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/cm vs 531 ± 29 dyn·s/cm, p < 0.05) and (Equation is included in full-text article.)(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-α 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 6h (CME 6h). 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 mm Hg). Mixed venous oxygen saturation at CME 6h 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.