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PubMed2000

Use of automated external defibrillators by a U.S. airline.

BACKGROUND: Passengers who have ventricular fibrillation aboard commercial aircraft rarely survive, owing to the delay in obtaining emergency care and defibrillation. METHODS: In 1997, a major U.S. airline began equipping its aircraft with automated external defibrillators. Flight attendants were trained in the use of the defibrillator and applied the device when passengers had a lack of consciousness, pulse, or respiration. The automated external defibrillator was also used as a monitor for other medical emergencies, generally at the direction of a passenger who was a physician. The electrocardiogram that was obtained during each use of the device was analyzed by two arrhythmia specialists for appropriateness of use. We analyzed data on all 200 instances in which the defibrillators were used between June 1, 1997, and July 15, 1999. RESULTS: Automated external defibrillators were used for 200 patients (191 on the aircraft and 9 in the terminal), including 99 with documented loss of consciousness. Electrocardiographic data were available for 185 patients. The administration of shock was advised in all 14 patients who had electrocardiographically documented ventricular fibrillation, and no shock was advised in the remaining patients (sensitivity and specificity of the defibrillator in identifying ventricular fibrillation, 100 percent). The first shock successfully defibrillated the heart in 13 patients (defibrillation was withheld in 1 case at the family's request). The rate of survival to discharge from the hospital after shock with the automated external defibrillator was 40 percent. A total of 36 patients either died or were resuscitated after cardiac arrest. No complications arose from use of the automated external defibrillator as a monitor in conscious passengers. CONCLUSIONS: The use of the automated external defibrillator aboard commercial aircraft is effective, with an excellent rate of survival to discharge from the hospital after conversion of ventricular fibrillation. There are not likely to be complications when the device is used as a monitor in the absence of ventricular fibrillation.

Aged↗

PubMed1993

A simplified, single-lead unipolar transvenous cardioversion-defibrillation system.

BACKGROUND: Transvenous implantable cardioverter-defibrillators provide significant advantages in the treatment of patients with life-threatening ventricular arrhythmias. However, present technology requires considerable electrophysiology expertise, multiple incisions, and long operative times for successful implementation. METHODS AND RESULTS: In this study, we present a prototype of a new, easy-to-insert unipolar transvenous defibrillation system that has the reliability of epicardial defibrillation but the ease of pacemaker insertion. This system incorporates a single anodal right ventricular defibrillation electrode using a 65% tilt biphasic pulse delivered to a 108-cm2 surface area pulse generator titanium alloy shell as an active cathode placed in a left infraclavicular pocket. Testing of this system was performed before implantation of a standard nonthoracotomy-transvenous defibrillation system in 40 consecutive patients with a history of ventricular tachycardia or fibrillation. The simplified unipolar single-lead system resulted in a defibrillation threshold of 9.3 +/- 6.0 J with 37 of 40 patients (93%) having a defibrillation threshold of less than 20 J. Moreover, the unipolar defibrillation system was efficiently used requiring only 3.4 +/- 0.8 ventricular fibrillation inductions to measure the defibrillation threshold and 100 +/- 28 minutes to implement. CONCLUSIONS: This new unipolar transvenous defibrillation system is as simple to insert as a pacemaker, requires few ventricular fibrillation inductions, demands less technical expertise, and provides defibrillation at energy levels comparable to that reported with epicardial lead systems. It should substantially reduce the morbidity, time, and cost of defibrillator implantation.

Adult↗

PubMed2002

[The future of electrical defibrillators for the heart].

The aim of electric defibrillation of the heart is to salvage a greater percentage of victims of cardiac arrest in the future. An initial decisive pathway towards this goal is to get a defibrillator to the victim as quickly as possible and apply an electric shock. This has now been implemented on a large scale--by means of the widespread propagation of (semi-)automatic external defibrillators (AED) and their PAD (Public Access Defibrillator) variant for use by laypersons. This is an initial necessary prerequisite which, however, is not sufficient to have a real impact on saving lives. For experience has shown that, despite the early use of AEDs, an appreciable proportion of the victims cannot be saved. The intention is to improve this situation by increasing the efficacy and reducing the harmful downside of the defibrillation waveforms applied. The solution is optimally dimensioned biphasic waveforms with high efficacy at low energy levels. In this connection, it is shown that the efficacy of high-energy defibrillation shocks is exceeded by their injurious effects, thus thwarting life-saving defibrillation. Examples of new waveforms of particularly high efficacy are presented. It is shown how such impulses should be physiologically dimensioned, and clinical results of cardioversion (atrial defibrillation) and initial out-of-hospital results of emergency defibrillation are discussed. In addition, new approaches for future waveforms enabling pulsed pulse-pause-modulated biphasic shocks are described. In this way, waveforms with a physiologically optimal effect on the heart can be produced which were previously impossible with portable defibrillators. Waveforms that have already been tested or are still in the research stage, justify hopes that improved survival of cardiac arrest victims may be expected. These new waveforms may also be of benefit in other types of defibrillators (e.g. cardioversion or implanted defibrillators).

Animals↗

PubMed2004

A model of ischemically induced ventricular fibrillation for comparison of fixed-dose and escalating-dose defibrillation strategies.

OBJECTIVES: Fixed- and escalating-dose defibrillation protocols are both in clinical use. Clinical observations suggest that the probability of successful defibrillation is not constant across a population of patients with ventricular fibrillation (VF). Common animal models of electrically induced VF do not represent a clinical VF etiology or reproduce clinical heterogeneity in defibrillation probability. The authors hypothesized that a model of ischemically induced VF would exhibit heterogeneous defibrillation shock strength requirements and that an escalating-dose strategy would more effectively achieve prompt defibrillation. METHODS: Forty-six swine were randomized to fixed, lower-energy (150 J) transthoracic shocks (group 1) or escalating, higher-energy (200 J-300 J-360 J) shocks (group 2). VF was induced by balloon occlusion of a coronary artery. After 1 or 5 minutes of VF, countershocks with a biphasic waveform were administered. The primary endpoint was successful defibrillation (termination of VF for 5 seconds) with < or =3 shocks. RESULTS: VF was induced with occlusion or after reperfusion in 35 animals. Only five of 17 group 1 animals (29%, 95% CI = 10 to 56) could be defibrillated with < or =3 shocks; 15 of 18 group 2 animals (83%, 95% CI = 59 to 96) were defibrillated with < or =3 shocks (p < 0.002 vs. group 1). Nine of the group 1 animals (75%) that could not be defibrillated with 150-J shocks were rescued with < or =3 shocks ranging from 200 to 360 J. CONCLUSIONS: In this ischemic VF animal model, defibrillation shock strength requirements varied among individuals, and when defibrillation was difficult, an escalating-dose strategy was more effective for prompt defibrillation than fixed, lower-energy shocks.

Animals↗

PubMed1992

Effects of chronic amiodarone therapy on defibrillation threshold.

In a prospective and parallel, randomized study, the long-term stability of epicardial defibrillation threshold was evaluated in 22 patients, using a patch-patch lead configuration at the time of implantation and generator replacement. The concomitant antiarrhythmic drug treatment consisted of either mexiletine (720 mg/day) or amiodarone (400 mg/day) and was administered to patients in a randomized and parallel manner. During a mean follow-up of 24 +/- 6 months, the defibrillation threshold increased significantly from 14.3 +/- 2.8 to 17.9 +/- 5.3 J (p < 0.05) for the entire patient group. The increase in the chronic defibrillation threshold was due to a marked increase in defibrillation energy needs in the subgroup of patients receiving amiodarone. Whereas no significant change in the defibrillation threshold was documented in the subgroup of patients receiving mexiletine, the mean defibrillation threshold increased from 14.1 +/- 3.0 to 20.9 +/- 5.4 J (p < 0.001) in those receiving amiodarone. In all patients with increased defibrillation thresholds, reevaluation showed a reduction in the defibrillation threshold after discontinuation of antiarrhythmic drug therapy. The only variable associated with an increase in the chronic defibrillation threshold was amiodarone treatment. These findings suggest that the defibrillation threshold should be measured at each generator replacement and in case of a change in antiarrhythmic drug treatment. In particular, if amiodarone treatment is initiated, it is recommended that the defibrillation threshold should be reevaluated to ensure an adequate margin of safety.

Amiodarone↗

PubMed1996

Optimal electrode position for transvenous defibrillation: a prospective randomized study.

OBJECTIVES: This study was performed to determine the optimal position for the proximal electrode in a two-electrode transvenous defibrillation system. BACKGROUND: Minimizing the energy required to defibrillate the heart has several potential advantages. Despite the increased use of two-electrode transvenous defibrillation systems, the optimal position for the proximal electrode has not been systematically evaluated. METHODS: Defibrillation thresholds were determined twice in random sequence in 16 patients undergoing implantation of a two-lead transvenous defibrillation system; once with the proximal electrode at the right atrial-superior vena cava junction (superior vena cava position) and once with the proximal electrode in the left subclavian-innominate vein (innominate vein position). RESULTS: The mean (+/- SD) defibrillation threshold with the proximal electrode in the innominate vein position was significantly lower than with the electrode in the superior vena cava position (13.4 +/- 5.7 J vs. 16.3 +/- 6.6 J, p = 0.04). Defibrillation threshold with the proximal electrode in the innominate vein position was lower or equal to that achieved in the superior vena cava position in 75% of patients. In patients with normal heart size (cardiothoracic ratio < or = 0.55), the improvement in defibrillation threshold with the proximal electrode in the innominate vein position was more significant than in patients with an enlarged heart (innominate vein 13.0 +/- 6.5 J vs. superior vena cava 17.9 +/- 5.1 J, p < 0.01). In patients with an enlarged heart, no difference between the two sites was observed (innominate vein 13.9 +/- 4.5 J vs. superior vena cava 13.6 +/- 8.3 J, p = NS). CONCLUSIONS: During implantation of a two-lead transvenous defibrillation system, positioning the proximal defibrillation electrode in the subclavian-innominate vein will lower defibrillation energy requirements in the majority of patients.

Aged↗

PubMed2004

Effect of stretch-activated channels on defibrillation efficacy.

OBJECTIVES: This study aims to explore whether defibrillation threshold elevation could be caused by sustained recruitment of stretch-activated channels (SACs) and, if so, what are the underlying mechanisms. BACKGROUND: Clinical studies have demonstrated that patients with dilated and overloaded ventricles have elevated defibrillation threshold. Prolonged ventricular stretch has been suggested as a possible factor in defibrillation threshold elevation; however, its role remains unclear. METHODS: A two-dimensional finite-element bidomain model of ventricular defibrillation was used in the study. Retaining the geometrical parameters in the model, defibrillation dose-response curves were constructed with and without SACs to isolate the effect of stretch on shock outcome. RESULTS: Simulations demonstrate that SAC activation leads to flattening of dose-response curve and increases in defibrillation threshold and effective dose for defibrillation by 31.4% and 18.8%, respectively. Examination of the electrophysiologic properties associated with sustained SAC recruitment pinpointed the main mechanisms responsible for the decrease in defibrillation efficacy. The lower conduction velocity of the shock-induced break excitations and the more positive transmembrane potential at the end of the effective refractory period in the tissue with SACs are proposed as main reasons for defibrillation threshold elevation. CONCLUSIONS: Demonstrating the contribution of SACs to defibrillation threshold elevation identifies SACs as an attractive pharmaceutical target to reduce defibrillation threshold in patients with dilated cardiomyopathy.

Cardiomyopathy, Dilated↗

PubMed1999

Effect of amiodarone and sotalol on the defibrillation threshold in comparison to patients without antiarrhythmic drug treatment.

AIM OF THE STUDY: It is generally accepted that chronic therapy with antiarrhythmic drugs might increase the defibrillation threshold at implantation of an implantable cardioverter defibrillator. A recently published animal study showed a minor effect of the class 1 antiarrhythmic drug lidocaine on the defibrillation threshold if biphasic shocks were used. METHODS AND RESULTS: We therefore performed a retrospective analysis in 89 patients who received an ICD capable of monophasic (n=18) or biphasic (n=71) shocks with a transvenous lead system. In all patients the defibrillation threshold was determined according to the same step down protocol. In the 18 patients with a monophasic device the effects of chronic therapy with amiodarone (n=7) on the defibrillation threshold were evaluated in comparison to a group without antiarrhythmic treatment (n=11). In those patients receiving a biphasic device the effects of chronic therapy with amiodarone (n=29), sotalol (n=20) or no antiarrhythmic medication (n=22) on the defibrillation threshold were evaluated. The groups receiving a monophasic device did not differ in respect to age, sex, underlying cardiac disease, clinical arrhythmia (VT/VF), clinical functional status, left ventricular ejection fraction and the number of patients with additional subcutaneous electrodes. These parameters as well as the type of implanted device were not different between patient groups receiving a biphasic device. Patients on chronic amiodarone therapy receiving a monophasic device had a significantly higher defibrillation threshold (29.1 +/- 8.8 J) than patients without antiarrhythmic treatment (19.1 +/- 5.1 J, P = 0.021). The groups did not differ significantly in respect to the impedance measured at the shocking lead (P = 0.13). In three patients on chronic amiodarone an epicardiac lead system had to be implanted due to an inadequate monophasic defibrillation threshold compared to no patient without antiarrhythmic drug treatment (P = 0.043). In the patients with a biphasic device the intraoperative defibrillation threshold was not significantly different between the three study groups (P = 0.44). No patient received an epicardiac lead system. The defibrillation threshold in the amiodarone group was 15.3 +/- 7.3 J, in the sotalol group 14.4 +/- 7.2 J and in the patients without antiarrhythmic drug treatment 17 +/- 6.1 J. As well, no significant difference was seen between the groups in respect of the impedance of the high voltage electrode (P = 0.2). CONCLUSION: With the use of a biphasic device in combination with a transvenous lead system the intraoperative defibrillation threshold is not significantly different between patients on chronic amiodarone in comparison to patients without antiarrhythmic drug treatment or patients on chronic oral sotalol. This is in contrast to our findings with a monophasic device.

Aged↗

PubMed1997

Biphasic transthoracic defibrillation causes fewer ECG ST-segment changes after shock.

STUDY OBJECTIVE: Electrocardiographic abnormalities are common after transthoracic defibrillation. ECG ST-segment changes are especially problematic after defibrillation and may indicate ischemic or shock-induced cardiac dysfunction after resuscitation. Biphasic defibrillation waveforms, compared with monophasic waveforms, diminish shock-induced cardiac dysfunction in laboratory preparations. This effect has not been validated in human subjects. We therefore evaluated in a prospective, blinded fashion the effect of biphasic and monophasic transthoracic defibrillation on the ECG ST segment in 30 consecutive patients during surgery for the implantation of a cardioverter-defibrillator. METHODS: In each patient two low-energy truncated biphasic transthoracic defibrillation shocks (115 and 130 J) were compared with a standard clinical 200 J monophasic damped-sine wave shock. The biphasic shocks and the damped-sine wave shock have been demonstrated to have equal defibrillation efficacy of 97%. Fifteen-second ECG signals recorded across transthoracic defibrillation electrodes were digitized before ventricular fibrillation induction and immediately after each defibrillation attempt. The ST segments 80 msec after the J point were analyzed in a blinded fashion by two reviewers. The ST-segment deflection, QRS-interval duration, QT interval, and heart rate after each therapy were compared with baseline values. RESULTS: ECG ST-segment elevation was significantly greater with the 200-J damped-sine waveform than with either biphasic waveform. The ECG ST-segment levels were -.55 +/- .36 at baseline, -.76 +/- .36 mm after internal shock, -.02-.36 mm after 115-J biphasic shock, .21 +/- .38 mm after 130-J biphasic shock, and 2.09 +/- .37 mm after 200-J damped-sine wave shock (P<.0001). QRS-interval duration, QT interval, and heart rate did not change significantly with any waveform. CONCLUSION: Transthoracic defibrillation with biphasic waveforms results in less postshock ECG evidence of myocardial dysfunction (injury or ischemia) than standard monophasic damped sine waveforms without compromise of defibrillation efficacy.

Adult↗

PubMed1999

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways.

OBJECTIVES: The purpose of this study was to compare transvenous atrial defibrillation thresholds with lead configurations consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown. METHODS: This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial). RESULTS: Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002). CONCLUSIONS: These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.

Aged↗

PubMed2000

Is there a need for routine testing of ICD defibrillation capacity? Results from more than 1000 studies.

AIMS: Benefits and complications of postoperative implantable cardioverter-defibrillator tests are controversial matters. This study sought to assess the necessity of defibrillation function tests after implantation. METHODS AND RESULTS: We retrospectively analysed 1007 implantable cardioverter-defibrillator tests in 587 systems and 556 patients. Nine hundred and thirty implantable cardioverter-defibrillator tests (89.4%) were routinely performed. Seventy-one tests (7%) were performed after a change in the antiarrhythmic drug regimen and six tests (0.60%) because of a suspected dysfunction of the implantable cardioverter-defibrillator. During routine tests, four systems (0.4%) failed to defibrillate the patient. However, in all but one test, abnormalities of the system had been observed before the test. After the addition of antiarrhythmic drugs, two of 71 implantable cardioverter-defibrillator systems (2.8%) failed to defibrillate the patient. One of six systems tested due to a suspected dysfunction failed to defibrillate the patient. During 16 tests (1.6%), complications occurred. CONCLUSIONS: Our experience demonstrates that postoperative tests of the defibrillation function of implantable cardioverter-defibrillators rarely reveal dysfunctions. As testing is unpleasant for the patient and not free of complications, tests might be restricted to those patients in whom a dysfunction is suspected and to those patients in whom class I or class III antiarrhythmic drugs have been added to the antiarrhythmic drug regimen.

Adolescent↗

PubMed1999

An abdominal active can defibrillator may facilitate a successful generator change when a lead failure is present.

AIMS: Defibrillator generator changes are frequently performed on patients with an implantable cardioverter defibrillator in an abdominal pocket. These patients usually have epicardial patches or older endocardial lead systems. At the time of a defibrillator generator change defibrillation may be unsuccessful as a result of lead failure. We tested the hypothesis that an active can defibrillator implanted in the abdominal pocket could replace a non-functioning endocardial lead or epicardial patch. METHODS AND RESULTS: An abdominal defibrillator generator change was performed in 10 patients, (mean age = 67 +/- 13 years, nine men). Initially, a defibrillation threshold (DFT) was obtained using a passive defibrillator and the chronic endocardial or epicardial lead system. DFTs were then performed using an active can emulator and one chronic lead to simulate endocardial or epicardial lead failure. We tested 30 lead configurations (nine endocardial and 21 epicardial). Although a DFT of 7.3 +/- 4.2 joules was obtained with the intact chronic lead system, the active can emulator and one endocardial or epicardial lead still yielded an acceptable DFT of 19.9 +/- 6.1 joules. In addition, a successful implant (DFT < or = 24 joules) could have been accomplished in 28 of 30 (93%) lead configurations. CONCLUSION: An active can defibrillator in an abdominal pocket may allow for a successful generator change in patients with defibrillator lead malfunction. This would be simpler than abandoning the abdominal implant and moving to a new pectoral device and lead or tunnelling a new endocardial electrode. However, loss of defibrillation capability with a particular complex lead may be a warning of impending loss of other functions (eg. sensing and/or pacing).

Abdomen↗

PubMed2006

Definition of successful defibrillation.

OBJECTIVES: The definition of defibrillation shock "success" endorsed by the International Liaison Committee on Resuscitation since the publication of Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiac Care has been removal of ventricular fibrillation at 5 secs after shock delivery. Although this success criterion provides a direct assessment of the primary task of a shock, it may not be the only clinically useful measure of shock outcome. We evaluated a different defibrillation success criterion to determine whether it could provide additional insight into the relative performance of different defibrillation shocks. DESIGN: A randomized study comparing monophasic and biphasic waveform shocks is reported with return of organized rhythm as the primary outcome measure of defibrillation success. PATIENTS: A total of 120 patients with out-of-hospital ventricular fibrillation as the first recorded rhythm were treated with defibrillation with automated external defibrillators. MEASUREMENTS AND MAIN RESULTS: Return of organized rhythm (two QRS complexes, <5 secs apart, <60 secs after defibrillation) was achieved in 31 monophasic shock (45%) and 35 biphasic shock (69%) patients (relative risk, 1.53, 95% confidence interval, 1.11-2.10). Logistic regression analysis revealed that shock waveform was the strongest independent predictor of return of organized rhythm (odds ratio, 4.0; 95% confidence interval, 1.67-10.0). Defibrillation success with the conventional International Liaison Committee on Resuscitation criterion was very high (91% and 98%, respectively) and not significantly different between groups. CONCLUSIONS: Return of organized rhythm proved to be a more sensitive measure of relative defibrillation shock performance than the conventional shock success criterion. Inclusion of return of organized rhythm as an end point in future clinical research could help discern more subtle defibrillation shock effects and contribute to further optimization of defibrillation technology.

Adult↗

PubMed1999

Local anaesthesia versus general anaesthesia for cardioverter-defibrillator implantation.

AIMS: Cardioverter-defibrillators are conventionally implanted under general anaesthesia. However, implantation under conscious sedation is being increasingly used. It has been shown that cardioverter-defibrillators can be implanted in a more pacemaker-like approach: under local anaesthesia for the surgical procedure, and with mild sedation for defibrillation threshold testing only. The aim of the present study was to compare local and general anaesthesia in defibrillation threshold testing and implantation of cardioverter-defibrillators. METHODS AND RESULTS: Forty patients were assigned to two groups: in the first 20 consecutive patients the cardioverter-defibrillator was implanted under general anaesthesia (GA), and in the subsequent 20 patients under local anaesthesia (LA). There was no significant difference between the two groups in regard of age, body weight, underlying disease, left ventricular ejection fraction, and NYHA classification. The defibrillation threshold was 13.7 +/- 5.5 J under local anaesthesia versus 10.7 +/- 4.7 J under general anaesthesia (n.s.). For defibrillation threshold testing 7.9 +/- 3.6 shocks had to be applied in patients under general anaesthesia versus 6.2 +/- 1.3 shocks under local anaesthesia (n.s.). Mean heart rate, arterial oxygen saturation and mean arterial blood pressure remained stable throughout defibrillation threshold testing, irrespective of the type of anaesthesia used. The duration of the surgical procedure was 62 +/- 16 min under GA and 60 +/- 14 min under LA (n.s.), however, the entire implantation procedure was significantly longer in patients under general anaesthesia than in those under local anaesthesia (124 +/- 24 min and 97 +/- 22 min, respectively, p < 0.005). There were no complications in either group and the procedure was well tolerated. With the use of local anaesthesia the cost of anaesthesia were reduced by 72%. CONCLUSION: Local anaesthesia in combination with mild sedation is as safe and well tolerated as general anaesthesia in cardioverter-defibrillator implantation. Lidocaine used for local anaesthesia does not adversely affect the defibrillation threshold. Device implantation in a pacemaker-like approach results in a significant reduction in total procedure time and costs, and facilitates scheduling of the procedure.

Anesthesia, General↗

PubMed1996

Multicenter experience with a pectoral unipolar implantable cardioverter-defibrillator. Active Can Investigators.

OBJECTIVES: The purpose of this study was to prospectively examine in a multicenter study the methods of use, efficacy and complications of a unipolar cardioverter-defibrillator in patients at risk for sudden cardiac death. BACKGROUND: Implantation of cardioverter-defibrillators in the pectoral region offers a significant opportunity to improve the management of patients with life-threatening arrhythmias. Unipolar, single-lead, pectoral implantable cardioverter-defibrillators might decrease related mortality, morbidity and costs in the care of such patients. METHODS: From November 3, 1993 to May 8, 1995, a unipolar defibrillator (Medtronic model 7219C) was selected for use in 473 patients from 74 centers (386 [82%] men, 87 [18%] women; mean [+/- SD] age 59 +/- 13 years, range 16 to 88). The clinical indication for use was ventricular fibrillation in 157 patients, sustained ventricular tachycardia in 236, both ventricular tachycardia and ventricular fibrillation in 53 and syncope or inducible ventricular tachycardia/ventricular fibrillation in 27. Coronary artery disease was present in 323 patients (68%). The mean left ventricular ejection fraction was 0.36 +/- 0.15 (range 0.10 to 0.85). The distribution of New York Heart Association congestive heart failure was class I = 34%; class II = 45%; class III = 17%; and class IV = 2%. RESULTS: The unipolar cardioverter-defibrillator was inserted successfully in 464 (98%) of 473 candidates. Effective defibrillation occurred with the first shock polarity tested in 88% of patients, after a polarity switch in 8% and after lead or generator repositioning in 2%. The stored energy defibrillation threshold was obtained at implantation in 339 patients (72%) and was 11.5 +/- 6.1 J, with 72% of patients having a defibrillation threshold < or = 12 J. The mean "skin-to-skin" implantation time was 96 +/- 45 min (range 25 to 335 min). Complications occurred in 29 patients (6%). Device therapy for 2,160 spontaneous ventricular tachycardia or fibrillation episodes occurred in 128 patients (27%) over a 2,732 device-month experience (range 0 to 17.2) and was effective in 98.7% of episodes. There were 14 deaths (10 nonsudden cardiac, 3 sudden cardiac, 1 noncardiac). Cumulative survival, on an intention-to-treat basis from all causes of death at 17.2 months, was 94.4%. CONCLUSIONS: Unipolar pectoral implantable cardioverter-defibrillators can be inserted with a high likelihood of success in a relatively brief procedure. Defibrillation thresholds are low, morbidity is modest, and survival rates are good with this new type of implantable cardioverter-defibrillator.

Cardiac Pacing, Artificial↗

PubMed1989

Evaluation of electrode polarity on defibrillation efficacy.

The effect of electrode polarity on defibrillation thresholds in humans is unknown. This prospective, randomized evaluation of electrode polarity on defibrillation thresholds was performed in 21 survivors of ventricular fibrillation (VF) undergoing cardiac surgery. Defibrillation was always performed with 2 identical large rectangular, wire mesh electrodes positioned over the anterior wall of the right ventricle and the posterolateral wall of the left ventricle. The initial electrode polarity for the left ventricular (LV) electrode was chosen randomly for determination of the defibrillation threshold. Subsequently, electrode polarity was reversed. The defibrillation threshold was defined as the lowest pulse amplitude that would effectively terminate VF with a single discharge delivered 10 seconds after initiation of an episode of VF with alternating current. For each defibrillation pulse, voltage, current, resistance and delivered energy were recorded. Of the 21 patients, 15 (71%) had a lower defibrillation threshold when the LV electrode was positive, 2 patients (10%) had a lower defibrillation threshold when the LV electrode was negative and 4 patients (19%) had equal defibrillation thresholds (within 0.5 J) regardless of polarity. The mean leading edge defibrillation threshold voltage was 370 +/- 88 volts when the LV electrode was negative and 320 +/- 109 volts (14% less) when the LV electrode was positive (p = 0.014). Mean leading edge defibrillation threshold current was 9.3 +/- 3.1 amps when the LV electrode was negative compared to 7.7 +/- 3.1 amps (17% less) when the LV electrode was positive (p = 0.0033). There were no differences in resistance with the 2 configurations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

A prospective, randomized evaluation of effect of ventricular fibrillation duration on defibrillation thresholds in humans.

The effect of ventricular fibrillation duration in humans on defibrillation efficacy as it pertains to the time of intervention of an automatic implantable defibrillator is unknown. If a difference in defibrillation efficacy exists in the early period after ventricular fibrillation onset, it may affect algorithms used by antiarrhythmic devices for arrhythmia detection and therapy. Therefore, a prospective, randomized evaluation was performed of the effect of ventricular fibrillation durations of 10 s and 20 s on defibrillation thresholds in 10 survivors of sudden cardiac arrest undergoing implantation of an automatic cardioverter defibrillator. The initial duration of ventricular fibrillation was chosen randomly. Subsequently, each patient served as his or her own control for the alternate duration of ventricular fibrillation to that chosen initially. The mean leading edge defibrillation threshold voltage was 411 +/- 114 V when ventricular fibrillation persisted for 10 s and 419 +/- 125 V when it persisted for 20 s (p = 0.73). The mean defibrillation threshold current was 11.4 +/- 2.8 A when ventricular fibrillation persisted for 10 s and 11.4 +/- 3.2 A when it persisted for 20 s (p = 0.97). The delivered energy defibrillation threshold was 11.5 +/- 5.9 J when ventricular fibrillation persisted for 10 s and 12.0 +/- 6.9 J when it persisted for 20 s (p = 0.67). These findings show that the defibrillation threshold does not change between 10 and 20 s of ventricular fibrillation in out-of-hospital survivors of cardiac arrest at the time of surgical implantation of an automatic defibrillator. The data may have influence on the programming of defibrillator detection algorithms.

Algorithms↗

PubMed1999

Waveforms of external defibrillators: analysis and energy contribution.

BACKGROUND AND OBJECTIVE: Defibrillation is the most important therapy for terminating ventricular fibrillation in cardiac arrest patients. In addition to performing defibrillation at the earliest possible time, appropriate pulse energy and optimal waveform seem to be crucial for success. Emergency medical service personnel use different defibrillators and rely on their similarity of energy content. This study examined the true pulse energy content and waveform of 17 commonly used defibrillators. METHODS AND RESULTS: Defibrillation energies were selected to be 30, 200 or 360 J and defibrillators were discharged into test resistors, simulating transthoracic impedances of 25, 50 or 100 Ohms. Pulse energy deviated by up to +23% or -29% from the selected energy. Pulse energy within the initial 8 ms ranged from 90 to 30% of total pulse energy. Fourteen defibrillators utilising damped sinusoidal waveforms produced a monophasic pulse when discharged into resistances of 50 Ohms and 100 Ohms. CONCLUSIONS: Defibrillators used at the same energy settings do not necessarily produce the same defibrillation pulse energy. All but one defibrillator actually use monophasic waveforms, leaving the potential advantage of biphasic waveforms unused. Energy accuracy of defibrillators needs to be improved, and biphasic waveforms should be used more.

Calibration↗