Myocardial dysfunction after electrical defibrillation

Comparison of amiodarone and esmolol for prevention of reperfusion ventricular fibrillation in individuals undergoing heart valve or aortic surgery: a study protocol for a randomized controlled clinical trial

BACKGROUND

Amiodarone and esmolol can help to prevent and treat post-cardiac surgery reperfusion ventricular fibrillation. However, the relative efficacies of these two drugs remain unknown. The aim of the current trial is to compare the performances of amiodarone and esmolol for preventing reperfusion ventricular fibrillation following open heart surgery.

METHODS/DESIGN

This is a single-center, prospective, double-blind, controlled clinical trial. A total of 260 patients undergoing heart valve or aortic surgery will be assigned randomly to treatment with prophylactic esmolol (intervention group) or amiodarone (control group). The main outcome is the incidence of reperfusion ventricular fibrillation following aortic opening during extracorporeal circulation. The secondary outcomes are the rate of automatic cardiac resuscitation, energy and frequency of electrical defibrillation, number of electrical defibrillations, and pacemaker use in the two groups of patients. Information on the patients' general condition and the durations of anesthesia, extracorporeal circulation, aortic occlusion, and operation time will be recorded. We will also compare the heart rate, mean arterial pressure, and central venous pressure between the two groups of patients at induction of anesthesia (T1), start of surgery (T2), start of extracorporeal circulation (T3), aortic block (T4), aortic opening (T5), after opening for 10 (T6), 20 (T7), and 30 min (T8), at cessation of extracorporeal circulation (T9), and at the end of surgery (T10) and compare blood gas analysis results at T1, T5, T9, and T10.

DISCUSSION

This study will determine if prophylactic esmolol is more effective than amiodarone for reducing the incidence of reperfusion ventricular fibrillation in patients undergoing heart valve or aortic surgery.

TRIAL REGISTRATION

China Clinical Trials Registry ChiCTR1900026429. Registered on 2019.10.9.

Amplitude spectral area of ventricular fibrillation and defibrillation success at low energy in out-of-hospital cardiac arrest

The optimal energy for defibrillation has not yet been identified and very often the maximum energy is delivered. We sought to assess whether amplitude spectral area (AMSA) of ventricular fibrillation (VF) could predict low energy level defibrillation success in out-of-hospital cardiac arrest (OHCA) patients. This is a multicentre international study based on retrospective analysis of prospectively collected data. We included all OHCAs with at least one manual defibrillation. AMSA values were calculated by analyzing the data collected by the monitors/defibrillators used in the field (Corpuls 3 and Lifepak 12/15) and using a 2-s-pre-shock electrocardiogram interval. We run two different analyses dividing the shocks into three tertiles (T1, T2, T3) based on AMSA values. 629 OHCAs were included and 2095 shocks delivered (energy ranging from 100 to 360 J; median 200 J). Both in the "extremes analysis" and in the "by site analysis", the AMSA values of the effective shocks at low energy were significantly higher than those at high energy (p = 0.01). The likelihood of shock success increased significantly from the lowest to the highest tertile. After correction for age, call to shock time, use of mechanical CPR, presence of bystander CPR, sex and energy level, high AMSA value was directly associated with the probability of shock success [T2 vs T1 OR 3.8 (95% CI 2.5-6) p < 0.001; T3 vs T1 OR 12.7 (95% CI 8.2-19.2), p < 0.001]. AMSA values are associated with the probability of low-energy shock success so that they could guide energy optimization in shockable cardiac arrest patients.

The Effect of Prophylactic Intravenous Amiodarone Administration on Reperfusion Ventricular Fibrillation in Patients With Left Ventricular Hypertrophy Undergoing Cardiopulmonary Bypass Surgery: Protocol for a Randomized Double-Blind Clinical Trial

BACKGROUND

Ventricular fibrillation (VF) is a common arrhythmia that occurs after the release of aortic cross-clamp (ACC) in patients undergoing cardiopulmonary bypass (CPB) surgery. Repeated defibrillation and long duration of VF could increase myocardial injuries. In patients with left ventricular hypertrophy (LVH), VF is easier to occur and more difficult to be terminated. Amiodarone, known as class III antiarrhythmic agent, has the prominent properties of converting VF and restoring the sinus rhythm. Before ACC release, administration of amiodarone has been confirmed useful to reduce occurrence of VF. However, few studies are focused on the effect of amiodarone before ACC release on reducing VF in patients with LVH.

OBJECTIVE

This study aimed at determining the efficacy of prophylactic intravenous amiodarone administration on reperfusion VF after release of ACC in patients with LVH undergoing CPB surgery.

METHODS

This will be a prospective, randomized, double-blind, placebo-controlled trial. The trial will enroll 54 patients with LVH aged 18-75 years who will undergo CPB surgery. All eligible participants will be randomly allocated to either the amiodarone or placebo group by using the block randomization in a 1:1 ratio. The primary end point will be the incidence rate of VF 30 minutes after ACC release and be assessed using the Fisher exact test. All data will be analyzed in accordance with the intention-to-treat principle.

RESULTS

The study began in August 2022, and the data collection will take place for the next 2 academic years. As of this writing, 21 participants have already been recruited for the study.

CONCLUSIONS

With this trial, we are hoping to demonstrate that prophylactic infusion of amiodarone before ACC release could reduce the occurrence of reperfusion VF in patients with LVH.

TRIAL REGISTRATION

ClinicalTrials.gov ChiCTR2000035057; https://www.chictr.org.cn/showprojen.aspx?proj=57145.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/40115.

Comparison of Resuscitation Outcomes Between 2- or 3-Stacked Defibrillation Strategies With Minimally Interrupted Chest Compression and the Single Defibrillation Strategy: A Swine Cardiac Arrest Model

Background There is controversy over whether the number and mode of electrical shock are optimal for successful defibrillation. Methods and Results Fifty-four pigs were randomly assigned to 3 groups. After inducing ventricular fibrillation and a 2-minute downtime, basic life support was initiated with a 30:2 compression/ventilation ratio for 8 minutes. Subsequently, 20 minutes of advanced life support, including asynchronous ventilation, every 10 chest compressions with 15 L/min of oxygen, was delivered. Animals of the single shock group received a single shock, animals of the 2-stacked shock group received 2 consecutive shocks, and animals of the 3-stacked shock group received 3 consecutive shocks. Animals with the return of spontaneous circulation underwent post-cardiac arrest care for 12 hours. The rates of successful defibrillation, return of spontaneous circulation, 24-hour survival, and 48-hour survival and neurological deficit score were compared between the groups. Hemodynamic parameters, arterial blood gas profiles, troponin I, and cardiac output were not different between the groups. There was a significant difference in chest compression fraction between the single and 3-stacked shock groups (P<0.001), although there was no difference between the single and 2-stacked shock groups (P=0.022) or the 2-stacked and 3-stacked shock groups (P=0.040). The rates of successful defibrillation, return of spontaneous circulation, 24-hour survival, and 48-hour survival were higher in the 2- and 3-stacked shock groups than in the single shock group (P=0.021, P=0.015, and P=0.021, respectively). Neurological deficit score at 48 hours was not different between the groups. Conclusions A stacked shock strategy was superior to a single shock strategy for successful defibrillation and better resuscitation outcomes in treating ventricular fibrillation.

The Defibrillation Conundrum: New Insights into the Mechanisms of Shock-Related Myocardial Injury Sustained from a Life-Saving Therapy

Implantable cardiac defibrillators (ICDs) are recommended to prevent the risk of sudden cardiac death. However, shocks are associated with an increased mortality with a dose response effect, and a strategy of reducing electrical therapy burden improves the prognosis of implanted patients. We review the mechanisms of defibrillation and its consequences, including cell damage, metabolic remodeling, calcium metabolism anomalies, and inflammatory and pro-fibrotic remodeling. Electrical shocks do save lives, but also promote myocardial stunning, heart failure, and pro-arrhythmic effects as seen in electrical storms. Limiting unnecessary implantations and therapies and proposing new methods of defibrillation in the future are recommended.

Heart defibrillation: relationship between pacing threshold and defibrillation probability

BACKGROUND

Considering the clinical importance of the ventricular fibrillation and that the most used therapy to reverse it has a critical side effect on the cardiac tissue, it is desirable to optimize defibrillation parameters to increase its efficiency. In this study, we investigated the influence of stimuli duration on the relationship between pacing threshold and defibrillation probability.

RESULTS

We found out that 0.5-ms-long pulses had a lower ratio of defibrillation probability to the pacing threshold, although the higher the pulse duration the lower is the electric field intensity required to defibrillate the hearts.

CONCLUSION

The appropriate choice of defibrillatory shock parameters is able to increase the efficiency of the defibrillation improving the survival chances after the occurrence of a severe arrhythmia. The relationship between pulse duration and the probability of reversal of fibrillation shows that this parameter cannot be underestimated in defibrillator design since different pulse durations have different levels of safety.

Subcutaneous cardioverter defibrillator has longer time to therapy but is less cardiotoxic than transvenous cardioverter defibrillator. Study carried out in a preclinical porcine model

Aims

Totally subcutaneous implantable cardioverter defibrillator (S-ICD) delivers higher shock energy and can have longer time to therapy compared to transvenous implantable cardioverter defibrillator (T-ICD). Aim of the study was to compare time to therapy and to investigate cardiac, cerebral and systemic injuries of S-ICD and T-ICD shocks delivered after ventricular fibrillation (VF) induction.

Methods and results

Fourteen pigs were randomly implanted with a S-ICD (n = 7) or a T-ICD (n = 7). Five VF episodes were induced in each pig. For each VF episode, up to two shocks could be delivered by the T-ICD or the S-ICD to terminate the arrhythmia. Cardiac, systemic, and cerebral toxicity were monitored. Mean time to therapy was longer in the S-ICD group compared to the T-ICD group (19[18; 23] s vs. 9 [7; 10] s; P = 0.001, respectively). High-sensitivity troponin T levels were significantly higher in the T-ICD group from 1 to 24 h after the procedure (P ≤ 0.02). Creatine phosphokinase activity levels were significantly higher in the S-ICD group, at 3, 6, and 24 h after the procedure (P ≤ 0.05). Lactate levels were not significantly different between groups. S100 protein level was similar in both groups at 1 h after the procedure and then decreased in the T-ICD group compared to the S-ICD group (P = 0.04).

Conclusions

Time to therapy in S-ICD was twice as long as for T-ICD, but didn't induce relevant brain injury. Conversely, S-ICD shocks were less cardiotoxic than T-ICD shocks.

Myocardial dysfunction after out-of-hospital cardiac arrest: predictors and prognostic implications

We aim to determine the incidence of early myocardial dysfunction after out-of-hospital cardiac arrest, risk factors associated with its development, and association with outcome. A retrospective chart review was performed among consecutive out-of-hospital cardiac arrest (OHCA) patients who underwent echocardiography within 24 h of return of spontaneous circulation at three urban teaching hospitals. Our primary outcome is early myocardial dysfunction, defined as a left ventricular ejection fraction < 40% on initial echocardiogram. We also determine risk factors associated with myocardial dysfunction using multivariate analysis, and examine its association with survival and neurologic outcome. A total of 190 patients achieved ROSC and underwent echocardiography within 24 h. Of these, 83 (44%) patients had myocardial dysfunction. A total of 37 (45%) patients with myocardial dysfunction survived to discharge, 39% with intact neurologic status. History of congestive heart failure (OR 6.21; 95% CI 2.54-15.19), male gender (OR 2.27; 95% CI 1.08-4.78), witnessed arrest (OR 4.20; 95% CI 1.78-9.93), more than three doses of epinephrine (OR 6.10; 95% CI 1.12-33.14), more than four defibrillations (OR 4.7; 95% CI 1.35-16.43), longer duration of resuscitation (OR 1.06; 95% CI 1.01-1.10), and therapeutic hypothermia (OR 3.93; 95% CI 1.32-11.75) were associated with myocardial dysfunction. Cardiopulmonary resuscitation immediately initiated by healthcare personnel was associated with lower odds of myocardial dysfunction (OR 0.40; 95% CI 0.17-0.97). There was no association between early myocardial dysfunction and mortality or neurological outcome. Nearly half of OHCA patients have myocardial dysfunction. A number of clinical factors are associated with myocardial dysfunction, and may aid providers in anticipating which patients need early diagnostic evaluation and specific treatments. Early myocardial dysfunction is not associated with neurologically intact survival.

INvestigation on Routine Follow-up in CONgestive HearT FAilure Patients with Remotely Monitored Implanted Cardioverter Defibrillators SysTems (InContact)

Background

In heart failure (HF) patients with implantable cardioverter defibrillators (ICD) or cardiac resynchronisation therapy defibrillators (CRT-D), remote monitoring has been shown to result in at least non-inferior outcomes relative to in-clinic visits. We aimed to provide further evidence for this effect, and to assess whether adding telephone follow-ups to remote follow-ups influenced outcomes.

Methods

InContact was a prospective, randomised, multicentre study. Subjects receiving quarterly automated follow-up only (telemetry group) were compared to those receiving personal physician contact. Personal contact patients were further divided into those receiving automated follow-up plus a telephone call (remote+phone subgroup) or in-clinic visits only.

Results

Two hundred and ten patients underwent randomisation (telemetry n = 102; personal contact n = 108 [remote+phone: n = 53; visit: n = 55]). Baseline characteristics were comparable between groups and subgroups. Over 12 months, 34.8% of patients experienced deterioration of their Packer Clinical Composite Response, with no significant difference between the telemetry group and personal care (p > 0.999), remote+phone (p = 0.937) or visit (p = 0.940) patients; predefined non-inferiority criteria were met. Mortality rates (5.2% overall) were comparable between groups and subgroups (p = 0.832/p = 0.645), as were HF-hospitalisation rates (11.0% overall; p = 0.605/p = 0.851). The proportion of patients requiring ≥1 unscheduled follow-up was nominally higher in telemetry and remote+phone groups (42.2 and 45.3%) compared to the visit group (29.1%). Overall, ≥ 1 ICD therapy was delivered to 15.2% of patients.

Conclusion

In HF patients with ICDs/CRT-Ds, quarterly remote follow-up only over 12 months was non-inferior to regular personal contact. Addition of quarterly telephone follow-ups to remote monitoring does not appear to offer any clinical advantage.

Trial registration

clinicaltrials.gov: NCT01200381 (retrospectively registered on September 13th 2010).

Efficacy of amiodarone and lidocaine for preventing ventricular fibrillation after aortic cross-clamp release in open heart surgery: a meta-analysis of randomized controlled trials

OBJECTIVE

The relative preventative efficacy of amiodarone and lidocaine for ventricular fibrillation (VF) after release of an aortic cross-clamp (ACC) during open heart surgery has not been determined. This meta-analysis was designed to systematically evaluate the influence of amiodarone, lidocaine, or placebo on the incidence of VF after ACC.

METHODS

Prospective randomized controlled trials (RCTs) that compared the VF-preventative effects of amiodarone with lidocaine, or amiodarone or lidocaine with placebo were included. PubMed, EMBASE, and the Cochrane Library were searched for relevant RCTs. Fixed or randomized effect models were applied according to the heterogeneity of the data from the selected studies.

RESULTS

We included eight RCTs in the analysis. Pooled results suggested that the preventative effects of amiodarone and lidocaine were comparable (relative risk (RR)=1.12, 95% confidence interval (CI): 0.70 to 1.80, P=0.63), but both were superior to the placebo (amiodarone, RR=0.71, 95% CI: 0.51 to 1.00, P=0.05; lidocaine, RR=0.63, 95% CI: 0.46 to 0.88, P=0.006). The percentage of patients requiring electric defibrillation counter shocks (DCSs) did not differ significantly among patients administered amiodarone (RR=0.21, 95% CI: 0.04 to 1.19, P=0.08), lidocaine (RR=2.44, 95% CI: 0.13 to 44.02, P=0.55), or the placebo (RR=0.56, 95% CI: 0.25 to 1.25, P=0.16).

CONCLUSIONS

Amiodarone and lidocaine are comparably effective in preventing VF after ACC, but the percentage of patients who subsequently require DCSs does not differ among those administered amiodarone, lidocaine, or placebo.

Novel CPR system that predicts return of spontaneous circulation from amplitude spectral area before electric shock in ventricular fibrillation

AIM

Amplitude spectral area (AMSA), an index for analysing ventricular fibrillation (VF) waveforms, is thought to predict the return of spontaneous circulation (ROSC) after electric shocks, but its validity is unconfirmed. We developed an equation to predict ROSC, where the change in AMSA (ΔAMSA) is added to AMSA measured immediately before the first shock (AMSA1). We examine the validity of this equation by comparing it with the conventional AMSA1-only equation.

METHOD

We retrospectively investigated 285 VF patients given prehospital electric shocks by emergency medical services. ΔAMSA was calculated by subtracting AMSA1 from last AMSA immediately before the last prehospital electric shock. Multivariate logistic regression analysis was performed using post-shock ROSC as a dependent variable.

RESULTS

Analysis data were subjected to receiver operating characteristic curve analysis, goodness-of-fit testing using a likelihood ratio test, and the bootstrap method. AMSA1 (odds ratio (OR) 1.151, 95% confidence interval (CI) 1.086-1.220) and ΔAMSA (OR 1.289, 95% CI 1.156-1.438) were independent factors influencing ROSC induction by electric shock. Area under the curve (AUC) for predicting ROSC was 0.851 for AMSA1-only and 0.891 for AMSA1+ΔAMSA. Compared with the AMSA1-only equation, the AMSA1+ΔAMSA equation had significantly better goodness-of-fit (likelihood ratio test P<0.001) and showed good fit in the bootstrap method.

CONCLUSIONS

Post-shock ROSC was accurately predicted by adding ΔAMSA to AMSA1. AMSA-based ROSC prediction enables application of electric shock to only those patients with high probability of ROSC, instead of interrupting chest compressions and delivering unnecessary shocks to patients with low probability of ROSC.

Decreased Defibrillation Threshold and Minimized Myocardial Damage With Left Axilla Implantable Cardioverter Defibrillator Implantation

BACKGROUND

To reduce myocardial damage caused by implantable cardioverter defibrillator (ICD) shock, the left axilla was studied as an alternative pulse generator implantation site, and compared with the traditional implantation site, the left anterior chest.

METHODS AND RESULTS

Computer simulation was used to study the defibrillation conduction pattern and estimate the simulated defibrillation threshold (DFT) and myocardial damage when pulse generators were placed in the left axilla and left anterior chest, respectively; pulse generators were also newly implanted in the left axilla (n=30) and anterior chest (n=40) to compare the corresponding DFT. On simulation, when ICD generators were implanted in the left axilla, compared with the left anterior chest, the whole heart may be defibrillated with a lower defibrillation energy (left axilla 6.4 J vs. left anterior chest 12.0 J) and thus the proportion of cardiac myocardial damage may be reduced (2.1 vs. 4.2%). Clinically, ventricular fibrillation was successfully terminated with a defibrillation output ≤5 J in 86.7% (26/30) of the left axillary group, and in 27.5% (11/40) of the left anterior group (P<0.001).

CONCLUSIONS

Clinically and theoretically, the left axilla was shown to be an improved ICD implantation site that may reduce DFT and lessen myocardial damage due to shock. Lower DFT also facilitates less myocardial damage, as a result of the lower shock required.

The effect of lidocaine and amiodarone on prevention of ventricular fibrillation in patients undergoing coronary artery bypass grafting

OBJECTIVE

Ventricular fibrillation is common after aortic declamping in patients undergoing open heart surgery. This situation has a negative impact on morbidity and mortality. The aim of this prospective study was to compare the effect of administering lidocaine versus amiodarone before aortic declamping during elective coronary bypass grafting, paying close attention to when the initial effect of amiodarone sets in.

METHODS

In this double blind, prospective, randomized, controlled study, 86 patients who were candidates for elective coronary artery bypass grafting were recruited into three groups: group lidocaine (group L, n=29); group amiodarone (group A, n=27); and group placebo (group P, n=30). Group L patients received 1.5 mg/kg of lidocaine 2 minutes before aortic declamping and group A patients received 300 mg of amiodarone intravenously 15 minutes before release of the aortic cross clamp. The primary endpoints were the incidence of ventricular fibrillation and the number of shocks required to terminate ventricular fibrillation.

RESULTS

The frequency of ventricular fibrillation occurrence was significantly higher in group P (70%) when compared with group A (37%) and group L (38%) (P=.017). There was no statistically significant difference between the amiodarone and the lidocaine groups regarding ventricular fibrillation. However, when ventricular fibrillation occurred, the percentage of patients requiring electrical defibrillation was significantly higher in both group L and group P when compared with group A (P=.023).

CONCLUSION

We suggest that during coronary arterial bypass surgery, administration of an amiodarone regime before release of the aortic cross clamp, paying particular attention to the start of the initial effect of amiodarone, is no more effective than lidocaine for prevention from arrhythmia; however, amiodarone reduces the need for electrical defibrillation.

The effects of α- and β-adrenergic blocking agents on postresuscitation myocardial dysfunction and myocardial tissue injury in a rat model of cardiac arrest

We investigated the relationship between the severity of postresuscitation (PR) myocardial tissue injury and myocardial dysfunction after the administration of epinephrine as well as the protective effects of α- and β-adrenergic blocking agents. Forty male Sprague-Dawley rats were randomized into 6 groups: (1) placebo; (2) epinephrine; (3) epinephrine pretreated with α1-blocker (prazosin); (4) epinephrine pretreated with α2-blocker (yohimbine); (5) epinephrine pretreated with β-blocker (propranolol); and (6) epinephrine pretreated with β- plus α1-blocker (propranolol and prazosin). Cardiopulmonary resuscitation was initiated after 8 minutes of untreated ventricular fibrillation and continued for an additional 8 minutes. The myocardial function and the serum concentrations of troponin I (Tn I) and N-terminal probrain natriuretic peptide (NT-proBNP) were measured at baseline and after resuscitation. After resuscitation, both Tn I and NT-proBNP were significantly increased in all groups, especially in the epinephrine and epinephrine pretreated with α2-blocker groups. Significantly better PR myocardial function and neurologic deficit score were observed in epinephrine pretreated with the α1- or β-blocker with decreased releases of Tn I and NT-proBNP. However, the most significant improvements were observed in the animals pretreated with β- plus α1-blocker. The present study demonstrated that myocardial stunning may not be the only mechanism of PR myocardial dysfunction. Administration of epinephrine increased the severity of PR myocardial tissue injury and dysfunction. The β- and β- plus α1-blocker pretreatment significantly reduced the severity of PR myocardial tissue injury and myocardial dysfunction with better neurologic function and prolonged duration of survival.

Unnecessary shock from an implantable cardioverter-defibrillator following transcutaneous pacing

As the population ages and cardiovascular disease becomes more prevalent, an increasing number of patients are receiving implantable cardioverter-defibrillators (ICDs). When these patients present to the emergency department, it is imperative that physicians are not only aware of the possible underlying medical issues that may have precipitated their admission but should also have a good understanding of the potential interactions that any medical intervention may have on the patient’s device. We discuss a case in which a patient known to have an ICD in situ was transcutaneously paced for the management of bradycardia, leading to an unnecessary shock.

Postcardioplegia ventricular fibrillation: no impact on subsequent survival

OBJECTIVES

At aortic declamping after cardioplegic cardiac arrest, the initial rhythm can be broadly classified as ventricular fibrillation (VF) or non-VF. VF can be treated with potassium-induced conversion and direct-current countershock is only applied if potassium treatment fails. We aimed to investigate whether there are any differences between these groups of patients in regard to outcomes.

DESIGN

From January 1999 through December 2010, 12,113 patients underwent various types of cardiac surgery. Data from every patient were consecutively registered. Survival was established through the Norwegian National Registry. Cox multivariable modeling with adjustment for clinical, biochemical, and medication baseline data was used for survival analysis.

RESULTS

The mean follow-up time was 7.4 years and total patient-years were 89,268. The percentage of all-cause deaths was 24.9. Adjusted survival for patients with no postcardioplegia VF (n = 9723) and patients with successful potassium-induced conversion (n = 1877) was completely identical. Four hundred patients with electrical conversion after failed potassium treatment had a nonsignificant trend toward an increased mortality (hazard ratio, 95% confidence interval: 1.19 (0.99-1.4); p = 0.07).

CONCLUSIONS

This is the first study reporting the association between postcardioplegia VF, its treatment with potassium and outcome. No impact was found on outcome as judged by all-cause mortality.

How to improve outcomes: should we put more emphasis on programming and medical care and less on patient selection?

Many factors contribute to the pathophysiology and progression of heart failure (HF), offering the potential for many synergistic therapeutic approaches to its management. For patients, who have systolic HF, prolonged QRS and receiving guideline-indicated pharmacological therapy, cardiac resynchronization therapy (CRT) may provide additional benefits in terms of symptom improvement and mortality reduction. Nevertheless, in many patients, moderate or severe symptoms may persist or recur after CRT implantation due to either the severity or progression of the underlying disease, the presence of important co-morbidities or suboptimal device programming. Identifying and, where possible, treating the reasons for persistent or recurrent symptoms in patients who have received CRT is an important aspect of patient care. The present review summarizes the available evidence on this topic.

Is there an association between external cardioversions and long-term mortality and morbidity? Insights from the Atrial Fibrillation Follow-up Investigation of Rhythm Management study

BACKGROUND

Cardiac electric therapies effectively terminate tachyarrhythmias. Recent data suggest a possible increase in long-term mortality associated with implantable cardioverter-defibrillator shocks. Little is known about the association between external cardioversion episodes (ECVe) and long-term mortality. We sought to assess the safety of repeated ECVe with regard to cardiovascular mortality and morbidity.

METHODS AND RESULTS

We analyzed the data of the 4060 patients from the AFFIRM (Atrial Fibrillation Follow-up Investigation of Rhythm Management) trial. In particular, associations of ECVe with all-cause mortality, cardiovascular mortality, and hospitalizations after ECVe were studied. Over an average follow-up of 3.5 years, 660 (16.3%) patients died, 331 (8.2%) from cardiovascular causes. A total of 207 (5.1%) and 1697 (41.8%) patients had low ejection fraction and nonparoxysmal atrial fibrillation, respectively; 2460 patients received no ECVe, whereas 1600 experienced ≥ 1 ECVe. Death occurred in 412 (16.7%), 196 (16.5%), 39 (13.5%), and 13 (10.4%) of patients with 0, 1, 2, and ≥ 3 ECVe, respectively. There was no significant association between ECVe and mortality within any of the 4 subgroups defined by ejection fraction and atrial fibrillation type, although myocardial infarction, coronary artery bypass graft, and digoxin were significantly associated with death (estimated hazard ratios, 1.65, 1.59, and 1.62, respectively; P < 0.0001). ECVe were associated with increased cardiac hospitalization reported at the next follow-up visit (39.3% versus 5.8%; estimated odds ratio, 1.39; P < 0.0001).

CONCLUSIONS

In the AFFIRM study, there was no significant association between ECVe and long-term mortality, even though ECVe were associated with increased hospitalizations from cardiac causes. Digoxin, myocardial infarction, and coronary artery bypass graft were significantly associated with mortality.

Prompt prediction of successful defibrillation from 1-s ventricular fibrillation waveform in patients with out-of-hospital sudden cardiac arrest

PURPOSE

Ventricular fibrillation (VF) is a common cardiac arrest rhythm that can be terminated by electrical defibrillation. During cardiopulmonary resuscitation, there is a strong need for a prompt and reliable predictor of successful defibrillation because myocardial damage can result from repeated futile defibrillation attempts. Continuous wavelet transform (CWT) provides excellent time and frequency resolution of signals. The purpose of this study was to evaluate whether features based on CWT could predict successful defibrillation.

METHODS

VF electrocardiogram (ECG) waveforms stored in ambulance-located defibrillators were collected. Predefibrillation waveforms were divided into 1.0- or 5.12-s VF waveforms. Indices in frequency domain or nonlinear analysis were calculated on the 5.12-s waveform. Simultaneously, CWT was performed on the 1.0-s waveform, and total low-band (1-3 Hz), mid-band (3-10 Hz), and high-band (10-32 Hz) energy were calculated.

RESULTS

In 152 patients with out-of-hospital cardiac arrest, a total of 233 ECG predefibrillation recordings, consisting of 164 unsuccessful and 69 successful episodes, were analyzed. Indices of frequency domain analysis (peak frequency, centroid frequency, and amplitude spectral area), nonlinear analysis (approximate entropy and Hurst exponent, detrended fluctuation analysis), and CWT analysis (mid-band and high-band energy) were significantly different between unsuccessful and successful episodes (P < 0.01 for all). However, logistic regression analysis showed that centroid frequency and total mid-band energy were effective predictors (P < 0.01 for both).

CONCLUSIONS

Energy spectrum analysis based on CWT as short as a 1.0-s VF ECG waveform enables prompt and reliable prediction of successful defibrillation.

Tunnel propagation following defibrillation with ICD shocks: hidden postshock activations in the left ventricular wall underlie isoelectric window

BACKGROUND

After near-defibrillation threshold (DFT) shocks from an implantable cardioverter-defibrillator (ICD), the first postshock activation that leads to defibrillation failure arises focally after an isoelectric window (IW). The mechanisms underlying the IW remain incompletely understood.

OBJECTIVE

The goal of this study was to provide mechanistic insight into the origins of postshock activations and IW after ICD shocks, and to link shock outcome to the preshock state of the ventricles. We hypothesized that the nonuniform ICD field results in the formation of an intramural excitable area (tunnel) only in the left ventricular (LV) free wall, through which both pre-existing and new shock-induced wavefronts propagate during the IW.

METHODS

Simulations were conducted using a realistic three dimensional (3D) model of defibrillation in the rabbit ventricles. Biphasic ICD shocks of varying strengths were delivered to 27 different fibrillatory states.

RESULTS

After near-DFT shocks, regardless of preshock state, the main postshock excitable area was always located within LV free wall, creating an intramural tunnel. Either pre-existing fibrillatory or shock-induced wavefronts propagated during the IW (duration of up to 74 ms) in this tunnel and emerged as breakthroughs on LV epicardium. Preshock activity within the LV played a significant role in shock outcome: a large number of preshock filaments resulted in an IW associated with tunnel propagation of pre-existing rather than shock-induced wavefronts. Furthermore, shocks were more likely to succeed if the LV excitable area was smaller.

CONCLUSION

The LV intramural excitable area is the primary reason for near-DFT failure. Any intervention that decreases the extent of this area will improve the likelihood of defibrillation success.

Comparison of low-energy versus high-energy biphasic defibrillation shocks following prolonged ventricular fibrillation

INTRODUCTION

Since the initial development of the defibrillator, there has been concern that, while delivery of a large electric shock would stop fibrillation, it would also cause damage to the heart. This concern has been raised again with the development of the biphasic defibrillator.

OBJECTIVE

To compare defibrillation efficacy, postshock cardiac function, and troponin I levels following 150-J and 360-J shocks.

METHODS

Nineteen swine were anesthetized with isoflurane and instrumented with pressure catheters in the left ventricle, aorta, and right atrium. The animals were fibrillated for 6 minutes, followed by defibrillation with either low-energy (n = 8) or high-energy (n = 11) shocks. After defibrillation, chest compressions were initiated and continued until return of spontaneous circulation (ROSC). Epinephrine, 0.01 mg/kg every 3 minutes, was given for arterial blood pressure < 50 mmHg. Hemodynamic parameters were recorded for four hours. Transthoracic echocardiography was performed and troponin I levels were measured at baseline and four hours following ventricular fibrillation (VF).

RESULTS

Survival rates at four hours were not different between the two groups (low-energy, 5 of 8; high-energy, 7 of 11). Results for arterial blood pressure, positive dP/dt (first derivative of pressure measured over time, a measure of left ventricular contractility), and negative dP/dt at the time of lowest arterial blood pressure (ABP) following ROSC were not different between the two groups (p = not significant [NS]), but were lower than at baseline. All hemodynamic measures returned to baseline by four hours. Ejection fractions, stroke volumes, and cardiac outputs were not different between the two groups at four hours. Troponin I levels at four hours were not different between the two groups (12 +/- 11 ng/mL versus 21 +/- 26 ng/mL, p = NS) but were higher at four hours than at baseline (19 +/- 19 ng/mL versus 0.8 +/- 0.5 ng/mL, p < 0.05, groups combined).

CONCLUSION

Biphasic 360-J shocks do not cause more cardiac damage than biphasic 150-J shocks in this animal model of prolonged VF and resuscitation.

Impact of implantable cardioverter-defibrillator, amiodarone, and placebo on the mode of death in stable patients with heart failure: analysis from the sudden cardiac death in heart failure trial

BACKGROUND

The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) demonstrated that implantable cardioverter-defibrillator (ICD) therapy reduces all-cause mortality in patients with New York Heart Association class II/III heart failure and a left ventricular ejection fraction < or =35% on optimal medical therapy. Whether ICD therapy reduced sudden death caused by ventricular tachyarrhythmias without affecting heart failure deaths in this population is unknown.

METHODS AND RESULTS

SCD-HeFT randomized 2521 subjects to placebo, amiodarone, or shock-only, single-lead ICD therapy. Over a median follow-up of 45.5 months, a total of 666 deaths occurred, which were reviewed by an Events Committee and initially categorized as cardiac or noncardiac. Cardiac deaths were further adjudicated as resulting from sudden death presumed to be ventricular tachyarrhythmic, bradyarrhythmia, heart failure, or other cardiac causes. ICD therapy significantly reduced cardiac mortality compared with placebo (adjusted hazard ratio, 0.76; 95% confidence interval, 0.60 to 0.95) and tachyarrhythmia mortality (adjusted hazard ratio, 0.40; 95% confidence interval, 0.27 to 0.59) and had no impact on mortality resulting from heart failure or noncardiac causes. The cardiac and tachyarrhythmia mortality reductions were evident in subjects with New York Heart Association class II but not in subjects with class III heart failure. The reduction in tachyarrhythmia mortality with ICD therapy was similar in subjects with ischemic and nonischemic disease. Compared with placebo, amiodarone had no significant effect on any mode of death.

CONCLUSIONS

ICD therapy reduced cardiac mortality and sudden death presumed to be ventricular tachyarrhythmic in SCD-HeFT and had no effect on heart failure mortality. Amiodarone had no effect on all-cause mortality or its cause-specific components, except an increase in non-cardiac mortality in class III patients. [corrected]

CLINICAL TRIAL REGISTRATION INFORMATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00000609.

Improved outcomes of cardiopulmonary resuscitation in rats with myocardial infarction treated with allogenic bone marrow mesenchymal stem cells

OBJECTIVE

We hypothesized that rats in which myocardial infarction had been treated with mesenchymal stem cells (MSCs) would have better outcomes following the global myocardial ischemia of cardiac arrest and cardiopulmonary resuscitation (CPR) compared with rats in which myocardial infarction had been treated with phosphate buffer solution (PBS).

DESIGN

Prospective, randomized controlled study.

SETTING

University-affiliated research institute.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Myocardial infarction was induced in 18 male Sprague-Dawley rats. Four weeks later, animals were randomized to receive 5 x 10 MSCs labeled with red fluorescent dye gel (PKH26) in PBS or a PBS-alone injection into right femoral vein.

MEASUREMENTS AND MAIN RESULTS

Echocardiographically measured myocardial function, including ejection fraction, left ventricular end-diastolic volume, and left ventricular end-systolic volume, was quantitated 2 and 4 weeks after administering MSCs or PBS. Four weeks after MSCs or PBS injection, 6 minutes of ventricular fibrillation (VF) and 6 minutes of CPR were performed before defibrillation. Myocardial function, including cardiac index, left ventricular, dP/dt max (dP/dt max), left ventricular negative dP/dt min (-dP/dt min), and left ventricular diastolic pressure, was measured before inducing VF and hourly following return of spontaneous circulation. Labeled MSCs were observed in 5-mum cryostat sections from each harvested heart. Significant improvements in ejection fraction, left ventricular end-diastolic volume, left ventricular end-systolic volume, cardiac index, dP/dt max, -dP/dt min, and left ventricular diastolic pressure followed injection of MSCs before inducing VF. Following return of spontaneous circulation, myocardial function was significantly better in animals pretreated with MSCs; this was associated with significantly increased duration of postresuscitation survival.

CONCLUSIONS

Myocardial function before and after CPR and duration of survival after CPR were significantly improved in animals in which myocardial infarction was treated with MSCs. MSCs existing in the myocardium resisted a secondary ischemic event and provided better postresuscitation myocardial function.

Prognostic importance of defibrillator shocks in patients with heart failure

BACKGROUND

Patients with heart failure who receive an implantable cardioverter-defibrillator (ICD) for primary prevention (i.e., prevention of a first life-threatening arrhythmic event) may later receive therapeutic shocks from the ICD. Information about long-term prognosis after ICD therapy in such patients is limited.

METHODS

Of 829 patients with heart failure who were randomly assigned to ICD therapy, we implanted the ICD in 811. ICD shocks that followed the onset of ventricular tachycardia or ventricular fibrillation were considered to be appropriate. All other ICD shocks were considered to be inappropriate.

RESULTS

Over a median follow-up period of 45.5 months, 269 patients (33.2%) received at least one ICD shock, with 128 patients receiving only appropriate shocks, 87 receiving only inappropriate shocks, and 54 receiving both types of shock. In a Cox proportional-hazards model adjusted for baseline prognostic factors, an appropriate ICD shock, as compared with no appropriate shock, was associated with a significant increase in the subsequent risk of death from all causes (hazard ratio, 5.68; 95% confidence interval [CI], 3.97 to 8.12; P<0.001). An inappropriate ICD shock, as compared with no inappropriate shock, was also associated with a significant increase in the risk of death (hazard ratio, 1.98; 95% CI, 1.29 to 3.05; P=0.002). For patients who survived longer than 24 hours after an appropriate ICD shock, the risk of death remained elevated (hazard ratio, 2.99; 95% CI, 2.04 to 4.37; P<0.001). The most common cause of death among patients who received any ICD shock was progressive heart failure.

CONCLUSIONS

Among patients with heart failure in whom an ICD is implanted for primary prevention, those who receive shocks for any arrhythmia have a substantially higher risk of death than similar patients who do not receive such shocks.

Postresuscitation myocardial stunning and its outcome: new approaches

What is the successful cardiopulmonary resuscitation? It is the few minutes postcardiopulmonary arrest that can answer. Twenty to 40 percent of patients who sustained cardiac arrest are initially resuscitated, but only 10% survive to hospital discharge, and more than 60% of victims succumb within 24 hours. This high fatality rate in the early hours and days after successful resuscitation is mainly related to the acute, intense, and reversible form of postresuscitation myocardial dysfunction (stunning) together with the ventricular tachyarrhythmia. It is a reversible process, provided that we are aware of the pertinent pathophysiology and then intervene accordingly. Herein I reviewed most of the published relevant articles concerning the causes, underlying mechanism, and the updated trials for management of postresuscitation myocardial stunning. I do agree that not only the restoration of the circulation but also long-term outcome should be the aim of resuscitation, and I readdress the role of epinephrine, dobutamine, biphasic defibrillator, with the new promising agent (ie, potassium channel opener), Delta-opioid receptor agonist, unloading intracellular calcium, antioxidants, and therapeutic hypothermia to halt this period of stunning. This will improve the outcome of the resuscitation efforts.

Alteration in transthoracic impedance following cardiac surgery

INTRODUCTION

Haemodynamically significant ventricular tachyarrhythmias are a frequent complication in the immediate post-operative period after cardiac surgery. Successful cardioversion depends on delivery of sufficient current, which in turn is dependent on transthoracic impedance (TTI). However, it is uncertain if there is a change in TTI immediately following cardiac surgery using cardiopulmonary bypass (CPB).

METHODS

TTI was measured on 40 patients undergoing first time isolated cardiac surgery using CPB. TTI was recorded at 30 kHz using Bodystat Multiscan 5000 equipment before operation (with and without a positive end-expiratory pressure (PEEP) of 5 cm of H(2)O) and then at 1, 4 and 24 h after the operation. Data was analyzed to determine the relationship between pre- and post-operative variables and TTI values.

RESULTS

Mean pre-operative TTI was 54.5+/-10.55 ohms without PEEP and 61.8+/-15.4 ohms on a PEEP of 5 cm of H(2)O. TTI dropped significantly (p<0.001) after the operation to 47.2+/-10.6 ohms at 1 h, 42.6+/-10.2 ohms at 4 h and 41.8+/-10.4 ohms at 24 h. A positive correlation was noted between duration of operation and TTI change at 1 h (r=0.38; p=0.016). There was no significant correlation between the duration of bypass and change in TTI.

CONCLUSION

TTI decreases by more than 30% in the immediate post-operative period following cardiac surgery. This state may favour defibrillation at lower energy levels.

Prediction of countershock success using single features from multiple ventricular fibrillation frequency bands and feature combinations using neural networks

Targeted defibrillation therapy is needed to optimise survival chances of ventricular fibrillation (VF) patients, but at present VF analysis strategies to optimise defibrillation timing have insufficient predictive power. From 197 patients with in-hospital and out-of-hospital cardiac arrest, 770 electrocardiogram (ECG) recordings of countershock attempts were analysed. Preshock VF ECG features in the time and frequency domain were tested retrospectively for outcome prediction. Using band pass filters, the ECG spectrum was split into various frequency bands of 2-26 Hz bandwidth in the range of 0-26 Hz. Neural networks were used for single feature combinations to optimise prediction of countershock success. Areas under curves (AUC) of receiver operating characteristics (ROC) were used to estimate prediction power of single and combined features. The highest ROC AUC of 0.863 was reached by the median slope in the interval 10-22 Hz resulting in a sensitivity of 95% and a specificity of 50%. The best specificity of 55% at the 95% sensitivity level was reached by power spectrum analysis (PSA) in the 6-26 Hz interval. Neural networks combining single predictive features were unable to increase outcome prediction. Using frequency band segmentation of human VF ECG, several single predictive features with high ROC AUC>0.840 were identified. Combining these single predictive features using neural networks did not further improve outcome prediction in human VF data. This may indicate that various simple VF features, such as median slope already reach the maximum prediction power extractable from VF ECG.

Postresuscitation myocardial dysfunction: correlated factors and prognostic implications

OBJECTIVE

To evaluate the clinical factors correlated with postresuscitation myocardial dysfunction and the prognostic implication such dysfunction may have.

DESIGN AND SETTING

Prospective observational study in a university medical center

PATIENTS

58 adult patients successfully resuscitated from nontraumatic out-of-hospital cardiac arrest over 2 years.

MEASUREMENTS AND RESULTS

Echocardiographic evaluation of the left ventricular systolic and diastolic functions was performed 6 h postresuscitation and was analyzed in correlation to the clinical features and resuscitation factors. Univariate analysis revealed left ventricular ejection fraction (LVEF) to be significantly lower in patients with hypertension, past history of myocardial infarction, resuscitation duration longer than 20 min, defibrillation, and use of more than 5 mg epinephrine. Isovolumic relaxation time (IVRT) was significantly longer in patients with noncardiac cause and initial rhythm of nonventricular fibrillation/tachycardia. Multiple regression analysis showed epinephrine dose and past history of myocardial infarction to be independent factors for LVEF, while the cause of cardiac arrest was independently associated with IVRT. For prognosis, 27 patients survived to hospital discharge. Both LVEF under 40% and IVRT 100 ms or longer were associated with poor survival outcomes. In Cox regression analysis IVRT 100 ms or longer served as an independent factor predicting poor survival prognosis.

CONCLUSIONS

Postresuscitation left ventricular dysfunction is correlated with a number of clinical factors, among which past history of myocardial infarction, epinephrine dose, and the cause of cardiac arrest play independent roles. Meanwhile, IVRT 100 ms or longer 6 h postresuscitation predicts poor survival outcomes and serves as a marker of poor prognosis.

A case of takotsubo-shaped hypokinesis of the left ventricle caused by a lightning strike

A 62-year-old woman was struck by lightning while on a mountain and fortunately did not suffer burns or unconsciousness. She stayed at a mountain lodge overnight and was taken to our hospital by helicopter the next day. Upon admission, electrocardiography showed ST segment elevation indicating acute lateral myocardial infarction, and echocardiography showed takotsubo-shaped hypokinesis of the left ventricle indicating an apical aneurysm. Her serum escaped enzyme levels were increased, as is typical in cases of myocardial infarction, however, she did not complain of cardiac symptoms. Coronary arteriography performed 4 days after admission showed a normal coronary artery while left ventriculography showed apical akinesia. An echocardiogram obtained 2 days later showed resolution of the LV wall motion abnormality. This is the first reported case of takotsubo cardiomyopathy caused by lightning. Takotsubo-shaped hypokinesis is not described as a complication of lightning-induced cardiac injury and its pathogenesis remains controversial.

The resuscitation outcome: revisit the story of the stony heart

Postresuscitation syndrome is a state of myocardial dysfunction after the restoration of circulation by successful resuscitation. Despite several advances in the field of resuscitation, the management of out-of-hospital cardiac arrest is still suboptimal. The high fatality rate shortly after successful resuscitation is mainly related to postresuscitation myocardial dysfunction. Postresuscitation myocardial stunning is reversible, while stony heart is irreversible due to prolonged unsuccessful resuscitation. This article reviews most of the published articles concerning the causes, mechanism, pathophysiology, and the updated trials for management of postresuscitation myocardial dysfunction. Further studies are warranted to highlight postresuscitation disease and its hemodynamic sequences and then to intervene according to the different phases of cardiac arrest. By modifying the conventional modalities of resuscitation together with new promising agents, the rescuers will be able to salvage the jeopardized postresuscitation myocardium and prevent its progression to the dismal stony heart. Community awareness and staff education are crucial to shorten resuscitation time and improve short-term and long-term outcomes. There is an urgent need to revise the guidelines for cardiopulmonary resuscitation in community setting, but how? It is a matter of where and when it is of enough value to be efficacious and cost-effective.

Effect of transthoracic shocks on left ventricular function

Although defibrillating shocks are thought to depress ventricular function transiently, the independent effects of high strength shocks (without the metabolic sequelae of pre-shock fibrillation) have not been assessed systematically in humans. Therefore, we delivered three consecutive synchronized monophasic transthoracic shocks (200, 200 and 360 J) at 60s intervals during sinus rhythm and evaluated the effect on left ventricular chamber size and function as determined by transesophageal echocardiography in 11 patients (mean age 67+/-8 years, 9M/2F) with depressed left ventricular function (left ventricular ejection fraction: 14-37%). The shocks did not alter hemodynamics consistently. On average, the shocks did not alter stroke volume, cardiac output, left ventricular ejection fraction or regional wall thickening (all p>0.05 versus baseline). This effect was highly variable and 36% of patients experienced a >25% reduction in cardiac output by the final shock. There was a tendency for regional wall thickening to worsen in the best baseline sextant with an offsetting significant increase in thickening in the worst baseline sextant (p=0.05). Thus, repetitive defibrillation strength transthoracic shocks do not impair left ventricular function consistently in patients with cardiomyopathy. However, the effect is widely variable and potentially important depression of left ventricular function does occur in some patients.

Comparison between dobutamine and levosimendan for management of postresuscitation myocardial dysfunction*

OBJECTIVE

To investigate the effects of levosimendan, a nonadrenergic inotropic calcium sensitizer, in comparison with adrenergic dobutamine for the management of postresuscitation myocardial dysfunction following resuscitation from prolonged cardiac arrest.

DESIGN

Randomized prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Male Yorkshire-cross domestic pigs

INTERVENTIONS

Ventricular fibrillation was induced in male domestic pigs weighing between 35 and 40 kg. Cardiopulmonary resuscitation, including precordial compression and mechanical ventilation, was started after 7 mins of untreated cardiac arrest. Electrical defibrillation was attempted after 5 mins of cardiopulmonary resuscitation. Each animal was successfully resuscitated without pharmacologic intervention. Resuscitated animals were randomized to treatment with levosimendan, dobutamine, or saline placebo. The inotropic agents or an equivalent volume of placebo diluents was administered 10 mins after restoration of spontaneous circulation. Levosimendan was administered in a loading dose of 20 microg.kg over 10 mins followed by a 220-min infusion of 0.4 microg.kg.min. Dobutamine was infused into the right atrium in an amount of 5 microg.kg.min. Treatment was continued for a total of 230 mins.

MEASUREMENTS AND MAIN RESULTS

Levosimendan and dobutamine produced comparable increases in cardiac output. However, levosimendan produced significantly greater left ventricular ejection fraction and fractional area changes compared with dobutamine and saline placebo.

CONCLUSIONS

Levosimendan has the potential of improving postresuscitation myocardial function. It is likely to serve as an alternative to dobutamine as an inotropic agent for management of postresuscitation myocardial dysfunction.

Amplitude spectrum area: Measuring the probability of successful defibrillation as applied to human data

OBJECTIVE

The objective of our study was to examine the effectiveness of an electrocardiographic predictor, amplitude spectral area (AMSA), for the optimal timing of defibrillation shocks in human victims of cardiac arrest. Based on the spectral characteristics of ventricular fibrillation potentials, we examined the probability of successful conversion to an organized viable rhythm, including the return of spontaneous circulation. The incentive was to predict the likelihood of successful defibrillation and thereby improve outcomes by minimizing interruptions in chest compression and minimizing electrically induced myocardial injury due to repetitive high-current shocks.

DESIGN

Observational study on human electrocardiographic recordings during cardiopulmonary resuscitation.

SETTING

Medical research laboratory of a university-affiliated research and educational institute.

PATIENTS

Victims of out-of-hospital cardiac arrest.

INTERVENTIONS

Iteration of electrocardiographic records, representing lead 2 equivalent recordings on 108 defibrillation attempts with an automated external defibrillator, of 46 victims of cardiac arrest due to ventricular fibrillation.

MEASUREMENTS AND MAIN RESULTS

Three seconds of ventricular fibrillation, recorded immediately preceding delivery of a shock, were analyzed utilizing the AMSA algorithm. AMSA represents a numerical value based on the sum of the magnitude of the weighted frequency spectrum between 3 and 48 Hz. The greater the AMSA value, the greater was the probability of reversal of ventricular fibrillation. At an AMSA value of >13.0 mV-Hz, successful defibrillation yielded a sensitivity of .91 and a specificity of .94.

CONCLUSION

AMSA predicts the success of electrical defibrillation with high specificity. AMSA therefore serves to minimize interruptions of precordial compression and the myocardial damage caused by delivery of repetitive and ineffective electrical shocks.

Milrinone Facilitates Resuscitation From Cardiac Arrest and Attenuates Postresuscitation Myocardial Dysfunction

Background— Left ventricular (LV) dysfunction with a low cardiac index after successful CPR contributes to early death attributable to multiorgan failure, and an effective treatment has not been identified. The purpose of this study was to investigate the use of milrinone, a selective phosphodiesterase III inhibitor, as treatment for LV dysfunction after resuscitation.

Methods and Results— Ventricular fibrillation (VF) was induced electrically in 32 swine. After 5 minutes of VF, CPR was initiated and animals were randomized to receive either saline (control group, n=16) as a bolus and infusion or milrinone 50 μg/kg as a bolus and then 0.5 μg/kg per min for 60 minutes (treatment group, n=16). After 2 minutes of CPR (total VF time, 7 minutes), countershocks were given. Coronary perfusion pressures during CPR were similar for the groups (24±2 versus 21±4 mm Hg). All animals were defibrillated; 6 of 16 control animals developed refractory postcountershock pulseless electrical activity compared with 0 of 16 treated animals ( P =0.018). At 30 minutes after restoration of spontaneous circulation, stroke volume (16±3 versus 26±7 mL, P <0.01) and LV dp/dt (793±197 versus 1108±316 mm Hg/s, P <0.02) were higher in the treatment group. Similar differences were observed 60 minutes after restoration of spontaneous circulation. Significant differences in heart rates between groups were not observed, and peripheral vascular resistance was significantly greater in the control group 30 and 60 minutes after resuscitation.

Conclusions— Milrinone facilitates resuscitation from prolonged VF and attenuates LV dysfunction after resuscitation without worsening major determinants of myocardial oxygen demand.

Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?

Sufficiently strong defibrillation shocks will cause temporary or permanent damage to the heart. Weak defibrillation shocks do not cause any damage to the heart but also do not defibrillate. A relevant and practical question is what range of shock energies is most likely to defibrillate while not causing damage to the heart. This question is most difficult to answer in the pre-hospital defibrillation setting where the patients' size and shape vary, placement of the defibrillation patches vary, and the etiology of their arrhythmia varies. Unlike internal defibrillators, which are tested at implantation, efficacy of an external defibrillator is determined only once, when it is most needed. This review discusses shock damage and dysfunction caused by monophasic waveforms as well as biphasic waveforms. Evidence is presented suggesting that for perfused hearts, the threshold for damage is well above any shock size delivered clinically. For non-perfused hearts, both in humans and animals, evidence is presented that monophasic shocks of up to 5 J/kg do not cause any more cardiac damage/dysfunction than that associated with smaller shocks and that much of this damage is caused by the ischemic period itself rather than the shock. Although many patients can be defibrillated with 150 J (2.2 J/kg) biphasic shocks, some patients may require biphasic shocks up to 360 J (5 J/kg) to be defibrillated. Studies still need to be performed comparing the efficacy and damaging effects of 360 J biphasic shocks to 150 J biphasic shocks. Until those studies are completed, it seems reasonable to use the same 360 J (5 J/kg) energy limit for biphasic shocks as for monophasic shocks.