Non-contact direct measurement of the magnetocaloric effect in thin samples

An experimental setup, based on a non-contact temperature sensor, is proposed to directly measure the magnetocaloric effect of samples few micrometers thick. The measurement of the adiabatic temperature change of foils and ribbons is fundamental to design innovative devices based on magnetocaloric thin materials or micro-structuring bulk samples. The reliability of the proposed setup is demonstrated by comparing the measurements performed on a bulk gadolinium sample with the results obtained by an experimental setup based on a Cernox bare chip thermoresistance and by in-field differential scanning calorimetry. We show that this technique can measure the adiabatic temperature variation on gadolinium sheets as thin as 27 µm. Heat transfer simulations are added to describe the capability of the presented technique

Co and In Doped Ni-Mn-Ga Magnetic Shape Memory Alloys: A Thorough Structural, Magnetic and Magnetocaloric Study

In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic to ferromagnetic, on heating) can be obtained, together with a change in the giant magnetocaloric effect from direct to inverse. Here we present a thorough study of the intrinsic magnetic and structural properties, including their dependence on hydrostatic pressure, that are at the basis of the multifunctional behavior of Co and In-doped alloys. We study in depth their magnetocaloric properties, taking advantage of complementary calorimetric and magnetic techniques, and show that if a proper measurement protocol is adopted they all merge to the same values, even in case of first order transitions. A simplified model for the estimation of the adiabatic temperature change that relies only on indirect measurements is proposed, allowing for the quick and reliable evaluation of the magnetocaloric potentiality of new materials starting from readily available magnetic measurements

From direct to inverse Giant Magnetocaloric Effect in Co-doped NiMnGa multifunctional alloys

We report the magnetic and magnetocaloric properties in Co-doped Ni–Mn–Ga Heusler alloys around the Mn-rich composition Ni50Mn30Ga20. The presence of Co affects profoundly the critical temperatures and alters the exchange interactions of martensite and austenite to different extents; by varying the composition it is possible to tune the critical temperatures and to induce a paramagnetic gap between the magnetically ordered martensite and magnetic austenite, thus giving rise to a reverse magnetostructural transformation. Contrary to the Co-free alloys, the saturation magnetization moment of austenite is strongly enhanced by Co with respect to the martensitic one: thus the magnetocaloric effect turns from direct into inverse. Remarkable values of the magnetic properties related to the magnetocaloric effect, e.g. the saturation magnetization jump at the transformation (DM) and the field dependence of the transformation temperature (dT/dH) are reported, together with high positive values of the isothermal magnetic entropy change (DS). The conditions for enhancing the magnetocaloric properties and triggering the sign reversal of the magnetocaloric effect are discussed

Conventional heart failure therapy in cardiac ATTR amyloidosis

BACKGROUND AND AIMS: The aims of this study were to assess prescription patterns, dosages, discontinuation rates and association with prognosis of conventional heart failure (HF) medications in patients with transthyretin cardiac amyloidosis (ATTR-CA). METHODS: A retrospective analysis of all consecutive patients diagnosed with ATTR-CA at the National Amyloidosis Centre between 2000-2022 identified 2371 patients with ATTR-CA. RESULTS: Prescription of HF medications was greater among patients with a more severe cardiac phenotype, comprising beta-blockers in 55.4%, angiotensin-converting enzyme inhibitors (ACEi)/angiotensin-II receptor blockers (ARB) in 57.4%, and mineralocorticoid receptor antagonists (MRAs) in 39.0% of cases. During a median follow-up of 27.8 months (IQR 10.6-51.3), 21.7% had beta-blockers discontinued, and 32.9% had ACEi/ARB discontinued. In contrast, only 7.5% had MRAs discontinued. Propensity score-matched analysis demonstrated that treatment with MRAs was independently associated with a reduced risk of mortality in the overall population (HR 0.77 [95% CI 0.66-0.89], P40% (HR 0.75 [95% CI 0.63-0.90], P=0.002); and treatment with low-dose beta-blockers was independently associated with a reduced risk of mortality in a pre-specified subgroup of patients with a LVEF ≤40% (HR 0.61 [95% CI 0.45-0.83], P=0.002). No convincing differences were found for treatment with ACEi/ARBs. CONCLUSIONS: Conventional HF medications are currently not widely prescribed in ATTR-CA, and those that received medication had more severe cardiac disease. Beta-blockers and ACEi/ARBs were often discontinued, but low-dose beta-blockers were associated with reduced risk of mortality in patients with a LVEF ≤40%. In contrast, MRAs were rarely discontinued and were associated with reduced risk of mortality in the overall population; but these findings require confirmation in prospective randomized controlled trials

Evaluation of the 2021 ESC recommendations for family screening in hereditary transthyretin cardiac amyloidosis

AIMS: The 2021 European Society of Cardiology (ESC) screening recommendations for individuals carrying a pathogenic transthyretin amyloidosis variant (ATTRv) are based on expert opinion. We aimed to (i) determine the penetrance of ATTRv cardiomyopathy (ATTRv-CM) at baseline; (ii) examine the value of serial evaluation; and (iii) establish the yield of first-line diagnostic tests (i.e. electrocardiogram, echocardiogram, and laboratory tests) as per 2021 ESC position statement.METHODS AND RESULTS: We included 159 relatives (median age 55.6 [43.2-65.9] years, 52% male) at risk for ATTRv-CM from 10 centres. The primary endpoint, ATTRv-CM diagnosis, was defined as the presence of (i) cardiac tracer uptake in bone scintigraphy; or (ii) transthyretin-positive cardiac biopsy. The secondary endpoint was a composite of heart failure (New York Heart Association class ≥II) and pacemaker-requiring conduction disorders. At baseline, 40/159 (25%) relatives were diagnosed with ATTRv-CM. Of those, 20 (50%) met the secondary endpoint. Indication to screen (≤10 years prior to predicted disease onset and absence of extracardiac amyloidosis) had an excellent negative predictive value (97%). Other pre-screening predictors for ATTRv-CM were infrequently identified variants and male sex. Importantly, 13% of relatives with ATTRv-CM did not show any signs of cardiac involvement on first-line diagnostic tests. The yield of serial evaluation (n = 41 relatives; follow-up 3.1 [2.2-5.2] years) at 3-year interval was 9.4%.CONCLUSIONS: Screening according to the 2021 ESC position statement performs well in daily clinical practice. Clinicians should adhere to repeating bone scintigraphy after 3 years, as progressing to ATTRv-CM without signs of ATTRv-CM on first-line diagnostic tests or symptoms is common.</p

Evaluation of the 2021 ESC recommendations for family screening in hereditary transthyretin cardiac amyloidosis

AIMS: The 2021 European Society of Cardiology (ESC) screening recommendations for individuals carrying a pathogenic transthyretin amyloidosis variant (ATTRv) are based on expert opinion. We aimed to (i) determine the penetrance of ATTRv cardiomyopathy (ATTRv-CM) at baseline; (ii) examine the value of serial evaluation; and (iii) establish the yield of first-line diagnostic tests (i.e. electrocardiogram, echocardiogram, and laboratory tests) as per 2021 ESC position statement.METHODS AND RESULTS: We included 159 relatives (median age 55.6 [43.2-65.9] years, 52% male) at risk for ATTRv-CM from 10 centres. The primary endpoint, ATTRv-CM diagnosis, was defined as the presence of (i) cardiac tracer uptake in bone scintigraphy; or (ii) transthyretin-positive cardiac biopsy. The secondary endpoint was a composite of heart failure (New York Heart Association class ≥II) and pacemaker-requiring conduction disorders. At baseline, 40/159 (25%) relatives were diagnosed with ATTRv-CM. Of those, 20 (50%) met the secondary endpoint. Indication to screen (≤10 years prior to predicted disease onset and absence of extracardiac amyloidosis) had an excellent negative predictive value (97%). Other pre-screening predictors for ATTRv-CM were infrequently identified variants and male sex. Importantly, 13% of relatives with ATTRv-CM did not show any signs of cardiac involvement on first-line diagnostic tests. The yield of serial evaluation (n = 41 relatives; follow-up 3.1 [2.2-5.2] years) at 3-year interval was 9.4%.CONCLUSIONS: Screening according to the 2021 ESC position statement performs well in daily clinical practice. Clinicians should adhere to repeating bone scintigraphy after 3 years, as progressing to ATTRv-CM without signs of ATTRv-CM on first-line diagnostic tests or symptoms is common.</p

Conventional heart failure therapy in cardiac ATTR amyloidosis

Background and Aims: The aims of this study were to assess prescription patterns, dosages, discontinuation rates and association with prognosis of conventional heart failure (HF) medications in patients with transthyretin cardiac amyloidosis (ATTR-CA). Methods: A retrospective analysis of all consecutive patients diagnosed with ATTR-CA at the National Amyloidosis Centre between 2000-2022 identified 2371 patients with ATTR-CA. Results: Prescription of HF medications was greater among patients with a more severe cardiac phenotype, comprising beta-blockers in 55.4%, angiotensin-converting enzyme inhibitors (ACEi)/angiotensin-II receptor blockers (ARB) in 57.4%, and mineralocorticoid receptor antagonists (MRAs) in 39.0% of cases. During a median follow-up of 27.8 months (IQR 10.6-51.3), 21.7% had beta-blockers discontinued, and 32.9% had ACEi/ARB discontinued. In contrast, only 7.5% had MRAs discontinued. Propensity score-matched analysis demonstrated that treatment with MRAs was independently associated with a reduced risk of mortality in the overall population (HR 0.77 [95% CI 0.66-0.89], P&lt;0.001) and in a pre-specified subgroup of patients with a left ventricular ejection fraction (LVEF) &gt;40% (HR 0.75 [95% CI 0.63-0.90], P=0.002); and treatment with low-dose beta-blockers was independently associated with a reduced risk of mortality in a pre-specified subgroup of patients with a LVEF ≤40% (HR 0.61 [95% CI 0.45-0.83], P=0.002). No convincing differences were found for treatment with ACEi/ARBs. Conclusions: Conventional HF medications are currently not widely prescribed in ATTR-CA, and those that received medication had more severe cardiac disease. Beta-blockers and ACEi/ARBs were often discontinued, but low-dose beta-blockers were associated with reduced risk of mortality in patients with a LVEF ≤40%. In contrast, MRAs were rarely discontinued and were associated with reduced risk of mortality in the overall population; but these findings require confirmation in prospective randomized controlled trials

Effetto Magnetocalorico in prossimità di transizioni del prim'ordine in materiali per la conversione di energia

The Magnetocaloric Effect is a promising phenomenon which supports the development of innovative refrigerators and heat pumps which will be environmentally friendly and characterized by higher efficiency if compared to actual technologies. The aim of this work is the study this effect across first order magneto-structural martensitic transformations of NiMnGa-based alloys. The possibility to ''tune'' the properties of this phase transition by suitably controlling the material composition makes them very attractive. The aim of this work is to study such transformations to understand the real applicative potential of these systems. Three different experimental approaches are compared: magnetic characterization, the direct measurement of the temperature change induced by the applied magnetic field and a in-field Differential Scanning Calorimeter which allows to study the transformation latent heat and the specific heat at different applied magnetic fields. The adiabatic temperature change probe and the DSC are purposely realized for this aim. Moreover a new experimental setup is presented to analyze the material MCE while it is stressed by magnetization and demagnetization cycles in nearly operative conditions.L'Effetto Magnetocalorico è un fenomeno promettente che stimola lo sviluppo di sistemi refrigeranti innovativi e pompe di calore, caratterizzati da una maggiore efficienza e un minore impatto ambientale se confrontati alle tecnologie attuali. Lo scopo di questo lavoro è lo studio di questo fenomeno in trasformazioni martensitiche del prim'ordine in leghe tipo NiMnGa. La possibilità di controllare le proprietà di questa transizione di fase opportunamente variando la composizione di tali materiali accresce l'interesse scientifico verso questi sistemi. Lo scopo di questo lavoro è dunque di studiare tali trasformazioni per capire le loro reali potenzialità applicative. Tre differenti approcci sperimentali sono messi a confronto: caratterizzazione magnetica, misura diretta della variazione di temperatura indotta dal campo magnetico e calorimetria a scansione differenziale in campo magnetico per l'analisi di calore latente di trasformazione e calore specifico a diversi campi magnetici applicati. La sonda per la misura della variazione di temperatura e la DSC sono due setup appositamente realizzati per questo scopo. Inoltre, è presentato un nuovo apparato sperimentale per analizzare l'MCE dei materiali mentre questi sono sollecitati da cicli di magnetizzazione e smagnetizzazione ad alte frequenze

Convergence of direct and indirect methods in the magnetocaloric study of first order transformations: the case of Ni-Co-Mn-Ga Heusler alloys

The study of two aspects of the magnetocaloric effect (MCE), namely, the matching between isothermal entropy change and direct adiabatic temperature change, is not straightforward since huge differences between these two quantities have often been reported. Here we put in relation the direct and indirect measurements on the first order magnetostructural martensitic transformation occurring in Ni-Co-Mn-Ga alloys. In order to complete the characterization of the MCE and to find an explanation of these mismatches, differential scanning calorimeter measurements have been performed at different applied magnetic fields