Michael Schwarzl

The induction of mild hypothermia improves systolic function of the resuscitated porcine heart at no further sympathetic activation

Aim:  Mild hypothermia (MH) after cardiac arrest attenuates hypoxic brain injury and improves survival. As MH increases contractility in normal hearts, we hypothesized that MH improves cardiovascular function after cardiac arrest.

A porcine model of hypertensive cardiomyopathy: implications for heart failure with preserved ejection fraction.

Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk factors. Relevant animal models to identify potential therapeutic targets and to test novel therapies for HFPEF are missing. We induced hypertension and hyperlipidemia in landrace pigs (n = 8) by deoxycorticosteroneacetate (DOCA, 100 mg/kg, 90-day-release subcutaneous depot) and a Western diet (WD) containing high amounts of salt, fat, cholesterol, and sugar for 12 wk. Compared with weight-matched controls (n = 8), DOCA/WD-treated pigs showed left ventricular (LV) concentric hypertrophy and left atrial dilatation in the absence of significant changes in LV ejection fraction or symptoms of heart failure at rest. The LV end-diastolic pressure-volume relationship was markedly shifted leftward. During simultaneous right atrial pacing and dobutamine infusion, cardiac output reserve and LV peak inflow velocities were lower in DOCA/WD-treated pigs at higher LV end-diastolic pressures. In LV biopsies, we observed myocyte hypertrophy, a shift toward the stiffer titin isoform N2B, and reduced total titin phosphorylation. LV superoxide production was increased, in part attributable to nitric oxide synthase (NOS) uncoupling, whereas AKT and NOS isoform expression and phosphorylation were unchanged. In conclusion, we developed a large-animal model in which loss of LV capacitance was associated with a titin isoform shift and dysfunctional NOS, in the presence of preserved LV ejection fraction. Our findings identify potential targets for the treatment of HFPEF in a relevant large-animal model.

Mild hypothermia attenuates circulatory and pulmonary dysfunction during experimental endotoxemia.

Objective:We tested whether mild hypothermia impacts on circulatory and respiratory dysfunction during experimental endotoxemia. Design:Randomized controlled prospective experimental study. Setting:Large animal facility, Medical University of Graz, Austria. Subjects:Thirteen anesthetized and mechanically ventilated pigs. Interventions:Lipopolysaccharide was administered for 4 hours. With the beginning of lipopolysaccharide infusion, animals were assigned to either normothermia (38°C, n = 7) or mild hypothermia (33°C, n = 6, intravascular cooling) and followed for 8 hours in total. Measurements and Main Results:At the end of the protocol, cardiac output was lower in mild hypothermia than in normothermia (4.5 ± 0.4 L/min vs 6.6 ± 0.4 L/min, p < 0.05), but systemic vascular resistance (885 ± 77 dyn·s/cm5 vs 531 ± 29 dyn·s/cm5, p < 0.05) and (77% ± 6% vs 54% ± 3%, p < 0.05) were higher. Indices of left ventricular contractility in vivo were not different between groups. The high-frequency band in spectral analysis of heart rate variability indicated a better preserved vagal autonomic modulation of sinuatrial node activity in mild hypothermia versus normothermia (87 ± 5 vs 47 ± 5, normalized units, p < 0.05). Plasma norepinephrine levels were elevated compared with baseline in normothermia (2.13 ± 0.27 log pg/mL vs 0.27 ± 0.17 log pg/mL, p < 0.05) but not in mild hypothermia (1.02 ± 0.31 vs 0.55 ± 0.26, p = not significant). At 38°C in vitro, left ventricular muscle strips isolated from the mild hypothermia group had a higher force response to isoproterenol. SaO2 (100% ± 0% vs 92% ± 3%, p < 0.05) and the oxygenation index (PO2/FIO2, 386 ± 52 mm Hg vs 132 ± 32 mm Hg, p < 0.05) were substantially higher in mild hypothermia versus normothermia. Plasma cytokine levels were not consistently different between groups (interleukin 10) or higher (tumor necrosis factor-&agr; and interleukin 6 and 8) during mild hypothermia versus normothermia. Conclusion:The induction of mild hypothermia attenuates cardiac and respiratory dysfunction and counteracts sympathetic activation during experimental endotoxemia. This was not associated with lower plasma cytokine levels, indicating a reduction of cytokine responsiveness by mild hypothermia.

Left ventricular diastolic dysfunction during acute myocardial infarction: effect of mild hypothermia.

Background Mild hypothermia (MH) decreases infarct size and mortality in experimental reperfused myocardial infarction, but may potentiate ischaemia-induced left ventricular (LV) diastolic dysfunction. Methods In anaesthetized pigs (70 ± 2 kg), polystyrol microspheres (45 μm) were infused repeatedly into the left circumflex artery until cardiac power output decreased >40%. Then, pigs were assigned to normothermia (NT, 38.0 °C, n = 8) or MH (33.0 °C, n = 8, intravascular cooling) and followed for 6 h (CME 6 h). *p < 0.05 vs baseline, †p < 0.05 vs NT. Results In NT, cardiac output (CO) decreased from 6.2 ± 0.3 to 3.4 ± 0.2* l/min, and heart rate increased from 89 ± 4 to 101 ± 6* bpm. LV end-diastolic volume fell from 139 ± 8 to 64 ± 4 ml*, while LV ejection fraction remained constant (49 ± 1 vs 53 ± 4%). The corresponding end-diastolic pressure–volume relationship was progressively shifted leftwards, reflecting severe LV diastolic dysfunction. In MH, CO fell to a similar degree. Spontaneous bradycardia compensated for slowed LV relaxation, and the leftward shift of the end-diastolic pressure–volume relationship was less pronounced during MH. MH increased systemic vascular resistance, such that mean aortic pressure remained higher in MH vs NT (69 ± 2† vs 54 ± 4 mmHg). Mixed venous oxygen saturation at CME 6 h was higher in MH than in NT (59 ± 4† vs 42 ± 2%) due to lowered systemic oxygen demand during cooling. Conclusion We conclude that (i) an acute loss of end-diastolic LV compliance is a major component of acute cardiac pump failure during experimental myocardial infarction, and that (ii) MH does not potentiate this diastolic LV failure, but stabilizes haemodynamics and improves systemic oxygen supply/demand imbalance by reducing demand.

Biomarkers for characterization of heart failure - Distinction of heart failure with preserved and reduced ejection fraction.

BACKGROUND Heart failure (HF) incidence is rising worldwide and HF with preserved ejection fraction (HFpEF) represents nearly half of all cases. Treatment options are still limited in HFpEF in comparison to HF with reduced ejection fraction (HFrEF). METHODS We analyzed biomarkers in the general population to characterize HFpEF and HFrEF and defined a biomarker index to differentiate HFpEF from HFrEF. Growth differentiation factor-15 (GDF-15), soluble source of tumorigenicity 2 (sST2), C-reactive protein (CRP) and NT-proBNP were measured in 5000 individuals of the population-based Gutenberg Health Study (GHS). The median follow-up time for all-cause mortality was 7.3years with 213 events. RESULTS Identification of subjects with HF was improved by GDF-15 (p<0.001) in addition to NT-proBNP with an odds ratio (OR) of 1.4 (95% confidence interval [CI]:1.1-1.7). Discrimination of subjects with and without HF was slightly higher for GDF-15 (area under the ROC curve [AUC]:0.79 [95%CI:0.75-0.83]) compared to NT-proBNP (AUC:0.77 [95% CI:0.72-0.82]). For subjects with HF, differentiating HFpEF from HFrEF was feasible with the index ((CRP+GDF-15+sST2)/NT-proBNP) with an OR of 3.7 (95% CI:1.9-8.5) (p<0.001). The best biomarkers predicting all-cause mortality were NT-proBNP and GDF-15 with a hazard ratio (HR) of 1.9 (95% CI:1.6-2.2) and 1.7 (95%CI:1.6-1.9) (both p<0.001), respectively. CONCLUSION GDF-15 was useful to detect prevalent HF in addition to NT-proBNP and was elevated in HFrEF and HFpEF, whereas NT-proBNP was higher in HFrEF than in HFpEF. All biomarkers were useful to predict mortality in the general population. The index of ((CRP+GDF-15s+sST2)/NT-proBNP) was able to discriminate HFpEF from HFrEF.

Inotropic Effects of Experimental Hyperthermia and Hypothermia on Left Ventricular Function in Pigs-Comparison With Dobutamine.

Objectives:The results from the recent Targeted Temperature Management trial raised the question whether cooling or merely the avoidance of fever mediates better neurologic outcome in resuscitated patients. As temperature per se is a major determinant of cardiac function, we characterized the effects of hyperthermia (40.5°C), normothermia (38.0°C), and mild hypothermia (33.0°C) on left ventricular contractile function in healthy pigs and compared them with dobutamine infusion. Design:Animal study. Setting:Large animal facility, Medical University of Graz, Graz, Austria. Subjects:Nine anesthetized and mechanically ventilated closed-chest Landrace pigs (67 ± 2 kg). Interventions:Core body temperature was controlled using an intravascular device. At each temperature step, IV dobutamine was titrated to double maximum left ventricular dP/dt (1.8 ± 0.1 µg/kg/min at normothermia). Left ventricular pressure-volume relationships were assessed during short aortic occlusions. Left ventricular contractility was assessed by the calculated left ventricular end-systolic volume at an end-systolic left ventricular pressure of 100 mm Hg. Measurements and Main Results:Heart rate (98 ± 4 vs 89 ± 4 vs 65 ± 2 beats/min; all p < 0.05) and cardiac output (6.7 ± 0.3 vs 6.1 ± 0.3 vs 4.4 ± 0.2 L/min) decreased with cooling from hyperthermia to normothermia and mild hypothermia, whereas left ventricular contractility increased (left ventricular end-systolic volume at a pressure of 100 mm Hg: 74 ± 5 mL at hyperthermia, 52 ± 4 mL at normothermia, and 41 ± 3 mL at mild hypothermia; all p < 0.05). The effect of cooling on left ventricular end-systolic volume at a pressure of 100 mm Hg (hyperthermia to normothermia: –28% ± 3% and normothermia to mild hypothermia: –20% ± 5%) was of comparable effect size as dobutamine at a given temperature (hyperthermia: –28% ± 4%, normothermia: –27% ± 6%, and mild hypothermia: –27% ± 9%). Conclusions:Cooling from hyperthermia to normothermia and from normothermia to mild hypothermia increased left ventricular contractility to a similar degree as a significant dose of dobutamine in the normal porcine heart. These data indicate that cooling can reduce the need for positive inotropes and that lower rather than higher temperatures are appropriate for the resuscitated failing heart.

Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs.

Mild hypothermia (MH) decreases left ventricular (LV) end‐diastolic capacitance. We sought to clarify whether this results from incomplete relaxation.

A porcine model of early atrial fibrillation using a custom-built, radio transmission-controlled pacemaker

Mechanisms underlying atrial remodeling toward atrial fibrillation (AF) are incompletely understood. We induced AF in 16 pigs by 6weeks of rapid atrial pacing (RAP, 600bpm) using a custom-built, telemetrically controlled pacemaker. AF evolution was monitored three times per week telemetrically in unstressed, conscious animals. We established a dose-response relationship between RAP duration and occurrence of sustained AF >60minutes. Left atrial (LA) dilatation was present already at 2weeks of RAP. There was no evidence of left ventricular heart failure after 6weeks of RAP. As a proof-of-principle, arterial hypertension was induced in 5/16 animals by implanting desoxycorticosterone acetate (DOCA, an aldosterone-analog) subcutaneously to accelerate atrial remodeling. RAP+DOCA resulted in increased AF stability with earlier onset of sustained AF and accelerated anatomical atrial remodeling with more pronounced LA dilatation. This novel porcine model can serve to characterize effects of maladaptive stimuli or protective interventions specifically during early AF.

Precursor proadrenomedullin influences cardiomyocyte survival and local inflammation related to myocardial infarction

Significance Myocardial infarction (MI) is one of the leading causes of death worldwide and is characterized by apoptosis and inflammation. While increased adrenomedullin (ADM) levels after MI are associated with disease severity, ADM infusion leads to antiapoptotic effects, suggesting a self-protective mechanism. ADM is cleaved from a full‐length precursor protein (ProADM), a putatively inactive prohormone. Our data show that ProADM is biologically active by reducing apoptosis to a similar extent as ADM. In contrast to ADM, ProADM has proinflammatory effects on cardiac fibroblasts but antiinflammatory effects on activated leukocytes. We assume that ProADM induces local inflammation but attenuates exaggerated inflammation. Our data suggest that both proteins are beneficial during MI by regulating inflammation and reducing apoptosis of cardiomyocytes. Increased adrenomedullin (ADM) levels are associated with various cardiac diseases such as myocardial infarction (MI). ADM is cleaved off from the full-length precursor protein proadrenomedullin (ProADM) during its posttranslational processing. To date, no biological effect of ProADM is reported, while ADM infusion leads to antiapoptotic effects and improved cardiac function. Using an MI mouse model, we found an induction of ProADM gene as well as protein expression during the early phase of MI. This was accompanied by apoptosis and increasing inflammation, which substantially influence the post-MI remodeling processes. Simulating ischemia in vitro, we demonstrate that ProADM expression was increased in cardiomyocytes and cardiac fibroblasts. Subsequently, we treated ischemic cardiomyocytes with either ProADM or ADM and found that both proteins increased survival. This effect was diminishable by blocking the ADM1 receptor. To investigate whether ProADM and ADM play a role in the regulation of cardiac inflammation, we analyzed chemokine expression after treatment of cells with both proteins. While ProADM induced an expression of proinflammatory cytokines, thus promoting inflammation, ADM reduced chemokine expression. On leukocytes, both proteins repressed chemokine expression, revealing antiinflammatory effects. However, ProADM but not ADM dampened concurrent activation of leukocytes. Our data show that the full-length precursor ProADM is biologically active by reducing apoptosis to a similar extent as ADM. We further assume that ProADM induces local inflammation in affected cardiac tissue but attenuates exaggerated inflammation, whereas ADM has low impact. Our data suggest that both proteins are beneficial during MI by influencing apoptosis and inflammation.

Distinct Hemodynamic Changes After Interventional Mitral Valve Edge‐to‐Edge Repair in Different Phenotypes of Heart Failure: An Integrated Hemodynamic Analysis

Background Percutaneous mitral valve edge‐to‐edge repair (pMVR) with a MitraClip is beneficial for the clinical symptoms of patients irrespective of the ejection fraction (EF). Nevertheless, the consequences on hemodynamics are poorly understood. Therefore, we used data from noninvasive pressure‐volume loops to investigate the left ventricular (LV) remodeling of patients after pMVR dependent on their baseline EF. Methods and Results In 130 patients with successful pMVR, the end‐diastolic pressure‐volume relationship (EDPVR) and end‐systolic pressure‐volume relationship were estimated noninvasively from echocardiographic data. We compared EDPVR and end‐systolic pressure‐volume relationship at discharge and follow‐up between patients with a reduced EF (<40%) and patients with a mid‐ranged or preserved EF (≥40%). Reduced EF was present in 71 patients (54%). Mean follow‐up duration was 277±117 days. We observed a significant reduction in degree of mitral regurgitation and an improvement in functional status at follow‐up irrespective of baseline EF. In patients with a mid‐ranged or preserved EF, the EDPVR and end‐systolic pressure‐volume relationship were shifted leftwards, suggesting an improvement in LV function. In contrast, in patients with a reduced EF, EDPVR and end‐systolic pressure‐volume relationship remained stable, although comparison with the baseline data indicates a rightward shift of the EDPVR. This indicates that there is no improvement in LV function after pMVR in patients with reduced EF. Conclusions The pMVR is associated with improved clinical symptoms in all patient subgroups. However, it leads to different hemodynamic responses. In patients with mid‐ranged or preserved EF, we found reverse remodeling with reduced LV dilatation and increased contractility. In contrast, in patients with reduced EF, we observed no reverse remodeling and no improvement in LV function.