Changes in cerebral oxygen uptake and cerebral electrical activity during defibrillation threshold testing

Enhancing cardiac arrest survival with extracorporeal cardiopulmonary resuscitation: insights into the process of death

Extracorporeal cardiopulmonary resuscitation (ECPR) is an emerging method of cardiopulmonary resuscitation to improve outcomes from cardiac arrest. This approach targets patients with out-of-hospital cardiac arrest previously unresponsive and refractory to standard treatment, combining approximately 1 h of standard CPR followed by venoarterial extracorporeal membrane oxygenation (VA-ECMO) and coronary artery revascularization. Despite its relatively new emergence for the treatment of cardiac arrest, the approach is grounded in a vast body of preclinical and clinical data that demonstrate significantly improved survival and neurological outcomes despite unprecedented, prolonged periods of CPR. In this review, we detail the principles behind VA-ECMO-facilitated resuscitation, contemporary clinical approaches with outcomes, and address the emerging new understanding of the process of death and capability for neurological recovery.

Electrocerebral Signature of Cardiac Death

BACKGROUND

Electroencephalography (EEG) findings following cardiovascular collapse in death are uncertain. We aimed to characterize EEG changes immediately preceding and following cardiac death.

METHODS

We retrospectively analyzed EEGs of patients who died from cardiac arrest while undergoing standard EEG monitoring in an intensive care unit. Patients with brain death preceding cardiac death were excluded. Three events during fatal cardiovascular failure were investigated: (1) last recorded QRS complex on electrocardiogram (QRS₀), (2) cessation of cerebral blood flow (CBF₀) estimated as the time that blood pressure and heart rate dropped below set thresholds, and (3) electrocerebral silence on EEG (EEG₀). We evaluated EEG spectral power, coherence, and permutation entropy at these time points.

RESULTS

Among 19 patients who died while undergoing EEG monitoring, seven (37%) had a comfort-measures-only status and 18 (95%) had a do-not-resuscitate status in place at the time of death. EEG₀ occurred at the time of QRS₀ in five patients and after QRS₀ in two patients (cohort median - 2.0, interquartile range - 8.0 to 0.0), whereas EEG₀ was seen at the time of CBF₀ in six patients and following CBF₀ in 11 patients (cohort median 2.0 min, interquartile range - 1.5 to 6.0). After CBF₀, full-spectrum log power (p < 0.001) and coherence (p < 0.001) decreased on EEG, whereas delta (p = 0.007) and theta (p < 0.001) permutation entropy increased.

CONCLUSIONS

Rarely may patients have transient electrocerebral activity following the last recorded QRS (less than 5 min) and estimated cessation of cerebral blood flow. These results may have implications for discussions around cardiopulmonary resuscitation and organ donation.

EEG-Based Prediction of the Recovery of Carotid Blood Flow during Cardiopulmonary Resuscitation in a Swine Model

The recovery of cerebral circulation during cardiopulmonary resuscitation (CPR) is important to improve the neurologic outcomes of cardiac arrest patients. To evaluate the feasibility of an electroencephalogram (EEG)-based prediction model as a CPR feedback indicator of high- or low-CBF carotid blood flow (CBF), the frontal EEG and hemodynamic data including CBF were measured during animal experiments with a ventricular fibrillation (VF) swine model. The most significant 10 EEG parameters in the time, frequency and entropy domains were determined by neighborhood component analysis and Student’s t-test for discriminating high- or low-CBF recovery with a division criterion of 30%. As a binary CBF classifier, the performances of logistic regression, support vector machine (SVM), k-nearest neighbor, random forest and multilayer perceptron algorithms were compared with eight-fold cross-validation. The three-order polynomial kernel-based SVM model showed the best accuracy of 0.853. The sensitivity, specificity, F1 score and area under the curve of the SVM model were 0.807, 0.906, 0.853 and 0.909, respectively. An automated CBF classifier derived from non-invasive EEG is feasible as a potential indicator of the CBF recovery during CPR in a VF swine model.

Frontal EEG Changes with the Recovery of Carotid Blood Flow in a Cardiac Arrest Swine Model

Monitoring cerebral circulation during cardiopulmonary resuscitation (CPR) is essential to improve patients’ prognosis and quality of life. We assessed the feasibility of non-invasive electroencephalography (EEG) parameters as predictive factors of cerebral resuscitation in a ventricular fibrillation (VF) swine model. After 1 min untreated VF, four cycles of basic life support were performed and the first defibrillation was administered. Sustained return of spontaneous circulation (ROSC) was confirmed if a palpable pulse persisted for 20 min. Otherwise, one cycle of advanced cardiovascular life support (ACLS) and defibrillation were administered immediately. Successfully defibrillated animals were continuously monitored. If sustained ROSC was not achieved, another cycle of ACLS was administered. Non-ROSC was confirmed when sustained ROSC did not occur after 10 ACLS cycles. EEG and hemodynamic parameters were measured during experiments. Data measured for approximately 3 s right before the defibrillation attempts were analyzed to investigate the relationship between the recovery of carotid blood flow (CBF) and non-invasive EEG parameters, including time- and frequency-domain parameters and entropy indices. We found that time-domain magnitude and entropy measures of EEG correlated with the change of CBF. Further studies are warranted to evaluate these EEG parameters as potential markers of cerebral circulation during CPR.

Increase in regional cerebral saturation after elective electrical cardioversion of atrial fibrillation is only transient and without beneficial effects on neuropsychological functioning: cerebral saturation during electrical cardioversion

We aimed to confirm the positive association between a successful electrical cardioversion (ECV) and increase in SctO₂ and investigated whether this increase is persisting or not. Secondary, the influence of a successful ECV on the neuropsychological function and the association with SctO₂ was assessed as well. SctO₂ was measured continuously during elective ECV using near-infrared spectroscopy. Measurements started before induction of sedation and ended 15 min after awakening. A second measurement took place 4 to 6 weeks after ECV. To assess neuropsychological functioning, patients performed standardized neuropsychological tests before ECV and at follow-up and were compared to healthy volunteers as control group. SctO₂ was measured in 60 patients during elective ECV. ECV was successful in 50 AF patients, while in ten patients sinus rhythm was not obtained. SctO₂ increased immediately after successful ECV in 50 patients (1% (- 5 to 4); p = 0.031), but not after unsuccessful ECV in 10 patients (- 1% (- 5;3); p = 0.481). This SctO₂ change was positively correlated with the instant change in blood pressure (R² = 0.391; p = 0.004). At follow-up, SctO₂ values were no longer increased. Nevertheless, successful ECV improved the patient's quality of life but did not influence neuropsychological functioning at follow-up. A transient, instant SctO₂ increase was observed after successful ECV. This temporary increase in SctO₂ did not influence the neuropsychological functioning of the patients. Though, the quality of life of patients with a successful ECV improved.

Exercise Interventions in Patients With Implantable Cardioverter-Defibrillators and Cardiac Resynchronization Therapy: A SYSTEMATIC REVIEW AND META-ANALYSIS

PURPOSE

Physical activity improves outcomes across a broad spectrum of cardiovascular disease. The safety and effectiveness of exercise-based interventions in patients with implantable cardioverter-defibrillators (ICDs) including cardiac resynchronization therapy defibrillators (CRT-Ds) remain poorly understood.

METHODS

We identified clinical studies using the following search terms: "implantable cardioverter-defibrillators"; "ICD"; "cardiac resynchronization therapy"; "CRT"; and any one of the following: "activity"; "exercise"; "training"; or "rehabilitation"; from January 1, 2000 to October 1, 2015. Eligible studies were evaluated for design and clinical endpoints.

RESULTS

A total of 16 studies were included: 8 randomized controlled trials, 5 single-arm trials, 2 observational cohort trials, and 1 randomized crossover trial. A total of 2547 patients were included (intervention groups = 1215 patients, control groups = 1332 patients). Exercise interventions varied widely in character, duration (median 84 d, range: 23-168 d), and follow-up time (median 109 d, range: 23 d to 48 mo). Exercise performance measures were the most common primary endpoints (87.5%), with most studies (81%) demonstrating significant improvement. Implantable cardioverter-defibrillator shocks were uncommon during active exercise intervention, with 6 shocks in 635 patients (0.9%). Implantable cardioverter-defibrillator shocks in follow-up were less common in patients receiving any exercise intervention (15.6% vs 23%, OR = 0.68; 95% CI, 0.48-0.80, P < .001). (Equation is included in full-text article.)O2 peak improved significantly in patients receiving exercise intervention (1.98 vs 0.36 mL/kg/min, P < .001).

CONCLUSION

In conclusion, exercise interventions in patients with ICDs and CRT-Ds appear safe and effective. Lack of consensus on design and endpoints remains a barrier to broader application to this important patient population.

Tachyarrhythmia Cycle Length in Appropriate versus Inappropriate Defibrillator Shocks in Brugada Syndrome, Early Repolarization Syndrome, or Idiopathic Ventricular Fibrillation

Background and Objectives

Implantable cardioverter–defibrillators (ICDs) are indicated in patients with Brugada syndrome (BS), early repolarization syndrome (ERS), or idiopathic ventricular fibrillation (IVF) who are at high risk for sudden cardiac death. The optimal ICD programming for reducing inappropriate shocks in these patients remains to be determined. We investigated the difference in the mean cycle length of tachyarrhythmias that activated either appropriate or inappropriate ICD shocks in these three patient groups to determine the optimal ventricular fibrillation (VF) zone for minimizing inappropriate ICD shocks.

Subjects and Methods

We selected 41 patients (35 men) (mean age±standard deviation=42.6±13.0 year) who received ICD shocks between April 1996 and April 2014 to treat BS (n=24), ERS (n=9), or IVF (n=8). Clinical and ICD interrogation data were retrospectively collected and analyzed for all events with ICD shocks.

Results

Of the 244 episodes, 180 (73.8%) shocks were appropriate and 64 (26.2%) were inappropriate. The mean cycle lengths of the tachyarrhythmias that activated appropriate and inappropriate shocks were 178.9±28.7 ms and 284.8±24.4 ms, respectively (p<0.001). The cutoff value with the highest sensitivity and specificity for discriminating between appropriate and inappropriate shocks was 235 ms (sensitivity, 98.4%; specificity, 95.6%). When we programmed a single VF zone of ≤270 ms, inappropriate ICD shocks were reduced by 70.5% and appropriate shocks were missed in 1.7% of these patients.

Conclusion

Programming of a single VF zone of ≤270 ms in patients with BS, ERS, or IVF could reduce inappropriate ICD shocks, with a low risk of missing appropriate shocks.

Effect of defibrillation threshold testing-induced ventricular fibrillation on renal function

INTRODUCTION

The effect of defibrillation threshold (DFT) testing with induction of ventricular fibrillation (VF) on renal function is currently unknown. This study examined the acute effect of DFT testing on renal function in patients undergoing implantable cardioverter defibrillator (ICD) implantation.

METHODS AND RESULTS

We performed a prospective cohort study of 148 consecutive patients who underwent ICD implantation from January 1, 2007 to May 30, 2008. Patients were assigned to one of two cohorts: a DFT group who underwent DFT testing at device implantation and a no-DFT group that was not tested. Baseline and 24-h postprocedure renal function were assessed with measurements of serum creatinine and estimated glomerular filtration rate (GFR) by the Modified Diet in Renal Disease equation. Changes in serum creatinine and estimated GFR were compared between cohorts. Ninety-eight patients (66%) underwent DFT testing (average VF induction count, 1.5 ± 0.9; mean VF duration, 10 ± 4 s). Fifty patients (34%) were not tested. Patients in the no-DFT group had lower mean left ventricular ejection fraction, higher New York Heart Association class, higher atrial fibrillation incidence, and greater intravenous contrast utilization at device implant. Baseline and postprocedure serum creatinine values were similar between groups (baseline, 1.25 ± 0.45 mg/dL; post-ICD, 1.26 ± 0.5 mg/dL). Baseline GFR was lower in the DFT cohort (55.2 ± 18.8 mL/min/BSA vs 63.7 ± 22.7 mL/min/BSA, p = 0.023). No significant differences between groups were observed in the mean change in serum creatinine or estimated GFR.

CONCLUSIONS

DFT testing at the time of ICD implantation is not associated with acute adverse effects on renal function.

The dilemma of ICD implant testing

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients. This review reappraises ICD implant testing. At implant, defibrillation success is influenced by both predictable and unpredictable factors, including those related to the patient, ICD system, drugs, and complications. For left pectoral implants of high-output ICDs, the probability of passing a 10 J safety margin is approximately 95%, the probability that a maximum output shock will defibrillate is approximately 99%, and the incidence of system revision based on testing is < or = 5%. Bayes' Theorem predicts that implant testing identifies < or = 50% of patients at high risk for unsuccessful defibrillation. Most patients who fail implant criteria have false negative tests and may undergo unnecessary revision of their ICD systems. The first-shock success rate for spontaneous VT/VF ranges from 83% to 93%, lower than that for induced VF. Thus, shocks for spontaneous VT/VF fail for reasons that are not evaluated at implant. Whether system revision based on implant testing improves this success rate is unknown. The risks of implant testing include those related to VF and those related to shocks alone. The former may be due to circulatory arrest alone or the combination of circulatory arrest and shocks. Vulnerability testing reduces risks related to VF, but not those related to shocks. Mortality from implant testing probably is 0.1-0.2%. Overall, VF should be induced to assess sensing in approximately 5% of ICD recipients. Defibrillation or vulnerability testing is indicated in 20-40% of recipients who can be identified as having a higher-than-usual probability of an inadequate defibrillation safety margin based on patient-specific factors. However, implant testing is too risky in approximately 5% of recipients and may not be worth the risks in 10-30%. In 25-50% of ICD recipients, testing cannot be identified as either critical or contraindicated.

Achieving Sufficient Safety Margins with Fixed Duration Waveforms and the Use of Multiple Time Constants

INTRODUCTION

There are several options to achieve a sufficient safety margin in a patient with a high defibrillation threshold (DFT), with varying and typically modest success. Programming fixed (millisecond) durations of both phases of a biphasic waveform in an implantable cardioverter defibrillator (ICD) has demonstrated utility.

METHODS

We established an informal multisite registry of ICD implanting facilities. Each facility agreed to attempt the use of fixed duration waveforms whenever there was an inadequate safety margin with tilt-based waveforms. A 3.5-ms-based fixed duration shock was tried first. If that failed to achieve a 10-J safety margin then a 2-ms-based shock was used. We also tabulated an HEDFT (high estimate DFT) as precise DFTs were not determined.

RESULTS

Sixteen patients (15 M, 1 F) were entered into the registry (age 58.2 +/- 17.9 years) with ejection fractions of .30 +/-.11. Superior vena cava coils were used in 7 patients according to physician preference. The tilt-based HEDFTs were 35.4 +/- 3.2 J delivered and 35.8 +/- 3.3 J stored energy. The 3.5-ms based shocks were evaluated on 14 patients and the HEDFT fell to 23.4 +/- 6.3 J delivered (P < 0.0001) and 26.2 +/- 6.9 J stored energy (P < 0.0001). The 2-ms-based fixed duration shocks were then evaluated on 6 patients and the delivered energy HEDFT was 22.2 +/- 5.8 J (P = 0.001 vs. tilt-based shocks) while the stored energy HEDFT was 27.9 +/- 6.4 J (P = 0.01 vs. tilt-based shocks). Using the better of the two fixed duration waveforms, the mean safety margin was improved from -1.2 +/- 1.9 J to 9.5 +/- 5.9 J (P < 0.00001). Multivariate predictors of the safety margin improvement were the absence of the Superior Vena Cava (SVC) coil and absence of Ventricular fibrillation (VF) presentation. Four patients still required lead repositioning after the use of the fixed duration waveforms. No additional leads were implanted.

CONCLUSION

The use of a selection of directly programmed fixed duration biphasic shocks had a striking impact on the HEDFT for these difficult patients. Adequate safety margins were obtained for 12 of 16 patients with no lead manipulation or other approaches.

Using the Upper Limit of Vulnerability to Assess Defibrillation Efficacy at Implantation of ICDs

The upper limit of vulnerability (ULV) is the weakest shock strength at or above which ventricular fibrillation (VF) is not induced when the shock is delivered during the vulnerable period. The ULV, a measurement made in regular rhythm, provides an estimate of the minimum shock strength required for reliable defibrillation that is as accurate or more accurate than the defibrillation threshold (DFT). The ULV hypothesis of defibrillation postulates a mechanistic relationship between the ULV-measured during regular rhythm-and the minimum shock strength that defibrillates reliably. Vulnerability testing can be applied at implantable cardioverter defibrillator (ICD) implant to confirm a clinically adequate defibrillation safety margin without inducing VF in 75%-95% of ICD recipients. Alternatively, the ULV provides an accurate patient-specific safety margin with a single fibrillation-defibrillation episode. Programming first ICD shocks based on patient-specific measurements of ULV rather than programming routinely to maximum output shortens charge time and may reduce the probability of syncope as ICDs age and charge times increase. Because the ULV is more reproducible than the DFT, it provides greater statistical power for clinical research with fewer episodes of VF. Limited evidence suggests that vulnerability testing is safer than conventional defibrillation testing.

Endogenous activation of adenosine A(1) receptors accelerates ischemic suppression of spontaneous electrocortical activity

Cerebral ischemia induces a rapid suppression of spontaneous brain rhythms prior to major alterations in ionic homeostasis. It was found in vitro during ischemia that the rapidly formed adenosine, resulting from the intracellular breakdown of ATP, may inhibit synaptic transmission via the A(1) receptor subtype. The link between endogenous A(1) receptor activation during ischemia and the suppression of spontaneous electrocortical activity has not yet been established in the intact brain. The aim of this study was to investigate in vivo the effects of A(1) receptor antagonism by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) on the time to electrocortical suppression during global cerebral ischemia. Adult male Wistar rats under chloral hydrate anesthesia were subjected to 1-min transient "four-vessel occlusion" ischemic episodes, separated by 20-min reperfusion. The rats were injected intraperitoneally with either 1.25 mg/kg DPCPX dissolved in 2 ml/kg dimethyl sulfoxide (DMSO) or the same volume of DMSO alone, 15 min before the third ischemic episode. Time to electrocortical suppression was estimated based on the decay of the root mean square of two-channel electrocorticographic recordings. During the first two ischemic episodes, electrocortical suppression appeared after approximately 12 s in both groups. After DMSO administration, ischemic suppression remained unchanged. After DPCPX administration, the time to electrocortical suppression was increased by approximately 10 s, and bursts of activity were recorded during the entire ischemia. These effects disappeared within 15 h after DPCPX administration. Our data provide evidence that during cerebral ischemia endogenous activation of A(1) receptors accelerates the electrical "shut-down" of the whole brain.

Cerebral Oxygenation During Defibrillator Threshold Testing of Implantable Cardioverter Defibrillators

BACKGROUND

The induction of ventricular fibrillation (VF) during defibrillator threshold testing of implantable cardioverter defibrillators (ICD) provokes global cerebral hypoperfusion and impaired oxygen delivery. Limited data are available on the neurophysiological effects of defibrillator threshold testing. Near infrared spectroscopy (NIRS) can noninvasively measure changes in specific chromophores, which reflect cerebral oxygenation at the intravascular and mitochondrial levels. We performed a prospective trial using NIRS to analyze cerebral cortical oxygenation during defibrillator threshold testing.

METHODS

Eleven patients (men = 9; age = 64 +/- 11 years: LVEF = 44 +/- 11%) underwent subpectoral ICD implantation and defibrillator threshold testing under general anesthesia. A NIRO 300 spectrometer was used to measure the absolute changes in the concentrations of oxyhemoglobin, de-oxyhemoglobin, and cytochrome c oxidase copper moiety during each procedure. The mean arterial blood pressure was monitored simultaneously.

RESULTS

The mean number of defibrillator threshold tests was two (range 2-6). Twenty-six episodes of VF (duration 13.1 +/- 9.7 seconds; cycle length 230.2 +/- 20.8 ms) and two episodes of VT (duration 15 +/- 2.8 seconds; cycle length 320 +/- 11.3 ms) were induced. Each episode of VF and VT resulted in a decrease in the mean arterial blood pressure to 23.9 +/- 7.5 mmHg (p < or = 0.05) and oxyhemoglobin (-4.2 +/- 1.7 micromol/L; p < or = 0.05) and an increase in de-oxyhemoglobin (2.7 +/- 1.4 micromol/L). There was no change in the cytochrome c oxidase copper moiety redox status (0.09 +/- 0. 30 micromol/L).

CONCLUSION

Our results suggest that impaired oxygen delivery during induced VF and VT does not affect oxygen availability at the cellular intra-mitochondrial level.

Electrophysiologic Study‐Guided Therapy with Sotalol for Life‐Threatening Ventricular Tachyarrhythmias

The aim of this study was to investigate the long-term efficacy and safety of electrophysiologic study (EPS)-guided sotalol administration combined with implantable cardioverter defibrillators (ICD) for ventricular tachyarrhythmias (VTA). This study enrolled 92 patients with both structural heart disease and sustained VTA. Sotalol was administered to 57 patients, and its efficacy was assessed by EPS. Long-term treatment was continued in combination with ICD in 31 patients (57%) whose VTA was no longer inducible (responder group) and in 16 patients whose VTA remained inducible (nonresponder group). The long-term outcomes were compared among the responder group, the nonresponder group, and 35 ICD recipients untreated with antiarrhythmic drugs (ICD-only group). During a mean follow-up of 44 +/- 33 months, the recurrence of VTA was not significantly different between all patients treated with sotalol (30%) and patients in the ICD-only group (46%). However, the recurrence of VTA was significantly lower in the responder (13%) than in the nonresponder (63%) or the ICD-only groups (46%). There was no significant difference in VTA recurrence between the nonresponder and the ICD-only groups. One patient each in the responder and the ICD-only groups died suddenly, and all-cause mortality was similar in the three groups. The incidence of inappropriate ICD discharges was less in the sotalol than in the ICD-only groups. No patient had to discontinue long-term sotalol treatment because of the adverse effects. In conclusion, sotalol reduced VTA recurrence in the responding patients and inappropriate ICD discharge. EPS may predict the efficacy of sotalol for VTA recurrence.

Prevention of implantable-defibrillator shocks by treatment with sotalol. d,l-Sotalol Implantable Cardioverter-Defibrillator Study Group

BACKGROUND

Patients with implantable cardioverter-defibrillators often receive adjunctive antiarrhythmic therapy to prevent frequent shocks. We tested the efficacy and safety of sotalol, a beta-blocker with class III antiarrhythmic effects, for this purpose.

METHODS

In a multicenter trial, patients were stratified according to left ventricular ejection fraction (< or =0.30 or >0.30), randomly assigned to double-blind treatment with 160 to 320 mg of sotalol per day (151 patients) or matching placebo (151 patients), and followed for 12 months. Kaplan-Meier analyses of the time to an event were performed. Three end points were used: the delivery of a first shock for any reason or death from any cause, the first appropriate shock for a ventricular arrhythmia or death from any cause, and the first inappropriate shock for a supraventricular arrhythmia or death from any cause.

RESULTS

Compliance with double-blind treatment was similar in the two groups. There were seven deaths in the placebo group and four in the sotalol group. As compared with placebo, treatment with sotalol was associated with a lower risk of death from any cause or the delivery of a first shock for any reason (reduction in risk, 48 percent; P<0.001 by the log-rank test), death from any cause or the delivery of a first appropriate shock (reduction in risk, 44 percent; P=0.007), or death from any cause or the delivery of a first inappropriate shock (reduction in risk, 64 percent; P=0.004). Sotalol also reduced the mean (+/-SD) frequency of shocks due to any cause (1.43+/-3.53 shocks per year, as compared with 3.89+/-10.65 in the placebo group; P=0.008). In the sotalol group, the reduction in the risk of death from any cause or the delivery of a first shock for any reason did not differ significantly between patients with ejection fractions of more than 0.30 and those with ejection fractions of 0.30 or less.

CONCLUSIONS

Oral sotalol was safe and efficacious in reducing the risk of death or the delivery of a first defibrillator shock whether or not ventricular function was depressed.