The pressure-derived microvascular resistance reserve and its correlation to Doppler MRR measurement-a proof of concept study.

Background: Microvascular resistance reserve (MRR) is a recently introduced specific index of coronary microcirculation. MRR calculation can utilize parameters deriving from coronary flow reserve (CFR) assessment, provided that intracoronary pressure data are also available. The previously proposed pressure-bounded CFR (CFRpb) defines the possible CFR interval on the basis of resting and hyperemic pressure gradients in the epicardial vessel, however, its correlation to the Doppler wire measurement was reported to be rather poor without the correction for hydrostatic pressure. Purpose: We aimed to determine the pressure-bounded coronary MRR interval with hydrostatic pressure correction according to the previously established equations of CFRpb adapted for the MRR concept. Furthermore, we also aimed to design a prediction model using the actual MRR value within the pressure-bounded interval and validate the results against the gold-standard Doppler wire technique. Methods: Hydrostatic pressure between the tip of the catheter and the sensor of the pressure wire was calculated by height difference measurement from a lateral angiographic view. In the derivation cohort the pressure-bounded MRR interval (between MRRpbmin and MRRpbmax) was determined solely from hydrostatic pressure-corrected intracoronary pressure data. The actual MRR was calculated by simple hemodynamic equations incorporating the anatomical data of the three-dimensionally reconstructed coronary artery (MRRp-3D). These results were analyzed by regression analyses to find relations between the MRRpb bounds and the actual MRRp-3D. Results: In the derivation cohort of 23 measurements, linear regression analysis showed a tight relation between MRRpbmax and MRRp-3D (r 2 = 0.74, p < 0.0001). Using this relation (MRRp-3D = 1.04 + 0.51 × MRRpbmax), the linear prediction of the MRR was tested in the validation cohort of 19 measurements against the gold standard Doppler wire technique. A significant correlation was found between the linearly predicted and the measured values (r = 0.54, p = 0.01). If the area stenosis (AS%) was included to a quadratic prediction model, the correlation was improved (r = 0.63, p = 0.004). Conclusions: The MRR can be predicted reliably to assess microvascular function by our simple model. After the correction for hydrostatic pressure error, the pressure data during routine FFR measurement provides a simultaneous physiological assessment of the macro- and microvasculature.

Add-on Sacubitril/Valsartan Therapy Induces Left Ventricular Remodeling in Non-responders to Cardiac Resynchronization Therapy to a Similar Extent as in Heart Failure Patients Without Resynchronization.

INTRODUCTION: Non-responders to cardiac resynchronization therapy (CRT-NR) have poor prognosis. Sacubitril/valsartan (SV) treatment improved the outcome of patients with heart failure with reduced left ventricular (LV) ejection fraction (HFrEF) in randomized trials with no data on the specific cohort of CRT-NRs. The aim of this study was to compare the echocardiographic and biomarker changes in CRT-NR patients treated with versus without SV, and in patients with HFrEF on SV therapy. METHODS: CRT-NR patients initiated on SV (group I), CRT-NR patients on angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (ACEi/ARB) (group II), and patients with HFrEF (without CRT) initiated on SV (group III) were identified in our heart failure (HF) registry. CRT-NR was defined as < 10% improvement in left ventricular ejection fraction (LV EF) 6 months after the implantation. Echocardiographic parameters and N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels at baseline and at the end of follow-up were compared. RESULTS: A total of 275 patients (group I, 70; group II, 70; and group III, 135) were included. After a follow-up of 7.54 ± 1.8 months (mean ± standard deviation [SD]), LV EF (%) increased in group I (25.2 ± 5.7 versus 29.4% ± 6.7; p < 0.001) and in group III (26.6 ± 6.4 versus 29.9 ± 6.7; p < 0.001). LV end-systolic diameters (mm) decreased in group I (56.6 ± 9.0 versus 54.3 ± 8.7; p = 0.004) and in group III (55.9 ± 9.9 versus 54.3 ± 11.2; p = 0.021). The levels of NT-proBNP (pg/mL) decreased in group I (2058.86 [1041.07-4502.51] versus 1121.55 [545-2541]; p < 0.001) and in group III (2223.35 [1233.03-4795.96] versus 1123.09 [500.38-2651.27]; p < 0.001). The extent of improvement was similar in groups I and III (p > 0.05). No significant changes were detected in group II. CONCLUSION: SV therapy induced similar improvements in echocardiographic parameters and in NT-proBNP levels in CRT-NR patients and in patients with HFrEF without resynchronization.

The feasibility of baroreflex sensitivity measurements in heart failure subjects: The role of slow-patterned breathing.

INTRODUCTION: Increased muscle sympathetic nerve activity (MSNA) indicates an adverse outcome in heart failure. Decreased baroreflex modulation of MSNA is a well-known feature of the disease. The determinability of cardiovagal baroreflex sensitivity (BRS) in heart failure is low, however, the determinability of sympathetic BRS is not known. METHODS: We have assessed the spontaneous, MSNA burst incidence-based baroreflex index (BRSsymp) in 33 stable heart failure patients and in 10 healthy controls using the traditional r ≥ .5 cutoff for acceptable individual diastolic pressure-burst incidence slopes, and also a more stringent r ≥ .7 cutoff. We have also assessed the influence of 6/min breathing. RESULTS: The determinability of BRSsymp in heart failure patients was 64% during spontaneous breathing with r ≥ .5 cutoff, and 39% using the r ≥ .7 cutoff. The determinability of these indices further decreased during 6/min breathing, dropping to 29% with the r ≥ .7 cutoff. In contrast, the determinability of the cardiovagal BRS indices increased significantly with 6/min breathing (from 24% to 66%; p < .001). Patients who still had determinable BRSsymp at the r ≥ .7 cutoff had a significantly lower baseline burst incidence than those with an undeterminable index (70 ± 14 vs. 89 ± 10 burst/100 cycles; p < .002). Neither the 6/min breathing, nor the r ≥ .7 cutoff limit influenced the high availability of BRSsymp in healthy subjects. CONCLUSION: The determinability of BRSsymp in heart failure patients is limited, especially with the 0.7 limit for correlation. Undeterminable BRSsymp in patients is associated with higher sympathetic activity. 6/min breathing improves the determinability of cardiovagal BRS indices, but not that of BRSsymp.

Anatomical Assessment vs. Pullback REsting full-cycle rAtio (RFR) Measurement for Evaluation of Focal and Diffuse CoronarY Disease: Rationale and Design of the "READY Register".

Background: The morphology and functional severity of coronary stenosis show poor correlation. However, in clinical practice, the visual assessment of the invasive coronary angiography is still the most common means for evaluating coronary disease. The fractional flow reserve (FFR), the coronary flow reserve (CFR), and the resting full-cycle ratio (RFR) are established indices to determine the hemodynamic significance of a coronary stenosis. Design/Methods: The READY register (NCT04857762) is a prospective, multicentre register of patients who underwent invasive intracoronary FFR and RFR measurement. The main aim of the registry is to compare the visual estimate of coronary lesions and the functional severity of the stenosis assessed by FFR, as well as the RFR pullback. Characterizations of the coronary vessel for predominantly focal, diffuse, or mixed type disease according to visual vs. RFR pullback determination will be compared. The secondary endpoint of the study is a composite of major adverse cardiac events, including death, myocardial infarction, and repeat coronary revascularization at 1 year. These endpoints will be compared in patients with non-ischemic FFR in the subgroup of cases where the local pressure drop indicates a focal lesion according to the definition of ΔRFR > 0.05 (for <25 mm segment length) and in the subgroup without significant ΔRFR. In case of an FFR value above 0.80, an extended physiological analysis is planned to diagnose or exclude microvascular disease using the CFR/FFR index. This includes novel flow dynamic modeling for CFR calculation (CFRp-3D). Conclusion: The READY register will define the effect of RFR measurement on visual estimation-based clinical decision-making. It can identify a prognostic value of ΔRFR during RFR pullback, and it would also explore the frequency of microvascular disease in the patient population with FFR > 0.80. Clinical Trial Registration: ClinicalTrials.gov (NCT04857762).

Sympathetic activation in heart failure with reduced and mildly reduced ejection fraction: the role of aetiology.

AIM: While sympathetic overactivity in heart failure (HF) with reduced ejection fraction (HFrEF; EF < 40%) is well-documented, it is ill-defined in patients with mildly reduced EF (HFmrEF; EF 40-49%). Furthermore, the significance of ischaemic versus non-ischaemic aetiology in sympathetic activation is also unclear and has yet to be studied in HF. Our goal was to compare muscle sympathetic nerve activity (MSNA) in HFmrEF and HFrEF patients and in healthy subjects, as well as to elucidate the influence of the underlying disease. METHODS AND RESULTS: Twenty-three HFrEF (age 58 ± 10 years), 33 HFmrEF patients (age 61 ± 10 years), including 11 subjects with non-ischaemic cardiomyopathy in each HF groups and 10 healthy controls (age 55 ± 10 years), were studied. MSNA-detected by peroneal microneurography, continuous arterial pressure, and ECG-was recorded. MSNA frequency (burst/min) and incidence (burst/100 cycles) were calculated. Association with the patients' characteristics were assessed, and aetiology-based comparisons were performed. Burst frequency demonstrated a significant stepwise increase in both HFmrEF (41 ± 11 burst/min) and HFrEF (58 ± 17 burst/min, P < 0.001) patients as compared with controls (27 ± 9; P < 0.001 for both HF groups). Similarly, burst incidences were 66 ± 17, 82 ± 15, and 36 ± 10 burst/100 cycles in HFmrEF, HFrEF patients, and in healthy controls, respectively (P < 0.001 for all). Burst frequencies in HF patients showed significant correlation with NT-proBNP levels, and significant inverse correlations with the subjects' mean RR intervals, stroke volumes, pulse pressures, and EF. CONCLUSIONS: Muscle sympathetic nerve activity parameters indicated significant sympathetic activation in both HFmrEF and HFrEF patients as compared with healthy controls with no difference in relation to ischaemic versus non-ischaemic aetiology.

Interventricular Differences of Signaling Pathways-Mediated Regulation of Cardiomyocyte Function in Response to High Oxidative Stress in the Post-Ischemic Failing Rat Heart.

Standard heart failure (HF) therapies have failed to improve cardiac function or survival in HF patients with right ventricular (RV) dysfunction suggesting a divergence in the molecular mechanisms of RV vs. left ventricular (LV) failure. Here we aimed to investigate interventricular differences in sarcomeric regulation and function in experimental myocardial infarction (MI)-induced HF with reduced LV ejection fraction (HFrEF). MI was induced by LAD ligation in Sprague-Dawley male rats. Sham-operated animals served as controls. Eight weeks after intervention, post-ischemic HFrEF and Sham animals were euthanized. Heart tissue samples were deep-frozen stored (n = 3-5 heart/group) for ELISA, kinase activity assays, passive stiffness and Ca2+-sensitivity measurements on isolated cardiomyocytes, phospho-specific Western blot, and PAGE of contractile proteins, as well as for collagen gene expressions. Markers of oxidative stress and inflammation showed interventricular differences in post-ischemic rats: TGF-ß1, lipid peroxidation, and 3-nitrotyrosine levels were higher in the LV than RV, while hydrogen peroxide, VCAM-1, TNFα, and TGF-ß1 were increased in both ventricles. In addition, nitric oxide (NO) level was significantly decreased, while FN-1 level was significantly increased only in the LV, but both were unchanged in RV. CaMKII activity showed an 81.6% increase in the LV, in contrast to a 38.6% decrease in the RV of HFrEF rats. Cardiomyocyte passive stiffness was higher in the HFrEF compared to the Sham group as evident from significantly steeper Fpassive vs. sarcomere length relationships. In vitro treatment with CaMKIIδ, however, restored cardiomyocyte passive stiffness only in the HFrEF RV, but had no effect in the HFrEF LV. PKG activity was lower in both ventricles in the HFrEF compared to the Sham group. In vitro PKG administration decreased HFrEF cardiomyocyte passive stiffness; however, the effect was more pronounced in the HFrEF LV than HFrEF RV. In line with this, we observed distinct changes of titin site-specific phosphorylation in the RV vs. LV of post-ischemic rats, which may explain divergent cardiomyocyte stiffness modulation observed. Finally, Ca2+-sensitivity of RV cardiomyocytes was unchanged, while LV cardiomyocytes showed increased Ca2+-sensitivity in the HFrEF group. This could be explained by decreased Ser-282 phosphorylation of cMyBP-C by 44.5% in the RV, but without any alteration in the LV, while Ser-23/24 phosphorylation of cTnI was decreased in both ventricles in the HFrEF vs. the Sham group. Our data pointed to distinct signaling pathways-mediated phosphorylations of sarcomeric proteins for the RV and LV of the post-ischemic failing rat heart. These results implicate divergent responses for oxidative stress and open a new avenue in targeting the RV independently of the LV.

Cardiovagal and sympathetic baroreflex regulation in heart failure / Cardiovagalis és szimpatikus artériás baroreflex szabályozásának vizsgálata szívelégtelenségben.

Összefoglaló. Bevezetés: Az artériás baroreflex-érzékenységi (BRS-) indexek egységnyi nyomásváltozásra adott élettani válaszokat írnak le. Az RR-intervallum gyors válaszait a cardiovagalis BRS-indexekkel, a vasomotorválaszokat az izom szimpatikus idegi aktivitás (MSNA) válaszain alapuló szimpatikus-BRS-indexekkel jellemezzük. Szívelégtelenségben kórosan csökkent értékeik kedvezotlen kimenetelt jeleznek. Betegek és módszerek: A BRS-indexek meghatározhatóságát 52, szívelégtelenségben szenvedo betegben (kor: 59 ± 10 év; EF: 37 ± 11%) és 11, kor szerint illesztett egészséges önkéntesben vizsgáltuk. EKG- és vérnyomásfelvételekbol három cardiovagalis BRS-indexet számítottunk; a növekvo, illetve csökkeno spontán szekvenciák módszerén alapuló up-BRS-t és down-BRS-t, továbbá az alacsony frekvenciatartomány-beli 'cross-spectralis ' indexet, az LF-alfát. Egy perifériás ideg (nervus peroneus) perkután punkciójával detektáltuk az MSNA szimpatikus csúcs incidenciáját (csúcs/100 szívciklus), s ezt korreláltattuk a diastolés nyomás 3 Hgmm sávokba rendezett értékeivel. Így nyertük a szimpatikus BRS jellemzoit, a BRSSY-incidencia-értékeket. Eredmények: Az up- és down-BRS-szekvenciák csak a betegek 19%-ában voltak meghatározhatók, az LF-alfa a 69%-ukban. Azok, akiknél cardiovagalis BRS nem volt meghatározható, szignifikánsan csökkent RR-intervallum-ingadozást és magasabb NT-proBNP-értékeket mutattak. A meghatározható cardiovagalis BRS-indexek nem különítették el a betegeket és a kontrollszemélyeket. A BRSSY-incidencia-érték 58%-ban állt rendelkezésre, s csakúgy, mint maga a "csúcs" incidencia, jól elkülönítette a betegeket és az önkénteseket. A hiányzó baroreflexérték a magas "csúcs" incidenciával állt összefüggésben. Következtetés: A cardiovagalis BRS-értékek csak korlátozottan alkalmasak egészséges önkéntesek és szívelégtelen betegek elkülönítésére, a meghatározhatatlan értékek súlyosabb betegségre utalnak. A BRSSY-incidencia elkülöníti az egészséges és a beteg csoportokat; a hiányzó érték a fokozott szimpatikus aktivitással áll összefüggésben. Orv Hetil. 2021; 162(3): 91-98. INTRODUCTION: Arterial baroreflex sensitivity (BRS) is characterized by the magnitude of physiological responses to arterial pressure changes. Rapid RR interval responses are quantified by cardiovagal BRS parameters, sympathetic responses could be assessed by changes in muscle sympathetic nerve activity (MSNA). Abnormal indices in heart failure are associated with poor outcome. PATIENTS AND METHODS: 52, heart failure patients (age 59 ± 10 years, EF 37 ± 11%), and 11, age-matched healthy volunteers were studied. From ECG and arterial pressure recordings up-BRS and down-BRS values were determined using the method of spontaneous sequences. The low frequency cross-spectral gain, the LF alpha was also determined. Percutaneous puncture of the peroneal nerves allowed determination of MSNA burst incidence (burst/100 cycles), which was correlated to corresponding diastolic pressure bins of 3 mmHg, yielding a sympathetic BRS, the BRSSY-incidence. RESULTS: Up- and down-BRS could be calculated in 19% of the patients, LF alpha was determined in 69%. Those with missing cardiovagal BRS values showed diminished RR interval variation, and higher levels of NT-proBNP. The measurable cardiovagal BRS indices did not separate patients and healthy volunteers. BRSSY-incidence could be determined in 58% of the patients. The sympathetic gain as well as the burst incidence differed significantly between patients and healthy volunteers. Missing BRSSY-incidence was associated with higher burst incidence. CONCLUSION: Cardiovagal BRS indices have limited value in differentiating healthy and heart failure subjects. Incalculable values among patients indicate more severe disease state. BRSSY-incidence does separate healthy and diseased population, the missing BRSSY-incidence values are related to increased sympathetic activity. Orv Hetil. 2021; 162(3): 91-98.

Theory and history of the study of muscle sympathetic nerve activity / Az izom szimpatikus idegaktivitás vizsgálatának elméleti alapjai és története

Heart failure is a rapidly growing epidemic in developed countries. It has been well documented that heart failure is associated with abnormal neurohumoral activation. The autonomic regulation is characterized by decreased parasympathetic and elevated sympathetic activity. While the cardiovagal activity could be easily assessed by various heart rate variability parameters, markers of the sympathetic activity are not readily available. Percutaneous insertion of microelectrodes in a peripheral nerve allows recording of the muscle sympathetic vasomotor nerve activity (MSNA). MSNA shows good correlation with the cardiac sympathetic activity, and also with the levels of circulating catecholamines. Besides determination of the baseline sympathetic activity, rapid sympathetic responses to various stimuli can be also described by changes of MSNA. Elevated MSNA has been documented in several diseases, including hypertension, obesity, myocardial ischemia and renal failure. In heart failure, the elevated MSNA is well correlated to the clinical severity of the patient's conditions, and serves as a prognostic marker of mortality. In our paper, we give a short account of the history of MSNA studies, describe its physiological background and clinical relevance with special regard to heart failure. Orv Hetil. 2020; 161(29): 1190-1199.

Myosin heavy chain and cardiac troponin T damage is associated with impaired myofibrillar ATPase activity contributing to sarcomeric dysfunction in Ca2+-paradox rat hearts.

This study aimed to explore the potential contribution of myofibrils to contractile dysfunction in Ca2+-paradox hearts. Isolated rat hearts were perfused with Krebs-Henseleit solution (Control), followed by Ca2+-depletion, and then Ca2+-repletion after Ca2+-depletion (Ca2+-paradox) by Langendorff method. During heart perfusion left ventricular developed pressure (LVDP), end-diastolic pressure (LVEDP), rate of pressure development (+ dP/dt), and pressure decay (-dP/dt) were registered. Control LVDP (127.4 ± 6.1 mmHg) was reduced during Ca2+-depletion (9.8 ± 1.3 mmHg) and Ca2+-paradox (12.9 ± 1.3 mmHg) with similar decline in +dP/dt and -dP/dt. LVEDP was increased in both Ca2+-depletion and Ca2+-paradox. Compared to Control, myofibrillar Ca2+-stimulated ATPase activity was decreased in the Ca2+-depletion group (12.08 ± 0.57 vs. 8.13 ± 0.19 µmol Pi/mg protein/h), besides unvarying Mg2+ ATPase activity, while upon Ca2+-paradox myofibrillar Ca2+-stimulated ATPase activity was decreased (12.08 ± 0.57 vs. 8.40 ± 0.22 µmol Pi/mg protein/h), but Mg2+ ATPase activity was increased (3.20 ± 0.25 vs. 7.21 ± 0.36 µmol Pi/mg protein/h). In force measurements of isolated cardiomyocytes at saturating [Ca2+], Ca2+-depleted cells had lower rate constant of force redevelopment (k tr,max, 3.85 ± 0.21) and unchanged active tension, while those in Ca2+-paradox produced lower active tension (12.12 ± 3.19 kN/m2) and k tr,max (3.21 ± 23) than cells of Control group (25.07 ± 3.51 and 4.61 ± 22 kN/m2, respectively). In biochemical assays, α-myosin heavy chain and cardiac troponin T presented progressive degradation during Ca2+-depletion and Ca2+-paradox. Our results suggest that contractile impairment in Ca2+-paradox partially resides in deranged sarcomeric function and compromised myofibrillar ATPase activity as a result of myofilament protein degradation, such as α-myosin heavy chain and cardiac troponin T. Impaired relaxation seen in Ca2+-paradoxical hearts is apparently not related to titin, rather explained by the altered myofibrillar ATPase activity.

Renin overexpression leads to increased titin-based stiffness contributing to diastolic dysfunction in hypertensive mRen2 rats.

Hypertension (HTN) is a major risk factor for heart failure. We investigated the influence of HTN on cardiac contraction and relaxation in transgenic renin overexpressing rats (carrying mouse Ren-2 renin gene, mRen2, n = 6). Blood pressure (BP) was measured. Cardiac contractility was characterized by echocardiography, cellular force measurements, and biochemical assays were applied to reveal molecular mechanisms. Sprague-Dawley (SD) rats (n = 6) were used as controls. Transgenic rats had higher circulating renin activity and lower cardiac angiotensin-converting enzyme two levels. Systolic BP was elevated in mRen2 rats (235.11 ± 5.32 vs. 127.03 ± 7.56 mmHg in SD, P < 0.05), resulting in increased left ventricular (LV) weight/body weight ratio (4.05 ± 0.09 vs. 2.77 ± 0.08 mg/g in SD, P < 0.05). Transgenic renin expression had no effect on the systolic parameters, such as LV ejection fraction, cardiomyocyte Ca(2+)-activated force, and Ca(2+) sensitivity of force production. In contrast, diastolic dysfunction was observed in mRen2 compared with SD rats: early and late LV diastolic filling ratio (E/A) was lower (1.14 ± 0.04 vs. 1.87 ± 0.08, P < 0.05), LV isovolumetric relaxation time was longer (43.85 ± 0.89 vs. 28.55 ± 1.33 ms, P < 0.05), cardiomyocyte passive tension was higher (1.74 ± 0.06 vs. 1.28 ± 0.18 kN/m(2), P < 0.05), and lung weight/body weight ratio was increased (6.47 ± 0.24 vs. 5.78 ± 0.19 mg/g, P < 0.05), as was left atrial weight/body weight ratio (0.21 ± 0.03 vs. 0.14 ± 0.03 mg/g, P < 0.05). Hyperphosphorylation of titin at Ser-12742 within the PEVK domain and a twofold overexpression of protein kinase C-α in mRen2 rats were detected. Our data suggest a link between the activation of renin-angiotensin-aldosterone system and increased titin-based stiffness through phosphorylation of titin's PEVK element, contributing to diastolic dysfunction.

Amelioration of cardiac remodeling in congestive heart failure by beta-adrenoceptor blockade is associated with depression in sympathetic activity.

This study investigated whether improvement in cardiac function and attenuation of cardiac remodeling by some beta-adrenoceptor (beta-AR) antagonists were associated with a depression in sympathetic activity in congestive heart failure (CHF) due to myocardial infarction (MI). Although cardiac dysfunction, hypertrophy and dilatation as well as increased plasma level of catecholamines are known to occur in CHF, the relationship between these parameters is poorly understood. Three weeks after occlusion of the coronary artery, rats were treated daily with 20 and 75 mg/kg of either atenolol or propranolol for 5 weeks. Sham-operated rats served as controls. Both atenolol and propranolol at 20 and 75 mg/kg doses attenuated the MI-induced cardiac hypertrophy, increases in left ventricular (LV) end-diastolic pressure, LV end-systolic volume and LV end-diastolic volume as well as depressions in LV systolic pressure, LV fractional shortening and cardiac output. PR interval was decreased and QT( c ) interval was increased in CHF; these alterations were ameliorated by both atenolol and propranolol. The increased level of plasma epinephrine in CHF was also depressed by both low and high doses of atenolol and propranolol whereas the increased level of plasma norepinephrine was reduced by high but not low doses of these drugs. The results indicate that the beneficial effects of beta-AR antagonists on cardiac remodeling and heart dysfunction in CHF may be due to the blockade of beta-ARs in the myocardium and a depression in the sympathetic activity.

Antiplatelet agents sarpogrelate and cilostazol affect experimentally-induced ventricular arrhythmias and mortality.

Antiplatelet agents, sarpogrelate (SAR), a 5-hydroxy tryptamine 2A receptor antagonist and cilostazol (CIL), a phosphodiesterase-III inhibitor, were observed to be beneficial in attenuating cardiac remodeling and improving cardiac function in congestive heart failure due to myocardial infarction in rats; however, CIL increased ventricular tachycardia and mortality. In order to study the effects of these antiplatelet agents on arrhythmias, Sprague-Dawley rats were pretreated with either SAR or CIL (5 mg/kg/day) for 2 weeks and were then either injected cumulative doses of epinephrine (Epi) or subjected to coronary occlusion. Saline-treated animals served as controls. Electrocardiographic analysis revealed that SAR pretreatment decreased the incidence and severity of ventricular arrhythmias (time of onset of arrhythmias as well as the occurrence of premature ventricular contractions, salvos, tachycardia, and fibrillations), whereas CIL treatment augmented the incidence of cardiac arrhythmias due to both Epi and coronary occlusion. None of the drugs affected the corrected QT interval significantly. Furthermore, the levels of cyclic adenosine monophosphate (cAMP) in left ventricle were markedly higher in CIL-pretreated rats when compared to SAR-pretreated or control rats. It is suggested that an excessive level of cAMP may contribute to increase incidence of ventricular arrhythmias and mortality in animals pretreated with CIL, unlike the SAR-pretreated rats.

Antiplatelet therapy mitigates cardiac remodeling and dysfunction in congestive heart failure due to myocardial infarction.

Antiplatelet agents such as sarpogrelate (SAR), a 5-hydroxytryptamine antagonist, and cilostazol (CIL), a phosphodiesterase-III inhibitor, are used in the management of peripheral vascular disease. In this study, we tested the hypothesis that both SAR and CIL prevent cardiac remodeling and improve cardiac function in congestive heart failure (CHF) due to myocardial infarction (MI). Post-MI rats (3 weeks after the occlusion of coronary artery) received either vehicle (MI+V, n = 36), SAR (MI+SAR; 5 mg xc kg(-1) x day(-1), n = 35) or CIL (MI+CIL; 5 mg x kg(-1) x day(-1), n = 34) from day 21 to day 56. Sham-operated rats (n = 29) served as controls. Electrocardiographic, echocardiographic, and hemodynamic parameters were measured on day 56. Treatment of infarcted animals with SAR or CIL significantly improved the left ventricular (LV) dimensions, LV fractional shortening, cardiac output, stroke volume, mean arterial pressure, LV diastolic function, and LV systolic pressure, as well as rates of LV pressure development and pressure decay. Although cardiac hypertrophy was reduced, both SAR and CIL had no effect on infarct size or MI-associated QTc prolongation. However, SAR decreased whereas CIL increased the incidence of ventricular arrhythmias and the mean number of episodes in infarcted animals. Mortality during the treatment period was decreased by 17% with SAR and increased by 10% with CIL, but these changes were not significant statistically. The data in this study suggest that both SAR and CIL prevent cardiac remodeling and improve cardiac function in MI-induced CHF; however, CIL unlike SAR increased the incidence of arrhythmias and adversely affected patient mortality.

Antiplatelet therapy attenuates subcellular remodelling in congestive heart failure.

Antiplatelet agents, sarpogrelate (SAR), a 5-HT(2A) receptor antagonist, and cilostazol (CIL), a phosphodiesterase III (PDE-III) inhibitor, are used for the treatment of peripheral vascular disease. We tested whether these agents affect cardiac function and subcellular remodelling in congestive heart failure (CHF) induced by myocardial infarction (MI). Three weeks after MI, rats were treated daily with 5 mg/kg SAR or CIL as well as vehicle for 5 weeks. Sham-operated animals served as controls. At end of the treatment period, haemodynamic measurements were performed and the left ventricle was processed for the determination of sarcoplasmic reticulum (SR) Ca(2+)-uptake and -release activities, and expression of SR Ca(2+)-pump, phospholamban and ryanodine receptors, as well as myofibrillar ATPase activities, expression of alpha- and beta-myosin heavy chain (MHC) isoforms, and phosphorylation of phospholamban and cardiac troponin-I (c Tn-I). Marked haemodynamic changes in the MI-induced CHF were associated with depressions in SR Ca (+)-uptake and -release activities as well as in protein content and gene expression for SR proteins. Furthermore, myofibrillar Ca(2+)-stimulated ATPase activity, as well as protein content and gene expression for alpha-MHC were decreased whereas those for beta-MHC were increased in the failing heart. Also, phosphorylation levels of phospholamban and cTn-I were reduced in failing hearts. The MI-associated changes in cardiac function, SR and myofibillar activities, as well as SR and myofibrillar protein and gene expression were attenuated by treatment with SAR or CIL. The results suggest that SAR and CIL improve cardiac function by ameliorating subcellular remodelling in the failing heart and indicate the potential therapy of CHF with antiplatelet agents.

Myofibrillar remodeling in cardiac hypertrophy, heart failure and cardiomyopathies.

BACKGROUND: A wide variety of pathological conditions have been shown to result in cardiac remodelling and myocardial dysfunction. However, the mechanisms of transition from adaptive to maladaptive alterations, as well as those for changes in cardiac performance leading to heart failure, are poorly understood. OBSERVATIONS: Extensive studies have revealed a broad spectrum of progressive changes in subcellular structures and function, as well as in signal transduction and metabolism in the heart, among different cardiovascular disorders. The present review is focused on identifying the alterations in molecular and biochemical structure of myofibrils (myofibrillar remodelling) in hypertrophied and failing myocardium in different types of heart diseases. Numerous changes at the level of gene expression for both contractile and regulatory proteins have already been reported in failing hearts and heart diseases; these changes are potential precursors for heart failure such as cardiac hypertrophy and cardiomyopathies. Myofibrillar remodelling, as a consequence of proteolysis, oxidation, and phosphorylation of some functional groups in both contractile and regulatory proteins in hearts failing due to different etiologies, has also been described. CONCLUSIONS: Although myofibrillar remodelling appears to be associated with cardiac dysfunction, alterations in both contractile and regulatory proteins are dependent on the type and stage of heart disease.

Subcellular remodeling as a viable target for the treatment of congestive heart failure.

It is now well known that congestive heart failure (CHF) is invariably associated with cardiac hypertrophy, and changes in the shape and size of cardiomyocytes (cardiac remodeling) are considered to explain cardiac dysfunction in CHF. However, the mechanisms responsible for the transition of cardiac hypertrophy to heart failure are poorly understood. Several lines of evidence both from various experimental models of CHF and from patients with different types of CHF have indicated that the functions of different subcellular organelles such as extracellular matrix, sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, and nucleus are defective. Subcellular abnormalities for protein contents, gene expression, and enzyme activities in the failing heart become evident as a consequence of prolonged hormonal imbalance, metabolic derangements, and cation maldistribution. In particular, the occurrence of oxidative stress, development of intracellular Ca2+ overload, activation of proteases and phospholipases, and alterations in cardiac gene expression result in changes in the biochemical composition, molecular structure, and function of different subcellular organelles (subcellular remodeling). Not only does subcellular remodeling appear to be intimately involved in the transition of cardiac hypertrophy to heart failure, the mismatching of the function of different subcellular organelles leads to the development of cardiac dysfunction. Although blockade of the renin-angiotensin system, sympathetic nervous system, and various other hormonal actions have been reported to produce beneficial effects on cardiac remodeling and heart dysfunction in CHF, the actions of various cardiac drugs on subcellular remodeling have not been examined extensively. Some recent studies have indicated that both the angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists attenuate changes in sarcolemma, sarcoplasmic reticulum, and myofibril enzyme activities, protein contents, and gene expression, and partly improve cardiac function in the failing hearts. It is suggested that subcellular remodeling is an excellent target for the development of improved drug therapy for CHF. Furthermore, extensive studies should investigate the effects of different agents individually or in combination on reverse subcellular remodeling, cardiac remodeling, and cardiac dysfunction in various experimental models of CHF.

Calpain-1-sensitive myofibrillar proteins of the human myocardium.

Calpain-1 is a ubiquitous intracellular Ca2+-activated protease, which has been implicated in the pathogenesis of reversible myocardial depression (i.e. myocardial stunning) that follows ischemia and reperfusion via myofibrillar protein degradation. However, the target proteins of this degradative process in the human myocardium have not yet been identified. In order to compare the levels of Calpain-1 susceptibility within a set of human myofibrillar proteins (titin, alpha-fodrin, desmin, troponin T (cTnT), troponin I (cTnI) and alpha-actinin), crude left ventricular tissue homogenates were incubated for 0.5, 15, 30, 60 or 120 min in the presence of Calpain-1 (1 U or 5 U). Differences in the kinetics and extents of protein degradation were subsequently evaluated by using silver-stained SDS-polyacrylamide gels and Western immunoblot analyses. These assays revealed myofibrillar proteins with high (titin and alpha-fodrin), moderate (desmin and cTnT), or low (cTnI and alpha-actinin) relative Calpain-1 susceptibilities. The level of phosphorylation of cTnI did not explain its relatively low Calpain-1 susceptibility. Moreover, the molecular mass distributions of the truncated alpha-fodrin, desmin and cTnI fragments resulting from Ca2+-dependent autoproteolysis exhibited marked similarities with those of their Calpain-1-clipped products. These in vitro results shed light on a number of structural (titin, alpha-fodrin, desmin and alpha-actinin) and regulatory (cTnT and cTnI) proteins within the contractile apparatus as potential targets of Calpain-1. Their degradation may contribute to the development of postischemic stunning in the human myocardium.

Molecular defects in cardiac myofibrillar proteins due to thyroid hormone imbalance and diabetes.

The heart very often becomes a victim of endocrine abnormalities such as thyroid hormone imbalance and insulin deficiency, which are manifested in a broad spectrum of cardiac dysfunction from mildly compromised function to severe heart failure. These functional changes in the heart are largely independent of alterations in the coronary arteries and instead reside at the level of cardiomyocytes. The status of cardiac function reflects the net of underlying subcellular modifications induced by an increase or decrease in thyroid hormone and insulin plasma levels. Changes in the contractile and regulatory proteins constitute molecular and structural alterations in myofibrillar assembly, called myofibrillar remodeling. These alterations may be adaptive or maladaptive with respect to the functional and metabolic demands on the heart as a consequence of the altered endocrine status in the body. There is a substantial body of information to indicate alterations in myofibrillar proteins including actin, myosin, tropomyosin, troponin, titin, desmin, and myosin-binding protein C in conditions such as hyperthyroidism, hypothyroidism, and diabetes. The present article is focussed on discussion how myofibrillar proteins are altered in response to thyroid hormone imbalance and lack of insulin or its responsiveness, and how their structural and functional changes explain the contractile defects in the heart.

Calpain-1-dependent degradation of troponin I mutants found in familial hypertrophic cardiomyopathy.

The mechanism by which mutations of the cardiac troponin I (cTnI) gene evoke familial hypertrophic cardiomyopathy (fHCM) is unknown. In this investigation the potential effects of three fHCM-related cTnI mutations on Calpain-1-induced cTnI degradation were tested, and a study was made of whether additional conformational changes due to troponin complex formation and protein kinase A-induced phosphorylation affect the intensity of cTnI proteolysis. Purified recombinant wild-type cTnI and three of its fHCM-related missense mutants (R145G, G203S and K206Q), alone or in the troponin complex (i.e. together with troponin C and troponin T), in the non-phosphorylated or protein kinase A-bisphosphorylated forms were proteolyzed in vitro in the presence of Calpain-1 (0.05-2.5 U) at 30 degrees C. Following incubation with Calpain-1 for 0.5, 30, 60 or 120 min, the extent of protein degradation was evaluated through the use of Western immunoblotting and densitometry. The results indicated that both the wild-type and the mutant cTnI molecules were susceptible to Calpain-1. However, the degradation of the cTnI molecules in the troponin complex was less intense than that of the non-complexed forms. Moreover, phosphorylation by protein kinase A conferred effective protection against cTnI proteolysis. The data suggested that mutations in the central inhibitory domain (R145G) and in the C-terminal region (G203S and K206Q) of cTnI do not affect its Calpain-1-mediated degradation, or the phosphorylation-induced protection against proteolysis.