Protecting mitochondrial bioenergetic function during resuscitation from cardiac arrest

Abstract

Successful resuscitation from cardiac arrest requires reestablishment of aerobic metabolism by reperfusion with oxygenated blood of tissues that have been deprived of oxygen for variables periods of time. However, reperfusion concomitantly activates pathogenic mechanisms known as “reperfusion injury.” At the core of reperfusion injury are mitochondria, playing a critical role as effectors and targets of such injury. Mitochondrial injury compromises oxidative phosphorylation and also prompts release of cytochrome c to the cytosol and bloodstream where it correlates with severity of injury. Main drivers of such injury include Ca2+ overload and oxidative stress. Preclinical work shows that limiting myocardial cytosolic Na+ overload at the time of reperfusion attenuates mitochondrial Ca2+ overload and maintains oxidative phosphorylation yielding functional myocardial benefits that include preservation of left ventricular distensibility. Preservation of left ventricular distensibility enables hemodynamically more effective chest compression. Similar myocardial effect have been reported using erythropoietin hypothesized to protect mitochondrial bioenergetic function presumably through activation of pathways similar to those activated during preconditioning. Incorporation of novel and clinical relevant strategies to protect mitochondrial bioenergetic function are expected to attenuate injury at the time of reperfusion and enhance organ viability ultimately improving resuscitation and survival from cardiac arrest.

Figures

Figure 1

Electron microscope photograph of left ventricular mitochondria isolated from a Sprague-Dawley retired breeder rat at the Resuscitation Institute. A: Intermyofibrillar mitochondria orderly organized within the zone demarcated by two Z lines (black arrow heads); the structure where adjacent sarcomeres connect and thin filaments anchor. B and C: Higher magnification of section in mitochondrion selected in panel A showing the outer mitochondrial membrane (arrow heads) and the inner mitochondrial membrane folding inside the mitochondrial matrix.

Figure 2

Schematic rendition of key mitochondrial components involved in ATP synthesis via oxidative phosphorylation. IMM, inner mitochondrial membrane; I, II, III, and IV, respiratory chain complexes; e−, electrons; Q, coenzyme Q; C, cytochrome c; ANT, adenine nucleotide translocator.

Figure 3

Serial measurements of plasma cytochrome c by reverse-phase high performance liquid chromatography in rats successfully resuscitated after 8 minutes of untreated ventricular fibrillation. Measurements were made until cytochrome c levels had returned to baseline or the rat had died. Gray symbols represent survivors (n = 3); black symbols represent non-survivors (n = 9) (Adapted from Ayoub et al. Crit Care Med 2008;36:S440).

Figure 4

The upper panel shows left ventricular (LV) wall thickening in a control pig (upper frames) but not in a pig treated with cariporide (lower frames). The images were obtained by transesophageal echocardiography at the end of mechanical diastole (baseline, BL) and at the end of “compression diastole” at 2 and 8 minutes of chest compression (CC). The endocardial border was delineated to facilitate visualization. The lower panel shows progressive decreases in the coronary perfusion pressure (CPP) coincident with progressive thickening of the left ventricular wall in pigs that received 0.9 % NaCl (closed symbols, n = 8) but not in pigs that received cariporide (open symbols, n = 8). NaCl or cariporide (drug, 3 mg/kg) was given immediately before starting chest compression. Mean ± SEM. *p < 0.05, †p < 0.001 vs cariporide by one-way ANOVA (Adapted from Ayoub I et al. Circulation 2003;107:1804).

Figure 5

Isolated perfused rat heart model of VF and simulated resuscitation. Upper horizontal bars represent perfusate flow, VF, and duration of cariporide or NaCl infusion. CVR denotes coronary vascular resistance; LVP, left ventricular end-diastolic pressure during sinus rhythm and “arrest” pressure during VF. Values are mean ± SEM. Closed symbols denote NaCl and open symbols cariporide. Differences in LVP and CVR between treatment groups were significant (p<0.0001 by 2-way ANOVA for treatment effect). *p<0.05, †p<0.01, ‡p<0.001 vs NaCl by 1-way ANOVA (Adapted from Gazmuri et al. Circulation 2001;104:234).

Figure 6

Left ventricular end-diastolic pressure (LVEDP)–volume (LVEDV) curves. PR denotes post-resuscitation 10 and 30 minutes. Measurements made in hearts from Figure 3 (Adapted from Gazmuri et al. Circulation 2001;104:234).

Figure 7

Cardiac index and organ blood flow as a function of depth of compression in rats during VF and closed-chest resuscitation. Rats were randomized to receive a bolus of cariporide (open symbols) or vehicle control (closed symbols) at the start of chest compression. The first symbol represents data from series 1 and the second symbol data from series2. For paired organs, triangles denote right and squares left. Values are mean ± SEM; *p<0.05 vs 0.9% NaCl by one-way ANOVA in series 2;†p<0.01 vs series 1 within each treatment group by one-way ANOVA (Adapted from Kolarova et al. Am J Physiol Heart Circ Physiol 2005;288:H2904).

Figure 8

Baseline and post-resuscitation left ventricular and hemodynamic function in pigs randomized to receive cariporide (open symbols) or 0.9% NaCl (closed symbols). Numbers in brackets indicate sample size. Values are mean±SEM. *p †p < 0.001 vs. 0.9% NaCl analyzed by one-way ANOVA (Adapted from Ayoub I et al. Resuscitation 2009;81:106).

Figure 9

Myocardial measurements in pigs randomly assigned to receive 3 mg/kg of zoniporide (black bars) or 0.9% NaCl (gray bars) after 8 minutes of untreated VF before starting extracorporeal circulation (ECC). Measurements were obtained at baseline (BL), during VF at ECC 4 and 8 minutes, and at 60 minutes post-resuscitation (PR). Each group had 8 pigs at baseline and ECC and 6 pigs in the zoniporide group and 5 in the NaCl group at PR. Mean ± SEM (Adapted from Ayoub et al. Crit Care Med 2007;35:2329).

Figure 10

Myocardial lactate measurements in experiments described in Figure 9. Numbers in brackets indicate when sample size decreased from the initial 8 or preceding ones. Insert shows the relationship between lactate and pCr/Cr ratio at ECC 8 minutes. The regression line represents an exponential decay function (R2 = 0.63, p<0.001). Mean ± SEM; *P<0.05, ‡P<0.001 vs NaCl by Student’s t-test (Adapted from Ayoub et al. Crit Care Med 2007;35:2329).

Figure 11

Ratio between coronary perfusion pressure and depth of compression (CPP/Depth) during closed-chest resuscitation in rats treated with rhEPO at baseline (rhEPOBL-15-min, n = 10; shaded symbols), during VF before starting chest compression (rhEPOVF 10-min, n = 10; closed symbols), or with 0.9% NaCl (control, n = 10; open symbols). Numbers of rats remaining in VF and therefore receiving chest compression are indicated in brackets. Mean ± SEM. * p < 0.05 vs control by Dunnett’s multicomparison method (Adapted from Singh D et al. Am J Ther 2007;14:361).

Figure 12

Mean aortic pressure after return of spontaneous circulation in rats treated with rhEPO as described in Figure 11 and the text. BL, baseline. Mean ± SEM. *P<0.05 vs control by Dunnett’s multicomparison method (Adapted from Singh D et al. Am J Ther 2007;14:361).

Figure 13

Resuscitation and survival outcomes in patients who received erythropoietin (black bars, n = 24) compared with concurrent controls (hatched bars, n = 30) and with matched controls (gray bars, n = 48). ROSC, return of spontaneous circulation; ICU, intensive care unit. Numbers inside bars denote patients for each outcome with the bar representing the percentage of the initial cohort. P-values were calculated by Chi-square test for each outcome adjusted by covariates with known predictive value (i.e., age, male sex, witnessed arrest, time from call to start CPR, pulseless electrical activity, asystole, and bystander CPR) and are shown above bars (Adapted from Grmec S et al. Resuscitation 2009;80:631).

Figure 14

End-tidal PCO2 (PETCO2) during cardiopulmonary resuscitation in patients who received erythropoietin (black bars, n = 24) compared with concurrent controls (hatched bars, n = 30) and with matched controls (gray bars, n = 48). Numbers inside bars denote patients remaining in cardiac arrest and receiving CPR. Data are presented as mean values with one standard deviation. P-values were calculated by unpaired t-test or by Mann-Whitney rank sum test for each time period and shown above bars (Adapted from Grmec S et al. Resuscitation 2009;80:631).