Effect of congestive heart failure on in vivo canine aortic elastic properties

Carotid arterial stiffness is increased and related to left ventricular function in patients with hypertrophic cardiomyopathy

Aims

To assess the carotid mechanical properties in patients with hypertrophic cardiomyopathy and the relation between arterial stiffness and left ventricular function in this setting.

Methods and results

We have prospectively enrolled 71 patients (52 ± 16 years, 34 men) with hypertrophic cardiomyopathy, divided into two groups depending on the presence (46 patients) or absence (25 patients) of cardiovascular risk factors associated with increased arterial stiffness. Twenty-five normal subjects similar by age and gender with hypertrophic cardiomyopathy patients without risk factors formed the control group. A comprehensive echocardiography was performed in all subjects. Carotid arterial stiffness index (β index), pressure–strain elastic modulus, arterial compliance, and pulse wave velocity were also obtained using an echo-tracking system. β index, pulse wave velocity, and pressure–strain elastic modulus were significantly higher in hypertrophic cardiomyopathy patients without risk factors compared to controls. After linear regression analysis, the increase in carotid β index was independently correlated with the presence of hypertrophic cardiomyopathy [beta = 0.49, 95% confidence interval (CI) = 1.04–3.02; P < 0.001]. In the entire hypertrophic cardiomyopathy population arterial stiffness parameters correlated with age, gender, hypertension degree, presence of hypercholesterolaemia, and the E/e′ ratio. In multivariable analysis, β index (beta = 0.36, 95% CI = 0.32–1.25; P = 0.001), global left ventricular longitudinal strain, and the presence of left ventricular outflow tract obstruction were independently correlated with the E/e′ ratio.

Conclusion

In patients with hypertrophic cardiomyopathy arterial stiffness is increased independently of age or presence of cardiovascular risk factors. Carotid artery stiffness is independently related to left ventricular filling pressure, increased arterial stiffness representing a possible marker of a more severe phenotype.

The effect of aldosterone-antagonist therapy on aortic elastic properties in patients with nonischemic dilated cardiomyopathy

BACKGROUND

Many studies proved the prognostic importance of aortic stiffness as an independent predictor of cardiovascular morbidity and all-cause mortality. The decrease of arterial compliance has a high prevalence in patients with heart failure and affects both hemodynamics and prognosis. Aortic stiffness is partially caused by excessive activation of the renin-angiotensin-aldosterone system. Spironolactone, a mineralcorticoid receptor antagonist (MRA), has been shown to decrease aortic stiffness and fibrosis in experimental models. However, there are few studies that describe the effects of MRA on aortic stiffness in patients with nonischemic dilated cardiomyopathy.

AIMS

To evaluate the effect of spironolactone on aortic stiffness in patients with nonischemic dilated cardiomyopathy.

MATERIALS AND METHODS

We randomized (1 : 1) 102 patients with nonischemic dilated cardiomyopathy with New York Heart Association class I-II to receive spironolactone 25 mg/day (up to 100 mg/day) or placebo, in addition to recommended therapy. Aortic stiffness index, aortic strain, aortic distensibility and aortic dimensions were assessed at baseline and after 6 months. All measures were obtained with echocardiography M-mode at 3 cm above the aortic valve on parasternal long axis view and simultaneous brachial arterial pressure with sphygmomanometer.

RESULTS

Ascending aorta diameters, aortic stiffness index, aortic distensibility and aortic strain were similar at randomization in the two groups. After 6 months of therapy in the treated group, we found a reduction of aortic stiffness index (7.2 ± 3.5 versus 9.6 ± 4.8 mmHg; P = 0.03) and an increase of aortic distensibility (3.77 ± 1.0 versus 2.92 ± 0.55 mmHg; P = 0.01) and systolic aortic strain (10.0 ± 5.0 versus 8.0% ± 2.1%; P = 0.01). There were no difference in systolic arterial pressure, diastolic arterial pressure and differential pressure in the two groups.

CONCLUSION

Therapy with spironolactone is effective in reducing aortic stiffness in patients with nonischemic dilated cardiomyopathy. This effect could improve hemodynamics supporting the use of MRAs in patients with low New York Heart Association class (I-II).

Echocardiographic elastic properties of ascending aorta and their relationship with exercise capacity in patients with non-ischemic dilated cardiomyopathy

Background

: Aortic stiffness, an independent predictor of mortality and cardiovascular events, is common among patients affected by non-ischemic dilated cardiomyopathy (NIDC) and heart failure (HF).

Methods

: A total of 55 patients with diagnosis of NIDC (aged 60 ± 11 years, mean ejection fraction (EF) 35.2% ± 7.7%) admitted consecutively to our department for mild to moderate HF (NYHA class II–III) underwent an echocardiographic study and cardiopulmonary exercise test (CPX). We evaluated elastic properties of ascending aorta, i.e. aortic stiffness and aortic distensibility (mm Hg^{− 1}), derived from ascending aorta systolic and diastolic diameter (mm/m²) measured 3 cm above the valvular plane through 2D-guided M-mode echocardiography.

Results

: Mean aortic stiffness was 15.63 ± 14.53 and aortic distensibility was 2.61 ± 2.39 mm Hg^{− 1}. Collected parameters at CPX were peak oxygen consumption (pVO₂) (ml/kg/min), anaerobic threshold (AT) and the slope of the relation between minute ventilation (VE) and carbon dioxide production (VCO₂). Mean pVO₂ was 15.4 ± 3.9 ml/kg/min, VE/VCO₂ ratio at AT was 36.1 ± 6.1. Functional capacity measured through peak VO₂ was found to be directly correlated with aortic distensibility (r = 0.47, p = − 0.0002) and negatively correlated to aortic stiffness index (r = − 0.51, p = − 0.0001). These results were the same at multivariate analysis, corrected by age, hypertension, diabetes mellitus and ejection fraction (respectively r = 0.27, p = 0.008 and r = − 1.75, p = 0.0002).

Conclusions

: HF patients due to NIDC elastic properties of ascending aorta, evaluated by echocardiography, are correlated with a reduced functional capacity.

Carotid arterial stiffness and its relationship to exercise intolerance in older patients with heart failure and preserved ejection fraction

Heart failure with a preserved ejection fraction (HFpEF) is the dominant form of heart failure in the older population. The primary chronic symptom in HFpEF is severe exercise intolerance; however, its pathophysiology and therapy are not well understood. We tested the hypothesis that older patients with HFpEF have increased arterial stiffness beyond what occurs with normal aging and that this contributes to their severe exercise intolerance. Sixty-nine patients ≥60 years of age with HFpEF and 62 healthy volunteers (24 young healthy subjects ≤30 years and 38 older healthy subjects ≥60 years old) were examined. Carotid arterial stiffness was assessed using high-resolution ultrasound, and peak exercise oxygen consumption was measured using expired gas analysis. Peak exercise oxygen consumption was severely reduced in the HFpEF patients compared with older healthy subjects (14.1±2.9 versus 19.7±3.7 mL/kg per minute; P<0.001) and in both was reduced compared with young healthy subjects (32.0±7.2 mL/kg per minute; both P<0.001). In HFpEF compared with older healthy subjects, carotid arterial distensibility was reduced (0.97±0.45 versus 1.33±0.55×10(-3) mm Hg(-1); P=0.008) and Young's elastic modulus was increased (1320±884 versus 925±530 kPa; P<0.02). Carotid arterial distensibility was directly (0.28; P=0.02) and Young's elastic modulus was inversely (-0.32; P=0.01) related to peak exercise oxygen consumption. Carotid arterial distensibility is decreased in HFpEF beyond the changes attributed to normal aging and is related to peak exercise oxygen consumption. This supports the hypothesis that increased arterial stiffness contributes to exercise intolerance in HFpEF and is a potential therapeutic target.

The effect of dobutamine without and with L-arginine on arterial compliance in heart failure patients

The effect of dobutamine on carotid and brachial arteries compliance and the association of L-arginine as a potential nitric oxide pathway restorer were evaluated in patients with heart failure. Twenty-seven outpatients participated. Drugs used for the treatment of heart failure were withheld at least 24 hours before the study. The carotid and brachial artery diameters and hemodynamic variables were evaluated by ultrasonography and Doppler in baseline conditions, with dobutamine, with flow-mediated dilatation (FMD), and with placebo or L-arginine alone and associated with dobutamine. There was a significant increase in carotid peak blood flow with dobutamine when compared with that at baseline (P = 0.0001) or with L-arginine or placebo (P = 0.0001 and P = 0.0001, respectively), with increase of the cardiac index (P = 0.0001). Dobutamine did not increase carotid arterial compliance. FMD significantly increased the brachial peak blood flow (P = 0.0022) and the artery diameter (P = 0.0001). Dobutamine did not change the brachial artery diameter. Brachial peak blood flow was increased with dobutamine alone or associated with placebo or L-arginine comparing with L-arginine or placebo alone (P = 0.0168 and P = 0.0140, respectively), but was not increased compared with that at baseline. L-arginine infusion was not associated with changes in carotid, brachial, or in the cardiac index. We concluded that dobutamine increased carotid peak blood flow in patients with heart failure, although without changing the arterial compliance. The FMD of brachial artery was maintained, while brachial artery response to dobutamine infusion was less reliable. The carotid artery may be under the direct influence of the heart, while the brachial artery may be under predominant local control.

Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy

Changes in blood flow influence the structure, function, mechanical properties, and remodeling of arteries. The objective of the present study was to investigate the role of increased blood flow on the biaxial incremental elastic moduli of the porcine right coronary artery (RCA) and to determine the microstructural basis for the changes in moduli. We hypothesized that an increase in RCA flow will lead to increased stiffness in conjunction with remodeling of elastin and collagen in the vessel wall. The control and experimental groups consisted of five RCA vessels each. The RCA of the experimental group was exposed to 4 wk of flow-overload in right ventricular hypertrophy induced by pulmonary artery banding. Stress-strain relationships were determined and the incremental elastic moduli were derived in the circumferential, axial, and cross directions. The results show a significant increase in the elastic moduli in the circumferential (262.7 +/- 15.7 vs. 120.2 +/- 12.4 kPa; P < 0.001), axial (177.8 +/- 25.5 vs. 100.3 +/- 11.9 kPa; P = 0.025), and cross directions (104.8 +/- 8.2 vs. 68.2 +/- 8.6 kPa; P = 0.016) of the experimental RCA compared with controls. Multiphoton microscopy was used to assess the changes in elastin and collagen content in the media and adventitia of the vessel wall. We found a significant increase in elastin and collagen area fraction particularly in the adventitial layer. These data suggest stiffening of the vessel wall as a result of increased elastin and more predominantly collagen.

Altered left ventricular–arterial coupling precedes pump dysfunction in early heart failure

The objective of this study was to define alterations in ventricular-arterial (V-A) coupling early in the development of tachycardia-induced heart failure (HF). Although HF is characterized by impaired V-A coupling, the temporal relationship of these derangements to overt left ventricular (LV) dysfunction is unknown. Six anesthetized dogs instrumented with LV manometers and piezoelectric crystals were studied before and after 24 h of rapid ventricular pacing (RVP). V-A coupling was indexed by the ratio between the end-systolic pressure-volume relation slope (endsystolic elastance, E(ES)) and effective arterial elastance (E(A)), and mechanical efficiency by the ratio of stroke work (SW) to pressure-volume area (PVA). After RVP, there was no significant depression of LV function, but E(A) and total peripheral resistance (R(T)) were increased (P < 0.05), indicating increased arterial load. After RVP, E(ES)/E(A) and SW/PVA were maintained during unstressed conditions, but upon changes in load induced by phenylephrine, E(ES)/E(A) declined more precipitously with equivalent increases in R (T) (slope E(ES)/E(A)-R(T) relation -16.7 +/- 4.6 vs -5.8 +/- 4.0 ml/mmHg.min, P < 0.025). Furthermore, after RVP there was significant (P < 0.05) blunting of dobutamine-induced augmentation of E(ES), E(ES)/E(A), and SW/PVA. Thus, after RVP there was a distinct loss of V-A coupling reserve during afterload and catecholamine stress. V-A coupling defects occur early in the development of tachycardia-induced HF prior to significant pump dysfunction, and are manifested primarily during hemodynamic and inotropic stress.

Alterations in aortic elasticity in noncompaction cardiomyopathy

Background

Noncompaction cardiomyopathy (NCCM) is a recently recognized disorder frequently associated with systolic and diastolic heart failures. This study was designed to examine aortic stiffness in NCCM patients and to compare these results to age- and gender-matched controls.

Methods

A total of 20 patients with typical echocardiographic features of NCCM (age 38 ± 16 years, eight males) were investigated. Their results were compared to 20 age- and gender-matched controls. All subjects underwent a complete two-dimensional transthoracic echocardiographic examination. Systolic (SD) and diastolic (DD) ascending aortic diameters were recorded in M-mode at a level of 3 cm above the aortic valve from a parasternal long-axis view. Aortic stiffness index (β) was calculated as a characteristic of aortic elasticity, as ln(SBP/DBP)/[(SD - DD)/DD], where SBP and DBP are the systolic and diastolic blood pressures, respectively, and ln is the natural logarithm.

Results

The number of noncompacted segments in the NCCM patients was 4.6 ± 2.0. NCCM patients had significantly increased left ventricular dimensions and reduced left ventricular ejection fraction. Compared to controls, aortic stiffness index (β) was significantly increased in NCCM patients (8.3 ± 5.2 vs. 3.5 ± 1.1, p < 0.001).

Conclusion

Increased aortic stiffness can be observed in patients with NCCM with moderate to severe heart failure. These alterations may be due to neurohormonal changes in heart failure.

Biomechanics of the cardiovascular system: the aorta as an illustratory example

Biomechanics relates the function of a physiological system to its structure. The objective of biomechanics is to deduce the function of a system from its geometry, material properties and boundary conditions based on the balance laws of mechanics (e.g. conservation of mass, momentum and energy). In the present review, we shall outline the general approach of biomechanics. As this is an enormously broad field, we shall consider a detailed biomechanical analysis of the aorta as an illustration. Specifically, we will consider the geometry and material properties of the aorta in conjunction with appropriate boundary conditions to formulate and solve several well-posed boundary value problems. Among other issues, we shall consider the effect of longitudinal pre-stretch and surrounding tissue on the mechanical status of the vessel wall. The solutions of the boundary value problems predict the presence of mechanical homeostasis in the vessel wall. The implications of mechanical homeostasis on growth, remodelling and postnatal development of the aorta are considered.

Ventricular structure and function in aged dogs with renal hypertension: a model of experimental diastolic heart failure

BACKGROUND

Heart failure (HF) with normal ejection fraction (diastolic HF [DHF]) usually occurs in elderly patients with hypertension. The presence and significance of altered systolic and diastolic ventricular function in DHF is increasingly controversial. Our objective was to develop a clinically relevant large-animal model to better understand the pathophysiology of DHF.

METHODS AND RESULTS

Ventricular structure and function were characterized in young control (YC group; n=6), old control (OC group; n=7), and old dogs made hypertensive by renal wrapping (experimental DHF [ExDHF] group; n=8). The ExDHF group was associated with normal left ventricular (LV) volume, increased LV mass, and myocardial fibrosis. LV relaxation was impaired in ExDHF (tau=53+/-6 ms) compared with OC (tau=35+/-3 ms; P<0.05) and YC (tau=33+/-6 ms; P<0.05) dogs. The percent diastole at which relaxation is complete was increased in ExDHF (116+/-30%) compared with OC (69+/-8%; P<0.05) and YC (35+/-5%; P<0.05) dogs. The coefficient of LV diastolic stiffness was similar in OC, YC, and ExDHF dogs. Diastolic pressures increased dramatically in response to increases in blood pressure. End-systolic LV stiffness was enhanced in ExDHF dogs and after load enhancement of myocardial performance was maintained. Arterial stiffness was increased in ExDHF dogs.

CONCLUSIONS

Aged dogs with chronic hypertension exhibit LV hypertrophy and fibrosis with impaired LV relaxation but no increase in the coefficient of LV diastolic stiffness. LV systolic and arterial stiffness are increased, which may exacerbate load-dependent impairment of relaxation and contribute to increased filling pressures with hypertensive episodes. This model mimics many of the structural and functional characteristics described in the limited studies of human DHF and provides insight into the pathogenesis of DHF.

Variation of mechanical properties along the length of the aorta in C57bl/6 mice

The objective of the present study is to obtain a systematic set of data on the mechanical properties along the entire length of the mouse aorta. The ascending aorta of seven mice was cannulated near the aortic valve, and the aorta was preconditioned with several cyclic changes in pressure. The perfusion pressure was then increased in 30-mmHg increments from 0 to 150 mmHg. Cab-O-Sil, colloidal silica, was mixed into the perfusate to prevent flow through the microvessels and hence attain zero-flow distensions. Our results show that the residual circumferential strain leads to a uniformity of transmural strain of the aorta in the loaded state along the entire length of the aorta. This uniformity is attained in the range of 60–120 mmHg. At pressures <60 mmHg, the outer strain is greater than the inner strain, whereas at pressures >120 mmHg, the converse is true. Furthermore, we found that the circumferential and longitudinal stress-strain relationships are linear in the pressure range of 30–120 mmHg. Finally, the circumferential modulus is greatest (most rigid) near the diaphragm, and the majority of volume compliance (85%) is in the thoracic compared with the abdominal aorta. These findings are important for an understanding of the hemodynamics of the cardiovascular system of the normal mouse and will serve as a reference state for the study of various diseases in knock-in and knock-out models of this species.

Aortic distensibility independently affects exercise tolerance in patients with dilated cardiomyopathy

BACKGROUND

Peak exercise oxygen consumption (VO2) is crucial for the prognostic stratification of patients with congestive heart failure, but its hemodynamic determinants are still not completely understood. Aortic wall elasticity modulates left ventricular function and coronary blood flow. Whether an increased aortic pulse-wave velocity (PWV), a known marker of arterial stiffness, may predict peak VO2 in patients with dilated cardiomyopathy (DCM) has to be clarified.

METHODS AND RESULTS

A total of 78 patients with clinical diagnosis of DCM (aged 62+/-11 years; female 29%; mean ejection fraction 34+/-9%) were selected. All patients underwent a complete echocardiographic-Doppler evaluation. Aortic PWV was measured by Doppler ultrasonography immediately before the exercise. A bicycle exercise test with expiratory gas exchange monitoring was performed to determine VO2 . Plasma concentration of the amino-terminal propeptide of type III procollagen (PIIINP), a marker of extracellular matrix turnover, was determined. Mean PWV was 5.7+/-2.2 m/s, and VO2 was 16.5+/-4.5 mL x kg(-1) x min(-1). The hemodynamic variables correlated with VO2 were PWV (r=-0.39, P=0.0007) and stroke volume (r=0.38, P=0.002). In a multivariate analysis, PWV (P=0.04) and stroke volume (P=0.05) were independently correlated with VO2 , accounting for 34% of its variance. PIIINP levels correlated with PWV (r=0.35, P=0.002) and a more restrictive diastolic filling pattern (r=0.40, P=0.02).

CONCLUSIONS

Increased aortic stiffness measured by PWV is an independent predictor of peak VO2 and could partially explain exercise intolerance in patients with DCM.

Relation of aortic distensibility determined by magnetic resonance imaging in patients > or =60 years of age to systolic heart failure and exercise capacity

Aortic stiffness increases with advancing age and is associated with the age-related decline in exercise capacity in healthy persons. Previous studies have suggested that aortic compliance is reduced in heart failure (HF). Older persons with systolic HF can have particularly severe exercise intolerance. However, the relation between increased aortic stiffness and exercise intolerance in elderly patients with systolic HF has not been examined. Therefore, aortic distensibility of the proximal ascending aorta (assessed by magnetic resonance imaging) and exercise tolerance (assessed by maximal exercise ergometry with expired gas analysis) was measured in 28 subjects (10 healthy subjects aged 20 to 30 years, 10 healthy subjects aged > or =60 years, and 8 subjects aged > or =60 years with systolic HF). Compared with healthy older subjects, patients with systolic HF had markedly decreased distensibility of the proximal aorta (0.5 +/- 0.4 vs 2.2 +/- 1.2 10(-3) mm Hg(-1), p <0.002), decreased peak exercise volume of oxygen consumption (VO2) (858 +/- 248 vs 1,436 +/- 344 ml/min, p <0.001), and increased aortic wall thickness (3.6 +/- 0.7 vs 2.9 +/- 0.4 mm, p <0.04). Aortic distensibility was significantly correlated with peak VO2 (r = 0.80, p <0.0001) and remained so even after being adjusted for age and left ventricular (LV) ejection fraction. These data suggest that decreased aortic distensibility may contribute to exercise intolerance in older patients with HF due to LV systolic dysfunction.

Aortic leucine-to-glutamate pathway: metabolic route and regulation of contractile responses

Rat aortic endothelium is differentiated regionally for three signal pathways capable of regulating the cGMP content of the underlying smooth muscle. Formation of nitric oxide (NO) from L-arginine and of glutamate from L-leucine increase cGMP; however, formation of prostaglandin H2 (PGH2) decreases cGMP. All three have peak activity in the windkessel area just distal to the aortic arch and decrease peripherally. We report evidence that the biochemical route of the leucine-to-glutamate (Leu-->Glu) pathway is via metabolism of leucine to acetyl CoA, that the controlling reaction of the pathway is mediated by the branched chain alpha-ketoacid dehydrogenase complex (BCDC), and that glutamate formation via the Leu-->Glu pathway is a major source of aortic segment free glutamate in vitro. Interruption of the pathway by treatment of precontracted rat aortic rings in vitro with each of three classes of inhibitors (leucine analogs, competitors for the BCDC reaction, or inhibitors of L-glutamate transport) enhances contractile responses. The enhancement requires an intact endothelium and is not owing to reductions in NO formation. The results support the hypothesis that the Leu-->Glu pathway functions in the regulation of aortic contractility and compliance.

Leukocyte attack in a 3D human coronary in-vitro model

OBJECTIVE

The importance of peripheral blood leukocytes for the development of early atherosclerosis and restenosis has confronted cardiologists with classical hematologic issues. Three-dimensional human coronary in-vitro units of leukocyte attack (3DLA-units) open the field for exact studies of leukocyte attack and its subsequent effects on human medial coronary smooth muscle cells (HCMSMC).

METHODS

Central part of 3DLA-units are polycarbonate membranes with a pore size of 5 microm that correspond to the internal elastic membrane. Human coronary endothelial cells (HCAEC) were cultured on one side of the membranes, HCMSMC on the other side. Before leukocyte attack expression of adhesion molecules was up-regulated by tumour necrosis factor-alpha (TNF-alpha). Leukocyte attack was mimicked by selective adding of human monocytes (MC), respectively human CD4+-lymphocytes (CD4+-LC) to the HCAEC side of the 3DLA-units. Three-dimensional leukocyte attack units were fixed and stained after a period of 30 min, 1, 2, 3, 4, 6, and 24 h. Cell divisions of HCMSMC were analysed by measuring the uptake of bromodeoxyuridine (BrdU).

RESULTS

Monocytes were able to adhere to the endothelial surface, pass through the filter-pores, and penetrate the HCMSMC side of the 3DLA-units. Human CD4+-lymphocytes (CD4+-LC) only attached to the HCAEC side, and no chemotaxis to the HCMSMC side was detected. Proliferation of HCMSMC was increased 2.9-fold (P< 0.001) after selective MC-attack and 3.5-fold after selective MC-attack and TNF-alpha stimulus. No significant increase was found after selective CD4+-LC attack, a significant increase (2.1-fold; P < 0.001) was seen after selective CD4+-LC attack and TNF-alpha, stimulus.

CONCLUSIONS

Within the given limitations of the model the study emphasizes a predominance of MC in comparison to CD4+-LC in the process of adhesion, chemotaxis, and triggered reactive proliferation of co-cultured HCMSMC within the first 24 h after leukocyte attack. 3DLA-units offer an elegant method to study directly the effects of intravascular and intramural treatment strategies.