Defibrillation Success Rate Research Articles

Tracing the elimination of reentry spiral waves in defibrillation: Temperature effects

The presence of spiral waves in cardiac tissue causes ventricular fibrillation (VF). Clinical studies have demonstrated that reducing the blood temperature to hypothermia can improve the success rate of electrical defibrillation when VF occurs. In this paper, the Hodgkin-Huxley-style model is used to simulate the effects of temperature and electric shock on the spiral waves present in mammalian tissues, and the phase singularity (PS) identification methods are used to track the wave behaviors in network, finally the Luo-Rudy model is used to test the applicability of our results for cardiac tissues. The results show that temperature modulates the optimal parameters for defibrillation: (1) Arnold's tongue structure shows that an alternating electric field close to the tissue natural frequency (e.g.: cardiac sinus rhythm) allows the nodes to be phase-locked or PS directionally drift at a smaller intensity, thus eliminating spiral waves more effectively than a constant electric field. (2) The average node frequency increases with temperature whether the network is synchronized or present spiral waves, and the statistics show that the robustness of electric defibrillation can be enhanced when the tissue is at moderate hypothermia. (3) More interestingly, we define the defibrillation score (DFS) and find that moderate hypothermia is a balance to improves defibrillation success, which may provide some insights for practical defibrillation studies.

PO-04-084 LOW SHOCK IMPEDANCE OF SUBCUTANEOUS IMPLANTABLE CARDIAC DEFIBRILLATOR (S-ICD) IN THE SETTING OF ACUTE DECOMPENSATED HEART FAILURE

Shock impedance represents the resistance between the coil and generator of subcutaneous ICDs. It is an important metric to predict device defibrillation success. Several factors have been implicated in determining system impedance of S-ICDs such as generator-lead distance, body habitus as well as generator position (subcutaneous vs. intermuscular pocket). We present a case report highlighting the impact of volume status on shock impedance. N/A A 60-year-old female presents to the office. She has a past medical history of obesity, Heart Failure with Preserved Ejection Fraction (HFpEF), ventricular fibrillation followed by implantation of transvenous ICD. This was complicated by device infection requiring device extraction and implantation of S-ICD. She has been having progressive shortness of breath with minimal exertion weeks prior to presentation. She denied chest pain, palpitations or dizziness but endorsed generalized fatigue as well as significant weight gain. She usually weighs around 165-170 lbs, but was 220 lbs on presentation. Her physical exam was remarkable for elevated jugular venous pressure, anasarca with crackles in the lung bases as well as abdominal ascites and lower extremity edema. Interrogation of her device was performed which showed no significant arrythmias. However, device detected low system impedance of <30 ohms. Her previous interrogation about 3 months earlier showed impedance of 50 Ohms. She was admitted for inpatient intravenous diuresis. Chest radiograph demonstrated normal position of the generator in the posterolateral chest wall and normal lead position in the parasternal area. Serial device interrogations were performed during the hospitalization showing gradual improvement in system impedance up to 45 Ohms once euvolemia was achieved (Figure 1). Due to improvement in shock impedance with diuresis, defibrillation threshold testing (DFT) was deferred and patient was discharged home in stable condition. Her repeat interrogation at follow up showed an impedance of 60 ohms. In the setting of heart failure exacerbation, excess fluid accumulation in the chest and abdominal cavities may result in a decrease in S-ICD shock impedance. Interpretation of device impedance should factor in patient’s volume status. Further studies are needed to ascertain if low impedance caused by fluid overload can impact device defibrillation success rate.

Automated external defibrillator electrode size and termination of ventricular fibrillation in out-of-hospital cardiac arrest

Smaller electrodes allow more options for design of automated external defibrillator (AED) user interfaces. However, previous studies employing monophasic-waveform defibrillators found that smaller electrode sizes have lower defibrillation shock success rates. We hypothesize that, for impedance-compensated, biphasic truncated exponential (BTE) shocks, smaller electrodes increase transthoracic impedance (TTI) but do not adversely affect defibrillation success rates. Methods and ResultsIn this prospective before-and-after clinical study, Amsterdam police and firefighters used AEDs with BTE waveforms: an AED with larger electrodes in 2016–2017 (113 cm2), and an AED with smaller electrodes in 2017–2020 (65 cm2). We analyzed 157 and 178 patient cases with an initial shockable rhythm where the larger and smaller electrodes were used, respectively. A single 200-J shock terminated ventricular fibrillation (VF) in 86% of patients treated with large electrodes and 89% of patients treated with smaller electrodes. Small electrodes had a non-inferior first shock defibrillation success rate compared to large electrodes, with a difference of 3% (95% CI: –3% −9%) with the lower confidence limit remaining above the defined non-inferiority threshold. TTI was significantly higher for the smaller electrodes (median: 100 Ω) compared to the larger electrodes (median: 88 Ω) (p < 0.001). ConclusionsFor AEDs with impedance-compensating BTE waveforms, TTI was higher for smaller electrodes than the large electrode electrodes. Overall defibrillation shock success for AEDs with smaller electrodes was non-inferior to the AEDs with larger electrodes.

A Model of Long-Term Ventricular Fibrillation in Isolated Rat Hearts

Ventricular fibrillation (VF) is a fatal arrhythmia with a high incidence in cardiac patients, but VF arrest under perfusion is a neglected method of intraoperative arrest in the field of cardiac surgery. With recent advances in cardiac surgery, the demand for prolonged VF studies under perfusion has increased. However, the field lacks simple, reliable, and reproducible animal models of chronic ventricular fibrillation. This protocol induces long-term VF through alternating current (AC) electrical stimulation of the epicardium. Different conditions were used to induce VF, including continuous stimulation with a low or high voltage to induce long-term VF and stimulation for 5 min with a low or high voltage to induce spontaneous long-term VF. The success rates of the different conditions, as well as the rates of myocardial injury and recovery of cardiac function, were compared. The results showed that continuous low-voltage stimulation induced long-term VF and that 5 min of low-voltage stimulation induced spontaneous long-term VF with mild myocardial injury and a high rate of recovery of cardiac function. However, the low-voltage, continuously stimulated long-term VF model had a higher success rate. High-voltage stimulation provided a higher rate of VF induction but showed a low defibrillation success rate, poor recovery of cardiac function, and severe myocardial injury. On the basis of these results, continuous low-voltage epicardial AC stimulation is recommended for its high success rate, stability, reliability, reproducibility, low impact on cardiac function, and mild myocardial injury.

Energy Level and Success of Internal Defibrillation for Shockable Rhythm during Cardiopulmonary Bypass in Cardiac Surgery: A Retrospective Study

Internal defibrillation is commonly indicated for shockable rhythm following cross-clamp removal in cardiac surgery. Low energy decreases the success rate of defibrillation but high energy can cause myocardial damage. This study aimed to determine the success rate of internal defibrillation for shockable arrhythmias after cardiac surgery.Retrospective data of 1,424 patients who developed shockable rhythms (ventricular fibrillation or ventricular tachycardia), and required internal defibrillation after aortic cross-clamp removal during cardiac surgery, without deep hypothermic circulatory arrest technique, from August 2015 to July 2017, were reviewed.The overall success rate of internal defibrillation in the first attempt of defibrillation was 61.5%. The success rate of the energy levels at 30, 10, and 7 Jules were 66.7, 64.9, and 61.5%, respectively. The success rate was higher in patients who had a better ejection fraction than those who failed after defibrillation. This was significantly associated with higher pH, higher bicarbonate, lower serum calcium, and lower total cardioplegic volume during cardiopulmonary bypass (CPB). Redo-valve surgery, valvular surgery, and combined coronary artery bypass graft with valvular surgery had a non-significantly lower success rate (p-value = 0.989). Incidence of failure for defibrillate patients in redo-valvular surgery, combined coronary artery bypass graft with valve surgery, adult congenital heart defect, and valvular surgery; requiring four or five shocks was non-significantly increased. Recurrent rate of ventricular fibrillation/ventricular tachycardia was 13.5%.The success rate of internal defibrillation was not related to the dose of energy used after being weaned off CPB.

Defibrillation success after subcutaneous implantable cardioverter-defibrillator generator replacement is not affected by impedance increase

Abstract Funding Acknowledgements Type of funding sources: None. Background Routine defibrillation testing during implant and replacement of the subcutaneous implantable cardioverter-defibrillator (S-ICD) is recommended per current guidelines. Recently, concerns have been raised about an increase in shock impedance and consequent shock failure during defibrillation testing in S-ICD patients undergoing a generator replacement. Purpose We aim to describe the defibrillation success rate in relation to the shock impedance in patients undergoing S-ICD generator replacement in our large tertiary center. Methods In this retrospective analysis, data from replacement procedures were collected from all patients who underwent an S-ICD generator replacement in our center from June 2014 to December 2020. Defibrillation testing was performed with at least one shock of ≤65J, and a successful shock was defined as terminating the ventricular arrhythmia within 5 seconds after the shock. Results A total of 133 patients underwent an S-ICD generator replacement, 5.8 ± 0.9 years after initial implant. Reasons for replacement were: reaching of elective replacement indicator (n = 119), early battery depletion (n = 9), complaints of generator pocket (n = 3) and device malfunction (n = 2). Defibrillation testing was performed in 111 patients (86.5%) undergoing a replacement procedure. Shock impedance data from both the implant and replacement procedure were available in 101 patients. The median shock impedance of these patients during their replacement procedure was significantly higher than during their implant, 79Ω (IQR 66-94) and 66Ω (IQR 57.5-81) respectively (Z = -5.552, p &amp;lt; 0.001). Despite the higher shock impedance, first shock during defibrillation testing was successful in 105/111 patients (94.6%), with a success rate of 97.3% after two attempts. In the remaining three patients, the ventricular arrhythmia could only be terminated with a 80J shock. This was the case during both their initial implant and their replacement procedure. Shock impedance increase between implant and replacement was not significantly higher in patients with a successful first shock compared to patients with an unsuccessful first shock (Δ+11.1 ± 20.0Ω versus Δ+12.7 ± 27.6Ω, p = 0.86). Conclusion In this large retrospective analysis, we have shown a first shock success rate during S-ICD generator replacement of 94.6%, which is similar to the success rate of defibrillation testing after initial implant. After multiple attempts, defibrillation testing success rate was 100%. Even though the median shock impedance during replacement was significantly higher than during the initial implant, there was no difference in impedance increase in patients with a successful shock compared to patients with an unsuccessful shock. Abstract Figure. Defibrillation success

Acute shock efficacy of the subcutaneous implantable cardioverter-defibrillator according to the implantation technique.

The traditional technique for subcutaneous implantable cardioverter defibrillator (S-ICD) implantation involves three incisions and a subcutaneous (SC) pocket. An intermuscular (IM) 2-incision technique has been recently adopted. We assessed acute defibrillation efficacy (DE) of S-ICD (DE ≤65 J) according to the implantation technique. We analyzed consecutive patients who underwent S-ICD implantation and DE testing at 53 Italian centers. Regression analysis was used to determine the association between DFT and implantation technique. A total of 805 patients were enrolled. Four groups were assessed: IM + 2 incisions (n = 546), SC + 2 incisions (n = 133), SC + 3 incisions (n = 111), and IM + 3 incisions (n = 15). DE was ≤65 J in 782 (97.1%) patients. Patients with DE ≤65 J showed a trend towards lower body mass index (25.1 vs. 26.5; p = .12), were less frequently on antiarrhythmic drugs (13% vs. 26%; p = .06) and more commonly underwent implantation with the 2-incision technique (85% vs. 70%; p = .04). The IM + 2-incision technique showed the lowest defibrillation failure rate (2.2%) and shock impedance (66 Ohm, interquartile range: 57-77). On multivariate analysis, the 2-incision technique was associated with a lower incidence of shock failure (hazard ratio: 0.305; 95% confidence interval: 0.102-0.907; p = .033). Shock impedance was lower with the IM than with the SC approach (66 vs. 70 Ohm p = .002) and with the 2-incision than the 3-incision technique (67 vs. 72 Ohm; p = .006). In a large population of S-ICD patients, we observed a high defibrillation success rate. The IM + 2-incision technique provides lower shock impedance and a higher likelihood of successful defibrillation.

Abstract 16124: Implantable Cardioverter Defibrillators in Patients With Hereditary Transthyretin Cardiac Amyloidosis

Introduction: Implantable cardioverter defibrillator (ICD) implantation in patients with cardiac amyloidosis is controversial, with no clear guidelines for clinical decision-making.. The role of ICD implantation in hereditary Transthyretin Amyloid Cardiomyopathy (hATTR-CM) is unclear. We sought to establish the burden of ventricular arrhythmias and the outcomes of ICD implantation in a single center cohort of hATTR-CM patients. Methods: A total of 69 patients with a confirmed diagnosis of hATTR-CM from genetic testing, and technetium pyrophosphate (PYP) scanning, or endomyocardial biopsy underwent retrospective chart review for demographic, clinical, and arrhythmia data. Results: Seventy-four percent of the cohort was male, with a mean age at diagnosis of 68 (SD=18 years). Sixty-five patients (94.2%) patients were African-American; all of whom carried the Valine 122 Isoleucine mutation. Most had systolic heart failure (New York Heart Association Staging II [18, 26%] and III [40, 58.8%]); 37 (54%) patients had an LVEF ≤ 35%. Thirty-six (52.2%) patients had documented episodes of non-sustained ventricular tachycardia (NSVT), three (4.3%) with ventricular tachycardia (VT), and one (1.5%) with ventricular fibrillation (VF). A total of 15 (21.7%) patients had ICDs placed for prevention of sudden cardiac death in the setting of low LVEF (EF &lt;35%). All recorded VT/VF episodes occurred in three patients with ICDs. Of these patients, one experienced two episodes of VT each successfully abated by antitachycardia pacing (ATP), another experienced a single episode of VT abated by ATP, while the final experienced VF with successful 36J shock as well as two episodes of VT each successfully treated with 36J shocks. No inappropriate ICD shocks were delivered, however, there were two instances of ATP for inappropriately detected atrial arrhythmias. Conclusions: In a cohort of patients with hATTR-CM, we observed a high incidence of NSVT, yet only 41% of patients with severe systolic heart failure had ICDs implanted. A high rate of successful defibrillation and no inappropriate ICD shocks were noted, suggesting that ICDs should be strongly considered, and may be underutilized, in patients with systolic heart failure and/or arrhythmias in the setting of hATTR-CM.

P1157Defibrillation threshold with subcutaneous implantable-cardioverter defibrillator implanted using an intermuscular 2-incision approach

Abstract Funding Acknowledgements NO FUNDING OnBehalf Rhythm Detect Registry Background Current subcutaneous implantable cardioverter–defibrillators (S-ICD) deliver 80J, and the conversion test is usually conducted by delivering shock energy of 65 J to ensure a safety defibrillation margin of at least 15 J. However, little is known about the real safety margin in real life clinical practice. Purpose To determine the defibrillation threshold (DFT) with S-ICD and to investigate its association with clinical characteristics. Methods De novo S-ICD patients were consecutively enrolled and DFT was evaluated using a pre-specified step-up protocol at implantation. Results 35 patients, BMI 25 ± 4 kg/m2, left ventricular ejection fraction (LVEF) 48 ± 19%, underwent S-ICD implantation. The generator was positioned in an intermuscular pocket and a 2-incision technique was applied in all patients. The mean DFT was 30 ± 10J and the DFT was &amp;gt;30J in 7 (20%) patients. A single patient had a &amp;gt;40J DFT. The time to shock was 11 ± 3 seconds and the shock impedance was 67 ±21 Ohm at the lowest effective energy. The DFT was comparable in patients with LVEF ≤35% (33 ± 15J) versus &amp;gt;35% (29 ± 5J, p = 0.278), and in patients with BMI ≤25 kg/m2 (30 ± 5J) versus &amp;gt;25kg/m2 (31 ± 14J, p = 0.864). Conclusions We observed low DFT and low shock impedance in patients who received S-ICD with an intermuscular 2-incision approach. The S-ICD defibrillation success rate at ≤30J was 80%, while 97% of patients were defibrillated at ≤ 40J. We found no difference in DFT according to the LVEF or the BMI.

P526Are 40 joules enough for successfully defibrillate with subcutaneous implantable cardioverter-defirbrillator?

Abstract Funding Acknowledgements NO FUNDING OnBehalf Rhythm Detect Registry Background The subcutaneous ICD (S-ICD) is an effective alternative to the traditional transvenous option. Due to its extracardiac design the S-ICD requires a higher shock output than the traditional ICD. Nonetheless, preliminary data suggest that acute defibrillation test may be successful even at energies lower than the usually tested value of 65J, and that optimization of implantation technique may increase the defibrillation safety margin among S-ICD recipients. Purpose To evaluate the efficacy of conversion test performed at 40J, and to investigate the association between shock efficacy, clinical characteristics and device position. Methods VF was induced and subsequently, conversion test was performed by delivering a 40J shock. Success was defined as termination of VF by the first shock. S-ICD system positioning was evaluated with the PRAETORIAN score using bidirectional chest X-rays. Cranial-caudal S-ICD placement was defined as superior if the entire generator was contained in the cardiac silhouette, inferior if partially or completely outside. Results 233 consecutive patients (83% male, 49 ± 14 years, BMI 26 ± 4kg/m2, ejection fraction 46 ± 17%, 112 (48%) ischemic/non-ischemic dilated cardiomyopathy) were enrolled and underwent S-ICD implantation with conversion test at 40J. The generator was positioned in an intermuscular pocket in 228 patients (98%). The PRAETORIAN score was &amp;lt;90 (low risk of conversion failure) in 218 (94%) patients. Cranial-caudal generator placement was superior in 188 (81%) patients. Overall, VF termination occurred in 191 (82%) patients with 40J. The BMI was similar in patients with successful and unsuccessful termination (26 ± 4kg/m2 versus 27 ± 6kg/m2, p = 0.195). The efficacy was comparable in patients with dilated cardiomyopathy (86%) versus other conditions (79%, p = 0.153). PRAETORIAN score was not associated with shock efficacy at 40J (82% with score &amp;lt;90 versus 87% with score ≥90, p = 1.000), while a trend toward higher efficacy was seen with superior generator placement (84% versus 73%, p = 0.093). Conclusions We observed high S-ICD defibrillation success rate at 40J, suggesting that the safety margin is frequently higher than the usually accepted 15J. We found no difference in efficacy according to the cardiac disease and no association between test failure and body habitus. The intermuscular positioning of the generator resulted in low values of the PRAETORIAN score that however did not appear associated with test efficacy.

Effects of high-frequency biphasic shocks on ventricular vulnerability and defibrillation outcomes through synchronized virtual electrode responses.

Electrical defibrillation is a well-established treatment for cardiac dysrhythmias. Studies have suggested that shock-induced spatial sawtooth patterns and virtual electrodes are responsible for defibrillation efficacy. We hypothesize that high-frequency shocks enhance defibrillation efficacy by generating temporal sawtooth patterns and using rapid virtual electrodes synchronized with shock frequency. High-speed optical mapping was performed on isolated rat hearts at 2000 frames/s. Two defibrillation electrodes were placed on opposite sides of the ventricles. An S1-S2 pacing protocol was used to induce ventricular tachyarrhythmia (VTA). High-frequency shocks of equal energy but varying frequencies of 125–1000 Hz were used to evaluate VTA vulnerability and defibrillation success rate. The 1000-Hz shock had the highest VTA induction rate in the shorter S1-S2 intervals (50 and 100 ms) and the highest VTA defibrillation rate (70%) among all frequencies. Temporal sawtooth patterns and synchronous shock-induced virtual electrode responses could be observed with frequencies of up to 1000 Hz. The improved defibrillation outcome with high-frequency shocks suggests a lower energy requirement than that of low-frequency shocks for successful ventricular defibrillation.

Factors Affecting Cardioversion and Defibrillation Success Rate

Factors Affecting Cardioversion and Defibrillation Success Rate

Abstract 127: The Effect of Cutoff Frequency Range on Amplitude Spectrum Area Performance in Predicting Defibrillation Outcome

Introduction: Both clinical and experimental studies have demonstrated that ventricular fibrillation (VF) waveform-based amplitude spectrum area (AMSA) predicts defibrillation outcome with high sensitivity and specificity. A commonly used cutoff frequency range for calculation of AMSA is 4-48 Hz, but the median VF frequency in patients is less than 7 Hz. In the present study, we investigated whether the AMSA performance in predicting defibrillation outcome may be affected by different cutoff frequency ranges. Hypothesis: A selected cutoff frequency range would affect AMSA performance in predicting defibrillation outcome in patients. Methods: A total of 450 segments (179-defibrillation success and 271-defibrillation failure) of VF waveforms from patients with out-of-hospital cardiac arrest were analyzed. Each 4.096-s segment prior to defibrillation was acquired with a sampling rate of 250 Hz. Using MATLAB (MathWorks, Natck, MA), the AMSA of each segment of VF waveform was calculated with five cutoff frequency ranges (Shown in Figure 1). Sensitivity and specificity were calculated when defibrillation success rate was 50% which was estimated by a logistic regression curve. Area under the receiver operating characteristic curve (AUC) was used to evaluate AMSA performance within different cutoff frequency ranges. Results: AMSA threshold was decreased from 20.5 to 6.5 mV·Hz when the cutoff frequency range was changed from 3-48 Hz to 3-10 Hz (Figure 1). Sensitivity of AMSA in 3-10 Hz was increased by 81.3% compared with that of AMSA in 3-48 Hz. Specificity of AMSA in 3-10 Hz was decreased by 8.1% compared with that of AMSA in 3-48 Hz. The corresponding AUC was increased from 0.724 (3-48 Hz) to 0.768 (3-10 Hz). Conclusions: A cutoff frequency range of 3-10 Hz significantly increases the sensitivity of AMSA for predicting defibrillation success in patients with cardiac arrest with a slight decrease in specificity.

Effect of transthoracic impedance on defibrillation efficacy and safety in a porcine model

Objective Two different transthoracic impedances were made with an adjustable impedance instrument to compare the success rate of defibrillation, heart and skin damage in a porcine model. Methods A total of sixteen pigs were randomly(random number) divided into two groups: low impedance group (about 50 Ω, n=8) and high impedance group (about 100 Ω, n=8). Defibrillation (recommended 150 J) was first attempted at 15 s after induction of ventricular fibrillation(VF). If spontaneous circulation was not recovered, 2-minute chest compression and subsequent defibrillation attempts (maximum 200 J) were attempted. Model animal kept stabilization for 30 min after return of spontaneous circulation before induction of the next episode of VF, which was induced five episodes in each pig. Results In the low impedance group, VF was induced 39 times, 39 of 43 attempted defibrillations were successful. In the high impedance group, VF was induced 40 times, 40 of 70 attempted defibrillations were successful. The current and success rate of the first defibrillation were (34.9±3.2)A and 94.9% respectively in the low impedance group, while those of the high impedance group were (19.1±2.1)A and 50% respectively(both P<0.05). There were no significant differences in skin damage between two groups, but myocardial injury was lighter in the high impedance group. Conclusions Success rate of the first defibrillation with recommend 150 J obviously decreases with the increase of transthoracic impedance. The main factor of myocardial injury is current instead of the numbers of defibrillation. Key words: Defibrillation; Transthoracic impedance; Current; Myocardial injury; Pig

Paddle Position and Contact Force: An Important Step to Check When Troubleshooting for Refractory Ventricular Fibrillation

Ventricular fibrillation (VF) is a lethal medical emergency that requires immediate defibrillation. VF is resistant when it persists after three or more defibrillator shocks. Successful defibrillation requires depolarisation of a critical mass of myocardium. Several variables, such as the length of time in VF, body type, total energy used, and energy waveform have been reported to be associated with the success rate of defibrillation. Correct paddle position and good contact force to create an adequate current flow through the heart is essential for defibrillation. We report a patient who developed VF because of acute myocardial infarction that was resistant to a total of 13 shocks. The cause of shock-resistant VF was diagnosed by noticing the skin marks caused by the defibrillator paddle that indicated incorrect paddle position and inadequate paddle force. By checking the skin marks, an emergency physician could make a correct diagnosis within a few seconds and save a patient.

Toward a More Efficient Implementation of Antifibrillation Pacing.

We devise a methodology to determine an optimal pattern of inputs to synchronize firing patterns of cardiac cells which only requires the ability to measure action potential durations in individual cells. In numerical bidomain simulations, the resulting synchronizing inputs are shown to terminate spiral waves with a higher probability than comparable inputs that do not synchronize the cells as strongly. These results suggest that designing stimuli which promote synchronization in cardiac tissue could improve the success rate of defibrillation, and point towards novel strategies for optimizing antifibrillation pacing.

Advantage of four-electrode over two-electrode defibrillators.

Defibrillation is the standard clinical treatment used to stop ventricular fibrillation. An electrical device delivers a controlled amount of electrical energy via a pair of electrodes in order to reestablish a normal heart rate. We propose a technique that is a combination of biphasic shocks applied with a four-electrode system rather than the standard two-electrode system. We use a numerical model of a one-dimensional ring of cardiac tissue in order to test and evaluate the benefit of this technique. We compare three different shock protocols, namely a monophasic and two types of biphasic shocks. The results obtained by using a four-electrode system are compared quantitatively with those obtained with the standard two-electrode system. We find that a huge reduction in defibrillation threshold is achieved with the four-electrode system. For the most efficient protocol (asymmetric biphasic), we obtain a reduction in excess of 80% in the energy required for a defibrillation success rate of 90%. The mechanisms of successful defibrillation are also analyzed. This reveals that the advantage of asymmetric biphasic shocks with four electrodes lies in the duration of the cathodal and anodal phase of the shock.

Abstract 16924: Initial AMSA and Increased AMSA After CPR Predict Second Shock Success in Initially Shock-resistant VF During Out-of-hospital Cardiac Arrest

Purpose: Amplitude spectrum area (AMSA), which is calculated from the ventricular fibrillation (VF) waveform using fast Fourier transformation, has been recognized as a predictor of successful defibrillation (DF) and as an index of myocardial perfusion and viability during resuscitation. In this study, we investigated whether a change in AMSA occurring during CPR would predict DF outcome for subsequent DF attempts after a failed DF. We hypothesized that a patient responding to CPR with an increase in AMSA would have an increased likelihood of DF success. Methods: This was a retrospective analysis of out-of-hospital cardiac arrest patients who received a second DF due to initially shock-resistant VF. A total of 193 patients with an unsuccessful first DF were identified in a manufacturer database of electrocardiographic defibrillator records. AMSA was calculated for the first DF (AMSA1) and the second DF (AMSA2) during a 2.1 sec window ending 0.5 sec prior to DF. A successful DF attempt was defined as the presence of an organized rhythm with a rate ≥ 40 / min starting within 60 sec from the DF and lasting for &gt; 30 sec. After the failed first DF, all patients received CPR for 2 to 3 minutes before delivery of the second DF. Change in AMSA (dAMSA) was calculated as dAMSA = AMSA2 - AMSA1. Results: The overall second DF success rate was 14.5%. Multivariable logistic regression showed that both AMSA1 and dAMSA were independent predictors of second DF success with odds ratios of 1.24 (95% CI 1.12 - 1.38, p&lt;0.001) and 1.27 (95% CI 1.16 - 1.41, p&lt;0.001) for each mVHz change in AMSA or dAMSA, respectively. Conclusions: In initially DF-resistant VF, a high initial AMSA value predicted an increased likelihood of second shock success. An increase of AMSA in response to CPR also predicted a higher second shock success rate. Monitoring of AMSA during resuscitation therefore may be useful to guide CPR efforts, possibly including timing of second shock delivery. These findings also further support the value of AMSA as indicator of myocardial viability.

Effects of rotigaptide (ZP123) on connexin43 remodeling in canine ventricular fibrillation.

The present study investigated the effects of rotigaptide (ZP123) on the expression, distribution and phosphorylation of connexin43 (Cx43) in myocardial cell membranes in cardioversion of ventricular fibrillation (VF). A model of prolonged VF (8, 12 and 30 min) was established in mongrel dogs (n=8/group), following treatment with ZP123 or normal saline (NS control). A sham control was included. Cardiopulmonary resuscitation was begun at the start of VF followed by defibrillation. Animals received a maximum of three defibrillations of increasing energy (70, 100 and 150 J biphasic shock) as required. The average defibrillation energy, defibrillation success rate, return of spontaneous circulation and survival rate were recorded. Cx43 and phosphorylated (p-) Cx43 expression in cardiomyocyte membranes was detected by western blot and immunofluorescence analyses. Compared with the NS-treated control groups, the success defibrillation rate in the 8-min and 12-min ZP123 groups was significantly higher (P<0.05), while the average defibrillation energy was significantly lower (P<0.05). Cx43 expression in the VF groups was significantly lower than that in the sham control group (P<0.05). Cx43 expression was higher in the 12-min and 30-min ZP123 groups than that in the NS control group (P<0.05), while p-Cx43 expression decreased, although the levels were significantly higher than those in the control groups (P<0.05). Cx43 expression was positively correlated with the defibrillation success rate (r=0.91; P<0.01) and negatively with the mean defibrillation energy (r=−0.854; P<0.01), while p-Cx43 expression was positively correlated with the success rate of the previous three defibrillations (r=0.926; P<0.01). In conclusion, ZP123 reduced Cx43 remodeling through regulating the expression, distribution and phosphorylation of Cx43, thereby reducing the defibrillation energy required for successful cardioversion.

Pre-shock chest compression pause effects on termination of ventricular fibrillation/tachycardia and return of organized rhythm within mechanical and manual cardiopulmonary resuscitation

BackgroundShorter manual chest compression pauses prior to defibrillation attempts is reported to improve the defibrillation success rate. Mechanical load-distributing band (LDB-) CPR enables shocks without compression pause. We studied pre-shock pause and termination of ventricular fibrillation/pulseless ventricular tachycardia 5s post-shock (TOF) and return of organized rhythm (ROOR) with LDB and manual (M-) CPR. MethodsIn a secondary analysis from the Circulation Improving Resuscitation Care trial, patients with initial shockable rhythm and interpretable post-shock rhythms were included. Pre-shock rhythm, pause duration (if any), and post-shock rhythm were obtained for each shock. Associations between TOF/ROOR and pre-shock pause duration, including no pause shocks with LDB-CPR, were analyzed with Chi-square test. A p-value <0.05 was considered statistically significant. ResultsFor TOF and ROOR analyses we included 417 LDB-CPR patients with 1476 and 1438 shocks, and 495 M-CPR patients with 1839 and 1796 shocks, respectively. For first shocks with LDB-CPR, pre-shock pause was associated with TOF (p=0.049) with lowest TOF (77%) for shocks given without pre-shock compression pause. This association was not significant when all shocks were included (p=0.07) and not for ROOR. With M-CPR there were no significant associations between shock-related chest compression pause duration and TOF or ROOR. ConclusionFor first shocks with LDB-CPR, termination of fibrillation was associated with pre-shock pause duration. There was no association for the rate of return of organized rhythm. For M-CPR, where no shocks were given during continuous chest compressions, there were no associations between pre-shock pause duration and TOF or ROOR.