Validation of a novel noninvasive cardiac index of left ventricular contractility in patients

Abstract

Although there are several excellent indexes of myocardial contractility, they require accurate measurement of pressure via left ventricular (LV) catheterization. Here we validate a novel noninvasive contractility index that is dependent only on lumen and wall volume of the LV chamber in patients with normal and compromised LV ejection fraction (LVEF). By analysis of the myocardial chamber as a thick-walled sphere, LV contractility index can be expressed as maximum rate of change of pressure-normalized stress (d*/dt max, where * ϭ /P and and P are circumferential stress and pressure, respectively). To validate this parameter, d*/dt max was determined from contrast cine-ventriculography-assessed LV cavity and myocardial volumes and compared with LVEF, dP/dt max, maximum active elastance (Ea,max), and singlebeat end-systolic elastance [E es(SB)] in 30 patients undergoing clinically indicated LV catheterization. Patients with different tertiles of LVEF exhibit statistically significant differences in d*/dt max. There was a significant correlation between d*/dt max and dP/dtmax (d*/ dt max ϭ 0.0075dP/dt max Ϫ 4.70, r ϭ 0.88, P Ͻ 0.01), E a,max (d*/dtmax ϭ 1.20Ea,max ϩ 1.40, r ϭ 0.89, P Ͻ 0.01), and Ees(SB) [d*/dtmax ϭ 1.60Ees(SB) ϩ 1.20, r ϭ 0.88, P Ͻ 0.01]. In 30 additional individuals, we determined sensitivity of the parameter to changes in preload (intravenous saline infusion, n ϭ 10 subjects), afterload (sublingual glyceryl trinitrate, n ϭ 10 subjects), and increased contractility (intravenous dobutamine, n ϭ 10 patients). We confirmed that the index is not dependent on load but is sensitive to changes in contractility. In conclusion, d*/dt max is equivalent to dP/dt max, Ea,max, and Ees(SB) as an index of myocardial contractility and appears to be load independent. In contrast to other measures of contractility, d*/dt max can be assessed with noninvasive cardiac imaging and, thereby, should have more routine clinical applicability. cardiac mechanics; ventricular elastance; ventriculography; wall stress THE QUEST TO DELINEATE and quantify myocardial inotropic function in humans, independent of ventricular loading conditions, is an ongoing preoccupation of researchers and clinicians (15-17, 19, 29, 45-47). In the left ventricle (LV), the peak first time derivative of LV intracavity pressure (dP/dt max ), which is reached just before aortic valve opening, is arguably the most sensitive cardiac index of inotropicity and is the "gold standard" (15, 16). Accurate determination of dP/dt max requires measurement of intraventricular LV pressure by invasive cardiac catheterization. In some individuals with mitral regurgitation, dP/dt max may be approximated from time-resolved mitral regurgitation velocities, which are acquired noninvasively using continuous-wave Doppler echocardiography (1). In general, however, accurate noninvasive assessment of ventricular pressure is very difficult.An additional difficulty with LV dP/dt max is that it is not preload independent (23). Conceivably, the LV pressure-volume relation and e...

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“…Usefulness of dσ*/dt max as Contractility Index: During LV systole, LV wall stress is generated intrinsically by sarcomere contraction and results in the development of extrinsic LV pressure. We have shown earlier that our novel LV contractility index, dσ*/dt max (maximal change rate of pressure-normalized wall stress) correlates well with LV dP/dt max [3]. We have proposed and validated a new LV contractility index, dσ*/dt max ,based on the maximal rate of development of LV wall stress with respect to LV pressure.…”

“…The traditional dP/dt max is based on left ventricular intra-cavitary pressure which is generated by an active myocardial stress. Hence, analogous to dP/dt max , which is based on LV intra-cavitary pressure, we have formulated a novel LV contractility index based on LV wall stress, namely the maximum rate of change during systole of LV wall stress normalized to LV intra-cavitary pressure, d(σ/P)/dt max or dσ*/dt max , where σ* = σ /P [3].…”

“…This is somewhat in keeping with cardiac output or maximal volume change having been used as a measure of myocardial contractility in rats or human, provided that the influence of afterload is taken into account. Figure 6, and demonstrated the index's load independence, albeit under conditions of limited preload and after load manipulations [3]. For this study, thirty volunteers [mean 58.1 (range 48-77) yr of age, 13:2 male-to-female ratio] with diverse cardiac conditions were recruited.…”

“…The patients were divided into three groups on the basis of tertiles of LVEF, with 10 individuals in each group, as shown in figure]. This figure is based on our work in Ref [3].…”

“…This index is easily measured non-invasively (i.e. from echocardiography or magnetic resonance imaging), is sensitive to LV inotropic changes, and has been demonstrated by us to be preload and afterload independent [3]. Importantly, it is measured at a single steadystate condition, as opposed to the multiple variably loaded cardiac cycles required for many of the other indices.…”