Cariporide given during resuscitation promotes return of electrically stable and mechanically competent cardiac activity

Cardiac arrest, stony heart, and cardiopulmonary resuscitation: An updated revisit

The post-resuscitation period is recognized as the main predictor of cardiopulmonary resuscitation (CPR) outcomes. The first description of post-resuscitation syndrome and stony heart was published over 50 years ago. Major manifestations may include but are not limited to, persistent precipitating pathology, systemic ischemia/reperfusion response, post-cardiac arrest brain injury, and finally, post-cardiac arrest myocardial dysfunction (PAMD) after successful resuscitation. Why do some patients initially survive successful resuscitation, and others do not? Also, why does the myocardium response vary after resuscitation? These questions have kept scientists busy for several decades since the first successful resuscitation was described. By modifying the conventional modalities of resuscitation together with new promising agents, rescuers will be able to salvage the jeopardized post-resuscitation myocardium and prevent its progression to a dismal, stony heart. Community awareness and staff education are crucial for shortening the resuscitation time and improving short- and long-term outcomes. Awareness of these components before and early after the restoration of circulation will enhance the resuscitation outcomes. This review extensively addresses the underlying pathophysiology, management, and outcomes of post-resuscitation syndrome. The pattern, management, and outcome of PAMD and post-cardiac arrest shock are different based on many factors, including in-hospital cardiac arrest vs out-of-hospital cardiac arrest (OHCA), witnessed vs unwitnessed cardiac arrest, the underlying cause of arrest, the duration, and protocol used for CPR. Although restoring spontaneous circulation is a vital sign, it should not be the end of the game or lone primary outcome; it calls for better understanding and aggressive multi-disciplinary interventions and care. The development of stony heart post-CPR and OHCA remain the main challenges in emergency and critical care medicine.

The Remaining Conundrum of the Role of the Na+/H+ Exchanger Isoform 1 (NHE1) in Cardiac Physiology and Pathology: Can It Be Rectified?

The mammalian Na + /H + exchanger (NHE) is a family of ubiquitous membrane proteins present in humans. Isoform one (NHE1) is present on the plasma membrane and regulates intracellular pH by removal of one intracellular proton in exchange for one extracellular sodium thus functioning as an electroneutral process. Human NHE1 has a 500 amino acid membrane domain plus a C-terminal 315 amino acid, regulatory cytosolic tail. It is regulated through a cytosolic regulatory C-terminal tail which is subject to phosphorylation and is modulated by proteins and lipids. Substantial evidence has implicated NHE1 activity in both myocardial ischemia and reperfusion damage and myocardial remodeling resulting in heart failure. Experimental data show excellent cardioprotection with NHE1 inhibitors although results from clinical results have been mixed. In cardiac surgery patients receiving the NHE1 inhibitor cariporide, subgroups showed beneficial effects of treatment. However, in one trial this was associated with a significantly increased incidence of ischemic strokes. This likely reflected both inappropriate dosing regimens as well as overly high drug doses. We suggest that further progress towards NHE1 inhibition as a treatment for cardiovascular disease is warranted through the development of novel compounds to inhibit NHE1 that are structurally different than those previously used in compromised clinical trials. Some novel pyrazinoyl guanidine inhibitors of NHE1 are already in development and the recent elucidation of the three-dimensional structure of the NHE1 protein and identity of the inhibitor binding site may facilitate development. An alternative approach may also be to control the endogenous regulation of activity of NHE1, which is activated in disease.

Targeted Delivery of Electrical Shocks and Epinephrine, Guided by Ventricular Fibrillation Amplitude Spectral Area, Reduces Electrical and Adrenergic Myocardial Burden, Improving Survival in Swine

Background

We previously reported that resuscitation delivering electrical shocks guided by real‐time ventricular fibrillation amplitude spectral area (AMSA) enabled return of spontaneous circulation (ROSC) with fewer shocks, resulting in less myocardial dysfunction. We now hypothesized that AMSA could also guide delivery of epinephrine, expecting further outcome improvement consequent to less electrical and adrenergic burdens.

Methods and Results

A swine model of ventricular fibrillation was used to compare after 10 minutes of untreated ventricular fibrillation a guidelines‐driven (n=8) resuscitation protocol, delivering shocks every 2 minutes and epinephrine every 4 minutes, with an AMSA‐driven shocks (n=8) protocol, delivering epinephrine every 4 minutes, and with an AMSA‐driven shocks and epinephrine (ADSE; n=8) protocol. For guidelines‐driven, AMSA‐driven shocks, and ADSE protocols, the time to ROSC (mean±SD) was 569±164, 410±111, and 400±80 seconds (P=0.045); the number of shocks (mean±SD) was 5±2, 3±1, and 3±2 (P=0.024) with ADSE fewer than guidelines‐driven (P=0.03); and the doses of epinephrine (median [interquartile range]) were 2.0 (1.3–3.0), 1.0 (1.0–2.8), and 1.0 (0.3–3.0) (P=0.419). The ROSC rate was similar, yet survival after ROSC favored AMSA‐driven protocols (guidelines‐driven, 3/6; AMSA‐driven shocks, 6/6; and ADSE, 7/7; P=0.019 by log‐rank test). Left ventricular function and survival after ROSC correlated inversely with electrical burden (ie, cumulative unsuccessful shocks, J/kg; P=0.020 and P=0.046) and adrenergic burden (ie, total epinephrine doses, mg/kg; P=0.042 and P=0.002).

Conclusions

Despite similar ROSC rates achieved with all 3 protocols, AMSA‐driven shocks and ADSE resulted in less postresuscitation myocardial dysfunction and better survival, attributed to attaining ROSC with less electrical and adrenergic myocardial burdens.

HOE-642 improves the protection of hypothermia on neuronal mitochondria after cardiac arrest in rats

HOE-642 has been shown to provide significant protection in a variety of models of cerebral and myocardial ischemia/reperfusion injury. In this study, we examined the impact of HOE-642, a selective Na⁺/H⁺ exchanger 1 inhibitor, with or without hypothermia on neuronal and neuronal mitochondrial function during resuscitation. Cardiac arrest was induced by 8 min of asphyxia in rats. Five groups were included in this study: sham; normothermia (N); HOE-642 (HOE, 1 mg/kg); hypothermia (Hypo, 33±0.5°C); and HOE-642 plus hypothermia (HOE+Hypo). Survival and neurological deficit scores (NDS) were evaluated after 24 h of resuscitation. ΔΨm, mitochondrial swelling, ROS production, mitochondrial complex I-IV activity, and ultrastructural changes of the hippocampal mitochondria were evaluated. Survival in the HOE+Hypo group (85.7%) was higher than in the N group (42.9%) and HOE group (31.8%), P<0.05. NDS in the Hypo and HOE+Hypo groups were lower than in the N and HOE groups, P<0.05. ΔΨm in the HOE group (2.7±0.9) were higher than in the N (1.3±0.3) and Hypo (1.4±0.4) groups, P<0.05. Mitochondrial swelling in the N group was severe than in the HOE and Hypo groups, P<0.05. The production of ROS in the HOE and HOE+Hypo groups were lower than in the N group, P<0.05. Complex I-IV activity in the HOE+Hypo group was higher than in the other groups. The ultrastructure of mitochondria in the N group was severely damaged. The mitochondria maintained structural integrity in the HOE, Hypo and HOE+Hypo groups. HOE-642 plus hypothermia during resuscitation was beneficial than HOE-642 or hypothermia alone.

Sodium-Hydrogen Exchanger Isoform-1 Inhibition: A Promising Pharmacological Intervention for Resuscitation from Cardiac Arrest

Out-of-hospital sudden cardiac arrest is a major public health problem with an overall survival of less than 5%. Upon cardiac arrest, cessation of coronary blood flow rapidly leads to intense myocardial ischemia and activation of the sarcolemmal Na⁺-H⁺ exchanger isoform-1 (NHE-1). NHE-1 activation drives Na⁺ into cardiomyocytes in exchange for H⁺ with its exchange rate intensified upon reperfusion during the resuscitation effort. Na⁺ accumulates in the cytosol driving Ca²⁺ entry through the Na⁺-Ca²⁺ exchanger, eventually causing cytosolic and mitochondrial Ca²⁺ overload and worsening myocardial injury by compromising mitochondrial bioenergetic function. We have reported clinically relevant myocardial effects elicited by NHE-1 inhibitors given during resuscitation in animal models of ventricular fibrillation (VF). These effects include: (a) preservation of left ventricular distensibility enabling hemodynamically more effective chest compressions, (b) return of cardiac activity with greater electrical stability reducing post-resuscitation episodes of VF, (c) less post-resuscitation myocardial dysfunction, and (d) attenuation of adverse myocardial effects of epinephrine; all contributing to improved survival in animal models. Mechanistically, NHE-1 inhibition reduces adverse effects stemming from Na⁺–driven cytosolic and mitochondrial Ca²⁺ overload. We believe the preclinical work herein discussed provides a persuasive rationale for examining the potential role of NHE-1 inhibitors for cardiac resuscitation in humans.

Exploration of the optimal dose of HOE-642 for the protection of neuronal mitochondrial function after cardiac arrest in rats

INTRODUCTION

It has been demonstrated HOE-642 ameliorates ischemic contracture, prevents post-resuscitation diastolic dysfunction, and favors the earlier return of contractile function. This study is the first report to explore the optimal dose of HOE-642 in protecting the neuronal mitochondrial function after cardiac arrest.

METHODS

Cardiac arrest was induced by 8 min asphyxia in rats. There were Sham (S), Normothermic (NORM), and Hypothermic (HYPO) groups. The NORM or HYPO groups consist of four subgroups: NORM/HYPO + HOE-642 0, 1, 3, and 5 mg/kg. Survival and NDS were evaluated after 24 h of resuscitation. ΔΨm, mitochondrial swelling, ROS production, and mitochondrial complex IIV activity of the hippocampus were detected.

RESULTS

Survival in the HYPO + 1 mg group was the best and significantly higher than in the NORM + 0 mg and NORM + 1 mg groups. NDS in the HYPO + 0 mg, HYPO + 1 mg, and HYPO + 3 mg groups was significantly lower than in the NORM + 0 mg group. ΔΨm in the NORM + 1 mg (n = 5) group was significantly higher than in the NORM + 0 mg (n = 8), NORM + 3 mg (n = 5), and NORM + 5 mg (n = 5) groups. The ROS production in the NORM + 1 mg and NORM + 3 mg groups were significantly lower than in the NORM + 0 mg and NORM + 5 mg groups. Complex I and III activities in the HYPO + 1 mg (n = 5) group were significantly higher than in the HYPO + 3 mg (n = 5), and HYPO + 5 mg (n = 5) groups. Complex II and IV activities in the NORM + 3 mg and HYPO + 3 mg groups were significantly higher than in the NORM + 0 mg, NORM + 1 mg, and HYPO + 0 mg (n = 4)groups.

CONCLUSIONS

HOE-642 1 or 3 mg/kg showed benefits compared to HOE-642 5 mg/kg used when initiating resuscitation. When combined with hypothermia after cardiac arrest, HOE-642 1 or 3 mg/kg improved survival and neurological function compared with hypothermia or HOE-642 alone, however, HOE-642 5 mg/kg plus hypothermia did not.

Real-Time Ventricular Fibrillation Amplitude-Spectral Area Analysis to Guide Timing of Shock Delivery Improves Defibrillation Efficacy During Cardiopulmonary Resuscitation in Swine

Background

The ventricular fibrillation amplitude spectral area (AMSA) predicts whether an electrical shock could terminate ventricular fibrillation and prompt return of spontaneous circulation. We hypothesized that AMSA can guide more precise timing for effective shock delivery during cardiopulmonary resuscitation.

Methods and Results

Three shock delivery protocols were compared in 12 pigs each after electrically induced ventricular fibrillation, with the duration of untreated ventricular fibrillation evenly stratified into 6, 9, and 12 minutes: AMSA‐Driven (AD), guided by an AMSA algorithm; Guidelines‐Driven (GD), according to cardiopulmonary resuscitation guidelines; and Guidelines‐Driven/AMSA‐Enabled (GDAE), as per GD but allowing earlier shocks upon exceeding an AMSA threshold. Shocks delivered using the AD, GD, and GDAE protocols were 21, 40, and 62, with GDAE delivering only 2 AMSA‐enabled shocks. The corresponding 240‐minute survival was 8/12, 6/12, and 2/12 (log‐rank test, P=0.035) with AD exceeding GDAE (P=0.026). The time to first shock (seconds) was (median [Q1–Q3]) 272 (161–356), 124 (124–125), and 125 (124–125) (P<0.001) with AD exceeding GD and GDAE (P<0.05); the average coronary perfusion pressure before first shock (mm Hg) was 16 (9–30), 10 (6–12), and 3 (−1 to 9) (P=0.002) with AD exceeding GDAE (P<0.05); and AMSA preceding the first shock (mV·Hz, mean±SD) was 13.3±2.2, 9.0±1.6, and 8.6±2.0 (P<0.001) with AD exceeding GD and GDAE (P<0.001). The AD protocol delivered fewer unsuccessful shocks (ie, less shock burden) yielding less postresuscitation myocardial dysfunction and higher 240‐minute survival.

Conclusions

The AD protocol improved the time precision for shock delivery, resulting in less shock burden and less postresuscitation myocardial dysfunction, potentially improving survival compared with time‐fixed, guidelines‐driven, shock delivery protocols.

Pathophysiological Trends During Withdrawal of Life Support: Implications for Organ Donation After Circulatory Death

BACKGROUND

Donation after circulatory death (DCD) provides an alternative pathway to deceased organ transplantation. Although clinical DCD lung, liver, and kidney transplantation are well established, transplantation of hearts retrieved from DCD donors has reached clinical translation only recently. Progress has been limited by concern regarding the viability of DCD hearts. The aim of this study was to document the pathophysiological changes that occur in the heart and circulation during withdrawal of life (WLS) support.

METHODS

In a porcine asphyxia model, we characterized the hemodynamic, volumetric, metabolic, biochemical, and endocrine changes after WLS for up to 40 minutes. Times to circulatory arrest and electrical asystole were recorded.

RESULTS

After WLS, there was rapid onset of profound hypoxemia resulting in acute pulmonary hypertension and right ventricular distension. Concurrently, progressive systemic hypotension occurred with a fall in left atrial pressure and little change in left ventricular volume. Mean times to circulatory arrest and electrical asystole were 8 ± 1 and 16 ± 2 minutes, respectively. Hemodynamic changes were accompanied by a rapid fall in pH, and rise in blood lactate, troponin-T, and potassium. Plasma noradrenaline and adrenaline levels rose rapidly with dramatic increases in coronary sinus levels indicative of myocardial release.

CONCLUSIONS

These findings provide insight into the nature and tempo of the damaging events that occur in the heart and in particular the right ventricle during WLS, and give an indication of the limited timeframe for the implementation of potential postmortem interventions that could be applied to improve organ viability.

Adverse postresuscitation myocardial effects elicited by buffer-induced alkalemia ameliorated by NHE-1 inhibition in a rat model of ventricular fibrillation

Major myocardial abnormalities occur during cardiac arrest and resuscitation including intracellular acidosis-partly caused by CO₂ accumulation-and activation of the Na⁺-H⁺ exchanger isoform-1 (NHE-1). We hypothesized that a favorable interaction may result from NHE-1 inhibition during cardiac resuscitation followed by administration of a CO₂-consuming buffer upon return of spontaneous circulation (ROSC). Ventricular fibrillation was electrically induced in 24 male rats and left untreated for 8 min followed by defibrillation after 8 min of cardiopulmonary resuscitation (CPR). Rats were randomized 1:1:1 to the NHE-1 inhibitor zoniporide or vehicle during CPR and disodium carbonate/sodium bicarbonate buffer or normal saline (30 ml/kg) after ROSC. Survival at 240 min declined from 100% with Zoniporide/Saline to 50% with Zoniporide/Buffer and 25% with Vehicle/Buffer (P = 0.004), explained by worsening postresuscitation myocardial dysfunction. Marked alkalemia occurred after buffer administration along with lactatemia that was maximal after Vehicle/Buffer, attenuated by Zoniporide/Buffer, and minimal with Zoniporide/Saline [13.3 ± 4.8 (SD), 9.2 ± 4.6, and 2.7 ± 1.0 mmol/l; P ≤ 0.001]. We attributed the intense postresuscitation lactatemia to enhanced glycolysis consequent to severe buffer-induced alkalemia transmitted intracellularly by an active NHE-1. We attributed the worsened postresuscitation myocardial dysfunction also to severe alkalemia intensifying Na⁺ entry via NHE-1 with consequent Ca²⁺ overload injuring mitochondria, evidenced by increased plasma cytochrome c Both buffer-induced effects were ameliorated by zoniporide. Accordingly, buffer-induced alkalemia after ROSC worsened myocardial function and survival, likely through enhancing NHE-1 activity. Zoniporide attenuated these effects and uncovered a complex postresuscitation acid-base physiology whereby blood pH drives NHE-1 activity and compromises mitochondrial function and integrity along with myocardial function and survival.

Myocardial Dysfunction and Shock after Cardiac Arrest

Postarrest myocardial dysfunction includes the development of low cardiac output or ventricular systolic or diastolic dysfunction after cardiac arrest. Impaired left ventricular systolic function is reported in nearly two-thirds of patients resuscitated after cardiac arrest. Hypotension and shock requiring vasopressor support are similarly common after cardiac arrest. Whereas shock requiring vasopressor support is consistently associated with an adverse outcome after cardiac arrest, the association between myocardial dysfunction and outcomes is less clear. Myocardial dysfunction and shock after cardiac arrest develop as the result of preexisting cardiac pathology with multiple superimposed insults from resuscitation. The pathophysiology involves cardiovascular ischemia/reperfusion injury and cardiovascular toxicity from excessive levels of inflammatory cytokine activation and catecholamines, among other contributing factors. Similar mechanisms occur in myocardial dysfunction after cardiopulmonary bypass, in sepsis, and in stress-induced cardiomyopathy. Hemodynamic stabilization after resuscitation from cardiac arrest involves restoration of preload, vasopressors to support arterial pressure, and inotropic support if needed to reverse the effects of myocardial dysfunction and improve systemic perfusion. Further research is needed to define the role of postarrest myocardial dysfunction on cardiac arrest outcomes and identify therapeutic strategies.

Novelties in pharmacological management of cardiopulmonary resuscitation

PURPOSE OF REVIEW

The ultimate goal of cardiopulmonary resuscitation is long-term neurologically intact survival. Despite numerous well-designed studies, the medications currently used in advanced cardiac life support have not demonstrated success in this regard. This review describes the novel therapeutics under investigation to improve functional recovery and survival.

RECENT FINDINGS

Whereas current medications focus on achieving return of spontaneous circulation and improved hemodynamics, novel therapies currently in development are focused on improving cellular survival and function by preventing metabolic derangement, protecting mitochondria, and preventing cell death caused by cardiac arrest. Improved cardiac and neurologic function and survival benefits have been observed using animal models of cardiopulmonary arrest.

SUMMARY

Although substantial data have shown benefits using robust animal models, further human studies are necessary to investigate the potential long-term benefits of these therapies.

Dantrolene improves survival after ventricular fibrillation by mitigating impaired calcium handling in animal models

BACKGROUND

Resistant ventricular fibrillation, refibrillation. and diminished myocardial contractility are important factors leading to poor survival after cardiac arrest. We hypothesized that dantrolene improves survival after ventricular fibrillation (VF) by rectifying the calcium dysregulation caused by VF.

METHODS AND RESULTS

VF was induced in 26 Yorkshire pigs for 4 minutes. Cardiopulmonary resuscitation was then commenced for 3 minutes, and dantrolene or isotonic saline was infused at the onset of cardiopulmonary resuscitation. Animals were defibrillated and observed for 30 minutes. To study the effect of VF on calcium handling and its modulation by dantrolene, hearts from 14 New Zealand rabbits were Langendorff-perfused. The inducibility of VF after dantrolene administration was documented. Optical mapping was performed to evaluate diastolic spontaneous calcium elevations as a measure of cytosolic calcium leak. The sustained return of spontaneous circulation (systolic blood pressure ≥60 mm Hg) was achieved in 85% of the dantrolene group in comparison with 39% of controls (P=0.02). return of spontaneous circulation was achieved earlier in dantrolene-treated pigs after successful defibrillation (21 ± 6 s versus 181 ± 57 s in controls, P=0.005). The median number of refibrillation episodes was lower in the dantrolene group (0 versus 1, P=0.04). In isolated rabbit hearts, the successful induction of VF was achieved in 83% of attempts in controls versus 41% in dantrolene-treated hearts (P=0.007). VF caused diastolic calcium leaks in the form of spontaneous calcium elevations. Administration of 20 μmol/L dantrolene significantly decreased spontaneous calcium elevation amplitude versus controls. (0.024 ± 0.013 versus 0.12 ± 0.02 arbitrary unit [200-ms cycle length], P=0.001).

CONCLUSIONS

Dantrolene infusion during cardiopulmonary resuscitation facilitates successful defibrillation, improves hemodynamics postdefibrillation, decreases refibrillation, and thus improves survival after cardiac arrest. The effects are mediated through normalizing VF-induced dysfunctional calcium cycling.

NHE-1: still a viable therapeutic target

The concept of NaH exchange (NHE) involvement in cardiac pathology has been espoused for decades and supported by a plethora of experimental studies demonstrating salutary effects of NHE inhibition in protecting the myocardium against ischemic and reperfusion injury as well as attenuating myocardial remodelling and heart failure. NHE is actually a family of sodium and proton transporting proteins of which 10 isoforms have been identified. Myocardial NHE is represented primarily by the ubiquitous NHE-1 subtype which is expressed in most tissues. The robust positive results seen with NHE-1 inhibitors in experimental studies have led to relatively rapid development of these pharmacological agents for clinical assessment especially as potential cardioprotective therapies. Yet clinical studies have revealed, at best, inconsistent results as evidenced by poor efficacy and serious side effects, the latter revealed with the use of the NHE-1 inhibitor cariporide in high-risk patients undergoing coronary artery bypass grafting and evidenced by an increased incidence of cerebrovascular events of thromboembolic origin. The lack of success in clinical trials coupled with potential for toxicity has had a negative impact on development of cardiac therapeutic agents which have been developed based on the concept of NHE-1 inhibition. Whether this response is justified is open for discussion although a close scrutiny of clinical trial outcomes suggests that it may not be and that NHE-1 inhibition, if applied appropriately continues to represent an effective, if not the most effective approach for myocardial salvage following ischemic insult. Moreover, in addition to its cardioprotective effects, emerging evidence further suggests that NHE-1 inhibition is an effective strategy to minimize myocardial remodelling as well as a potentially effective strategy to improve efficacy of resuscitation following cardiac arrest. Thus, NHE-1 inhibition continues to represent a potentially highly effective therapeutic approach for the treatment of heart disease. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".

Dietary Omega-3 Polyunsaturated Fatty Acids Suppress NHE-1 Upregulation in a Rabbit Model of Volume- and Pressure-Overload

BACKGROUND

Increased consumption of omega-3 polyunsaturated fatty acids (ω3-PUFAs) from fish oil (FO) may have cardioprotective effects during ischemia/reperfusion, hypertrophy, and heart failure (HF). The cardiac Na(+)/H(+)-exchanger (NHE-1) is a key mediator for these detrimental cardiac conditions. Consequently, chronic NHE-1 inhibition appears to be a promising pharmacological tool for prevention and treatment. Acute application of the FO ω3-PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibit the NHE-1 in isolated cardiomyocytes. We studied the effects of a diet enriched with ω3-PUFAs on the NHE-1 activity in healthy rabbits and in a rabbit model of HF induced by volume- and pressure-overload.

METHODS

Rabbits were allocated to four groups. The first two groups consisted of healthy rabbits, which were fed either a diet containing 1.25% (w/w) FO (ω3-PUFAs), or 1.25% high-oleic sunflower oil (ω9-MUFAs) as control. The second two groups were also allocated to either a diet containing ω3-PUFAs or ω9-MUFAs, but underwent volume- and pressure-overload to induce HF. Ventricular myocytes were isolated by enzymatic dissociation and used for intracellular pH (pH(i)) and patch-clamp measurements. NHE-1 activity was measured in HEPES-buffered conditions as recovery rate from acidosis due to ammonium prepulses.

RESULTS

In healthy rabbits, NHE-1 activity in ω9-MUFAs and ω3-PUFAs myocytes was not significantly different. Volume- and pressure-overload in rabbits increased the NHE-1 activity in ω9-MUFAs myocytes, but not in ω3-PUFAs myocytes, resulting in a significantly lower NHE-1 activity in myocytes of ω3-PUFA fed HF rabbits. The susceptibility to induced delayed afterdepolarizations (DADs), a cellular mechanism of arrhythmias, was lower in myocytes of HF animals fed ω3-PUFAs compared to myocytes of HF animals fed ω9-MUFAs. In our rabbit HF model, the degree of hypertrophy was similar in the ω3-PUFAs group compared to the ω9-MUFAs group.

CONCLUSION

Dietary ω3-PUFAs from FO suppress upregulation of the NHE-1 activity and lower the incidence of DADs in our rabbit model of volume- and pressure-overload.

Management of postcardiac arrest myocardial dysfunction

PURPOSE OF REVIEW

Recent recognition of the importance of postresuscitation care has stimulated interest and new reports concerning therapies for postcardiac arrest myocardial dysfunction. Such cardiac dysfunction after successful resuscitation can be severe and even lethal; however, it is also transient emphasizing the importance of early supportive therapies.

RECENT FINDINGS

The most important strategies for dealing with postresuscitation myocardial dysfunction include a community-formalized effort by individual communities to shorten the time from arrest to restoration of spontaneous circulation, use of therapeutic hypothermia for myocardial preservation, not just cerebral, and early coronary angiography and intervention for all survivors with a high suspicion of a cardiac cause for their arrest. Exciting specific therapies targeted for one or another of the ischemia/reperfusion myocardial injuries associated with cardiac arrest include manipulation of the nitric oxide production in the myocardium, treatment of myocardial microcirculatory dysfunction post resuscitation, inhibition of Na+/H+ exchange, and treatment of calcium flux abnormalities.

SUMMARY

Every community should be striving to provide more timely restoration of pulse and circulation, whereas every medical center receiving patients resuscitated from out-of-hospital cardiac arrest should be providing therapeutic hypothermia for both central nervous system and myocardial preservation. The ability and commitment to provide '24/7' early coronary angiography and percutaneous intervention for all resuscitated victims of sudden cardiac death with a likely cardiac cause for their arrest is also key.

AVE4454B--a novel sodium-hydrogen exchanger isoform-1 inhibitor--compared less effective than cariporide for resuscitation from cardiac arrest

We compared the efficacy of the novel sodium-hydrogen exchanger (NHE-1) inhibitor AVE4454B with cariporide for resuscitation from ventricular fibrillation (VF) assessing the effects on left ventricular myocardial distensibility during chest compression, myocardial function after the return of spontaneous circulation, and survival. Three groups of 10 rats each were subjected to 10 min of untreated VF and resuscitation attempted by providing chest compression for up to 8 min with the depth of compression adjusted to attain an aortic diastolic pressure between 26 and 28 mmHg (to secure a coronary perfusion pressure above 20 mmHg) followed by electrical shocks. Rats received AVE4454B (1 mg/kg), cariporide (1 mg/kg), or vehicle control immediately before chest compression. We observed that NHE-1 inhibition (NHEI) preserved left ventricular myocardial distensibility during chest compression evidenced by less depth of compression required to attain the target aortic diastolic pressure corresponding to (mean ± standard deviation) 14.1 ± 1.1 mm in the AVE4454B group (P < 0.001 versus control), 15.0 ± 1.4 mm in the cariporide group (P < 0.01 versus control), and 17.0 ± 1.2 mm in controls. When the depth of compression was related to the coronary perfusion pressure generated-an index of left ventricular distensibility-only the cariporide group attained statistical significance. Postresuscitation, both compounds ameliorated myocardial dysfunction evidenced by lesser reductions in mean aortic pressure and the maximal rate of left ventricular pressure increase as well as earlier normalization of left ventricular end-diastolic pressure increases. This effect was associated with improved survival corresponding to 55% in the AVE4454B group (not significant) and 70% in the cariporide group (P < 0.01 versus control by Gehan-Breslow analysis) at 240 min postresuscitation. An inverse correlation was found between plasma cytochrome c and indices of left ventricular function at 240 min postresuscitation suggesting that NHEI exerts beneficial effects in part by attenuating mitochondrial injury. We conclude that cariporide is more effective than AVE4454B for resuscitation from cardiac arrest given its more prominent effect on preserving left ventricular myocardial distensibility and promoting survival.