Pre-ejectional left ventricular wall motions studied on conscious dogs using Doppler myocardial imaging: relationships with indices of left ventricular function

Abstract

Duration of the pre-ejection period is a sensitive index of myocardial function. Our purpose was to document normal pre-ejectional left ventricular (LV) wall motions at rest and under dobutamine using Doppler myocardial imaging (DMI), and to correlate posterior wall velocities with indices of LV systolic function. M-mode recordings of both walls were imaged on eight conscious dogs chronically instrumented. Subendocardial pre-ejectional velocities were digitized and measured every 3.8 ms. DMI analysis consisted of sign recognition, velocity measurement, duration and timing from the Q wave of the electrocardiogram. Isovolumic contraction time (Ict) was represented by the time interval from onset to peak of the first derivative of LV pressure. Conventional Doppler labelling of velocity signs, positive toward and negative away from the transducer, was applied to the direction of encoded wall motions. For physiological understanding, wall motions of both walls were also labelled inward and outward with respect to the left ventricular cavity center. In each wall, PEP was shown as several colored strips, each strip representing the period of time that the wall was moving in one direction. Changes in velocity sign corresponding to changes in direction of motion were opposed in each wall (p < 0.001), featuring successive inward and outward wall motions. There was a markedly sustained inward motion during Ict. Its velocity amplitude increased with dobutamine. There was a positive correlation between velocities of the inward motion contemporaneous of Ict and ejection fraction (r = 0.72, p < 0.003). Values of Ict respectively drawn from DMI and from hemodynamics were also significantly correlated (r = 0.85, p < 0.007). Thus, the inward motion evidenced by DMI during Ict appears promising to assess myocardial function and effect of drugs.

Introduction

Noninvasive studies of the pre-ejection period (PEP) in the past have yielded useful information on myocardial function in case of heart failure and on the effect of drugs. PEP was better correlated with cardiac index and, in addition, was less influenced by heart rate than the ejection time Harris et al 1967, Leighton et al 1971, Spodick and Kumar 1968, Weissler et al 1968. Studies plateaued both on animals and on man, because they only provided information related to PEP duration Laniado et al 1973, Leighton et al 1971, Reale 1967. Indeed, these data are crucial for a physiological understanding because PEP is a composite interval, consisting of two parts timed by changes in the left ventricular (LV) pressure as demonstrated by experiments Laniado et al 1973, Metzger et al 1970, Willems et al 1971 (Fig. 1): The first component, also called the “electrical-mechanical delay” is in continuity with end-diastole and runs from the Q wave of the electrocardiogram to the crossover point of left atrial and ventricular pressures. It is followed by a second component, namely the isovolumic contraction, which occurs during the LV pressure rapid rise up to the diastolic aortic pressure crossover level. This definition does not take into account wall mechanical events. However, at angiography, a decrease in LV minor diameter with respect to end-diastolic LV boundaries indirectly drew attention to wall events during PEP (Karliner et al. 1971). This decrease in diameter was demonstrated on conscious dogs (Bishop et al. 1969). A wall thickening was shown in a study using ultrasonic crystals implanted on each side of one LV wall (Rankin et al. 1976). So far, no noninvasive study has quantified the amplitude and measured the duration of such brief motions simultaneously imaged within both cardiac walls Hishida et al 1976, Windle et al 1986. Computerized standard pulse echo (Gibson and Brown 1973) provides a refined quantitative analysis with higher temporal resolution than two-dimensional (2-D) imaging, but it needs an optimal M-mode recording, and endocardial displacement displays PEP wall boundary events as motions of insignificant amplitude (Fig. 12–18 in Feigenbaum 1976). We hypothesized that the new Doppler myocardial imaging (DMI) technique might single out brief motions within the cardiac walls on the basis of digitized color-coded images. The technique has been validated by several studies in healthy subjects and patients Garcia et al 1996, Isaaz et al 1989, McDicken et al 1992, Nakayama et al 1998, Palka et al 1995, Uematsu et al 1995. According to the Doppler effect, velocities encode wall motions away from or toward the probe. Changes in velocity signs turn out to be markers of inward and outward motions for walls bordering the LV cavity when the parasternal approach is used. The purpose of our study was to specify PEP LV wall motion characteristics, particularly the inward motion, in terms of velocity and duration at baseline and under drug administration in experiments, and to investigate relationships of wall motions with indices of LV function.