Induction of mild systemic hypothermia with endovascular cooling during primary percutaneous coronary intervention for acute myocardial infarction

Early targeted brain COOLing in the cardiac CATHeterisation laboratory following cardiac arrest (COOLCATH)

INTRODUCTION

Trials demonstrate significant clinical benefit in patients receiving therapeutic hypothermia (TH) after cardiac arrest. However, incidence of mortality and morbidity remains high in this patient group. Rapid targeted brain hypothermia induction, together with prompt correction of the underlying cause may improve outcomes in these patients. This study investigates the efficacy of Rhinochill, an intranasal cooling device over Blanketrol, a surface cooling device in inducing TH in cardiac arrest patients within the cardiac catheter laboratory.

METHODS

70 patients were randomized to TH induction with either Rhinochill or Blanketrol. Primary outcome measures were time to reach tympanic ≤34 °C from randomisation as a surrogate for brain temperature and oesophageal ≤34 °C from randomisation as a measurement of core body temperature. Secondary outcomes included first hour temperature drop, length of stay in intensive care unit, hospital stay, neurological recovery and all-cause mortality at hospital discharge.

RESULTS

There was no difference in time to reach ≤34 °C between Rhinochill and Blanketrol (Tympanic ≤34 °C, 75 vs. 107 mins; p=0.101; Oesophageal ≤34 °C, 85 vs. 115 mins; p=0.151). Tympanic temperature dropped significantly with Rhinochill in the first hour (1.75 vs. 0.94 °C; p<0.001). No difference was detected in any other secondary outcome measures. Catheter laboratory-based TH induction resulted in a survival to hospital discharge of 67.1%.

CONCLUSION

In this study, Rhinochill was not found to be more efficient than Blanketrol for TH induction, although there was a non-significant trend in favour of Rhinochill that potentially warrants further investigation with a larger trial.

Prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation model

BACKGROUND

Hypothermia when cardiopulmonary resuscitation begins may help achieve defibrillation and return of spontaneous circulation (ROSC), but few data are available.

OBJECTIVE

The objective of this study was to determine whether prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation (VF) model.

RESULTS

Thirty-six New Zealand rabbits were randomized equally to receive normothermia (Norm) (~39°C), post-ROSC hypothermia (~33°C), or prearrest hypothermia (~33°C). Ventricular fibrillation was induced by alternating current. After 4 minutes of VF, rabbits were defibrillated and given cardiopulmonary resuscitation until ROSC or no response (≥30 minutes). Hemodynamics and electrocardiogram were monitored; N-terminal pro-brain natriuretic peptideand troponin I were determined by enzyme-linked immunosorbent assay. Myocardial histology and echocardiographic data were evaluated. First-shock achievement of perfusion rhythm was more frequent in prearrest than normothermic animals (7/12 vs 1/12; P=.027). After ROSC, dp/dtmax was higher in prearrest than normothermic animals (P<.001). Left ventricular end-systolic pressure was higher in prearrest than normothermic animals (P=.001). At 240 minutes after ROSC, troponin I and N-terminal pro-brain natriuretic peptide were lower in prearrest than normothermic animals (15.74±2.26 vs 25.09±1.85 ng/mL and 426±23 vs 284±45 pg/mL, respectively), the left ventricular ejection fraction and cardiac output were lower in the Norm group than other 2 groups (P<.01). Myocardial histology was more disturbed in normothermic than post-ROSC and prearrest animals, but was not different in the latter 2 groups.

CONCLUSIONS

Induction of hypothermia before VF led to improved cardiac function in a rabbit VF model through improving achievement of perfusing rhythm by first-shock defibrillation and facilitating resuscitation.

Hypothermia in the setting of experimental acute myocardial infarction: a comprehensive review

A door-to-balloon time of less than 90 minutes is the gold standard for reperfusion therapy to treat acute myocardial infarction (MI). Because 30-day mortality remains ∼ 10%, new methods must be cultivated to limit myocardial injury. Therapeutic hypothermia has long been experimentally used to attenuate myocardial necrosis during MI with promising results, but the treatment has yet to gain popularity among most clinicians. Hypothermia, in the basic science setting, has been achieved using many techniques. In our review, we examine past and current methods of inducing hypothermia, benefits and setbacks of such methods, current and future clinical trials, and potential mechanisms.

Dexmedetomidine Reduces Shivering during Mild Hypothermia in Waking Subjects

Background and Purpose

Reducing body temperature can prolong tolerance to ischemic injury such as stroke or myocardial infarction, but is difficult and uncomfortable in awake patients because of shivering. We tested the efficacy and safety of the alpha-2-adrenergic agonist dexmedetomidine for suppressing shivering induced by a rapid infusion of cold intravenous fluids.

Methods

Ten subjects received a rapid intravenous infusion of two liters of cold (4°C) isotonic saline on two separate test days, and we measured their core body temperature, shivering, hemodynamics and sedation for two hours. On one test day, fluid infusion was preceded by placebo infusion. On the other test day, fluid infusion was preceded by 1.0 μg/kg bolus of dexmedetomidine over 10 minutes.

Results

All ten subjects experienced shivering on placebo days, with shivering beginning at a mean (SD) temperature of 36.6 (0.3)°C. The mean lowest temperature after placebo was 36.0 (0.3)°C (range 35.7-36.5°C). Only 3/10 subjects shivered on dexmedetomidine days, and the mean lowest temperature was 35.7 (0.4)°C (range 35.0-36.3°C). Temperature remained below 36°C for the full two hours in 6/10 subjects. After dexmedetomidine, subjects had moderate sedation and a mean 26 (13) mmHg reduction in blood pressure that resolved within 90 minutes. Heart rate declined a mean 23 (11) bpm after both placebo and dexmedetomidine. Dexmedetomidine produced no respiratory depression.

Conclusion

Dexmedetomidine decreases shivering in normal volunteers. This effect is associated with decreased systolic blood pressure and sedation, but no respiratory depression.

Setting Up an Efficient Therapeutic Hypothermia Team in Conscious ST Elevation Myocardial Infarction Patients: A UK Heart Attack Center Experience

Patients presenting with ST elevation myocardial infarction (STEMI) are routinely treated with percutaneous coronary intervention to restore blood flow in the occluded artery to reduce infarct size (IS). However, there is evidence to suggest that the restoration of blood flow can cause further damage to the myocardium through reperfusion injury (RI). Recent research in this area has focused on minimizing damage to the myocardium caused by RI. Therapeutic hypothermia (TH) has been shown to be beneficial in animal models of coronary artery occlusion in reducing IS caused by RI if instituted early in an ischemic myocardium. Data in humans are less convincing to date, although exploratory analyses suggest that there is significant clinical benefit in reducing IS if TH can be administered at the earliest recognition of ischemia in anterior myocardial infarction. The Essex Cardiothoracic Centre is the first UK center to have participated in administering TH in conscious patients presenting with STEMI as part of the COOL-AMI case series study. In this article, we outline our experience of efficiently integrating conscious TH into our primary percutaneous intervention program to achieve 18 minutes of cooling duration before reperfusion, with no significant increase in door-to-balloon times, in the setting of the clinical trial.

Therapeutic hypothermia for the treatment of acute myocardial infarction-combined analysis of the RAPID MI-ICE and the CHILL-MI trials

In the randomized rapid intravascular cooling in myocardial infarction as adjunctive to percutaneous coronary intervention (RAPID MI-ICE) and rapid endovascular catheter core cooling combined with cold saline as an adjunct to percutaneous coronary intervention for the treatment of acute myocardial infarction CHILL-MI studies, hypothermia was rapidly induced in conscious patients with ST-elevation myocardial infarction (STEMI) by a combination of cold saline and endovascular cooling. Twenty patients in RAPID MI-ICE and 120 in CHILL-MI with large STEMIs, scheduled for primary percutaneous coronary intervention (PCI) within <6 hours after symptom onset were randomized to hypothermia induced by rapid infusion of 600-2000 mL cold saline combined with endovascular cooling or standard of care. Hypothermia was initiated before PCI and continued for 1-3 hours after reperfusion aiming at a target temperature of 33°C. The primary endpoint was myocardial infarct size (IS) as a percentage of myocardium at risk (IS/MaR) assessed by cardiac magnetic resonance imaging at 4±2 days. Patients randomized to hypothermia treatment achieved a mean core body temperature of 34.7°C before reperfusion. Although significance was not achieved in CHILL-MI, in the pooled analysis IS/MaR was reduced in the hypothermia group, relative reduction (RR) 15% (40.5, 28.0-57.6 vs. 46.6, 36.8-63.8, p=0.046, median, interquartile range [IQR]). IS/MaR was predominantly reduced in early anterior STEMI (0-4h) in the hypothermia group, RR=31% (40.5, 28.8-51.9 vs. 59.0, 45.0-67.8, p=0.01, median, IQR). There was no mortality in either group. The incidence of heart failure was reduced in the hypothermia group (2 vs. 11, p=0.009). Patients with large MaR (>30% of the left ventricle) exhibited significantly reduced IS/MaR in the hypothermia group (40.5, 27.0-57.6 vs. 55.1, 41.1-64.4, median, IQR; hypothermia n=42 vs. control n=37, p=0.03), while patients with MaR<30% did not show effect of hypothermia (35.8, 28.3-57.5 vs. 38.4, 27.4-59.7, median, IQR; hypothermia n=15 vs. control n=19, p=0.50). The prespecified pooled analysis of RAPID MI-ICE and CHILL-MI indicates a reduction of myocardial IS and reduction in heart failure by 1-3 hours with endovascular cooling in association with primary PCI of acute STEMI predominantly in patients with large area of myocardium at risk. (ClinicalTrials.gov id NCT00417638 and NCT01379261).

Induction of therapeutic hypothermia by pharmacological modulation of temperature-sensitive TRP channels: theoretical framework and practical considerations

Therapeutic hypothermia has emerged as a remarkably effective method of neuroprotection from ischemia and is being increasingly used in clinics. Accordingly, it is also a subject of considerable attention from a basic scientific research perspective. One of the fundamental problems, with which current studies are concerned, is the optimal method of inducing hypothermia. This review seeks to provide a broad theoretical framework for approaching this problem, and to discuss how a novel promising strategy of pharmacological modulation of the thermosensitive ion channels fits into this framework. Various physical, anatomical, physiological and molecular aspects of thermoregulation, which provide the foundation for this text, have been comprehensively reviewed and will not be discussed exhaustively here. Instead, the first part of the current review, which may be helpful for a broader readership outside of thermoregulation research, will build on this existing knowledge to outline possible opportunities and research directions aimed at controlling body temperature. The second part, aimed at a more specialist audience, will highlight the conceptual advantages and practical limitations of novel molecular agents targeting thermosensitive Transient Receptor Potential (TRP) channels in achieving this goal. Two particularly promising members of this channel family, namely TRP melastatin 8 (TRPM8) and TRP vanilloid 1 (TRPV1), will be discussed in greater detail.

Current Concepts and New Trends in the Treatment of Cardiogenic Shock Complicating Acute Myocardial Infarction

Cardiogenic shock (CS) is a critical condition which often complicates the evolution of an acute myocardial infarction (AMI). At the same time, co-existence of chronic multi-vessel disease can lead to the development of cardiogenic shock in cases with pronounced haemodynamic instability. Different clinical studies have tried to identify the most appropriate treatment for critical cases of CS complicating AMI. This review aims to present the current status of recommended therapeutic strategies for severe cases of CS presenting as a complication of AMI, and try to shed light on the most appropriate therapeutic strategy as outlined in the current literature. The paper will discuss the different current strategies available for use in the treatment of this condition, includig interventional revascularisation, (complete or culprit), the role of new devices for providing mechanical circulatory support, and the potential role of new drug therapies and of hypothermia.

Drug-induced hypothermia by 5HT1A agonists provide neuroprotection in experimental stroke: new perspectives for acute patient treatment

BACKGROUND

Drug-induced hypothermia reduces brain damage in animal stroke models and is an undiscovered potential in human stroke treatment. We studied hypothermia induced by the serotonergic agonists S14671 (1-[2-(2-thenoylamino)ethyl]-4[1-(7- methoxynaphtyl)]piperazine) and ipsapirone in a rat stroke model and in man by literature meta-analysis.

METHODS

Rats had 60 minutes of middle cerebral artery occlusion (MCAO) and then 7 days of survival. Body temperatures were monitored for 22 hours. Thirty minutes after MCAO, 1 group (n = 9) received bolus of S14671 (.75 mg/kg) and continuous infusion of .06 mg/kg hour(-1) S14671 for 20 hours. Other MCAO rats (n = 7) had bolus of ipsapirone (.75 mg/kg) and continuous infusion of .25 mg/kg hour(-1) ipsapirone for 3 hours. Controls (n = 9; n = 5) received similar amounts of vehicle as bolus and continuous infusion for 20 hours/3 hours. Additional controls of the S14761 effect in MCAO were performed as previously mentioned (n = 10) but with rats kept normothermic by a heating lamp for 22 hours. Finally, a meta-analysis of ipsapirone-induced hypothermia in man was included.

RESULTS

Infarct volumes were reduced by 50% in hypothermic rats versus controls (P < .05). S14671 rats kept normothermic did not show infarct reduction (P > .05). The body temperature after stroke was reduced 1.0-3.0°C compared with controls for 20 hours with S14671 treatment and for 6 hours with ipsapirone treatment. In humans, ipsapirone reduced temperature in average with .55 °C ranging between .1-1.4 °C.

CONCLUSIONS

5-hydroxytryptamine receptor 1A (5HT(1A)) agonists significantly reduce infarct volumes in MCAO rats primarily because of the hypothermic drug effect. 5HT(1A) agonists may be introduced to reduce body temperatures rapidly and prepare patients for further therapeutic hypothermia.

Hypothermia after cardiac arrest as a novel approach to increase survival in cardiopulmonary cerebral resuscitation: a review

Context:

The aim of this review study was to evaluate therapeutic mild hypothermia, its complications and various methods for induced mild hypothermia in patients following resuscitation after out-of-hospital cardiac arrest.

Evidence Acquisition:

Studies conducted on post-cardiac arrest cares, history of induced hypothermia, and therapeutic hypothermia for patients with cardiac arrest were included in this study. We used the valid databases (PubMed and Cochrane library) to collect relevant articles.

Results:

According to the studies reviewed, induction of mild hypothermia in patients after cardiopulmonary resuscitation would lead to increased survival and better neurological outcome; however, studies on the complications of hypothermia or different methods of inducing hypothermia were limited and needed to be studied further.

Conclusions:

This study provides strategic issues concerning the induction of mild hypothermia, its complications, and different ways of performing it on patients; using this method helps to increase patients’ neurological survival rate.

Rapid Induction of Hypothermia by the ThermoSuit System Profoundly Reduces Infarct Size and Anatomic Zone of No Reflow Following Ischemia-Reperfusion in Rabbit and Rat Hearts

INTRODUCTION

Although hypothermia reduces myocardial infarct size, noninvasive and rapid cooling methods are lacking. This study tests the effectiveness of a novel cooling apparatus on myocardial infarct size and no-reflow area in 2 models of coronary artery occlusion (CAO).

METHODS AND RESULTS

Animals were randomized to normothermic (N) or hypothermic (H) groups after isolation of a proximal coronary artery. Animals were subjected to 30 minutes CAO and 3 hours reperfusion. In protocol 1 (rabbit, n = 8 per group), hypothermia was initiated, using the ThermoSuit apparatus (convective-immersion cooling), 5 minutes after the onset of CAO to a goal temperature of ∼32°C. In protocol 2 (rat, n = 5 per group), hypothermia was initiated 2 minutes after the onset of CAO to a goal temperature of ∼30°C. Goal temperature was reached in ∼20 minutes. In protocol 1, hypothermia caused an 82% reduction in infarct size as a percentage of the ischemic risk zone (N, 44% ± 5%; H; 8% ± 2%, P < 0.001) and an 89% reduction in the no-reflow area (N, 44% ± 4%; H, 5% ± 1%, P < 0.001). In protocol 2, hypothermia caused a 73% infarct size reduction (N, 51% ± 5%; H, 14% ± 6%, P < 0.01) and a 99% reduction in the no-reflow area (N, 33% ± 5%; H, 0.4% ± 0.3%, P < 0.01).

CONCLUSION

The ThermoSuit device induced rapid hypothermia and limited infarct size and no reflow to the greatest extent ever observed in this laboratory with a single intervention.

Therapeutic hypothermia following cardiac arrest

More than 10 years ago, the randomised studies of therapeutic hypothermia after cardiac arrest showed significant improvement of neurological outcome and survival. Since then, it has become clear that most of the possible adverse events of therapeutic hypothermia are mild and can easily be controlled by proper administration of intensive care. Although implementation of this effective therapy is quite successful, many questions of the exact treatment protocol still remain unanswered. Therapeutic hypothermia treatment therefore must be tailored to the specific patient's needs. Hence, the exact level of target temperature, duration of cooling, rewarming, timing of the therapy and concomitant medication to facilitate therapeutic hypothermia will be important in the future. Additionally, the use of a post-resuscitation treatment bundle (specialised cardiac-arrest centres including intensive post-resuscitation care, appropriate haemodynamic and respiratory management, therapeutic hypothermia and percutaneous coronary intervention) could further improve treatment of cardiac arrest.

Clinical perspectives on reperfusion injury in acute myocardial infarction

Prompt reperfusion therapy in acute myocardial infarction enhances clinical outcome. However, reperfusion itself may contribute to myocardial cell death. The current review outlines the multifocal mechanisms of reperfusion injury and focuses on understanding the potential role of each element and its contribution to the injury pattern inflicted upon the myocardium. We evaluate the spectrum of contemporary therapies that have been tested in an attempt to reduce myocardial injury. Finally, we explore promising innovative strategies targeting novel reperfusion injury pathways to protect ischemic myocardium during reperfusion.

Clinical applications of targeted temperature management

Targeted temperature management (TTM) has been investigated experimentally and used clinically for over 100 years. The initial rationale for the clinical application of TTM, historically referred to as therapeutic hypothermia, was to decrease the metabolic rate, allowing the injured brain time to heal. Subsequent research demonstrated the temperature dependence of diverse cellular mechanisms including endothelial dysfunction, production of reactive oxygen species, and apoptosis. Consequently, modern use of TTM centers on neuroprotection following focal or global neurologic injury. Despite a solid basic science rationale for applying TTM in a variety of disease processes, including cardiac arrest, traumatic brain injury, ischemic stroke, neonatal ischemic encephalopathy, sepsis-induced encephalopathy, and hepatic encephalopathy, human efficacy data are limited and vary greatly from disease to disease. Ten years ago, two landmark investigations yielded high-quality data supporting the application of TTM in comatose survivors of out-of-hospital cardiac arrest. Additionally, TTM has been demonstrated to improve outcomes for neonatal patients with anoxic brain injury secondary to hypoxic ischemic encephalopathy. Trials are currently under way, or have yielded conflicting results in, examining the utility of TTM for the treatment of ischemic stroke, traumatic brain injury, and acute myocardial infarction. In this review, we place TTM in historic context, discuss the pathophysiologic rationale for its use, review the general concept of a TTM protocol for the management of brain injury, address some of the common side effects encountered when lowering human body temperature, and examine the data for its use in diverse disease conditions with in-depth examination of TTM for postarrest care and pediatric applications.

Rapid endovascular catheter core cooling combined with cold saline as an adjunct to percutaneous coronary intervention for the treatment of acute myocardial infarction. The CHILL-MI trial: a randomized controlled study of the use of central venous catheter core cooling combined with cold saline as an adjunct to percutaneous coronary intervention for the treatment of acute myocardial infarction

OBJECTIVES

The aim of this study was to confirm the cardioprotective effects of hypothermia using a combination of cold saline and endovascular cooling.

BACKGROUND

Hypothermia has been reported to reduce infarct size (IS) in patients with ST-segment elevation myocardial infarctions.

METHODS

In a multicenter study, 120 patients with ST-segment elevation myocardial infarctions (<6 h) scheduled to undergo percutaneous coronary intervention were randomized to hypothermia induced by the rapid infusion of 600 to 2,000 ml cold saline and endovascular cooling or standard of care. Hypothermia was initiated before percutaneous coronary intervention and continued for 1 h after reperfusion. The primary end point was IS as a percent of myocardium at risk (MaR), assessed by cardiac magnetic resonance imaging at 4 ± 2 days.

RESULTS

Mean times from symptom onset to randomization were 129 ± 56 min in patients receiving hypothermia and 132 ± 64 min in controls. Patients randomized to hypothermia achieved a core body temperature of 34.7°C before reperfusion, with a 9-min longer door-to-balloon time. Median IS/MaR was not significantly reduced (hypothermia: 40.5% [interquartile range: 29.3% to 57.8%; control: 46.6% [interquartile range: 37.8% to 63.4%]; relative reduction 13%; p = 0.15). The incidence of heart failure was lower with hypothermia at 45 ± 15 days (3% vs. 14%, p < 0.05), with no mortality. Exploratory analysis of early anterior infarctions (0 to 4 h) found a reduction in IS/MaR of 33% (p < 0.05) and an absolute reduction of IS/left ventricular volume of 6.2% (p = 0.15).

CONCLUSIONS

Hypothermia induced by cold saline and endovascular cooling was feasible and safe, and it rapidly reduced core temperature with minor reperfusion delay. The primary end point of IS/MaR was not significantly reduced. Lower incidence of heart failure and a possible effect in patients with early anterior ST-segment elevation myocardial infarctions need confirmation. (Efficacy of Endovascular Catheter Cooling Combined With Cold Saline for the Treatment of Acute Myocardial Infarction [CHILL-MI]; NCT01379261).

Therapeutic hypothermia after cardiopulmonary resuscitation

Full cerebral recovery after cardiopulmonary resuscitation is still a rare event. Unfortunately, up to now, no specific and outcome-improving therapy was available after such events. From several cases it is known that low body and brain temperature during a cardiocirculatory arrest improves the neurological outcome following these events. As it is not possible in acute events to induce hypothermia beforehand, whether cooling after the insult could also be protective was evaluated. After animal studies in the 1990s and first clinical pilot trials of mild therapeutic and induced hypothermia, two randomized trials of hypothermic therapy after successful resuscitation after cardiac arrest were conducted. These studies demonstrated that hypothermia after cardiac arrest could improve neurological outcome as well as overall mortality.

A pooled analysis of the effect of endovascular cooling on infarct size in patients with ST-elevation myocardial infarction

AIMS

Prior evaluations of endovascular cooling during primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) have suggested variability in treatment effect related to core temperature at the time of reperfusion, to infarct location and time from symptom onset to reperfusion. Recent results from a randomised feasibility study suggest rapid induction of hypothermia in primary PCI results in a significant reduction in infarct size (IS).

METHODS AND RESULTS

Outcomes from two randomised trials of hypothermia in primary PCI were pooled to examine IS as a percentage of left ventricular myocardium assessed by SPECT or magnetic resonance imaging. Compared with controls (n=103), hypothermia (n=94) was associated with a significant 24% relative reduction (RR) in IS (10.7±1.3% vs. 14.1±1.6%, mean±SEM, p=0.049). Among hypothermia-treated patients for whom core temperature <35C° was achieved before reperfusion, IS was reduced by 37% (8.8±1.7% vs. 14.1±1.6%, p=0.01), a benefit observed for both anterior (14.9±2.9% vs. 22.2±2.7%, RR 33%; p=0.03) and inferior infarcts (4.5±1.4% vs. 7.7±1.3%, RR 42%; p=0.04).

CONCLUSIONS

In a pooled analysis of randomised trials evaluating adjunctive hypothermia in primary PCI, achievement of core body temperature <35°C before reperfusion may reduce infarct size with a similar efficacy for both anterior and inferior MI.

Conditioning the heart to prevent myocardial reperfusion injury during PPCI

For patients presenting with a ST-segment elevation myocardial infarction (STEMI), early myocardial reperfusion by primary percutaneous coronary intervention (PPCI) remains the most effective treatment strategy for limiting myocardial infarct size, preserving left ventricular systolic function, and preventing the onset of heart failure. Recent advances in PCI technology to improve myocardial reperfusion and the introduction of novel anti-platelet and anti-thrombotic agents to maintain the patency of the infarct-related coronary artery continue to optimize PPCI procedure. However, despite these improvements, STEMI patients still experience significant major adverse cardiovascular events. One major contributing factor has been the inability to protect the heart against the lethal myocardial reperfusion injury, which accompanies PPCI. Past attempts to translate cardioprotective strategies, discovered in experimental studies to prevent lethal myocardial reperfusion injury, into the clinical setting of PPCI have been disappointing. However, a number of recent proof-of-concept clinical studies suggest that the heart can be 'conditioned' to protect itself against lethal myocardial reperfusion injury, as evidenced by a reduction in myocardial infarct size. This can be achieved using either mechanical (such as ischaemic postconditioning, remote ischaemic preconditioning, therapeutic hypothermia, or hyperoxaemia) or pharmacological (such as cyclosporin-A, natriuretic peptide, exenatide) 'conditioning' strategies as adjuncts to PPCI. Furthermore, recent developments in cardiac magnetic resonance (CMR) imaging can provide a non-invasive imaging strategy for assessing the efficacy of these novel adjunctive therapies to PPCI in terms of key surrogate clinical endpoints such as myocardial infarct size, myocardial salvage, left ventricular ejection fraction, and the presence of microvascular obstruction or intramyocardial haemorrhage. In this article, we review the therapeutic potential of 'conditioning' to protect the heart against lethal myocardial reperfusion injury in STEMI patients undergoing PPCI.

The effect of hypothermia "dose" on vasopressor requirements and outcome after cardiac arrest

OBJECTIVES

We evaluated the association between TH use and "dose" and cumulative vasopressor and inotrope requirement, survival, and neurologic outcome.

BACKGROUND

Therapeutic hypothermia (TH) improves outcome after cardiac arrest, but may increase vasopressor and inotrope requirements.

METHODS

Chart review of in- and out-of-hospital cardiac arrests between 1/1/2005 and 3/15/2010. Data included demographic information, category of post-cardiac arrest illness severity ((I) awake, (II) coma (not following commands but intact brainstem responses)+mild cardiopulmonary dysfunction (SOFA [Sequential Organ Failure Assessment] cardiac+respiratory score<4), (III) coma+moderate-severe cardiopulmonary dysfunction (SOFA cardiac+respiratory score≥4), and (IV) coma without brainstem reflexes), cumulative vasopressor index (CVI), inotrope use, survival, and neurologic outcome. The "dose" of TH (hours*temperature below threshold) was calculated using thresholds of ≤34 °C and ≤35 °C. Data were analyzed using descriptive statistics, Student's t-test, Wilcoxon test, and chi-squared analysis. Linear and logistic regression evaluated the effect of hypothermia "dose" on total CVI, survival and neurologic outcome.

RESULTS

Among 361 comatose patients, 233 (65%) received TH. Vasopressor administration (measured by CVI) was higher in normothermic subjects (60.2% vs. 46.4%; p=0.016). Using a 34 °C threshold, SOFA respiratory subscore and PEA arrest predicted total CVI. Using a 35 °C threshold, severity of coma, SOFA respiratory subscore, PEA arrest and use of inotropic agents in addition to vasopressors predicted total CVI. Initial motor examination predicted survival and neurologic outcome, while TH "dose" did not.

CONCLUSIONS

TH delivery is not associated with vasopressor requirement. TH "dose" is not associated with total CVI, survival, or good outcome. Vasopressor or inotropic requirement should not contraindicate TH use.

Mild hypothermia decreases arrhythmia susceptibility in a canine model of global myocardial ischemia*

OBJECTIVES

Although the majority of sudden cardiac arrests occur in patients with ischemic heart disease, the effect of therapeutic hypothermia on arrhythmia susceptibility during acute global ischemia is not well understood. While both ischemia and severe hypothermia are arrhythmogenic, patients undergoing therapeutic hypothermia do not have an increase in arrhythmias, despite the fact that most sudden cardiac arrest occur in the setting of ischemia. We hypothesized that mild hypothermia induced prior to myocardial ischemia and reperfusion will have a beneficial effect on ischemia-related arrhythmia substrates.

DESIGN

We developed a model of global ischemia and reperfusion in the canine wedge preparation to study the transmural electrophysiologic effects of ischemia at different temperatures.

SETTING

Animal study.

SUBJECTS

Male mongrel dogs.

INTERVENTIONS

Canine left ventricle wedge preparations at 1) control (36°C) or 2) mild hypothermia, to simulate temperatures used in therapeutic hypothermia (32°C), were subjected to 15 mins of no-flow ischemia and subsequently reperfused.

MEASUREMENTS AND MAIN RESULTS

Optical action potentials were recorded spanning the transmural wall of left ventricle. Action potential duration for epicardial, mid-myocardial, and epicardial cells was measured. Transmural dispersion of repolarization and conduction velocity were measured at baseline, during ischemia, and during reperfusion. No difference was seen at baseline for conduction velocity or dispersion of repolarization between groups. Conduction velocity decreased from 0.46 ± 0.02 m/sec to 0.23 ± 0.07 m/sec, and dispersion of repolarization increased from 30 ± 5 msecs to 57 ± 4 msecs in the control group at 15 mins of ischemia. Mild hypothermia attenuated both the ischemia-induced conduction velocity slowing (decreasing from 0.44 ± 0.02 m/sec to 0.35 ± 0.03 m/sec; p = .019) and the ischemia-induced increase in dispersion of repolarization (25 ± 3 msecs to 37 ± 7 msecs; p = .037). Epicardial conduction block was observed in six of seven preparations of the control group, but no preparations in the mild hypothermia group developed conduction block (0/6).

CONCLUSIONS

Mild hypothermia attenuated ischemia-induced increase in dispersion of repolarization, conduction slowing, and block, which are known mechanisms of arrhythmogenesis in ischemia. These data suggest that therapeutic hypothermia may decrease arrhythmogenesis during myocardial ischemia.

Delayed treatment with hypothermia protects against the no-reflow phenomenon despite failure to reduce infarct size

BACKGROUND

Many studies have shown that when hypothermia is started after coronary artery reperfusion (CAR), it is ineffective at reducing necrosis. However, some suggest that hypothermia may preferentially reduce no-reflow. Our aim was to test the effects of hypothermia on no-reflow when initiated close to reperfusion and 30 minutes after reperfusion, times not associated with a protective effect on myocardial infarct size.

METHODS AND RESULTS

Rabbits received 30 minutes coronary artery occlusion/3 hours CAR. In protocol 1, hearts were treated for 1 hour with topical hypothermia (myocardial temperature ≈32°C) initiated at 5 minutes before or 5 minutes after CAR, and the results were compared with a normothermic group. In protocol 2, hypothermia was delayed until 30 minutes after CAR and control hearts remained normothermic. In protocol 1, risk zones were similar and infarct size was not significantly reduced by hypothermia initiated close to CAR. However, the no-reflow defect was significantly reduced by 43% (5 minutes before CAR) and 38% (5 minutes after CAR) in hypothermic compared with normothermic hearts (P=0.004, ANOVA, P=ns between the 2 treated groups). In protocol 2, risk zones and infarct sizes were similar, but delayed hypothermia significantly reduced no-reflow in hypothermic hearts by 30% (55±6% of the necrotic region in hypothermia group versus 79±6% with normothermia, P=0.008).

CONCLUSION

These studies suggest that treatment with hypothermia reduces no-reflow even when initiated too late to reduce infarct size and that the microvasculature is especially receptive to the protective properties of hypothermia and confirm that microvascular damage is in large part a form of true reperfusion injury.

[Prehospital cardiac arrest. Therapeutic hypothermia in adults]

Therapeutic hypothermia is one of the few advances in recent years that has improved survival and neurological outcome of survivors of cardiac arrest. Therapeutic hypothermia is part of current guidelines and, therefore, should be part of the routine procedure in postresuscitation care of patients still comatose after primarily successful resuscitation. Early induction of hypothermia may be achieved even in the prehospital setting with different cooling techniques which, however, are less suitable to maintain a constant temperature and additionally do not allow precisely controlled re-warming. To achieve the goal of a target temperature of 32-34°C for 12-24 h, controlled feedback systems are more reliable and also can be used for patients during percutaneous coronary intervention. The optimal time point to start cooling is not well defined, even if theoretical considerations and animal experiments are in favor of beginning early. Another question is whether therapeutic hypothermia is of benefit for patients with cardiac arrest due to asystole and pulseless electrical activity in contrast to patients with ventricular fibrillation where it is of proven value.

Tc-99m SPECT sestamibi for the measurement of infarct size

There are a variety of approaches to assess the efficacy of reperfusion therapy, and myocardial protection, in acute myocardial infarction. This review summarizes the available evidence validating the use of technetium-99m sestamibi single-photon emission computed tomography (SPECT) for this purpose. Multiple lines of evidence have validated its clinical utility. SPECT sestamibi infarct size has been used as an endpoint in multiple randomized clinical trials. A smaller number of clinical trials have used both early and later imaging with SPECT sestamibi to assess myocardium at risk and myocardial salvage. SPECT sestamibi has a number of limitations which must be recognized. Nevertheless, SPECT sestamibi infarct size is a well-validated measurement with a long track record of performance as an endpoint in multicenter, randomized clinical trials.

Surface cooling for induction of mild hypothermia in conscious healthy volunteers - a feasibility trial

Introduction

Animal and human studies suggest beneficial outcome effects of mild hypothermia for stroke, for acute myocardial infarction, and for cardiogenic shock. The aim of this study was to investigate the feasibility and safety of non-invasive surface cooling for induction and maintenance of mild hypothermia (32 to 34°C) in healthy, conscious volunteers.

Methods

The trial was set at a clinical research ward in a tertiary care center, and included 16 healthy male volunteers 18 to 70 years old. Surface cooling was established by a novel non-invasive cooling pad with an esophageal target temperature of 32 to 34°C and maintenance for six hours. Shivering-control was achieved with meperidine and buspirone and additional administration of magnesium in eight subjects.

Results

The primary endpoint to reach a target temperature of 32 to 34°C was only reached in 6 of the 16 participating subjects. Temperatures below 35°C were reached after a median cooling time of 53 minutes (38 to 102 minutes). Cooling rate was 1.1°C/h (0.7 to 1.8°C). Additional administration of magnesium had no influence on cooling rate. At no time during the cooling procedure did the participants report uncomfortable conditions for which termination of cooling had to be considered. No severe skin damage was reported.

Conclusions

Cooling to body temperature below 35°C by the use of non-invasive surface cooling is feasible and safe in conscious healthy volunteers. Further studies are needed to investigate an altered cooling protocol to achieve temperatures below 35°C.

Trial Registration

ISRCTN: ISRCTN50530495

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

Systemic hypothermia to prevent radiocontrast nephropathy (from the COOL-RCN Randomized Trial)

Radiocontrast nephropathy (RCN) develops in a substantial proportion of patients with chronic kidney disease (CKD) after invasive cardiology procedures and is strongly associated with subsequent mortality and adverse outcomes. We sought to determine whether systemic hypothermia is effective in preventing RCN in patients with CKD. Patients at risk for RCN (baseline estimated creatinine clearance 20 to 50 ml/min) undergoing cardiac catheterization with iodinated contrast ≥50 ml were randomized 1:1 to hydration (control arm) versus hydration plus establishment of systemic hypothermia (33°C to 34°C) before first contrast injection and for 3 hours after the procedure. Serum creatinine levels at baseline, 24 hours, 48 hours, and 72 to 96 hours were measured at a central core laboratory. The primary efficacy end point was development of RCN, defined as an increase in serum creatinine by ≥25% from baseline. The primary safety end point was 30-day composite rate of adverse events consisting of death, myocardial infarction, dialysis, ventricular fibrillation, venous complication requiring surgery, major bleeding requiring transfusion ≥2 U, or rehospitalization. In total 128 evaluable patients (mean creatinine clearance 36.6 ml/min) were prospectively randomized at 25 medical centers. RCN developed in 18.6% of normothermic patients and in 22.4% of hypothermic patients (odds ratio 1.27, 95% confidence interval 0.53 to 3.00, p = 0.59). The primary 30-day safety end point occurred in 37.1% versus 37.9% of normothermic and hypothermic patients, respectively (odds ratio 0.97, 95% confidence interval 0.47 to 1.98, p = 0.93). In conclusion, in patients with CKD undergoing invasive cardiology procedures, systemic hypothermia is safe but is unlikely to prevent RCN.

Ultrafast and whole-body cooling with total liquid ventilation induces favorable neurological and cardiac outcomes after cardiac arrest in rabbits

BACKGROUND

In animal models of cardiac arrest, the benefit afforded by hypothermia is closely linked to the rapidity of the decrease in body temperature after resuscitation. Because total liquid ventilation (TLV) with temperature-controlled perfluorocarbons induces a very rapid and generalized cooling, we aimed to determine whether this could limit the post-cardiac arrest syndrome in a rabbit model. We especially focused on neurological, cardiac, pulmonary, liver and kidney dysfunctions.

METHODS AND RESULTS

Anesthetized rabbits were submitted to either 5 or 10 minutes of untreated ventricular fibrillation. After cardiopulmonary resuscitation and resumption of a spontaneous circulation, the animals underwent either normothermic life support (control) or therapeutic hypothermia induced by TLV. The latter procedure decreased esophageal and tympanic temperatures to 32°C to 33°C within only 10 minutes. After rewarming, the animals submitted to TLV exhibited an attenuated neurological dysfunction and decreased mortality 7 days later compared with control. The neuroprotective effect of TLV was confirmed by a significant reduction in brain histological damages. We also observed limitation of myocardial necrosis, along with a decrease in troponin I release and a reduced myocardial caspase 3 activity, with TLV. The beneficial effects of TLV were directly related to the rapidity of hypothermia induction because neither conventional cooling (cold saline infusion plus external cooling) nor normothermic TLV elicited a similar protection.

CONCLUSIONS

Ultrafast cooling instituted by TLV exerts potent neurological and cardiac protection in an experimental model of cardiac arrest in rabbits. This could be a relevant approach to provide a global and protective hypothermia against the post-cardiac arrest syndrome.

Neurologic and cardiac benefits of therapeutic hypothermia

Numerous studies have shown the favorable effects of lowering the core temperature of the body in various conditions such as acute myocardial infarction, acute cerebrovascular disease, acute lung injury, and acute spinal cord injury. Therapeutic hypothermia (TH) works at different molecular and cellular levels. TH improves oxygen supply to ischemic areas and increases blood flow by decreasing vasoconstriction, as well as oxygen consumption, glucose utilization, lactate concentration, intracranial pressure, heart rate, cardiac output, and plasma insulin levels. TH has been shown to improve neurologic outcome in acute cerebrovascular accidents. Furthermore, recent studies revealed that TH is a useful method of neuroprotection against ischemic neuronal injury after cardiac arrest. TH in out-of-hospital cardiac arrest is becoming a standard practice nationwide. Further studies need to be performed to develop a better understanding of the benefits and detrimental effects of TH, to identify the most efficacious TH strategy, and the candidates most likely to derive benefit from the procedure. Although many animal studies have demonstrated benefit, larger human clinical trials are recommended to investigate the beneficial effect of TH on reducing myocardial infarction size and coronary reperfusion injuries.

Influence of age on heart rate variability during therapeutic hypothermia in a rat model

OBJECTIVES

To evaluate the effect of age on heart rate variability (HRV) in a rat model of therapeutic hypothermia.

METHODS

Thirty-six male Sprague-Dawley rats (18 were 2 months old and 18 were 18 months old) were randomized into one of three groups: normothermia (37°C), mild hypothermia (34°C), and moderate hypothermia (31°C). An electrocardiogram (ECG) was recorded at baseline and continuously for 1h once the target core body temperature was reached. Various heart rate variability measurements were calculated.

RESULTS

Significant effects of age were observed in respect to the ratio of standard deviation of all normal to normal R-R [NN] intervals (SDNN)/standard deviation of the differences between adjacent NN intervals (SD of delta NN) (P=0.037), low frequency (LF) power, normalized units (nu, %) (P<0.001), and the ratio of LF and high frequency (HF) (P<0.001). Significant effects of temperature were found in LF power and a significant body-temperature interaction was found in HF power. HF power was significantly lower in the young rats at mild and moderate hypothermic conditions. For the LF/HF, the ratio was significantly lower in the young animals compared to the older animals at normal body temperatures and during mild hypothermia. LF/HF increased significantly at both 34°C and 31°C in the young rats compared to the young rats at 37°C. In contrast, LF/HF was significantly lower in the older group of rats at 34°C and 31°C compared to the older group of rats maintained under normothermic conditions.

CONCLUSIONS

This study noted that autonomic regulation determined via HRV, primarily the ratio of LF to HF, was different between different age groups. Additional studies on this topic are needed to achieve a more detailed understanding of therapeutic hypothermia.

Adenosine and Opioid Receptors Do Not Trigger the Cardioprotective Effect of Mild Hypothermia

Mild hypothermia (32°C-34°C) exerts a potent cardioprotection in animal models of myocardial infarction. Recently, it has been proposed that this beneficial effect is related to survival signaling. We, therefore, hypothesized that the well-known cardioprotective pathways dependent on adenosine and/or opioid receptors could be the trigger of hypothermia-induced salvage. Open-chest rabbits were accordingly exposed to 30 minutes of coronary artery occlusion (CAO) under normothermic (NT) or hypothermic ([HT] 32°C) conditions. In the latter, hypothermia was induced by total liquid ventilation with temperature-controlled perfluorocarbons in order to effect ultrafast cooling and to accurately control cardiac temperature. After 4 hours of reperfusion, infarct and no-reflow zone sizes were assessed and quantified as a percentage of the risk zone. In animals experiencing HT ischemia, the infarct size was dramatically reduced as compared to NT animals (9% ± 3% vs 55% ± 2% of the risk zone, respectively). Importantly, administration of opioid and adenosine receptor antagonists (naloxone [6 mg/kg iv] and 8-( p-sulfophenyl) theophylline [20 mg/kg iv], respectively) did not alter the infarct size or affect the cardioprotective effect of hypothermia. Doses of these 2 antagonists were appropriately chosen since they blunted infarct size reduction induced by selective opioid or adenosine receptor stimulation with morphine (0.3 mg/kg iv) or N6-cyclopentyladenosine ([CPA] 100 μg/kg iv), respectively. Therefore, the cardioprotective effect of mild hypothermia is not triggered by either opioid or adenosine receptor activation, suggesting the involvement of other cardioprotective pathways.

Cardiogenic shock and heart failure post-percutaneous coronary intervention in ST-elevation myocardial infarction: observations from "Assessment of Pexelizumab in Acute Myocardial Infarction"

BACKGROUND

Mortality after ST-elevation myocardial infarction (STEMI) has reduced with reperfusion by primary percutaneous coronary intervention (PCI), which may have impacted on the adverse outcomes of cardiogenic shock (CS) and congestive heart failure (CHF).

METHODS AND RESULTS

In the APEX-AMI trial, 5,745 patients with STEMI and planned primary PCI were randomly assigned pexelizumab or matching placebo. Post-randomization CS or CHF was adjudicated by a clinical endpoints committee. Treatment assignment to pexelizumab did not influence either endpoint or mortality rates. Cardiogenic shock developed in 196 patients (3.4%) at a median of 6.0 hours (interquartile range 3.9-28.3) post-randomization, and mortality at 90 days was 54.6%. Congestive heart failure occurred in 254 of patients (4.4%) at a median of 2.6 days (IQR 1.0-16.6), and mortality through 90 days was 10.2%; mortality among those with neither endpoint was 2.1%. Patients with CS or CHF were older, were more often female, and had more hypertension and diabetes, but smoked less compared with non-CS/CHF patients (all P < .05). Independent mortality predictors among those with CS or CHF were hyperlipidemia and a history of angina (interaction P = .011 and .008, respectively); procedural predictors among survivors to PCI were pre-PCI Thrombolysis In Myocardial Infarction (TIMI) flow 0-1 and post-PCI TIMI flow <3 (P = .013 and <.0001, respectively).

CONCLUSIONS

Survival after CS remains poor despite aggressive reperfusion. Both CS and CHF remain the major causes of death among STEMI patients undergoing primary PCI. Future studies should examine treatments that aim to reduce mortality in these highest risk patients.