Biphasic Shocks Research Articles

The optimal phasic relationship between synchronized shock and mechanical chest compressions

Objective Pauses for shock delivery in chest compressions are detrimental to the success of resuscitation and may be eliminated with the use of mechanical chest compressors. However, the optimal phasic relationship between mechanical chest compression and defibrillation is still unknown. We therefore undertook a study to assess the effects of timing of defibrillation in the mechanical chest compression cycle on the defibrillation threshold (DFT) using a porcine model of cardiac arrest. Methods Ventricular fibrillation was electrically induced and untreated for 10 s in 8 domestic pigs weighing between 26 and 30 kg. Mechanical chest compression was then continuously performed for 25 s, followed by a biphasic electrical shock which was delivered to the animal at 6 randomized coupling phases, including a control phase, with a pre-determined energy setting. The control phase was chosen at a constant 2 s following discontinued chest compression. A novel grouped up-and-down DFT testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 min, the testing sequence was repeated, resulting in a total of 60 test shocks delivered to each animal. Results No difference between the delivered shock energy, voltage and current were observed among the 6 study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of mechanical chest compression. Conclusion Defibrillation efficacy is maximal when electrical shock is delivered in the upstroke phase of mechanical chest compression.

Defibrillation delivered during the upstroke phase of manual chest compression improves shock success*

The current standard of manual chest compression during cardiopulmonary resuscitation requires pauses for rhythm analysis and shock delivery. However, interruptions of chest compression greatly decrease the likelihood of successful defibrillations, and significantly better outcomes are reported if this interruption is avoided. We therefore undertook a prospective randomized controlled animal study in an electrically induced ventricular fibrillation pig model to assess the effects of timing of defibrillation on the manual chest compression cycle on the defibrillation threshold. Prospective, randomized, controlled animal study. University-affiliated research laboratory. Yorkshire-X domestic pigs (Sus scrofa). In eight domestic male pigs weighing between 24 and 31 kg, ventricular fibrillation was electrically induced and untreated for 10 secs. Manual chest compression was then performed and continued for 25 secs with the protection of an isolation blanket. The depth and frequency of chest compressions were guided by a cardiopulmonary resuscitation prompter. Animals were randomized to receive a biphasic electrical shock in five different compression phases with a predetermined energy setting. A control phase was chosen at a constant 2 secs after discontinued chest compression. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 mins, the sequence was repeated for a total of 60 test shocks for each animal. No difference in coronary perfusion pressure before delivering of the shock was observed among the six study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of manual chest compression. Defibrillation efficacy is maximal when electrical shock is delivered during the upstroke phase of manual chest compression.

ICD shocks: Not just the “straw that broke the camel's back”

ICD shocks: Not just the “straw that broke the camel's back”

Continuous chest compression resuscitation in arrested swine with upper airway inspiratory obstruction

Background This study was designed to compare 24-h survival rates and neurological function of swine in cardiac arrest treated with one of three forms of simulated basic life support CPR. Methods Thirty swine were randomized equally among three experimental groups to receive either 30:2 CPR with an unobstructed endotracheal tube (ET) or continuous chest compression (CCC) CPR with an unobstructed ET or CCC CPR with a collapsable rubber sleeve on the ET allowing air outflow but completely restricting air inflow. The swine were anesthetized but not paralyzed. Two min of untreated VF was followed by 9 min of simulated single rescuer bystander CPR. In the 30:2 CPR group, each set of 30 chest compressions was followed by a 15-s pause to simulate the realistic duration of interrupted chest compressions required for a single rescuer to deliver 2 mouth-to-mouth ventilations. The other two groups were provided continuous chest compressions (CCC) without assisted ventilations. At 11 min post-arrest a biphasic defibrillation shock (150 J) was administered followed by a period of advanced cardiac life support. Results In the 30:2 group, 8 of 10 animals had good neurological function at 24-h post-resuscitation. In the CCC open airway group, 10 of 10, and in the CCC inspiratory obstructed group, 9 of 10. The number of shocks ( P < 0.05) and epinephrine doses ( P < 0.05) required for ROSC was greater in the 30:2 CPR group than in the other two groups. Conclusions There were no differences in 24-h survival with good neurological function among these three different CPR protocols.

Optimization of initial energy for cardioversion of atrial tachyarrhythmias with biphasic shocks

Objective Recommendations for optimal first-shock energies with biphasic waveforms are conflicting. We evaluated prospectively the relation between type and duration of atrial tachyarrhythmias and the probability of successful cardioversion with a specific biphasic shock waveform to develop recommendations for the initial energy setting aiming at the lowest total cumulative energy with 2 or less consecutive shocks. Methods We analyzed 453 consecutive patients undergoing their first transthoracic electrical cardioversion, including 358 attempts for atrial fibrillation (AF) and 95 attempts for atrial flutter (AFL) or atrial tachycardia (AT). A step-up protocol with a truncated exponential biphasic waveform starting at 50 J was used. Total cumulative energies were estimated under the assumption of a 2-tiered escalating shock protocol with different initial energy settings and a “rescue shock” of 250 J for AFL/AT or 360 J for AF. The initial energy setting leading to the lowest total cumulative energy was regarded as the optimal first-shock level. Results Cardioversion was successful in 448 patients (cumulative efficacy, 99 %). In patients with AFL/AT, the lowest total cumulative energy was attained with an initial energy setting of 50 J. In patients with AF, lowest values were achieved with an initial energy of 100 J for arrhythmia durations of 2 days or less and an initial energy of 150 J for arrhythmia durations of more than 2 days. Conclusion We recommend an initial energy setting of 50 J in patients with AFL/AT, of 100 J in patients with AF 2 days or less, and of 150 J with AF more than 2 days.

205 ST segment changes after external cardioversion using direct current shock: incidence, characteristics and predeictive factors

DC shock is commonly used for external cardioversion of cardiac arrhythmias. Incidence, characteristics and predictive factors of transient ST-segment changes after DC shock are poorly known. 91 consecutive pts referred for external cardioversion of atrial fibrillation (AFib) (61 men, 69 ± 10 yo) were prospectively included. Duration and amplitude of ST elevation or depression were quantified on12 lead-ECG immediately after the first DC shock. Correlations with DC shock characteristics clinical variables, underlying heart disease, echocardiographic parameters, biological parameters, medications, anesthesic drugs as well with morphological features were made. 18 and 20 pts underwent 200 J or 300 J monophasic and 53 pts 200 J biphasic DC shocks. Immediate success rate was 95%.We found an incidence of 48% for ST segment changes: 35% for ST elevation (0,81 ± 0,44 mV) and 13% for ST depression (0,2 ± 0,07 mV, p<0,0001). ST changes were essentially seen in the right precordial leads. Major ST elevation was observed in 27% which could sometimes display Brugada-like pattern. ST changes durations were similar for ST elevation and ST depression (60 ± 43 vs 50 ± 26 sec, p=ns) and were correlated to the amplitude of ST changes. ST changes did not induce significant cardiac events or alter immediate or late AFib recurrences. ST changes were not related to energy but ST elevation was significantly more often induced by monophasic (76% vs 6%, p<0,0001) and ST depression by biphasic DC shocks (26% vs 3%, p=0,01). Using multivariate analysis, independent predictors for ST elevation were the use of monophasic DC shocks, use of propofol and increased CRP, while a low ejection fraction and use of biphasic DC hocks were independent predictors of ST depression. ST segment changes after external cardioversion with DC shock are common, short living and do not seem to carry clinical significance. They are related to the monophasic or biphasic configuration of DC shock, to the use of propofol, to the ejection fraction and to an increased CRP. Direct membrane injury by electroporation is suspected.

ST-segment changes after direct current external cardioversion for atrial fibrillation. Incidence, characteristics and predictive factors

Background Incidence, characteristics and predictive factors of transient ST-segment changes after DC shock are poorly known. Methods 91 consecutive pts referred for external cardioversion of atrial fibrillation (AF) (61 men, 69 ± 10 yo) were prospectively included. The presence of ST elevation or depression was assessed on 12 lead-ECG immediately after the first DC shock. Correlations with DC shock characteristics (monophasic/biphasic and energy), clinical variables, echocardiographic parameters, biological parameters, medications, anesthesic drugs as well with morphological features were made. Results 18 and 20 pts underwent 200 J or 300 J monophasic and 53 pts 200 J biphasic DC shocks. We found an incidence of 48% for ST-segment changes: 35% for ST elevation and 13% for ST depression. ST changes did not induce significant cardiac events or alter AF recurrences. ST changes were not related to energy but ST elevation was significantly more often induced by monophasic (76% vs 6%, p < 0.0001) and ST depression by biphasic DC shocks (26% vs 3%, p = 0.01). Using multivariate analysis, independent predictors for ST elevation were the use of monophasic DC shocks, of propofol and increased CRP, while a low ejection fraction and use of biphasic DC shocks were independent predictors of ST depression. Conclusion ST-segment changes after external cardioversion with DC shock are common, short living and do not carry clinical significance. They are related to the monophasic or biphasic configuration of DC shock, to the use of propofol, to the ejection fraction and to an increased CRP.

Estudio aleatorizado sobre la posición de electrodos en la cardioversión eléctrica electiva de la fibrilación auricular

Aim To compare the effectiveness of left anteroposterior (A-P) and apex-anterior (A-A) electrode position in the electrical cardioversion (ECV) of patients with atrial fibrillation (AF). Design Randomized clinical trial. Location ICU of a second-level hospital. Patients and methods Ambulatory AF patients admitted to ICU for ECV with biphasic shocks. Up to a maximum of 3 shocks (150–200–200 J) are given in the electrode position determined by random numbers, and if sinus rhythm (SR) is not restored, electrode position is changed and 2 additional 200 J shocks are allowed. Both electrode positions are analyzed and compared to determine which one allows restoration of SR with the lowest number of shocks and least energy. Results Forty-six patients were included in the A-A group, and 45 in the A-P group. Sinus rhythm was restored in 92% of cases, although patients in the A-A group needed a lower number of shocks and less energy: 1 versus 2 shocks (p=0,003) and 150 versus 350 J (p=0.017). Only one out of 5 patients in whom the A-A position had failed was reverted to RS with the A-P position, whereas 10 out of 13 patients in which A-P position had failed were reverted in the A-A position (p=0.038). Conclusions The A-A position is more effective in the elective electrical cardioversion of atrial fibrillation, so we recommend this position as the first choice.

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.

The effects of phase duration on defibrillation success of dual time constant biphasic waveforms

Aim of Study The effects of first and second phase duration of biphasic waveforms on defibrillation success were evaluated in a guinea pig model of ventricular fibrillation (VF). We hypothesized that waveform duration, and especially the first phase duration, played a main role on defibrillation efficacy in comparison to energy, current and voltage, when a dual time constant biphasic shock was employed. Methods VF was induced and untreated for 5 s in 30 male guinea pigs, prior to attempting a single defibrillatory shock with one of 5 defibrillation waveforms which had different durations of the first and second phase. A five step up–down protocol was utilized for determining the defibrillation efficacy. After a 3-min interval, the procedure was repeated. A total of 25 cardiac arrest events and defibrillations were investigated for each animal. Results The defibrillation waveforms with an intermediate first phase of 5 ms, yielded the highest defibrillation success ( p < 0.05). These waveforms also presented significantly lower energy, current and voltage in comparison to waveforms with shorter or longer first phase durations ( p < 0.001). However, no differences on defibrillation success were observed among waveforms with different second phase durations varying from 1.5 ms to 3.5 ms. Conclusions For dual time constant biphasic waveforms, the first phase duration played a main role on defibrillation success. The intermediate first phase duration of 5 ms, yielded the best defibrillation efficacy compared with shorter or longer first phase durations. While the second phase duration did not affect defibrillation outcomes.

Comparison of Antero-Lateral Versus Antero-Posterior Electrode Position for Biphasic External Cardioversion of Atrial Flutter

External cardioversion is an established and very important tool to terminate symptomatic atrial flutter. The superiority of the biphasic waveform has been demonstrated for atrial flutter, but whether electrode position affects the efficacy of cardioversion in this population is not known. The aim of this trial was to evaluate whether anterior-lateral (A-L) compared with anterior-posterior (A-P) electrode position improves cardioversion results. Of 130 screened patients, 96 (72 men, mean age 62 +/- 12 years) were included and randomly assigned to a cardioversion protocol with either A-L or A-P electrode position. In each group, 48 patients received sequential biphasic waveform shocks using a step-up protocol consisting of 50, 75, 100, 150, or 200 J. The mean energy (65 +/- 13 J for A-L vs 77 +/- 13 J for A-P, p = 0.001) and mean number of shocks (1.48 +/- 1.01 for A-L vs 1.96 +/- 1.00 for A-P, p = 0.001) required for successful cardioversion were significantly lower in the A-L group. The efficacy of the first shock with 50 J in the A-L electrode position (35 of 48 patients [73%]) was also highly significantly greater than the first shock with 50 J in the A-P electrode position (18 of 48 patients [36%]) (p = 0.001). In conclusion, the A-L electrode position increases efficacy and requires fewer energy and shocks in external electrical cardioversion of common atrial flutter. Therefore, A-L electrode positioning should be recommended for the external cardioversion of common atrial flutter.

A comparison between monophasic and biphasic defibrillation for the cardioversion of persistent atrial fibrillation in patients with and without heart failure

Atrial fibrillation (AF) and heart failure commonly coexist. Restoring sinus rhythm using external direct current cardioversion (DCCV) may improve left ventricular function, exercise capacity and quality of life (QoL). However, DCCV may be less successful at restoring sinus rhythm in patients with heart failure. We aimed to determine whether biphasic DCCV was superior to monophasic DCCV for the restoration of sinus rhythm in patients with heart failure. 592 consecutive cardioversion procedures were performed on 503 patients for persistent AF, 261 (44%) procedures using monophasic defibrillation and 331 (56%) using biphasic. Patients with symptomatic heart failure were identified for further analysis. 173 cardioversions were performed on 149 patients with heart failure. The overall success rate of cardioversion in this group was 82.7% (83.3% and 82.2% for monophasic and biphasic respectively). There was no difference in the success rate of cardioversion for those with heart failure compared to those without heart failure (p = 0.141). Furthermore, there was no substantial difference in success rates according to defibrillation type (83.3% v. 84.2% for monophasic and 82.2% v. 88.5% for biphasic, p = 0.502 and 0.085 respectively). External defibrillation is similarly effective at restoring SR in patients with and without HF and both mono- and biphasic shocks have a high rate of success. However, significantly less energy (maximal and cumulative) is required to restore SR using biphasic defibrillation.

Comparison of neurological outcomes following witnessed out-of-hospital ventricular fibrillation defibrillated with either biphasic or monophasic automated external defibrillators

Background:Biphasic waveform defibrillation results in higher rates of termination of fibrillation than monophasic waveform defibrillation but has not been shown to improve survival outcomes.Objective:To compare the effectiveness of a biphasic...

Successful biphasic transthoracic defibrillation of a dog with prolonged, refractory ventricular fibrillation

To describe a case of spontaneous ventricular fibrillation in a dog in which biphasic defibrillation was life saving. Ventricular fibrillation occurred in a 7-year-old female Australian Heeler during recovery from anesthesia following pacemaker implantation. Resuscitative efforts including immediate delivery of transthoracic monophasic defibrillation shocks of escalating energy and administration of vasopressors were unsuccessful. However, a single biphasic shock restored sinus rhythm despite prolonged duration of the arrhythmia. This case suggests greater efficacy of biphasic defibrillation compared with traditional monophasic defibrillation. In this dog the newer, biphasic technology was life saving after monophasic shocks failed repeatedly to terminate ventricular fibrillation.

Multiple monophasic shocks improve electrotherapy of ventricular tachycardia in a rabbit model of chronic infarction

We previously showed that the cardioversion threshold (CVT) for ventricular tachycardia (VT) is phase dependent when a single monophasic shock (1MP) is used. The purpose of this study was to extend these findings to a biphasic shock (1BP) and to compare the efficacy of phase-independent multiple monophasic (5MP) and biphasic shocks (5BP). Panoramic optical mapping with blebbistatin (5 microM) was performed in postmyocardial infarction rabbit hearts (n = 8). Flecainide (1.64 +/- 0.68 microM) was administered to promote sustained arrhythmias. 5MP and 5BP were applied within one VT cycle length (CL). Results were compared to 1BP and antitachycardia pacing. We observed monomorphic VT with CL = 149.6 +/- 18.0 ms. Similar to 1MP, CVTs of 1BP were found to be phase dependent, and the maximum versus minimum CVT was 8.6 +/- 1.7 V/cm versus 3.7 +/- 1.9 V/cm, respectively (P = .0013). Efficacy of 5MP was higher than that of 1BP and 5BP. CVT was 3.2 +/- 1.4 V/cm for 5MP versus 5.3 +/- 1.9 V/cm for 5BP (P = .00027). 5MP versus averaged 1BP CVT was 3.6 +/- 2.1 V/cm versus. 6.8 +/- 1.5 V/cm, respectively (P = .00024). Antitachycardia pacing was found to be completely ineffective in this model. Maintenance of shock-induced virtual electrode polarization by multiple monophasic shocks over a VT cycle is responsible for unpinning of reentry leading to self-termination. Elimination of virtual electrode polarization by shock polarity reversal during multiple biphasic shocks proved ineffective. A significant reduction in CVT can be achieved by applying multiple monophasic shocks within one VT CL or one single shock at the proper coupling interval.

Multiple Shocks Affect Thoracic Electrical Impedance During External Cardioversion of Atrial Fibrillation

Thoracic impedance (TI) influences the success of external cardioversion (ECV) or defibrillation because current intensity traversing the heart is inversely related to TI. Experimental data suggest that TI decreases after multiple shocks. We undertook a clinical study to determine changes of TI values in patients with atrial fibrillation or flutter requiring ECV. We enrolled 222 consecutive patients (age 73 +/- 11 years; males 67%; body weight 75 +/- 13 kg) who underwent ECV between January 2004 and February 2007. Biphasic shocks were delivered through adhesive pads placed in the anteroposterior position. The initial energy was set at 1 J/kg, with progressive increases up to a maximum of 180 J in case of failure. In the last 39 elective patients, plasma concentration of interleukin-6 (IL-6) and tumor necrosis factor (TNF)-alpha were determined before and 6 hours after ECV. Sinus rhythm was restored in 202 patients (91.0%). Of these, 155 (69.8%) required more than one shock (on average, 2.5 +/- 1.5 shocks/patient). Final values of energy and peak current intensity were 136 +/- 47 J and 50 +/- 14 A, respectively. TI decreased significantly by 6.2% from baseline after > or =2 shocks (P < 0.001). The absolute reduction was correlated with baseline TI, number of delivered shocks, and hemoglobin oxygen saturation. IL-6 and TNF-alpha increased with ECV (P < 0.001 and P = 0.014, respectively). TI decreases significantly after multiple shocks, possibly by activation of acute inflammation.

Inducibility of Atrial Fibrillation with a Synchronized External Low Energy Shock Post‐Pulmonary Vein Isolation Predicts Recurrent Atrial Fibrillation

Inducibility of atrial fibrillation (AF) with burst pacing after pulmonary vein (PV) isolation is associated with recurrent AF. This study evaluated whether an external 30 Joule (J) shock synchronized to the R wave, during the vulnerable period of atrial repolarization, is able to risk-stratify patients further for AF recurrence after PV isolation. One hundred and sixteen consecutive patients underwent PV isolation for AF. Atrial burst pacing was performed after PV isolation. In patients without AF induced by burst pacing, a biphasic external 30 J shock synchronized to the R wave was delivered as a further test for inducible AF. Patients were followed for a mean of 16 months, and recurrent AF was defined as more than 10 sec of AF on ambulatory monitoring. AF was induced in 19 (16%) of patients with burst pacing. Eighty-one patients who were noninducible with burst pacing had a 30 J shock administered, which induced AF in 16 (20%). In follow-up, 21% of patients who were noninducible with burst pacing or low-energy shock vs 54% who were inducible with either test developed recurrent AF at one year (HR 3.18, P = 0.0004 on multivariate analysis). Among patients who were noninducible with burst pacing, 18% who were noninducible with a low-energy shock vs 60% who were inducible with shock developed recurrent AF at one year (HR = 4.63, P = 0.0006 on multivariate analysis). Inducibility of AF by a 30 J shock delivered during atrial repolarization after PV isolation may predict AF recurrence. Evaluation of inducibility of AF with burst pacing and a biphasic external synchronized shock after PV isolation may help guide postprocedure management.

High-energy defibrillation impairs myocyte contractility and intracellular calcium dynamics

We examined the effects of energy delivered with electrical defibrillation on myocyte contractility and intracellular Ca2+ dynamics. We hypothesized that increasing the defibrillation energy would produce correspondent reduction in myocyte contractility and intracellular Ca2+ dynamics. Randomized prospective study. University-affiliated research laboratory. Ventricular myocytes from male Sprague-Dawley rat hearts. Ventricular cardiomyocytes loaded with Fura-2/AM were placed in a chamber mounted on an inverted microscope and superfused with a buffer solution at 37 degrees C. The cells were field stimulated to contract and mechanical properties were assessed using a video-based edge-detection system. Intracellular Ca2+ dynamics were evaluated with a dual-excitation fluorescence photomultiplier system. Myocytes were then randomized to receive 1) a single 0.5-J biphasic shock; 2) a single 1-J biphasic shock; 3) a single 2-J biphasic shock; and 4) a control group without shock. After the shock, myocytes were paced for an additional 4 mins. A single 0.5-J shock did not have effects on contractility and intracellular Ca2+ dynamics. Higher energy shocks, i.e., 1- or 2-J shocks, significantly impaired contractility and intracellular Ca2+ dynamics. The adverse effects were greater after a 2-J shock compared with a 1-J shock. Higher defibrillation energy significantly impairs ventricular contractility at the myocyte level. Reductions in cardiomyocyte shortening and intracellular Ca2+ dynamics abnormalities were greater when higher energy shock was used.

Lethal Effect of Electric Fields on Isolated Ventricular Myocytes

Defibrillator-type shocks may cause electric and contractile dysfunction. In this study, we determined the relationship between probability of lethal injury and electric field intensity (E in isolated rat ventricular myocytes, with emphasis on field orientation and stimulus waveform. This relationship was sigmoidal with irreversible injury for E > 50 V/cm . During both threshold and lethal stimulation, cells were twofold more sensitive to the field when it was applied longitudinally (versus transversally) to the cell major axis. For a given E, the estimated maximum variation of transmembrane potential (Delta V(max)) was greater for longitudinal stimuli, which might account for the greater sensitivity to the field. Cell death, however, occurred at lower maximum Delta V(max) values for transversal shocks. This might be explained by a less steep spatial decay of transmembrane potential predicted for transversal stimulation, which would possibly result in occurrence of electroporation in a larger membrane area. For the same stimulus duration, cells were less sensitive to field-induced injury when shocks were biphasic (versus monophasic). Ours results indicate that, although significant myocyte death may occur in the E range expected during clinical defibrillation, biphasic shocks are less likely to produce irreversible cell injury.

Minimal interruption of cardiopulmonary resuscitation for a single shock as mandated by automated external defibrillations does not compromise outcomes in a porcine model of cardiac arrest and resuscitation

Current automated external defibrillations require interruptions in chest compressions to avoid artifacts during electrocardiographic analyses and to minimize the risk of accidental delivery of an electric shock to the rescuer. The earlier three-shock algorithm, with prolonged interruptions of chest compressions, compromised outcomes and increased severity of postresuscitation myocardial dysfunction. In the present study, we investigated the effect of timing of minimal automated external defibrillation-mandated interruptions of chest compressions on cardiopulmonary resuscitation outcomes, using a single-shock algorithm. We hypothesized that an 8-sec interruption of chest compressions for a single shock, as mandated by automated external defibrillations, would not impair initial resuscitation and outcomes of cardiopulmonary resuscitation. Randomized prospective animal study. University affiliated research laboratory. Domestic pigs. In 24 domestic male pigs weighing 41 +/- 2 kg, ventricular fibrillation was induced by left anterior descending coronary artery occlusion and untreated for 7 min. Cardiopulmonary resuscitation, including chest compressions and ventilation with oxygen, was then performed for an interval of 2 min before attempted defibrillation. Animals were randomized into three groups: A) interruption immediately before defibrillation; B) interruption after 1 min of cardiopulmonary resuscitation; or C) no interruption. Chest compressions were delivered with the aid of a mechanical chest compressor at a rate of 100 compressions/min and compression/ventilation ratio of 30:2. Defibrillation was attempted with a single biphasic 150-J shock. Each animal was successfully resuscitated and survived for >72 hr. No differences in the number of shocks before return of spontaneous circulation, frequency of recurrent ventricular fibrillation, duration of cardiopulmonary resuscitation, and severity of postresuscitation myocardial dysfunction were observed. In this experimental model of cardiac arrest and cardiopulmonary resuscitation, minimal automated external defibrillation-mandated interruption of chest compressions for a single-shock algorithm did not have adverse effects on postresuscitation myocardial or neurologic function. All animals, whether subjected to cardiopulmonary resuscitation interruptions or not, survived.