Prognostic utility of pulse pressure in patients with heart failure with preserved ejection fraction: The RICA Registry.

BACKGROUND AND AIMS: The prognostic role of pulse pressure (PP) in heart failure (HF) patients with preserved left ventricular ejection fraction (LVEF) is not well understood. Our aim was to evaluate it in acute and stable HF. MATERIAL AND METHODS: This work is a retrospective observational study of patients included in the RICA registry between 2008 and 2021. Blood pressure was collected on admission (decompensation) and 3 months later on an outpatient basis (stability). Patients were categorized according to whether the PP was greater or less than 50mmHg. All-cause mortality was assessed at 1year after admission. RESULTS: A total of 2291 patients were included, with mean age 80.1±7.7 years. 62.9% were women and 16.7% had a history of coronary heart disease. In the acute phase, there was no difference in mortality according to PP values, but in the stable phase PP<50mmHg was independently associated with all-cause mortality at 1-year follow-up (HR 1.57, 95% CI 1.21-2.05, p=0.001), after adjusting for age, sex, New York Heart Association functional class, previous HF, chronic kidney disease, valvular heart disease, cerebrovascular disease, score on the Barthel and Pfeiffer scales, hemoglobin and sodium levels. CONCLUSIONS: Low stable-phase PP was associated with increased all-cause mortality in HF patients with preserved LVEF. However, PP was not useful as a prognostic marker of mortality in acute HF. Further studies are needed to assess the relationship of this variable with mortality in HF patients.

Is cutting stress responsible for the limited durability of heart valve bioprostheses?

The limited durability of the valve bioprostheses made from calf pericardium is partially due to the calcification of this biomaterial and to mechanical fatigue of the tissue. The object of this study is to determine the harmful effect on the pericardial membrane of cutting caused by the suture thread by showing the different elastic behaviors of the biomaterials employed. This cutting stress is established during the process of molding the valve leaflet, creating a vulnerable point from the very moment of construction, which is an important factor in the limited duration of the bioprosthesis.

The relationship between stress and relaxation in calf pericardium used in the construction of cardiac bioprostheses.

Assessment of relaxation (loss of load within a given time) without apparent deformation is a necessary step before durability assay of biomaterials. From results obtained using calf pericardium, the following conclusions were drawn: (a) there is no limit to relaxation for this biomaterials; (b) the lesser the load applied, the greater the relaxation; and (c) the relaxation curve follows the logarithmic function y = K1 - K2 - Int. These findings demonstrate the poor behaviour of the biomaterial at supposedly low loads and suggest that rupture-point load is not a reliable reference to determine the safety coefficient of calf pericardium used in cardiac bioprostheses.

Effect of the suture on the durability of bovine pericardium used in cardiac bioprostheses.

Our study of the different biomaterials used in the construction of biological cardiac prostheses has shown it to be of vital importance that the physical properties of the tissue and of the suture that anchors it to the rigid polymeric support are compatible. By means of dynamic tests, we have determined the fatigue curve in sutured bovine pericardial tissue, expressed by the equation log y = 1.27 +/- 0.18 (0.26 +/- 0.05) log t, where y is the initial fatigue stress (MPa) and t is the time (min) it takes to achieve permanent deformation of the tissue. By applying this correction, we determine a set of values for stress-time which, when compared with those obtained with a non-sutured sample, reveal a significant fall in this ratio and, thus, a decrease in the durability. The use of suture threads of lesser elasticity than the pericardium may play an important role in reducing the durability of the bioprosthesis constructed with these materials.

Behaviour of the bovine pericardium used in cardiac bioprostheses when subjected to a real fatigue assay.

The behaviour of bovine pericardium was studied using a fatigue assay. Twenty-three samples were assayed, maintaining the preset initial stress and measuring the time it took for the onset of load loss due to permanent deformation. The results indicated a mathematical relationship defined by the expression: log y = 1.3 - 0.211 log t, where y is the fatigue stress (MPa) and t the duration of the assay. The correlation coefficient was 0.948 (P < 0.001). The safety coefficient of the material diminished significantly as the period of time during which it was subjected to fatigue increased. The theoretical durability of the tissue was much greater than the real durability of the prostheses, which is determined by unsolved problems such as calcification and those derived from suture-related cutting.

Description of the mathematical law that defines the relaxation of bovine pericardium subjected to stress.

A material subjected to traction stress increases in length; if we maintain the elongation constant, the stress varies over a period of time. This phenomenon has been referred to as relaxation. The purpose of this study was to define a mathematical law that relates the variation in stress to time when elongation remains constant in bovine pericardium. The mathematical function obtained after assaying 34 samples to the point of relaxation, subjected to initial stresses ranging from 0.17-10.07 MPa, responds to the following equation: y = -0.0252 + 0.953 alpha - (0.0165 + 0.015 alpha)lnt, where y is the stress withstood at an instant in time, t, after initial stress alpha. A normogram, validated by assays of up to 6,340 min duration (4.40 days), is presented for graphic calculation, permitting the computation of the loss of stress due to relaxation of this biomaterial, with initial stresses ranging from 1-10 MPa.

Comparison of elasticities of components of a cardiac bioprosthesis leaflet.

The mechanoelastic behavior of calf pericardium employed in cardiac bioprostheses was compared with that of three types of thread (Nylon, Prolene, and silk) used to suture this biological tissue. The elastic limit (EL) of each material was determined by means of tensile tests and the mathematical functions that govern the stress/strain curves within the EL have been described. The first derivative of these functions for each point to the curves allowed the immediate calculation of the elastic modulus (EM), which was considered the best parameter for comparing the elasticities of the materials being assessed. It was observed that the deformation of the pericardium produced by the working stress of a pericardial leaflet was approximately 1000 times greater than that produced in the surgical threads. When the elasticities were compared on the basis of the EM, that of pericardium was 749.06, 626.95, and 1253.17 times greater than that of the Nylon, Prolene, and silk suture threads, respectively. These results demonstrate that the interaction between these materials (pericardium and the threads) could be generating detrimental forces that can diminish the durability of the leaflets of the bioprostheses constructed of calf pericardium.