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PubMed1999

Fully discharging phases. A new approach to biphasic waveforms for external defibrillation.

BACKGROUND: Phase-2 voltage and maximum pulse width are dependent on phase-1 pulse characteristics in a single-capacitor biphasic waveform. The use of 2 separate output capacitors avoids these limitations and may allow waveforms with lower defibrillation thresholds. A previous report also suggested that the optimal tilt may be >70%. This study was designed to determine an optimal biphasic waveform by use of a combination of 2 separate and fully (95% tilt) discharging capacitors. METHODS AND RESULTS: We performed 2 external defibrillation studies in a pig ventricular fibrillation model. In group 1, 9 waveforms from a combination of 3 phase-1 capacitor values (30, 60, and 120 microF) and 3 phase-2 capacitor values (0=monophasic, 1/3, and 1.0 times the phase-1 capacitor) were tested. Biphasic waveforms with phase-2 capacitors of 1/3 times that of phase 1 provided the highest defibrillation efficacy (stored energy and voltage) compared with corresponding monophasic and biphasic waveforms with the same capacitors in both phases except for waveforms with a 30-microF phase-1 capacitor. In group 2, 10 biphasic waveforms from a combination of 2 phase-1 capacitor values (30 and 60 microF) and 5 phase-2 capacitor values (10, 20, 30, 40, and 50 microF) were tested. In this range, phase-2 capacitor size was more critical for the 30-microF phase-1 than for the 60-microF phase-1 capacitor. The optimal combinations of fully discharging capacitors for defibrillation were 60/20 and 60/30 microF. Conclusions-Phase-2 capacitor size plays an important role in reducing defibrillation energy in biphasic waveforms when 2 separate and fully discharging capacitors are used.

Animals↗
PubMed1992

Influence of left ventricular function on outcome of patients treated with implantable defibrillators.

BACKGROUND: The outcomes of patients treated with implantable defibrillators were compared between patients with left ventricular ejection fraction greater than or equal to 30% and less than 30%. METHODS AND RESULTS: Of 68 consecutive patients treated with implantable defibrillators, 40 patients (group 1) had left ventricular ejection fraction greater than or equal to 30%, and 28 patients (group 2) had left ventricular ejection fraction less than 30%. Sudden death, surgical mortality, nonsudden arrhythmia-related death (death within 24 hours after an arrhythmic event despite initial termination of the arrhythmia by the implantable defibrillator), total arrhythmia-related death (including sudden death, surgical death, and nonsudden arrhythmia-related death), and total cardiac death were compared between the two groups. Surgical mortality was 4.4% (0% in group 1, 11% in group 2). During the follow-up of 31 +/- 27 months, actuarial survival rates free of events were 97%, 97%, and 97% in group 1 and 96%, 91%, and 82% in group 2 at 12, 24, and 36 months, respectively, for sudden death (p = NS); 97%, 97%, and 97% in group 1 and 85%, 81%, and 72% in group 2 at 12, 24, and 36 months, respectively, for sudden death and surgical mortality (p less than 0.05); 97%, 97%, and 97% in group 1 and 82%, 78%, and 70% in group 2 at 12, 24, and 36 months, respectively, for total arrhythmia-related death (p less than 0.05); and 95%, 95%, and 95% in group 1 and 82%, 69%, and 57% in group 2 at 12, 24, and 36 months, respectively, for total cardiac death (p less than 0.05). Four (57%) of seven nonsudden cardiac deaths during the initial 36-month follow-up period were causally related to arrhythmia (three surgical deaths and one arrhythmia-related nonsudden death). CONCLUSIONS: The outcome of patients treated with implantable defibrillators is strongly influenced by the degree of left ventricular dysfunction. In group 1 patients, surgical mortality, sudden death, and total cardiac death are rare. In group 2, sudden death rate may not be markedly different from that of group 1 patients. However, the risk of therapy (surgical mortality) is high. Many nonsudden cardiac deaths are causally related to arrhythmia (surgical mortality or nonsudden arrhythmia-related death). Therefore, the survival rate free of total arrhythmia-related death is significantly lower in group 2 (70% versus 97% in group 1 at 3 years). Further studies are needed to determine the roles of defibrillator therapy and other therapies in various clinical settings.

Actuarial Analysis↗
PubMed1994

Relation between shock-related myocardial injury and defibrillation efficacy of monophasic and biphasic shocks in a canine model.

BACKGROUND: Certain biphasic waveforms with specific time ratios of positive and negative components require less energy for successful defibrillation of the fibrillating ventricles than monophasic waveforms. However, if more efficient waveforms were also to be associated with more injurious effects on myocardial function, they might not provide a true biological advantage. This study investigates the relation between defibrillation efficacy and potential toxicity of monophasic and asymmetric, single capacitor, biphasic waveforms with equal durations of positive and negative components. METHODS AND RESULTS: The myocardial lactate extraction rate (LER) was used to measure the injurious effects on myocardial oxidative metabolism of two synchronized 35-J shocks in sinus rhythm. LER, mean arterial pressure (MAP) and, in a subset of experiments, cardiac output (CO) and coronary blood flow (CBF) were measured at baseline, 30 seconds, 60 seconds, 90 seconds, 150 seconds, 300 seconds, and 600 seconds after the shocks. In 12 dogs, three different waveforms (M 10: monophasic 10 milliseconds; BI 10: biphasic 10 milliseconds; BI 20: biphasic 20 milliseconds) were tested as series of two consecutive shocks (60 seconds apart) resulting in a total of 36 sets of data. At baseline, LER was 25 +/- 11%. After monophasic shocks, LER decreased significantly more than after biphasic shocks (LER at 150 seconds: M 10: -6 +/- 31% versus BI 10: 21 +/- 15% versus BI 20: 21 +/- 16%; M 10 versus BI 10 and M 10 versus BI 20, P < .05) and showed also a slower recovery (LER at 300 seconds: M 10: 1 +/- 24% versus BI 10: 20 +/- 11% versus BI 20: 20 +/- 15%; M 10 versus BI 10 and M 10 versus BI 20, P < .05). The maximal decrease in LER was 41 +/- 27% for M 10 compared with 18 +/- 15% for BI 10 and 15 +/- 11% for BI 20 (both, M 10 versus BI 10 and M 10 versus BI 20, P < .05). There was a similar decrease in CO and MAP, with the lowest MAP after monophasic shocks. The maximal decrease in MAP was significantly greater after M 10 compared with BI 20 (-29 +/- 15 mm Hg versus -13 +/- 11 mm Hg, P < .05). The defibrillation threshold was 18.6 +/- 8 J for M 10 compared with 11.5 +/- 4.0 J for BI 10 (P < .05) and 15.0 +/- 6.1 J for BI 20, respectively (P = NS). CONCLUSIONS: Our results suggest that these specific biphasic waveforms are associated with less injurious effects on myocardial oxidative metabolism and hemodynamic performance. Given their higher defibrillation efficacy as well, biphasic waveforms may provide important long-term benefits in patients receiving frequent shocks from implantable cardioverter-defibrillators.

Animals↗
PubMed1995

Endocardial carbon-braid electrodes. A new concept for lower defibrillation thresholds.

BACKGROUND: In the treatment of patients with life-threatening ventricular arrhythmia, transvenous implantable cardioverter/defibrillators provide significant advantages over devices requiring a thoracotomy. This study tested the hypothesis that a new carbon-fiber electrode, designed at the Technische Universität in Munich, Germany, has a lower defibrillation threshold (DFT) than standard transvenous defibrillation electrodes. METHODS AND RESULTS: In 8 mongrel dogs (weight, 25.2 +/- 0.8 kg; heart weight, 192 +/- 19 g), we examined the efficacy and electrical characteristics of a right ventricular endocardial carbon prototype defibrillation electrode (9.5F, 4.4-cm2 surface) compared with a standard CPI 0062 Endotak electrode and a Medtronic 6966 Transvene endocardial right ventricular defibrillation electrode. The new electrode consists of 24 braided, tubular carbon filaments, each containing 1000 highly isotropic carbon fibers of 7-microns diameter, yielding a theoretical electrical surface of 480 cm2. The DFTs were determined in random order between each of the three right ventricular electrodes and a subcutaneous wire array anode placed on the left thorax. A standard step-down/up DFT protocol of 20-V shock steps was applied. Two different biphasic waveforms with a 1-ms delay between phases were tested: 3.2-ms first phase/2.0-ms second phase, and 6.0-ms first phase/6.0-ms second phase. For the 3.2/2.0-ms waveform, we found a significantly lower DFT for the carbon lead (4.96 +/- 1.58 J) compared with the CPI 0062 (6.93 +/- 1.67 J) and the Medtronic 6966 (7.49 +/- 0.99 J) leads. For the 6.0/6.0-ms waveform, the DFT for the carbon electrode (5.97 +/- 2.09 J) was significantly lower than for the Medtronic 6966 lead (8.55 +/- 1.93 J) but not for the CPI 0062 lead (6.30 +/- 1.41 J). The impedance with carbon was lower than with the other two leads for the 6.0/6.0-ms waveform but not for the 3.2/2.0-ms waveform. For the carbon electrode, the 3.2/2.0-ms waveform had a lower DFT than the 6.0/6.0-ms waveform. CONCLUSIONS: The present canine study found a lower DFT for a new carbon electrode compared with DFTs for endocardial defibrillation electrodes made of standard metal. Further long-term animal studies and clinical studies are needed to determine whether carbon materials and braided-lead technology are practical and beneficial in patients.

Animals↗
PubMed1996

Reduced arrhythmogenicity of biphasic versus monophasic T-wave shocks. Implications for defibrillation efficacy.

BACKGROUND: Biphasic waveforms defibrillate more effectively than monophasic waveforms; however, the mechanism remains unknown. The "upper-limit-of-vulnerability" hypothesis of defibrillation suggests that unsuccessful defibrillation is due to reinduction of ventricular fibrillation (VF). Thus, VF induction mechanisms may be important for the understanding of defibrillation mechanisms. We therefore compared myocardial VF vulnerability for monophasic versus biphasic shocks. METHODS AND RESULTS: In 10 Langendorff-perfused rabbit hearts, monophasic and biphasic T-wave shocks were randomly administered over a wide range of shock coupling intervals and shock strengths, and the two-dimensional coordinates within which VF was induced were used to calculate the area of vulnerability (AOV) for both shock waveforms. The arrhythmic response to biphasic shocks differed from that to monophasic shocks in three distinct ways: (1) the AOV was smaller (8.9 +/- 4.2 versus 13.9 +/- 6.0 area units, P < .02), (2) the transition zone between VF-inducing and nonarrhythmogenic shocks was narrower (14.7 +/- 4.8 versus 29.9 +/- 6.4 area units, P < .001), and (3) the entire AOV shifted toward longer coupling intervals (by 11.0 +/- 8.8 ms at the left border [P < .005] and 6.0 +/- 5.2 ms at the right border [P = .005] of the AOV). CONCLUSIONS: Biphasic shocks encounter a smaller AOV than monophasic shocks, a narrower transition zone from VF to no arrhythmia induction, and a lesser effectiveness in inducing VF at short coupling intervals. In keeping with the upper-limit-of-vulnerability hypothesis, these waveform-dependent differences in VF inducibility might help explain the lower defibrillation threshold for biphasic shocks.

Animals↗
PubMed1997

Internal cardioversion of atrial fibrillation: marked reduction in defibrillation threshold with dual current pathways.

BACKGROUND: The ultimate acceptance of a fully automatic atrial defibrillator will depend on the reduction of pain to acceptable levels, requiring a marked decrease in defibrillation thresholds. The purpose of this study was to determine whether atrial defibrillation thresholds can be reduced by sequential shocks delivered through two current pathways. METHODS AND RESULTS: Sustained atrial fibrillation was induced with rapid atrial pacing in 12 adult sheep. Defibrillation electrodes were positioned in the right atrial appendage (RAap), distal coronary sinus (DCS), proximal coronary sinus (CSos), main/left pulmonary artery junction (PA), and right ventricular apex (RV). Single-capacitor biphasic waveforms (3/1 ms) were delivered through combinations of these electrodes. Probability-of-success curves were determined for single shocks with a single current pathway and sequential shocks with either single- or dual current pathways. The ED50 for delivered energy for the dual current pathway RAap to DCS then CSos to PA was 0.36+/-0.13 J, which was significantly lower than the ED50 of the standard single current pathway RAap to DCS (1.31+/-0.3 J) and was significantly lower than all other configurations tested. CONCLUSIONS: Internal atrial defibrillation thresholds can be markedly reduced with two sequential biphasic shocks delivered over two current pathways compared with the standard single shock delivered over a single current pathway or with sequential shocks delivered over a single current pathway.

Animals↗
PubMed1998

Relative efficacy of monophasic and biphasic waveforms for transthoracic defibrillation after short and long durations of ventricular fibrillation.

BACKGROUND: Recently, interest has arisen in using biphasic waveforms for external defibrillation. Little work has been done, however, in measuring transthoracic defibrillation efficacy after long periods of ventricular fibrillation. In protocol 1, we compared the efficacy of a quasi-sinusoidal biphasic waveform (QSBW), a truncated exponential biphasic waveform (TEBW), and a critically damped sinusoidal monophasic waveform (CDSMW) after 15 seconds of fibrillation. In protocol 2, we compared the efficacy of the more efficacious biphasic waveform from protocol 1, QSBW, with CDSMW after 15 seconds and 5 minutes of fibrillation. METHODS AND RESULTS: In protocol 1, 50% success levels, ED50, were measured after 15 seconds of fibrillation for the 3 waveforms in 6 dogs. In protocol 2, defibrillation thresholds were measured for QSBW and CDSMW after 15 seconds of fibrillation and after 3 minutes of unsupported fibrillation followed by 2 minutes of fibrillation with femoral-femoral cross-circulation. In protocol 1, QSBW had a lower ED50, 16.0+/-4.9 J, than TEBW, 20.3+/-4.4 J, or CDSMW, 27.4+/-6.0 J. In protocol 2, QSBW had a lower defibrillation threshold after 15 seconds, 38+/-10 J, and after 5 minutes, 41.5+/-5 J, than CDSMW after 15 seconds, 54+/-19 J, and 5 minutes, 80+/-30 J, of fibrillation. The defibrillation threshold remained statistically the same for QSBW for the 2 fibrillation durations but rose significantly for CDSMW. CONCLUSIONS: In this animal model of sudden death and resuscitation, these 2 biphasic waveforms are more efficacious than the CDSMW at short durations of fibrillation. Furthermore, the QSBW is even more efficacious than the CDSMW at longer durations of fibrillation.

Animals↗
PubMed1989

Improved safety factor for triphasic defibrillator waveforms.

Newly developed biphasic waveforms improve defibrillation efficacy both by reduction of defibrillation threshold and by amelioration of shock-induced dysfunction depending on the relative shape of the first and second pulses. Each of these independent effects improves the waveform's safety factor, the ratio between the shock intensity that produces a specific degree of postshock dysfunction and the shock intensity that produces defibrillation (or cellular excitation). Symmetrical waveforms reduce defibrillation threshold to about 60% that of the corresponding monophasic waveform, probably by reduction of excitation threshold for ischemic cells, but increase postshock arrhythmias. Biphasic waveforms with 10% "tails" reduce postshock arrhythmias. This study tests the hypothesis that these independent mechanisms for improvement of defibrillation efficacy can be combined into a single triphasic waveform that will have a higher safety factor than either of the two biphasic waveforms of which it is composed. Cultured myocardial cells were subjected to high-intensity electric-field stimulation with a control monophasic rectangular waveform, a symmetrical biphasic waveform, and a triphasic waveform consisting of the biphasic waveform with an added 10% "tail." Each waveform portion was 5 msec in duration. Photocell mechanograms monitored contractile activity. We found that the duration of postshock arrest of spontaneous contractile activity increased with stimulus intensity for all waveforms. The voltage gradient producing a 4-second arrest after the biphasic waveform shock was 80.6 +/- 1.3% that of the control waveform (100%), while the voltage gradient for the triphasic waveforms was 87.1 +/- 0.73% of control. The difference between biphasic and triphasic waveforms was significant (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Hypothermia improves defibrillation success and resuscitation outcomes from ventricular fibrillation.

BACKGROUND: Induced hypothermia is recommended to improve neurological outcomes in unconscious survivors of out-of-hospital ventricular fibrillation (VF) cardiac arrest. Patients resuscitated from a VF arrest are at risk of refibrillation, but there are few data on the effects of already existing hypothermia on defibrillation and resuscitation. METHODS AND RESULTS: Thirty-two swine (mean+/-SE weight, 23.0+/-0.6 kg) were divided into 4 groups: normothermia (n=8), mild hypothermia (35 degrees C) (n=8), moderate hypothermia (33 degrees C) (n=8), and severe hypothermia (30 degrees C) (n=8). Hypothermia was induced by surrounding the animal with ice, and VF was electrically induced. After 8 minutes of unsupported VF (no CPR), the swine were defibrillated (biphasic waveform) with successive shocks as needed and underwent CPR until resumption of spontaneous circulation or no response (> or =10 minutes). First-shock defibrillation success was higher in the moderate hypothermia group (6 of 8 hypothermia versus 1 of 8 normothermia; P=0.04). The number of shocks needed for late defibrillation (> or =1 minute after initial shock) was less in all 3 hypothermia groups compared with normothermia (all P<0.05). None of the 8 animals in the normothermia group achieved resumption of spontaneous circulation compared with 3 of 8 mild hypothermia (P=NS), 7 of 8 moderate hypothermia (P=0.001), and 5 of 8 severe hypothermia (P=0.03) animals. Coronary perfusion pressure during CPR was not different between the groups. CONCLUSIONS: When VF was induced in the setting of moderate or severe hypothermia, resuscitative measures were facilitated with significantly improved defibrillation success and resuscitation outcome. The beneficial effect of hypothermia was not due to alteration of coronary perfusion pressure, which suggests that changes in the mechanical, metabolic, or electrophysiological properties of the myocardium may be responsible.

Animals↗
PubMed1996

Influence of hypertonic saline solution infusion on defibrillation efficacy.

Hypertonic saline solution may enhance cardiac conduction via the fast inward sodium channel and alter transmembrane Ca+2 conductance via the sodium-calcium exchanger. Evidence suggests that both Ca+2 conductance and myocardial conduction velocity may affect ventricular defibrillation. Since hypertonic saline solution solutions (ie, sodium bicarbonate) may be administered to patients who have conditions that often require ventricular defibrillation (ie, cardiac arrest or hypovolemic shock), we studied the effect of hypertonic saline solution on the defibrillation threshold (DFT) in 16 pentobarbital-anesthetized domestic farm swine (20 to 30 kg). Defibrillation was performed using two interfaced epicardial electrode patches. DFTs were determined at baseline and during treatment phase. Pigs were randomly assigned to treatment consisting of either hypertonic saline solution (6 mmol/kg load, 2.0 to 3.0 mmol/kg infusion) to maintain serum sodium concentrations 10 to 15 mmol/L above baseline or control (D5W given in equal volume). DFT values (joules) that predicted 50% success were modeled from a best-fit histogram. Hypertonic saline solution did not change DFT values from baseline values (10.2 +/- 4.3 vs 10.8 +/- 7.0, respectively). Likewise, placebo (D5W) did not change DFT values from baseline values (10.1 +/- 4.5 vs 11.3 +/- 4.3). During treatment phase, DFT values were 99 +/- 28% of baseline values in the hypertonic saline solution group and 116 +/- 23% of baseline values in the D5W groups (p = 0.21). The administration of hypertonic saline solution also did not affect ventricular conduction velocity, right ventricular action potential duration, or right ventricular effective refractory period. These data indicate that hypertonic saline solution does not appreciably affect defibrillation efficacy or electrical treatment of ventricular fibrillation.

Animals↗
PubMed2001

A comparison of biphasic and monophasic waveform defibrillation after prolonged ventricular fibrillation.

STUDY OBJECTIVE: To compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function, and duration of survival after prolonged duration of untreated ventricular fibrillation (VF), including the effects of epinephrine. DESIGN: Prospective, randomized, animal study. SETTING: Animal laboratory and university-affiliated research and educational institute. PARTICIPANTS: Domestic pigs. INTERVENTIONS: VF was induced in 20 anesthetized domestic pigs receiving mechanical ventilation. After 10 min of untreated VF, the animals were randomized. Defibrillation was attempted with up to three 150-J biphasic waveform shocks or a conventional sequence of 200-J, 300-J, and 360-J monophasic waveform shocks. When reversal of VF was unsuccessful, precordial compression was performed for 1 min, with or without administration of epinephrine. The protocol was repeated until spontaneous circulation was restored or for a maximum of 15 min. MEASUREMENTS AND RESULTS: No significant differences in the success of initial resuscitation or in the duration of survival were observed. However, significantly less impairment of myocardial function followed biphasic shocks. Administration of epinephrine reduced the total electrical energy required for successful resuscitation with both biphasic and monophasic waveform shocks. CONCLUSIONS: Lower-energy biphasic waveform shocks were as effective as conventional higher-energy monophasic waveform shocks for restoration of spontaneous circulation after 10 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation. Administration of epinephrine after prolonged cardiac arrest decreased the total energy required for successful resuscitation.

Animals↗
PubMed2000

Serum levels of vascular endothelial growth factor and transforming growth factor-beta1 in patients with atrial fibrillation undergoing defibrillation therapy.

We have previously reported that pulsatile mechanical stretch in vitro induced rapid secretion of vascular endothelial growth factor (VEGF) by cultured cardiac myocytes and that the stretch-induced secretion of VEGF was mainly mediated by secretion of transforming growth factor (TGF)-beta1 by cardiac myocytes in an autocrine fashion. To investigate whether tachycardia-induced mechanical overload increases serum levels of VEGF and TGF-beta1, we investigated the serum levels of VEGF and TGF-beta1 in patients with atrial fibrillation undergoing defibrillation therapy. The serum VEGF level before defibrillation was significantly increased in 13 out of 20 patients (89.48 +/- 16.09 pg/ml [mean +/- SE]). After defibrillation, the serum VEGF level in these 13 patients significantly (p = 0.019) decreased (65.04 +/- 16.61 pg/ml [mean +/- SE]), although it increased slightly in one patient. The serum TGF-beta1 level before defibrillation therapy (13.01 +/- 1.97 pg/ml [mean +/- SE]) in these 12 patients also decreased after defibrillation therapy (11.47 +/- 2.06 pg/ml [mean +/- SE]). The changes in serum VEGF level significantly correlated with those in the serum TGF-beta1 level in these 12 patients (r = 0.73, p < 0.05, n = 12). Our data suggest that tachyarrhythmia-induced mechanical overload can increase the serum VEGF level, which can be a useful clinical marker for relative myocardial oxygen shortage in such patients.

Aged↗
PubMed2003

Treatment of cardiac arrest with automatic external defibrillators: impact on outcome.

Sudden cardiac death is the leading cause of death in the US and most developed nations. Ventricular fibrillation (VF) is the most common initial rhythm in survivors of cardiac arrest. The most important factor in determining survival from VF is the time from collapse to administration of the first defibrillation shock. Automatic external defibrillators (AEDs) have been developed and widely deployed in an attempt to reduce the time to defibrillation. Data on early defibrillation using AEDs has led to a number of public access defibrillator placements in the US and ongoing studies of public access AED use. The safety of lay person AED use is clear. Clearly some concentrated captive populations (e.g. airports, airplanes) may benefit from public access AEDs. Therefore, widespread AED education as a means of increasing public acceptance of lay person AED use must be a priority. As technology evolves costs will decline, however, the current economic reality requires careful consideration of the cost effectiveness of specific AED placement.

Death, Sudden, Cardiac↗
PubMed1987

The automatic implantable cardioverter-defibrillator in drug-refractory ventricular tachyarrhythmias.

STUDY OBJECTIVE: To assess the efficacy of the automatic implantable cardioverter-defibrillator in preventing sudden death in high-risk patients. DESIGN: Nonrandomized cohort study. SETTING: A university teaching hospital with 500 beds. PATIENTS: Consecutive sample of 78 patients with symptomatic, sustained ventricular tachyarrhythmias that were previously drug-refractory. INTERVENTIONS: Before February 1985, patients received treatment with the defibrillator and amiodarone if they presented with loss of consciousness (group A) and amiodarone alone if they did not lose consciousness (group C). After February 1985, because the availability of the defibrillator was severely curtailed, patients who lost consciousness received treatment with amiodarone alone (group B). MEASUREMENTS AND MAIN RESULTS: The risk for recurrent arrhythmias was similar between groups. The actuarial risk for sudden death in group B was 31% (95% confidence interval, 11% to 51%) at 1 and 2 years, a value that was significantly higher than that for group A (p less than 0.003) or group C (p less than 0.03). The risk for dying suddenly with the first recurrence was 0.78 in group B, a value that was significantly higher than that for group A (p less than 0.003) or group C (p less than 0.002). CONCLUSION: The defibrillator is highly effective in preventing sudden death in patients whose presenting arrhythmias caused loss of consciousness (group A). In patients whose presenting arrhythmias did not result in loss of consciousness (group C), initial treatment with the defibrillator appears unnecessary.

Aged↗
PubMed2002

[The shock for life: early defibrillation in first aid and by the professional paramedic].

The Automated External Defibrillation is the key link of the chain of survival for patients in cardiac arrest. A lot of case series and trials have shown the effectiveness of early defibrillation by first rescuers and trained lay persons. The earlier the defibrillation is performed, the better is the rate of survival to hospital discharge. To increase the survival rate healthcare providers, first rescuer citizens at worksites and trained lay rescuers should be authorized, equipped and encouraged to perform early defibrillation combined with effective cardiopulmonary resuscitation (CPR). The new generation of Automated External Defibrillators (AED) are sophisticated, computerized devices that are reliable and simple to operate, enabling also lay rescuers to administer this lifesaving intervention to victims of cardiac arrest. For the concept of recurrent adequate and qualified training in the use of the AED integrated in effective DPR is recommended.

Allied Health Personnel↗
PubMed2003

[Out-of-hospital cardiac arrest. Mechanisms and treatment with automated external defibrillator].

In Denmark, approximately 4500 persons suffer yearly from an out-of-hospital cardiac arrest with mortality close to 100%. The principal arrhythmia is ventricular fibrillation, which can only be treated effectively with prompt external defibrillation. Automatic external defibrillators (AED) are small, portable, easily operated devices. They have documented high specificity and sensitivity. Moreover, biphasic automatic external defibrillators are at least as effective as traditional monophasic defibrillators. Survival rates with good neurological status as high as 60% have been reported. Better survival of out-of-hospital cardiac arrest victims requires, however, improvements throughout the chain of survival, not only more automatic external defibrillators. Therefore, the health care system has to discuss thoroughly and solve important questions regarding organisation, logistics, education, and legal aspects in order to improve survival for out-of-hospital cardiac arrest victims.

Automation↗
PubMed2003

Is public access defibrillation needed in Hong Kong?

The survival rate for non-traumatic out-of-hospital cardiac arrest in Hong Kong is low (1.25%-1.6%). Despite the reduced time interval between call receipt and first defibrillatory shock to 11.12 minutes during the past decade, the time interval between collapse/recognition and first defibrillatory shock, at 14.25 minutes, is too long. Studies of out-of-hospital cardiac arrest performed in Hong Kong were reviewed to ascertain whether a public access defibrillation programme can improve survival in Hong Kong. Three delays were found in the traditional response by emergency medical service, namely in the collapse/recognise-to-call receipt, call receipt-to-vehicle stops, and vehicle stops-to-first defibrillatory shock time intervals. The first delay is related to public education, while the second and third delays are intrinsic to a dispatched response. A public access defibrillation programme employing responders at scenes of cardiac arrests can eliminate the collapse/recognise-to-call receipt and call receipt-to-vehicle stops time intervals before defibrillation. Possible sites of public access defibrillation could include the airport and other immigration points, which have a high volume of people passing through, with projected figures for out-of-hospital cardiac arrest at these sites supporting this consideration. For successful implementation of public access defibrillation, a comprehensive educational programme and coordination with the emergency medical service are required.

Cardiopulmonary Resuscitation↗
PubMedDate not supplied

Considerations in the development of the automatic implantable defibrillator.

A highly reliable ventricular fibrillation detector and a satisfactory electrode system for delivering defibrillating pulses to the heart play a central role in the development of an automatic implantable defibrillator suitable for clinical use. Among the four implanted electrode designs tested, the combination of an electrode placed in the superior vena cava with a conformal electrode on the apex of the heart provided satisfactory defibrillation thresholds with ease of implantation. A new sensing method is also described for which an electrogram derived from the defibrillating electrodes is used as input. A form of a density function is developed for a filtered version of the input, ventricular fibrillation being characterized by a density curve lacking a large peak occurring at a level corresponding to the baseline of the filtered signal. These ideas are being incorporated into the design of a prototype implantable defibrillator delivering pulses of 24 joules.

Animals↗