of the Myocardial Performance Index Using a Mathematical Model: How to Use the Myocardial Performance Index in Clinical Practice?
Introduction: The myocardial performance index (MPI), defined as isovolumic contraction time plus isovolumic relaxation time divided by ejection time, is widely used as a useful indicator of cardiac function along with ejection fraction (EF) or fractional shorting (FS). While EF or FS reflects ventricular-arterial coupling (Ea/Ees), the implication of changes in MPI has not been well understood.
Methods: We developed a lumped parameter model for systemic circulation based on the 3-element windkessel model coupled with the time-varying elastance model of the ventricles. The response characteristics were compared between MPI and FS by changing hemodynamic parameters within the physiological range.
Results: At baseline, MPI was 0.48 and FS 0.38. Changes in circulating blood volume, proximal aortic stiffness, and left ventricular stiffness minimally affected MPI and FS (<10%). Changes in left ventricular end-systolic elastance (–4 to +8 mmHg/mL) resulted in alterations of MPI and FS to a similar extent (–20 to +26% vs. –26 to +19%). Changes in systemic vascular resistance (–8 to +15 Wood Unit х m2) led to a greater shift in MPI than in FS (–38 to +52% vs. –18 to +15%). Moreover, changes in aortic compliance, left ventricular relaxation time constant, and heart rate were reflected more strongly by MPI than by FS. Under a variety of hemodynamic statuses, MPI significantly related to Ea/Ees (r = 0.66, p < 0.0001), but the coefficient of regression differed considerably depending on the hemodynamic parameters that were changed (Figure).
Conclusions: MPI globally represents ventricular-arterial coupling, but it is more affected by a wider variety of hemodynamic parameters than EF. As each hemodynamic component affects MPI in different ways and to different degrees, a major component of hemodynamic change needs to be identified in interpreting MPI. To use MPI effectively in clinical practice, understanding of the different pathophysiology present in each disease is essential.
- © 2013 by American Heart Association, Inc.