Differences In Left Ventricular Contractility Research Articles

Echocardiography-based pressure-volume loop assessment in the evaluation for the effects of indoxyl sulfate on cardiovascular function.

Indoxyl sulfate (IS), a uremic toxin, has been reported to have hypertrophic effects on the heart. Previous studies, however, have shown no association between elevated IS levels and cardiovascular outcomes in hemodialysis patients. We hypothesized that, despite left ventricular (LV) hypertrophy, myocardial contractility and ventricular-arterial coupling would remain preserved, and that this would explain the reason for the absence of prognostic impact of IS. We evaluated the association of IS with LV structure, contractility, vascular function, and mechanical efficiency (ventricular-arterial coupling and stroke work/pressure volume area) in 154 patients on hemodialysis, using echocardiography-based pressure-volume loop assessment. As expected, subjects in the high IS group (IS ≥ 33.8μg/mL) had greater LV mass index and end-diastolic volume index compared to subjects in the low IS group (IS < 33.8μg/mL). These differences remained significant after adjusting for age, sex, body mass index, diabetic nephropathy, duration of hemodialysis, and NT-proBNP levels, suggesting a potential role of elevated IS levels in LV remodeling. However, no differences in LV contractility (preload recruitable stroke work, peak power index, and systolic mitral annular velocity) and mechanical efficiency (ventricular-arterial coupling and stroke work/pressure volume area) were observed between the groups. Deleterious effects of IS on LV remodeling are not accompanied by impaired LV contractility or mechanical efficiency, which could contribute to the absence of cardiovascular prognostic impact observed in previous studies performed on hemodialysis patients.

Computational Investigation of Transmural Differences in Left Ventricular Contractility.

Myocardial contractility of the left ventricle (LV) plays an essential role in maintaining normal pump function. A recent ex vivo experimental study showed that cardiomyocyte force generation varies across the three myocardial layers of the LV wall. However, the in vivo distribution of myocardial contractile force is still unclear. The current study was designed to investigate the in vivo transmural distribution of myocardial contractility using a noninvasive computational approach. For this purpose, four cases with different transmural distributions of maximum isometric tension (Tmax) and/or reference sarcomere length (lR) were tested with animal-specific finite element (FE) models, in combination with magnetic resonance imaging (MRI), pressure catheterization, and numerical optimization. Results of the current study showed that the best fit with in vivo MRI-derived deformation was obtained when Tmax assumed different values in the subendocardium, midmyocardium, and subepicardium with transmurally varying lR. These results are consistent with recent ex vivo experimental studies, which showed that the midmyocardium produces more contractile force than the other transmural layers. The systolic strain calculated from the best-fit FE model was in good agreement with MRI data. Therefore, the proposed noninvasive approach has the capability to predict the transmural distribution of myocardial contractility. Moreover, FE models with a nonuniform distribution of myocardial contractility could provide a better representation of LV function and be used to investigate the effects of transmural changes due to heart disease.

Noninvasive quantification of left ventricular elastance and ventricular-arterial coupling using three-dimensional echocardiography and arterial tonometry

Most techniques previously used to assess left ventricular (LV) end-systolic elastance (E(es)) and ventricular-arterial coupling (C(LV-A)) relied on invasive measurements and data acquisition over a wide range of loading conditions. Our goals were to 1) assess the feasibility of noninvasive assessment of E(es) and C(LV-A) using real-time three-dimensional echocardiography (RT3DE) and arterial tonometry; 2) test the ability of this approach to detect changes in LV contractility; and 3) study its reproducibility. We studied pharmacologically induced changes in inotropic state (5 and 10 μg·kg(-1)·min(-1) dobutamine) in normal volunteers (N = 8) and compared 10 normal volunteers with 10 patients with dilated cardiomyopathy (DCM; ejection fraction < 35%). RT3DE LV images, calibrated carotid artery tonometry, and Doppler tracings were obtained to noninvasively estimate E(es) and C(LV-A), using two alternative calculations. Dobutamine caused a significant stepwise increase in blood pressure, heart rate, ejection fraction, and E(es) and a decreased C(LV-A). In patients with DCM, E(es) was significantly reduced and C(LV-A) elevated, compared with controls. Both inter- and intraobserver variability were good for all measured parameters, as reflected by intraclass correlation coefficients (>0.8) and coefficients of variation (<20%). While both E(es) estimates showed significant differences between DCM patients and controls, one estimate resulted in no overlap and better reproducibility (interobserver intraclass correlation coefficient: 0.83 vs. 0.47, coefficients of variation: 20 vs. 29%). This is the first study to test the feasibility of using RT3DE-derived LV volumes in conjunction with arterial tonometry to noninvasively quantify LV elastance and C(LV-A). This approach was found to be sensitive enough to detect expected differences in LV contractility and reproducible. Due to its noninvasive nature, this methodology may have clinical implications in various disease states.

Subclinical Systolic Dysfunction in Pediatric Patients with Chronic Kidney Disease

Midwall shortening (mwSF) is thought to be a more accurate measure of myocardial performance in the presence of left ventricular hypertrophy (LVH). We examined mwSF in pediatric patients with varying degrees of chronic kidney disease (CKD). Fifty-seven children with CKD stages 2 to 4, 25 who were undergoing hemodialysis and 49 who were transplant recipients, were compared with 35 healthy control subjects. Left ventricular (LV) geometry and indices of LV function were assessed echocardiographically. There were no significant differences in LV contractility or endocardial shortening fraction between patients and control subjects. Yet, patients undergoing hemodialysis had significantly lower mwSF compared with control subjects (P < .01) and patients with stage 2 to 4 CKD (P < .01). Renal transplant patients had lower mwSF compared with control subjects (P < .01). The prevalence of abnormal mwSF (ie, <16) was significantly higher in patients undergoing hemodialysis (40%) compared with patients who were renal transplant recipeints (12%) and patients with CKD stages 2 to 4 (9%; P = .03). With stepwise regression, mwSF was demonstrated to be predicted by using relative wall thickness (P < .0001), dialysis group (P = .005), and endocardial shortening fraction (P = .001; model R(2) = 0.86). Children undergoing maintenance hemodialysis and children with concentric LVH have subclinical systolic dysfunction, which might be an indicator for the development of more severe cardiac disease.

Physiologie hypertrophy: Effects on left ventricular systolic mechanics in athletes

Physiologic hypertrophy resulting from intense athletic participation has been reported to result in normal, reduced and augmented overall left ventricular performance. Rather than representing true differences in left ventricular contractility, these data may reflect the variable degree of ventricular dilation and increased wall thickness that occur with different types of exercise. As such, the resultant altered loading conditions may diminish the ability of the usual indexes of left ventricular function to accurately assess the left ventricular contractile state. Therefore, three groups of elite athletes with distinct patterns of myocardial hypertrophy were investigated utilizing recently developed load-independent contractility indexes. Age-matched control subjects (n = 33) were compared with 11 swimmers, 11 long-distance runners and 11 power lifters. Rest echocardiogram, phonocardiogram and calibrated carotid pulse tracing were used to calculate left ventricular dimensions, wall thickness, mass, fractional shortening, velocity of shortening and mean, peak and end-systolic wall stresses and the stress-time and minute stress-time integrals. Compared with control subjects, all athletes had increased left ventricular mass, even when values were normalized for body surface area. Runners had a dilated left ventricular and normal wall thickness, swimmers had a mildly dilated ventricle with increased wall thickness and power lifters had normal cavity size with markedly increased wall thickness. Peak systolic wall stress was normal in runners and swimmers and reduced in power lifters, whereas end-systolic stress was low in swimmers and power lifters and normal in runners. The minute stress-time integral, a measure of myocardial oxygen consumption, was normal in runners and swimmers but was significantly reduced in lifters.(ABSTRACT TRUNCATED AT 250 WORDS)