Mild hypothermia attenuates ischaemia/reperfusion injury: insights from serial non-invasive pressure-volume loops

The protective effects of gallic acid and SGK1 inhibitor on cardiac damage and genes involved in Ca2+ homeostasis in an isolated heart model of ischemia/reperfusion injury in rat

Serum and glucocorticoid-induced kinase 1 (SGK1) is an enzyme that may play a vital role in myocardial ischemia/reperfusion (I/R) injury. This enzyme may affect sarcoplasmic reticulum Ca2+ ATPase (SERCA2), ryanodine receptor (RyR2) and sodium/calcium exchanger (NCX1) during myocardial ischemia/reperfusion injury. The objective of this investigation was to analyze the effects of the combination of GSK650394 (SGK1 inhibitor) and gallic acid on the calcium ions regulation, inflammation, and cardiac dysfunction resulting from ischemia/reperfusion (I/R) injury in the heart. Sixty male Wistar rats were randomly divided into six groups, pretreated with gallic acid or vehicle for 10 days. Then the heart was isolated and exposed to I/R. In the SGK1 inhibitor groups, GSK650394 was infused 5 min before ischemia induction. After that, Ca2+ homeostasis, inflammatory factors, cardiac function, antioxidant activity, and myocardial damage were evaluated. The findings suggested that the use of two drugs in combination therapy produced more significant improvements in left ventricular end diastolic pressure, left ventricular systolic pressure, RR-interval, ST-elevation, inflammation factors, and antioxidant enzymes activity as compared to the use of each drug. Despite this, there was a significant decrease observed in heart marker enzymes (including lactate dehydrogenase (LDH), troponin-I (cTn-I), creatine kinase-MB (CK-MB) and creatine phosphokinase (CPK) when compared to the ischemic group. Additionally, the expression of RyR2, NCX1, and SERCA2 genes showed a noteworthy increase as compared to the ischemic group. The findings of this study propose that using both of these agents on myocardial I/R injury could have superior advantages compared to using only one of them.

Noninvasive Pressure-Volume Loops Predict Major Adverse Cardiac Events in Heart Failure With Reduced Ejection Fraction

Background

Heart failure with reduced ejection fraction (HFrEF) is characterized by ventricular remodeling and impaired myocardial energetics. Left ventricular pressure-volume (PV) loop analysis can be performed noninvasively using cardiovascular magnetic resonance (CMR) imaging to assess cardiac thermodynamic efficiency.

Objectives

The aim of the study was to investigate whether noninvasive PV loop parameters, derived from CMR, could predict major adverse cardiac events (MACE) in HFrEF patients.

Methods

PV loop parameters (stroke work, ventricular efficiency, external power, contractility, and energy per ejected volume) were computed from CMR cine images and brachial blood pressure. The primary end point was MACE (cardiovascular death, heart failure (HF) hospitalization, myocardial infarction, revascularization, ventricular tachycardia/fibrillation, heart transplantation, or left ventricular assist device implantation within 5 years). Associations between PV loop parameters and MACE were evaluated using multivariable Cox regression.

Results

One hundred and sixty-four HFrEF patients (left ventricular ejection fraction ≤40%, age 63 [IQR: 55-70] years, 79% male) who underwent clinical CMR examination between 2004 and 2014 were included. Eighty-eight patients (54%) experienced at least one MACE after an average of 2.8 years. Unadjusted models demonstrated a significant association between MACE and all PV loop parameters (P < 0.05 for all), HF etiology (P < 0.001), left ventricular ejection fraction (P = 0.003), global longitudinal strain (P < 0.001), and N-terminal prohormone of brain natriuretic peptide level (P = 0.001). In the multivariable Cox regression analysis adjusted for age, sex, hypertension, diabetes, and HF etiology, ventricular efficiency was associated with MACE (HR: 1.04 (95% CI: 1.01-1.08) per-% decrease, P = 0.01).

Conclusions

Ventricular efficiency, derived from noninvasive PV loop analysis from standard CMR scans, is associated with MACE in patients with HFrEF.

Contractility, ventriculoarterial coupling, and stroke work after acute myocardial infarction using CMR-derived pressure-volume loop data

BACKGROUND

Noninvasive left ventricular (LV) pressure-volume (PV) loops derived by cardiac magnetic resonance (CMR) have recently been shown to enable characterization of cardiac hemodynamics. Thus, such PV loops could potentially provide additional diagnostic information such as contractility, arterial elastance (Ea ) and stroke work (SW) currently not available in clinical routine. This study sought to investigate to what extent PV-loop variables derived with a novel noninvasive method can provide incremental physiological information over cardiac dimensions and blood pressure in patients with acute myocardial infarction (MI).

METHODS

A total of 100 patients with acute MI and 75 controls were included in the study. All patients underwent CMR 2-6 days after MI including assessment of myocardium at risk (MaR) and infarct size (IS). Noninvasive PV loops were generated from CMR derived LV volumes and brachial blood pressure measurements. The following variables were quantified: Maximal elastance (Emax ) reflecting contractility, Ea , ventriculoarterial coupling (Ea /Emax ), SW, potential energy, external power, energy per ejected volume, and efficiency.

RESULTS

All PV-loop variables were significantly different in MI patients compared to healthy volunteers, including contractility (Emax : 1.34 ± 0.48 versus 1.50 ± 0.41 mmHg/mL, p = .024), ventriculoarterial coupling (Ea /Emax : 1.27 ± 0.61 versus 0.73 ± 0.17, p < .001) and SW (0.96 ± 0.32 versus 1.38 ± 0.32 J, p < .001). These variables correlated to both MaR and IS (Emax : r2  = 0.25 and r2  = 0.29; Ea /Emax : r2  = 0.36 and r2  = 0.41; SW: r2  = 0.21 and r2  = 0.25).

CONCLUSIONS

Noninvasive PV-loops provide physiological information beyond conventional diagnostic variables, such as ejection fraction, early after MI, including measures of contractility, ventriculoarterial coupling, and SW.

Non-invasive left ventricular pressure-volume loops from cardiovascular magnetic resonance imaging and brachial blood pressure: validation using pressure catheter measurements

Aims

Left ventricular (LV) pressure-volume (PV) loops provide gold-standard physiological information but require invasive measurements of ventricular intracavity pressure, limiting clinical and research applications. A non-invasive method for the computation of PV loops from magnetic resonance imaging and brachial cuff blood pressure has recently been proposed. Here we evaluated the fidelity of the non-invasive PV algorithm against invasive LV pressures in humans.

Methods and results

Four heart failure patients with EF < 35% and LV dyssynchrony underwent cardiovascular magnetic resonance (CMR) imaging and subsequent LV catheterization with sequential administration of two different intravenous metabolic substrate infusions (insulin/dextrose and lipid emulsion), producing eight datasets at different haemodynamic states. Pressure-volume loops were computed from CMR volumes combined with (i) a time-varying elastance function scaled to brachial blood pressure and temporally stretched to match volume data, or (ii) invasive pressures averaged from 19 to 30 sampled beats. Method comparison was conducted using linear regression and Bland-Altman analysis. Non-invasively derived PV loop parameters demonstrated high correlation and low bias when compared to invasive data for stroke work (R2 = 0.96, P < 0.0001, bias 4.6%), potential energy (R2 = 0.83, P = 0.001, bias 1.5%), end-systolic pressure-volume relationship (R2 = 0.89, P = 0.0004, bias 5.8%), ventricular efficiency (R2 = 0.98, P < 0.0001, bias 0.8%), arterial elastance (R2 = 0.88, P = 0.0006, bias -8.0%), mean external power (R2 = 0.92, P = 0.0002, bias 4.4%), and energy per ejected volume (R2 = 0.89, P = 0.0001, bias 3.7%). Variations in estimated end-diastolic pressure did not significantly affect results (P > 0.05 for all). Intraobserver analysis after one year demonstrated 0.9-3.4% bias for LV volumetry and 0.2-5.4% for PV loop-derived parameters.

Conclusion

Pressure-volume loops can be precisely and accurately computed from CMR imaging and brachial cuff blood pressure in humans.

Hypothermic neuroprotection by targeted cold autologous blood transfusion in a non-human primate stroke model

Over decades, nearly all attempts to translate the benefits of therapeutic hypothermia in stroke models of lower-order species to stroke patients have failed. Potentially overlooked reasons may be biological gaps between different species and the mismatched initiation of therapeutic hypothermia in translational studies. Here, we introduce a novel strategy of selective therapeutic hypothermia in a non-human primate ischemia-reperfusion model, in which autologous blood was cooled ex vivo and the cool blood transfusion was administered at the middle cerebral artery just after the onset of reperfusion. Cold autologous blood cooled the targeted brain rapidly to below 34 °C while the rectal temperature remained around 36 °C with the assistance of a heat blanket during a 2-h hypothermic process. Therapeutic hypothermia or extracorporeal-circulation related complications were not observed. Cold autologous blood treatment reduced infarct sizes, preserved white matter integrity, and improved functional outcomes. Together, our results suggest that therapeutic hypothermia, induced by cold autologous blood transfusion, was achieved in a feasible, swift, and safe way in a non-human primate model of stroke. More importantly, this novel hypothermic approach conferred neuroprotection in a clinically relevant model of ischemic stroke due to reduced brain damage and improved neurofunction. This study reveals an underappreciated potential for this novel hypothermic modality for acute ischemic stroke in the era of effective reperfusion.