Short-acting beta-adrenergic antagonist esmolol given at reperfusion improves survival after prolonged ventricular fibrillation

The first case series analysis on efficacy of esmolol injection for in-hospital cardiac arrest patients with refractory shockable rhythms in China

Background: This study assessed the effects of esmolol injection in patients with in-hospital cardiac arrest (IHCA) with refractory ventricular fibrillation (VF)/pulseless ventricular tachycardia (pVT).

Methods: From January 2018 to December 2021, 29 patients with IHCA with refractory shockable rhythm were retrospectively reviewed. Esmolol was administered after advanced cardiovascular life support (ACLS)-directed procedures, and outcomes were assessed.

Results: Among the 29 cases, the rates of sustained return of spontaneous circulation (ROSC), 24-h ROSC, and 72-h ROSC were 79%, 62%, and 59%, respectively. Of those patients, 59% ultimately survived to discharge. Four patients with cardiac insufficiency died. The duration from CA to esmolol infusion was significantly shorter for patients in the survival group (SG) than for patients in the dead group (DG) (12 min, IQR: 8.5–19.5 vs. 23.5 min, IQR: 14.4–27 min; p = 0.013). Of those patients, 76% (22 of 29) started esmolol administration after the second dose of amiodarone. No significant difference was observed in the survival rate between this group and groups administered an esmolol bolus simultaneously or before the second dose of amiodarone (43% vs. 64%, p = 0.403). Of those patients, 31% (9 of 29) were administered an esmolol bolus for defibrillation attempts ≤ 5, while the remaining 69% of patients received an esmolol injection after the fifth defibrillation attempt. No significant differences were observed in the rates of ≥ 24-h ROSC (67% vs. 60%, p = 0.73), ≥ 72-h ROSC (67% vs. 55%, p = 0.56), and survival to hospital discharge (67% vs. 55%, p = 0.56) between the groups administered an esmolol bolus for defibrillation attempts ≤ 5 and defibrillation attempts > 5.

Conclusion: IHCA patients with refractory shockable rhythms receiving esmolol bolus exhibited a high chance of sustained ROSC and survival to hospital discharge. Patients with end-stage heart failure tended to have attenuated benefits from beta-blockers. Further large-scale, prospective studies are necessary to determine the effects of esmolol in patients with IHCA with refractory shockable rhythms.

Feasibility of prehospital esmolol for refractory ventricular fibrillation

Background

Esmolol may increase survival for patients with refractory ventricular fibrillation (RVF); however, information related to esmolol use in the prehospital environment is limited. We aimed to assess the feasibility of prehospital bolus dose esmolol for patients with RVF treated by a high‐volume, ground‐based emergency medical services (EMS) agency.

Methods

 Esmolol (0.5 mg/kg single bolus) was added to the RVF protocol on December 10, 2018. Feasibility was defined as esmolol administration in >75% of RVF cases. Secondarily, we compared the proportion of patients with prehospital return of spontaneous circulation (ROSC), 24‐hour survival, and survival to hospital discharge during the intervention period (December 10, 2018–June 10, 2020) to a historical control period (June 10, 2017–December 9, 2018) using chi‐square tests.

Results

Before the protocol change, 63 patients with RVF were identified. After esmolol was added, 70 patients with RVF were identified and 61 (87%) received esmolol. Prehospital ROSC was higher in the esmolol group compared to the historical control group, though statistical significance was not reached (38% versus 24%, P = 0.09). Overall, few patients survived to 24 hours (esmolol n = 15, pre‐esmolol n = 16) and fewer survived to hospital discharge (esmolol n = 5, pre‐esmolol n = 5), precluding stable statistical comparisons.

Conclusion

Collectively, these findings suggest that EMS clinicians are able to accurately identify RVF and administer esmolol in the prehospital setting and that ROSC may be increased. Further large‐scale studies are needed to determine the effect of prehospital esmolol for RVF as it relates to neurologically intact hospital discharge.

Current and investigational therapies for the treatment of refractory ventricular fibrillation

DISCLAIMER

In an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

Esmolol, dual sequential defibrillation, vector change defibrillation, and left stellate ganglion block are presented and reviewed for the treatment of refractory ventricular fibrillation.

SUMMARY

Although no formal definition has been established for refractory ventricular fibrillation, the literature describes it as a pulseless ventricular arrhythmia that persists despite 3 standard defibrillation attempts, administration of amiodarone 300 mg intravenously, and provision of three 1-mg intravenous doses of epinephrine. Evolving literature surrounding resuscitation in this particular subset of cardiac arrest challenges the efficacy of traditional therapies, such as epinephrine, and suggests that other treatment modalities may improve outcomes. Case reports, case series, and small retrospective studies have pointed to benefit when utilizing a variety of therapies, namely, esmolol, dual sequential defibrillation, vector change defibrillation, or left stellate ganglion block, in patients with refractory ventricular fibrillation arrest.

CONCLUSION

A mounting, although limited, body of evidence suggests that esmolol, dual sequential defibrillation, vector change defibrillation, or left stellate ganglion block may be effective at terminating refractory ventricular fibrillation and improving patient outcomes. Further evidence is required before these therapies can be adopted as standard practice; however, as key members of the code response team, it is imperative for pharmacists to be familiar with the supporting evidence, safety considerations, and logistical challenges of utilizing these treatments during arrest.

Beta-Adrenergic Blockade in Critical Illness

Catecholamine upregulation is a core pathophysiological feature in critical illness. Sustained catecholamine β-adrenergic induction produces adverse effects relevant to critical illness management. β-blockers (βB) have proposed roles in various critically ill disease states, including sepsis, trauma, burns, and cardiac arrest. Mounting evidence suggests βB improve hemodynamic and metabolic parameters culminating in decreased burn healing time, reduced mortality in traumatic brain injury, and improved neurologic outcomes following cardiac arrest. In sepsis, βB appear hemodynamically benign after acute resuscitation and may augment cardiac function. The emergence of ultra-rapid βB provides new territory for βB, and early data suggest significant improvements in mitigating atrial fibrillation in persistently tachycardic septic patients. This review summarizes the evidence regarding the pharmacotherapeutic role of βB on relevant pathophysiology and clinical outcomes in various types of critical illness.

Esmolol during cardiopulmonary resuscitation reduces neurological injury in a porcine model of cardiac arrest

Primary vasopressor efficacy of epinephrine during cardiopulmonary resuscitation (CPR) is due to its α-adrenergic effects. However, epinephrine plays β1-adrenergic actions, which increasing myocardial oxygen consumption may lead to refractory ventricular fibrillation (VF) and poor outcome. Effects of a single dose of esmolol in addition to epinephrine during CPR were investigated in a porcine model of VF with an underlying acute myocardial infarction. VF was ischemically induced in 16 pigs and left untreated for 12 min. During CPR, animals were randomized to receive epinephrine (30 µg/kg) with either esmolol (0.5 mg/kg) or saline (control). Pigs were then observed up to 96 h. Coronary perfusion pressure increased during CPR in the esmolol group compared to control (47 ± 21 vs. 24 ± 10 mmHg at min 5, p < 0.05). In both groups, 7 animals were successfully resuscitated and 4 survived up to 96 h. No significant differences were observed between groups in the total number of defibrillations delivered prior to final resuscitation. Brain histology demonstrated reductions in cortical neuronal degeneration/necrosis (score 0.3 ± 0.5 vs. 1.3 ± 0.5, p < 0.05) and hippocampal microglial activation (6 ± 3 vs. 22 ± 4%, p < 0.01) in the esmolol group compared to control. Lower circulating levels of neuron specific enolase were measured in esmolol animals compared to controls (2[1-3] vs. 21[16-52] ng/mL, p < 0.01). In this preclinical model, β1-blockade during CPR did not facilitate VF termination but provided neuroprotection.

Esmolol in the management of pre-hospital refractory ventricular fibrillation: A systematic review and meta-analysis

BACKGROUND

Esmolol has been proposed as a viable adjunctive therapy for pre-hospital refractory ventricular fibrillation/pulseless ventricular tachycardia (VF/pVT).

OBJECTIVES

We performed a systematic review and meta-analysis to assess the effectiveness of esmolol on pre-hospital refractory VF/pVT, compared with standard of care.

METHODS

MEDLINE, Embase, Scopus, and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched for eligible studies. Two investigators independently extracted relevant data and assessed the methodological quality of each included study using the ROBINS-I tool. The quality of evidence for summary estimates was assessed according to GRADE guidelines. Pooled risk ratios (RRs) with 95% confidence intervals (CIs) for each outcome of interest were calculated.

RESULTS

The search yielded 3253 unique records, of which two studies were found to be in accordance with the research purpose, totaling 66 patients, of whom 33.3% (n = 22) received esmolol. Additional evidence was provided in the paper but was not relevant to the analysis and was therefore not included. Esmolol was likely associated with an increased rate of survival to discharge (RR 2.82, 95% CI 1.01-7.93, p = 0.05) (GRADE: Very low) and survival with favorable neurological outcome (RR 3.44, 95% CI 1.11-10.67, p = 0.03) (GRADE: Very low). Similar results were found for return of spontaneous circulation (ROSC) (RR 2.63, 95% CI 1.37-5.07, p = 0.004) (GRADE: Very low) and survival to intensive care unit (ICU)/hospital admission (RR 2.63, 95% CI 1.37-5.07, p = 0.004) (GRADE: Very low).

CONCLUSION

The effectiveness of esmolol for refractory VF/pVT remains unclear. Trial sequential analysis (TSA) indicates that the evidence is inconclusive and that further trials are required in order to reach a conclusion. Therefore, it is imperative to continue to accumulate evidence in order to obtain a higher level of scientific evidence.

Fast in vivo detection of myocardial norepinephrine levels in the beating porcine heart

The sympathetic nervous system modulates cardiac function by controlling key parameters such as chronotropy and inotropy. Sympathetic control of ventricular function occurs through extrinsic innervation arising from the stellate ganglia and thoracic sympathetic chain. In the healthy heart, sympathetic release of norepinephrine (NE) results in positive modulation of chronotropy, inotropy, and dromotropy, significantly increasing cardiac output. However, in the setting of myocardial infarction or injury, sympathetic activation persists, contributing to heart failure and increasing the risk of arrhythmias, including sudden cardiac death. Methodologies for detection of norepinephrine in cardiac tissue are limited. Present techniques rely on microdialysis for analysis by high-performance liquid chromatography coupled to electrochemical detection (HPLC-ED), radioimmunoassay, or other immunoassays, such as enzyme-linked immunosorbent assay (ELISA). Although significant information about the release and action of norepinephrine has been obtained with these methodologies, they are limited in temporal resolution, require large sample volumes, and provide results with a significant delay after sample collection (hours to weeks). In this study, we report a novel approach for measurement of interstitial cardiac norepinephrine, using minimally invasive, electrode-based, fast-scanning cyclic voltammetry (FSCV) applied in a beating porcine heart. The first multispatial and high temporal resolution, multichannel measurements of NE release in vivo are provided. Our data demonstrate rapid changes in interstitial NE profiles with regional differences in response to coronary ischemia, sympathetic nerve stimulation, and alterations in preload/afterload.

NEW & NOTEWORTHY Pharmacological, electrical, or surgical regulation of sympathetic neuronal control can be used to modulate cardiac function and treat arrhythmias. However, present methods for monitoring sympathetic release of norepinephrine in the heart are limited in spatial and temporal resolution. Here, we provide for the first time a methodology and demonstration of practice and rapid measures of individualized regional autonomic neurotransmitter levels in a beating heart. We show dynamic, spatially resolved release profiles under normal and pathological conditions.

Esmolol for cardioprotection during resuscitation with adrenaline in an ischaemic porcine cardiac arrest model

Background

The effectiveness of adrenaline during resuscitation continues to be debated despite being recommended in international guidelines. There is evidence that the β-adrenergic receptor (AR) effects of adrenaline are harmful due to increased myocardial oxygen consumption, post-defibrillation ventricular arrhythmias and increased severity of post-arrest myocardial dysfunction. Esmolol may counteract these unfavourable β-AR effects and thus preserve post-arrest myocardial function. We evaluated whether a single dose of esmolol administered prior to adrenaline preserves post-arrest cardiac output among successfully resuscitated animals in a novel, ischaemic cardiac arrest porcine model.

Methods

Myocardial infarction was induced in 20 anaesthetized pigs by inflating a percutaneous coronary intervention (PCI) balloon in the circumflex artery 15 min prior to induction of ventricular fibrillation. After 10 min of untreated VF, resuscitation with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) was initiated and the animals were randomized to receive an injection of either 1 mg/kg esmolol or 9 mg/ml NaCl, prior to adrenaline. Investigators were blinded to allocation. Successful defibrillation was followed by a 1-h high-flow VA-ECMO before weaning and an additional 1-h stabilization period. The PCI-balloon was deflated 40 min after inflation. Cardiac function pre- and post-arrest (including cardiac output) was assessed by magnetic resonance imaging (MRI) and invasive pressure measurements. Myocardial injury was estimated with MRI, triphenyl tetrazolium chloride (TTC) staining and serum concentrations of cardiac troponin T.

Results

Only seven esmolol and five placebo-treated pigs were successfully resuscitated and available for post-arrest measurements (p = 0.7). MRI revealed severe but similar reductions in post-arrest cardiac function with cardiac output 3.5 (3.3, 3.7) and 3.3 (3.2, 3.9) l/min for esmolol and control (placebo) groups, respectively (p = 0.7). The control group had larger left ventricular end-systolic and end-diastolic ventricular volumes compared to the esmolol group (75 (65, 100) vs. 62 (53, 70) ml, p = 0.03 and 103 (86, 124) vs. 87 (72, 91) ml, p = 0.03 for control and esmolol groups, respectively). There were no other significant differences in MRI characteristics, myocardial infarct size or other haemodynamic measurements between the two groups.

Conclusions

We observed similar post-arrest cardiac output with and without a single dose of esmolol prior to adrenaline administration during low-flow VA-ECMO in an ischaemic cardiac arrest pig model.

A case of refractory ventricular fibrillation successfully treated with low-dose esmolol

Current advanced cardiac life support (ACLS) guidelines for the management of ventricular fibrillation (VF) and pulseless ventricular tachycardia is defibrillation. However, refractory VF, which is defined as VF that persists despite three defibrillation attempts, is challenging for all ACLS providers; the best resuscitation strategy for patients that persist in refractory VF remains unclear. We report on a 51-year-old man who presented to the emergency department with chest pain and subsequently went into witnessed VF cardiac arrest. Despite standard ACLS management consisting of high-quality cardiopulmonary resuscitation, serial epinephrine and serial defibrillation, the return of spontaneous circulation (ROSC) was unable to be achieved. Double sequential defibrillation (DSD) was attempted multiple times unsuccessfully. After administration of low-dose esmolol, he immediately achieved ROSC. DSD and β-blockade are increasingly recognised in the literature and practice for refractory VF. However, to the best of our knowledge, this is the first case of refractory VF that responded to low-dose esmolol β-blockade.

Selective beta-blocker esmolol improves cerebral cortex microcirculation in a swine ventricular fibrillation model

OBJECTIVE

This study aimed to identify whether esmolol attenuates cerebral cortex microcirculation blood flow due to epinephrine in prolonged ventricular fibrillation (VF) and cardiopulmonary resuscitation (CPR), and may improve neurological prognosis.

METHODS

Male pigs were randomized into the esmolol+epinephrine group (group EE), the epinephrine group (group EP), and the normal saline group (group NS) (n = 8 each group). Untreated VF for 8 minutes was induced in pigs. After CPR for 2 minutes, group EE received esmolol (500 µg/kg)+epinephrine (20 µg/kg), group EP received epinephrine 20 µg/kg, and group NS received 5 mL normal saline. Then, a 120 J electric shock was delivered. If the return of spontaneous circulation (ROSC) failed, epinephrine (20 µg/kg) was repeated in group EP and EE, followed by another 2 minutes of CPR, a 150 J electric shock was delivered every 2 minutes until ROSC. Cerebral microcirculation images were obtained at 0.5, 6, 12, and 24 hours by cranial windows after ROSC. Cerebral performance category scores and neurological deficit scores (NDS) were calculated. The frontal cortices were harvested after the animals were euthanized.

RESULTS

The NDS, the perfused vessel density, and the microcirculatory flow index of group EE were better than other two groups. The morphology of endothelial cells in the group EE remained intact; however, it was destroyed in the group EP.

CONCLUSIONS

Administration of esmolol with epinephrine may alleviate the impairment of cerebral microcirculation blood flow caused by the administration of epinephrine in prolonged VF and thereby improves neurological outcomes in a swine model.

Left Ventricle Function During Therapeutic Hypothermia with Beta1-Adrenergic Receptor Blockade

Therapeutic hypothermia is an established treatment in patients resuscitated from cardiac arrest. It is usually well-tolerated circulatory, but hypothermia negatively effects myocardial contraction and relaxation velocities and increases diastolic filling restrictions. A significant proportion of resuscitated patients are treated with long-acting beta-receptor blocking agents' prearrest, but the combined effects of hypothermia and beta-blockade on left ventricle (LV) function are not previously investigated. We hypothesized that beta₁-adrenergic receptor blockade (esmolol infusion) exacerbates the negative effects of hypothermia on active myocardial motions, affecting both systolic and diastolic LV function. A pig (n = 10) study was performed to evaluate the myocardial effects of esmolol during hypothermia (33°C) and during normothermia, at spontaneous and pacing-increased heart rates (HRs). LV function was assessed by a LV pressure transducer, an epicardial ultrasonic transducer (wall thickness, wall thickening/thinning velocity) and an aortic ultrasonic flow-probe (stroke volume, cardiac output). The data were compared using a paired two-tailed Students t-test, and also analyzed using a linear mixed model to handle dependencies introduced by repeated measurements within each subject. The significance level was p ≤ 0.05. The effects of hypothermia and beta blockade were distinct and additive. Hypothermia reduced myocardial motion velocities and increased diastolic filling restrictions, but end-systolic wall thickness increased, and stroke volume and dP/dt_max (pumping function) were maintained. In contrast, esmolol predominantly affected systolic pumping function, by a negative inotropic effect. In combination, hypothermia and esmolol reduced myocardial velocities in systole and diastole by ∼40%, compared with normothermia without esmolol, inducing in combination both systolic and diastolic LV function impairment. The cardiac dysfunction deteriorated at increased HRs during hypothermia. Beta₁-adrenergic receptor blockade (esmolol) exacerbates the negative effects of hypothermia on active myocardial contraction and relaxation. The combination of hypothermia with beta-blockade induces both systolic and diastolic LV function impairment.

β-Adrenergic Inhibition Prevents Action Potential and Calcium Handling Changes during Regional Myocardial Ischemia

β-adrenergic receptor (β-AR) blockers may be administered during acute myocardial infarction (MI), as they reduce energy demand through negative chronotropic and inotropic effects and prevent ischemia-induced arrhythmogenesis. However, the direct effects of β-AR blockers on ventricular electrophysiology and intracellular Ca²⁺ handling during ischemia remain unknown. Using optical mapping of transmembrane potential (with RH237) and sarcoplasmic reticulum (SR) Ca²⁺ (with the low-affinity indicator Fluo-5N AM), the effects of 15 min of regional ischemia were assessed in isolated rabbit hearts (n = 19). The impact of β-AR inhibition on isolated hearts was assessed by pre-treatment with 100 nM propranolol (Prop) prior to ischemia (n = 7). To control for chronotropy and inotropy, hearts were continuously paced at 3.3 Hz and contraction was inhibited with 20 μM blebbistatin. Untreated ischemic hearts displayed prototypical shortening of action potential duration (APD₈₀) in the ischemic zone (IZ) compared to the non-ischemic zone (NI) at 10 and 15 min ischemia, whereas APD shortening was prevented with Prop. Untreated ischemic hearts also displayed significant changes in SR Ca²⁺ handling in the IZ, including prolongation of SR Ca²⁺ reuptake and SR Ca²⁺ alternans, which were prevented with Prop pre-treatment. At 5 min ischemia, Prop pre-treated hearts also showed larger SR Ca²⁺ release amplitude in the IZ compared to untreated hearts. These results suggest that even when controlling for chronotropic and inotropic effects, β-AR inhibition has a favorable effect during acute regional ischemia via direct effects on APD and Ca²⁺ handling.

Neurocardiology: Structure-Based Function

Cardiac control is mediated via a series of reflex control networks involving somata in the (i) intrinsic cardiac ganglia (heart), (ii) intrathoracic extracardiac ganglia (stellate, middle cervical), (iii) superior cervical ganglia, (iv) spinal cord, (v) brainstem, and (vi) higher centers. Each of these processing centers contains afferent, efferent, and local circuit neurons, which interact locally and in an interdependent fashion with the other levels to coordinate regional cardiac electrical and mechanical indices on a beat-to-beat basis. This control system is optimized to respond to normal physiological stressors (standing, exercise, and temperature); however, it can be catastrophically disrupted by pathological events such as myocardial ischemia. In fact, it is now recognized that autonomic dysregulation is central to the evolution of heart failure and arrhythmias. Autonomic regulation therapy is an emerging modality in the management of acute and chronic cardiac pathologies. Neuromodulation-based approaches that target select nexus points of this hierarchy for cardiac control offer unique opportunities to positively affect therapeutic outcomes via improved efficacy of cardiovascular reflex control. As such, understanding the anatomical and physiological basis for such control is necessary to implement effectively novel neuromodulation therapies. © 2016 American Physiological Society. Compr Physiol 6:1635-1653, 2016.

β-Adrenergic stimulation and rapid pacing mutually promote heterogeneous electrical failure and ventricular fibrillation in the globally ischemic heart

Global ischemia, catecholamine surge, and rapid heart rhythm (RHR) due to ventricular tachycardia or ventricular fibrillation (VF) are the three major factors of sudden cardiac arrest (SCA). Loss of excitability culminating in global electrical failure (asystole) is the major adverse outcome of SCA with increasing prevalence worldwide. The roles of catecholamines and RHR in the electrical failure during SCA remain unclear. We hypothesized that both β-adrenergic stimulation (βAS) and RHR accelerate electrical failure in the globally ischemic heart. We performed optical mapping of the action potential (OAP) in the right ventricular (RV) and left (LV) ventricular epicardium of isolated rabbit hearts subjected to 30-min global ischemia. Hearts were paced at a cycle length of either 300 or 200 ms, and either in the presence or in the absence of β-agonist isoproterenol (30 nM). 2,3-Butanedione monoxime (20 mM) was used to reduce motion artifact. We found that RHR and βAS synergistically accelerated the decline of the OAP upstroke velocity and the progressive expansion of inexcitable regions. Under all conditions, inexcitability developed faster in the LV than in the RV. At the same time, both RHR and βAS shortened the time to VF (TVF) during ischemia. Moreover, the time at which 10% of the mapped LV area became inexcitable strongly correlated with TVF (R(2) = 0 .72, P < 0.0001). We conclude that both βAS and RHR are major factors of electrical depression and failure in the globally ischemic heart and may contribute to adverse outcomes of SCA such as asystole and recurrent/persistent VF.

The protective effects of a phosphodiesterase 5 inhibitor, sildenafil, on postresuscitation cardiac dysfunction of cardiac arrest: metabolic evidence from microdialysis

INTRODUCTION

Recent experimental and clinical studies have indicated the cardioprotective role of sildenafil during ischemia/reperfusion injury. The aim of this study was to determine, by obtaining metabolic evidence from microdialysis, if sildenafil could reduce the severity of postresuscitation myocardial dysfunction and lead to cardioprotection through beneficial effects on energy metabolism.

METHODS

Twenty-four male piglets were randomly divided into three groups: sildenafil (n = 8), saline (SA; n = 8) and sham operation (n = 8). Sildenafil pretreatment consisted of 0.5 mg/kg sildenafil administered once intraperitoneally 30 minutes prior to ventricular fibrillation (VF). The myocardial interstitial fluid (ISF) concentrations of glucose, lactate, pyruvate, glutamate and glycerol were determined by microdialysis before VF. Afterward, the piglets were subjected to 8 minutes of untreated VF followed by 15 minutes of open-chest cardiopulmonary resuscitation. ISF was collected continuously, and the experiment was terminated 24 hours after resuscitation.

RESULTS

After 8 minutes of untreated VF, the sildenafil group exhibited higher glucose and pyruvate concentrations of ISF and lower lactate and glutamate levels in comparison with the SA group, and these data reached statistical significance (P < 0.05). Advanced cardiac life support was delivered to both groups, with a 24-hour survival rate showing a promising trend in the sildenafil group (7 of 8 versus 3 of 8 survivors, P < 0.05). Compared with the SA group, the sildenafil group had a better outcome in terms of hemodynamic and oxygen metabolism parameters (P < 0.05). Myocardial tissue analysis revealed a dramatic increase in the contents of ATP, ADP and phosphocreatine in the sildenafil group versus the SA group at 24 hours after return of spontaneous circulation (ROSC; P = 0.03, P = 0.02 and P = 0.02, respectively). Furthermore, 24 hours after ROSC, the sildenafil group had marked elevations in activity of left ventricular Na(+)-K(+)-ATPase and Ca(2+)-ATPase compared with the SA group (P = 0.03, P = 0.04, respectively).

CONCLUSIONS

Sildenafil could reduce the severity of postresuscitation myocardial dysfunction, and it produced better clearance of metabolic waste in the ISF. This work might provide insights into the development of a novel strategy to treat postresuscitation myocardial dysfunction.

Neuroprotective effect of Shenfu Injection () following cardiac arrest in pig correlates with improved mitochondrial function and cerebral glucose uptake

OBJECTIVE

To test whether Shenfu Injection (, SFI) might attenuate the impact of cerebral energy dysfunction after resuscitation in a pig model of cardiac arrest (CA).

METHODS

Thirty-four Wuzhishan miniature inbred pigs were randomly divided into three groups: the SFI group (n=12), the saline group (SA group, n=12), and the sham-operated group (sham group, n=10). Following successful return of spontaneous circulation (ROSC) from 8-min untreated ventricular fibrillation, animals received a continuous infusion of either SFI (0.2 mL/min) or saline for 6 h. Cerebral performance category score was evaluated at 24 and 48 h after ROSC, followed by positron emission tomography and computed tomography scans of cerebral glucose uptake. Surviving pigs were euthanized 48 h after ROSC, and the brains were removed for detecting mitochondrial function.

RESULTS

Compared with the SA group, SFI treatment produced a better neurologic outcome 48 h after ROSC (P<0.05). However, there was no significant difference of survival rate between the SA and SFI groups (83.3% vs. 81.8%, P>0.05). After ROSC, the SA group showed a decrease in the maximum standardized uptake value of different regions in the brain tissue, where SFI treatment can ameliorate these decreases (P<0.01 or P<0.05). Improved mitochondrial respiratory properties and higher mitochondrial membrane potential were also found following SFI treatment compared with the SA group at 48 h after ROSC (P<0.05 or P<0.01).

CONCLUSION

SFI treatment after resuscitation has significant neuroprotective effects against disruption of cerebral energy metabolism from CA by improving glucose uptake and by normalizing mitochondrial function.

Verapamil reduces incidence of reentry during ventricular fibrillation in pigs

The characteristics of reentrant circuits during short duration ventricular fibrillation (SDVF; 20 s in duration) and the role of Ca(++) and rapid-activating delayed rectifier potassium currents during long duration ventricular fibrillation (LDVF; up to 10 min in duration) were investigated using verapamil and sotalol. Activation mapping of the LV epicardium with a 21 × 24 electrode plaque was performed in 12 open-chest pigs. Pigs were given either verapamil (0.136 mg/kg) or sotalol (1.5 mg/kg) and verapamil. Reentry patterns were quantified for SDVF, and, for LDVF, activation patterns were compared with our previously reported control LDVF data. Verapamil significantly increased conduction velocity around the reentrant core by 10% and reduced the reentrant cycle length by 15%, with a net reduction in reentry incidence of 70%. Sotolol had an opposite effect of decreasing the conduction velocity around the core by 6% but increasing the reentrant cycle length by 13%, with a net reduction of reentry incidence of 50%. After 200 s of VF, verapamil significantly slowed wavefront conduction velocity and activation rate compared with control data. Verapamil decreased the incidence of reentry in SDVF by accelerating conduction velocity to increase the likelihood of conduction block, possibly through increased sympathetic tone. The drug slowed activation rate and conduction velocity after 200 s of VF, suggesting that L-type Ca(++) channels remain active and may be important in the maintenance of LDVF. Sotalol in addition to verapamil caused no additional antiarrhythmic effect.

Cardiac arrest: should we consider norepinephrine instead of epinephrine?

A patient scheduled for a laparoscopic cholecystectomy had an anaphylactic shock during induction of anesthesia. After the injection of vecuronium, an unusual fall of arterial pressure occurred, with bradycardia, enlargement of the QRS complex, then a circulatory arrest. Chest compressions were initiated, while intravenous epinephrine 1 mg was administered. The cardiac rhythm turned into a ventricular fibrillation (VF). Despite continuous chest compressions with repeated boluses of epinephrine and several external electric shocks, the patient remained in VF. Because of obviously β-adrenergic adverse effects, epinephrine was replaced with norepinephrine. Return of spontaneous circulation was observed, with the recovering of sinusal activity. After staying for several weeks in intensive care unit because of multiorgan failure, the patient recovered without sequelae. Blood samples and cutaneous testing confirmed an allergy to vecuronium. This case report of a cardiac anaphylaxis with prolonged cardiac arrest illustrates the dual activity and adverse effects of epinephrine. Although vasoconstriction is mandated during cardiopulmonary resuscitation to provide an acceptable perfusion pressure to organs, β-adrenergic stimulation seems deleterious to the heart. Experimental studies have shown that blocking the β-adrenergic effects of epinephrine attenuates postresuscitation myocardial dysfunction or helps the return of spontaneous circulation after VF. Norepinephrine, a potent α-adrenergic drug nearly devoid of β-adrenergic properties, could be an interesting alternative to epinephrine. It can improve organ perfusion during cardiopulmonary resuscitation and could be more efficient than epinephrine in case of VF.

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.

Combination of epinephrine with esmolol attenuates post-resuscitation myocardial dysfunction in a porcine model of cardiac arrest

Background

Recent experimental and clinical studies have indicated that the β-adrenergic effect of epinephrine significantly increases the severity of post resuscitation myocardial dysfunction. The aim of the study was to investigate whether the short-acting β₁-selective adrenergic blocking agent, esmolol, would attenuate post resuscitation myocardial dysfunction in a porcine model of cardiac arrest.

Methods and Results

After 8 min of untreated ventricular fibrillation and 2 min of basic life support, 24 pigs were randomized to three groups (n = 8 per group), which received central venous injection of either epinephrine combined with esmolol (EE group), epinephrine (EP group), or saline (SA group). Hemodynamic status and blood samples were obtained at 0, 30, 60, 120, 240 and 360 min after return of spontaneous circulation (ROSC). Surviving pigs were euthanatized at 24 h after ROSC, and the hearts were removed for analysis by electron microscopy, Western blotting, quantitative real-time polymerase chain reaction, and terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL) assay. Compared with the EP and SA groups, EE group had a better outcome in hemodynamic function, (improved dp/dt maxima and minima and cardiac output) (P<0.05), and improved oxygen metabolism (oxygen delivery and oxygen consumption) (P<0.05), which suggesting that EE can protect myocardial tissue from injury and improve post-resuscitation myocardial dysfunction. The protective effect of EE also correlated with reducing cardiomyocyte apoptosis, evidenced by reducing TUNEL-positive cells, increasing anti-apoptotic Bcl-2/Bax ratio and suppression of caspase-3 activity in myocardium.

Conclusions

Esmolol, a short-acting β₁-selective adrenergic blocking agent, given during CPR has significant effects on attenuating post resuscitation myocardial dysfunction. The current study provides a potential pharmacologic target for post resuscitation myocardial dysfunction.

Protective effect of esmolol on myocardial ischemic injury during open heart surgery in children

OBJECTIVES

To investigate the efficacy of esmolol in protecting the myocardium from ischemia during pediatric cardiac surgery.

BACKGROUND

Esmolol, an ultra-short acting beta 1-adrenoceptor blocker, reduces myocardial injury in adult cardiac operations. However, this technique is rarely used in pediatric cardiac surgery.

METHODS

Thirty children with ventricular septal defect were randomly allocated to the esmolol group and the control group. Patients received intravenous esmolol (0.05 mg·kg(-1) ·min(-1) after tracheal intubation, 0.3 mg·kg(-1) ·min(-1) during cardiopulmonary bypass (CPB) and 0.03-0.05 mg·kg(-1) ·min(-1) until the end of surgery) or placebo, respectively.

RESULTS

Plasma levels of creatine kinase-MB, cardiac troponin I in the esmolol group 2 min after completion of CPB, at the end of surgery, 4 h after surgery, and the first postoperative day were significantly lower than those in the control group. Values of heart rate 10 min after induction, 2 min before institution of CPB, 2 min after completion of CPB, and at the end of surgery were significantly lower in the esmolol group; however, mean arterial pressure, CPB time, cross-clamp time, and the rate of heart spontaneous rebeating were not statistically different between two groups. Cumulative postoperative dosage of dopamine in the esmolol group (100.1 ± 53.1 mg) was significantly less than that in the control group (171.4 ± 92.1 mg).

CONCLUSIONS

Esmolol can protect the myocardium from ischemic injury during CPB in children and significantly reduce the use of inotropic drug.

Use of beta-blockers for the treatment of cardiac arrest due to ventricular fibrillation/pulseless ventricular tachycardia: a systematic review

INTRODUCTION

Advanced Life Support guidelines recommend the use of epinephrine during Cardiopulmonary Resuscitation (CPR), as to increase coronary blood flow and perfusion pressure through its alpha-adrenergic peripheral vasoconstriction, allowing minimal rises in coronary perfusion pressure to make defibrillation possible. Contrasting to these alpha-adrenergic effects, epinephrine's beta-stimulation may have deleterious effects through an increase in myocardial oxygen consumption and a reduction of subendocardial perfusion, leading to postresuscitation cardiac dysfunction.

OBJECTIVE

The present paper consists of a systematic review of the literature regarding the use of beta-blockade in cardiac arrest due to ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT).

METHODS

Studies were identified through MEDLINE electronic databases research and were included those regarding the use of beta-blockade during CPR.

RESULTS

Beta-blockade has been extensively studied in animal models of CPR. These studies not only suggest that beta-blockade could reduce myocardial oxygen requirements and the number of shocks necessary for defibrillation, but also improve postresuscitation myocardial function, diminish arrhythmia recurrences and prolong survival. A few case reports described successful beta-blockade use in patients, along with two prospective human studies, suggesting that it could be safe and effectively used during cardiac arrest in humans.

CONCLUSION

Even though the existing literature points toward a beneficial effect of beta-blockade in patients presenting with cardiac arrest due to VF/pulseless VT, high quality human trials are still lacking to answer this question definitely.

Heart protection by combination therapy with esmolol and milrinone at late-ischemia and early reperfusion

INTRODUCTION

The present study determined whether late-ischemia/early reperfusion therapy with the β(1)-adrenergic receptor (AR) blocker esmolol and phosphodiesterase III inhibitor milrinone reduced left ventricular (LV) myocardial infarct size (IS).

METHODS AND RESULTS

In an ischemia/reperfusion rat model (30-min ischemia/4-hr reperfusion), esmolol, milrinone or esmolol + milrinone were intravenous (IV) infused over 10 min (from the last 5 min of ischemia to the first 5 min of reperfusion). LV-IS were 48.9 ± 8.9%, 41.5 ± 5.4%, 25.8 ± 7.7% and 16.8 ± 7.3% for saline, esmolol, milrinone, and esmolol + milrinone, respectively (n = 12/group). Esmolol + milrinone further reduced LV-IS compared with esmolol or milrinone alone (p < 0.05). LV-IS-reduction induced by esmolol + milrinone was eliminated in the presence of protein kinase A-(PKA)-inhibitor (Rp-cAMPS) or Akt-inhibitor (AKT 1/2 kinase inhibitor). In mixed rat ventricular cardiomyocyte cultures, intra-ischemic application of esmolol, milrinone or esmolol + milrinone reduced myocyte death rates by 5.5%, 13.3%, and 16.8%, respectively, compared with saline (p < 0.01). This cell protective effect by esmolol + milrinone was abrogated in the presence of PKA-inhibitor or Akt-inhibitor. Esmolol, milrinone or esmolol + milrinone increased myocardial PKA activity by 22%, 28% and 59%, respectively, compared with saline (n = 6, p < 0.01). No non-specific adverse effect of Rp-cAMPS on myocytes was identified in a purified myocyte preparation during hypoxia/re-oxygenation. Antiapoptotic pathways were assessed by measuring myocardial phosphorylated Akt (pAkt) levels combined with terminal dUTP nick-end labelling staining analysis. Ten minutes following infusion of esmolol, milrinone or esmolol + milrinone, there were 1.7-, 2.7-, and 6-fold increase in tissue pAkt levels, respectively. This esmolol + milrinone induced pAkt activation was abolished in the presence of PKA inhibitor. Esmolol, milrinone and esmolol + milrinone reduced myocyte apoptosis rates by 22%, 37% and 60%, respectively, compared with saline (p < 0.01).

CONCLUSIONS

Late-ischemia/early reperfusion therapy with esmolol + milrinone additively reduces LV-IS associated with robust activation of myocardial PKA and subsequent Akt-antiapoptotic pathway.

Effect of short-acting beta blocker on the cardiac recovery after cardiopulmonary bypass

The objective of this study was to investigate the effect of beta blocker on cardiac recovery and rhythm during cardiac surgeries. Sixty surgical rheumatic heart disease patients were received esmolol 1 mg/kg or the same volume of saline prior to removal of the aortic clamp. The incidence of cardiac automatic re-beat, ventricular fibrillation after reperfusion, the heart rate after steady re-beat, vasoactive drug use during weaning from bypass, the posterior parallel time and total bypass time were decreased by esmolol treatment.

IN CONCLUSION

Esmolol has a positive effect on the cardiac recovery in cardiopulmonary bypass surgeries.

Asphyxial cardiac arrest, resuscitation and neurological outcome in a Landrace/Large-White swine model

The vast majority of laboratory studies on animals have focused on ventricular fibrillation (VF) and not on cardiac arrest (CA) resulting from asphyxia. The aim of this study was to develop a clinically relevant animal model in Landrace/Large-White swine of asphyxial CA resuscitated using the European Resuscitation Council guidelines. Survival and 24 h neurological outcome in terms of functional deficit were also evaluated. Asphyxial arrest was induced by clamping the endotracheal tube (ETT) in 10 Landrace/Large-White piglets. After 4 min of untreated arrest, resuscitation was initiated by unclamping the ETT, 100% oxygen mechanical ventilation, 2 min chest compressions and epinephrine administration. Advanced Life Support algorithm was followed. In case of restoration of spontaneous circulation, the animals were supported for one hour and then observed for 23 h. Coronary perfusion pressure was significantly higher in surviving animals (P < 0.001) during cardiopulmonary resuscitation. End-tidal CO(2) was significantly higher in the animals that survived than in non-surviving animals (P = 0.001). All of the animals were severely neurologically impaired 24 h after CA. This refined model of asphyxia CA is easily reproducible and may be used for pharmacological studies in CA.

Effect and mechanism of esmolol given during cardiopulmonary resuscitation in a porcine ventricular fibrillation model

OBJECTIVES

The aim of the study was to investigate the effect on calcium cycling protein and electrical restitution of beta(1)-adrenergic receptor antagonist esmolol administered during cardiopulmonary resuscitation in the porcine ventricular fibrillation model.

METHODS

Ventricular fibrillation untreated for four minutes was induced by dynamic steady state pacing protocol in 40 healthy male pigs, in which local unipolar electrograms were recorded using one 10-electrode catheter that was sutured to the left ventricular epicardium. During CPR, animals were randomized into two groups to receive saline as placebo or esmolol after two standard doses of epinephrine. At post-resuscitation 2-h, six pigs were randomly selected from each group and the second VF induction was performed. Local activation-recovery intervals (ARI) restitutions and the VF inducibility between control group and esmolol group were compared. Western blotting was performed to determine expression of Ca(2+)/calmodulin-dependent protein kinase IIdelta(CaMKIIdelta) and cardiac ryanodine receptor (RyR2) protein, and their phosphorylation status.

RESULTS

Injection of esmolol combined with epinephrine during CPR significantly decreased recurrent rate of ventricular fibrillation during 2-h post-resuscitation, meanwhile it has no adverse affect on the restore of spontaneous circulation. Esmolol significantly flattened ARI restitution slope, lessened regional difference of ARI restitution, decreased the VF inducibility, and alleviated CaMKIIdelta hyper-activation and RyR2 hyper-phosphorylation.

CONCLUSIONS

Esmolol given during CPR has significant effects on modulating electrical restitution property and intracellular calcium handling, which contributes the most important reasons why beta(1)-blockade significantly reduced the onset and maintenance of VF.

The potential beneficial effects of beta adrenergic blockade in the treatment of ventricular fibrillation

Cardiac arrest remains a major medical emergency in Western societies, with ventricular fibrillation being the initial rhythm in a significant proportion of cases. Adrenaline is generally accepted to improve the resuscitation outcome, since it improves coronary and cerebral blood flow during cardiopulmonary resuscitation, but several detrimental effects have been associated with its use, most of which are thought to be mediated by its beta adrenergic properties. Several animal studies suggest that beta adrenergic blockade during resuscitation, is associated with increased rates of resuscitation and improved post-resuscitation myocardial function. This article reviews the presence and function of beta-adrenoceptor subtypes in the intact and diseased human myocardium, as well as the differences observed in beta(1)- and beta(2) adrenoceptor subtypes in different species.

Burst Stimulation Improves Hemodynamics During Resuscitation After Prolonged Ventricular Fibrillation

Background— Although return of spontaneous circulation is frequently achieved during resuscitation for sudden cardiac arrest, systolic blood pressure can then decrease, requiring additional myocardial support. Previous studies have shown that a series of 1-ms electric pulses delivered through the defibrillation patches during ventricular fibrillation can stimulate the autonomic nervous system to increase myocardial function after defibrillation. We hypothesized that a similar series of electric pulses could increase myocardial function and blood pressure during the early postresuscitation period.

Methods and Results— Six swine were studied that underwent 6 to 7 minutes of fibrillation. Each animal received 5, 10, 15, or 20 pulse packets consisting of six 10-A, 1-ms pulses every 3 to 4 s in random order whenever systolic blood pressure became <50 mm Hg. All 4 sets of pulse packets were delivered to each animal. Systolic blood pressure and cardiac function (left ventricular+dP/dt) were increased to above prestimulation levels or above by all 4 sets of pulse packets. The increases were significantly greater for the longer than the shorter number of pulse packets. The mean�SD duration of the time that the systolic pressure remained above 50 mm Hg after pulse delivery was 4.2�2.5 minutes.

Conclusions— Electric stimulation during regular rhythm after prolonged ventricular fibrillation and resuscitation can increase blood pressure and cardiac function to above prestimulation levels.

Vasopressin and epinephrine in the treatment of cardiac arrest: an experimental study

BACKGROUND

Epinephrine remains the drug of choice for cardiopulmonary resuscitation. The aim of the present study is to assess whether the combination of vasopressin and epinephrine, given their different mechanisms of action, provides better results than epinephrine alone in cardiopulmonary resuscitation.

METHODS

Ventricular fibrillation was induced in 22 Landrace/Large-White piglets, which were left untreated for 8 minutes before attempted resuscitation with precordial compression, mechanical ventilation and electrical defibrillation. Animals were randomized into 2 groups during cardiopulmonary resuscitation: 11 animals who received saline as placebo (20 ml dilution, bolus) + epinephrine (0.02 mg/kg) (Epi group); and 11 animals who received vasopressin (0.4 IU/kg/20 ml dilution, bolus) + epinephrine (0.02 mg/kg) (Vaso-Epi group). Electrical defibrillation was attempted after 10 minutes of ventricular fibrillation.

RESULTS

Ten of 11 animals in the Vaso-Epi group restored spontaneous circulation in comparison to only 4 of 11 in the Epi group (p = 0.02). Aortic diastolic pressure, as well as, coronary perfusion pressure were significantly increased (p < 0.05) during cardiopulmonary resuscitation in the Vaso-Epi group.

CONCLUSION

The administration of vasopressin in combination with epinephrine during cardiopulmonary resuscitation results in a drastic improvement in the hemodynamic parameters necessary for the return of spontaneous circulation.

Clinical role and efficacy of landiolol in the intensive care unit

Beta-adrenergic receptor blockers have proved to be effective for the management of various cardiovascular diseases and the prevention of perioperative cardiac events and cerebrovascular accidents. Landiolol is a short-acting beta-blocker, with high beta 1-selectivity and a short duration of action. We thought landiolol was valuable and suitable for intensive care unit (ICU) patients, and conducted a retrospective study. The records of 80 patients (58 post-surgical patients; group S and 22 internal medicine patients; group IM) were reviewed. Thirty-seven (64%) of the group S patients were post-coronary artery bypass graft surgery, and the IM group consisted mostly of patients with acute myocardial infarction. The most common indication for landiolol in group S was the prevention of myocardial ischemia (50%), and in group IM, it was atrial fibrillation (45%). The median infusion rate of landiolol was 5 microg.kg(-1).min(-1) and the median infusion time was 2 days. Twenty-six patients were continued on oral beta-adrenergic receptor blockers. Landiolol reduced heart rate significantly without reducing blood pressure, and stabilized hemodynamics. We confirmed that landiolol is valuable as a bridge to starting oral beta-adrenergic receptor blockers and as an anti-arrhythmic agent, and that it is suitable for ICU patients due to its high beta 1-selectivity and rapid onset and offset of action.

β-Blockers for the treatment of cardiac arrest from ventricular fibrillation?

More than 160,000 people suffer sudden cardiac death each year in the US. It is estimated that ventricular fibrillation (VF) is the initial rhythm in approximately 30% of these cases. Ventricular fibrillation that does not respond to the first few defibrillation attempts is associated with mortality rates of up to 97%. Currently, no pharmacological intervention has been shown to increase long-term survival in patients with shock-refractory VF. The purpose of this review article is to evaluate whether beta-blocker administration during the resuscitation of cardiac arrest from VF or pulseless ventricular tachycardia (VT) improves outcome. We searched the MEDLINE and EMBASE databases for human clinical trials, animal experimental trials, review articles, case reports and abstracts published between 1966 and September 2006. No human prospective randomized controlled trial has studied the effects of beta-blocker administration during VF directly. Prospective trials of anti-arrhythmics with beta-blocking properties have been published, as well as several case reports/case series and experimental animal studies. The evidence thus far suggests that beta-blockade during resuscitation from VF may be associated with increasing rates of resuscitation, greater post-resuscitation survival, and improved post-resuscitation myocardial function. These positive effects on outcome may be mediated by a decrease in the oxygen requirements of the fibrillating heart, thus improving the overall balance between myocardial oxygen supply and demand during resuscitation. While no significant detrimental effects directly related to low dose beta-blockade during VF have been reported in the studies reviewed, concerns relating to possible loss of myocardial contractility and hypotension remain. To this day, high quality human trials are lacking. Preliminary human studies are needed to assess the effects of beta-blockers in the treatment of cardiac arrest from ventricular fibrillation or pulseless VT further.

Beta-blocker use and the changing epidemiology of out-of-hospital cardiac arrest rhythms

BACKGROUND

The incidence of ventricular fibrillation (VF) as the presenting rhythm in out-of-hospital cardiac arrest (OHCA) is declining, whereas pulseless electrical activity (PEA) is increasing. This changing epidemiology has occurred concomitant with an increase in beta-blocker use.

AIMS

The aim of this study was to measure the association of beta-blocker use among prehospital cardiac arrest patients with PEA versus VF as presenting rhythm.

MATERIALS AND METHODS

In this retrospective cohort study, records of all OHCA patients presenting to a single municipal hospital between 1 January 2001 and 31 December 2006 were reviewed. Age, sex, race, first documented rhythm, estimated down time, presence of bystander CPR, return of spontaneous circulation, beta-blocker use, and comorbid illnesses were noted. A Mantel-Haenzel chi-square was computed to describe the association between beta-blocker use and PEA, compared to beta-blocker use and VF. A sensitivity analysis was also performed to account for missing data, misclassification of beta-blocker use, misclassification of initial rhythm, confounding by unknown factors, and random error.

RESULTS

After exclusion of patients with asystole and patients in whom beta-blocker use was unclear/unknown, a cohort of 179 arrests was evaluated. The odds ratio for beta-blocker use among PEA versus VF patients was 3.7 (95% CI 1.9-7.2), and probabilistic adjustment for exposure and outcome misclassification, confounding, and random error increased the odds ratio to 5.0 (95% CI 1.1-31.0).

CONCLUSIONS

There appears to be an association between beta-blockers and the changing epidemiology of arrest rhythms, which may account for the increasing incidence of PEA and concomitant decrease in VF.

I(Ks) block by HMR 1556 lowers ventricular defibrillation threshold and reverses the repolarization shortening by isoproterenol without rate-dependence in rabbits

INTRODUCTION

The slow delayed rectifier K+ current (I(Ks)) contributes little to ventricular repolarization at rest. It is unclear whether I(Ks) plays a role during ventricular fibrillation (VF) or ventricular repolarization at rapid rates during beta-adrenergic stimulation.

METHODS AND RESULTS

In an in vivo rabbit model, we evaluated the effects of HMR 1556 (1 mg Kg(-1) + 1 mg kg(-1) hr(-1) i.v.), a selective I(Ks) blocker, on monophasic action potential duration at 90% repolarization (MAPD90), ventricular effective refractory period (VERP), and defibrillation threshold (DFT). In perfused rabbit hearts, the effects of HMR 1556 (10 and 100 nM) in the presence of isoproterenol (5 nM) on MAPD90 and VERP were studied at cycle lengths (CLs) 200-500 msec. In vivo, HMR 1556 prolonged MAPD90 by 6 +/- 1 msec at CL 200 msec (P < 0.01, n = 6), lowered DFT from 558 +/- 46 V to 417 +/- 31 V (P < 0.01), and decreased the coefficient of variation in the VF inter-beat deflection intervals from 8.9 +/- 0.6% to 6.5 +/- 0.4% (P < 0.05) compared with control. In perfused rabbit hearts, isoproterenol shortened MAPD90 by 5 +/- 1 msec at CL 200 msec and 11 +/- 4 msec at CL 500 msec (P < 0.05, n = 7). This shortening was reversed by HMR 1556 (P < 0.05), and both effects were rate-independent.

CONCLUSION

I(Ks) block increases VF temporal organization and lowers DFT, and I(Ks) that is activated following beta-adrenergic stimulation contributes to ventricular repolarization without rate dependence.