Clinical assessment of left ventricular relaxation

Ventricular relaxation is altered in a number of cardiac disorders affectin g domestic animals. Clinical determination of the ventricular relaxation ra te can provide useful information regarding disease severity and response t o therapy. We believe that the current gold standard for assessing left ven tricular relaxation requires measurement of ventricular luminal pressure at end-expiration using a high-fidelity catheter. Ventricular pressure should be digitized at greater than or equal to 200 Hz for the period of pressure fall between the minimum rate of change of ventricular pressure and 10 mm Hg above left ventricular end-diastolic pressure of the preceding beat. The rate of relaxation then should be determined from the digitized data by Ma rquardt nonlinear least squares parameter estimation using an exponential d ecay model with nonzero asymptote. The major disadvantage in using an invas ive method for evaluating left ventricular relaxation is that it requires g eneral anesthesia in animals that frequently are categorized as high-risk a nesthetic patients. Noninvasive estimates of ventricular relaxation using e chocardiographic parameters such as isovolumic relaxation time, peak early filling rate, and time from end-systole to peak filling rate provide a crud e and nonspecific assessment of ventricular relaxation that can be obtained from conscious animals. Determinations of these echocardiographic indices are of limited usefulness in assessing changes in Ventricular relaxation as sociated with disease progression or therapeutic intervention, unless concu rrent estimates of left atrial pressure, mitral valve characteristics, and left ventricular compliance are available.