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At least 145 records · Page 8Linked to original sources
PubMed2005

Internal defibrillation with minimal skeletal muscle activation: a new paradigm toward painless defibrillation.

BACKGROUND: Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue. OBJECTIVES: The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system. METHODS: Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration. RESULTS: Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J. CONCLUSION: Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Animals↗
PubMed2000

High dispersion of ventricular repolarization after an implantable defibrillator shock predicts induction of ventricular fibrillation as well as unsuccessful defibrillation.

OBJECTIVES: To test the hypothesis that post-shock dispersion of repolarization (PSDR) is higher in T wave shocks that induce ventricular fibrillation (VF) than in those that do not, as well as in implantable cardioverter defibrillator (ICD) defibrillation shocks which fail to terminate VF when compared with those that are successful. BACKGROUND: Ventricular fibrillation has been linked to the presence of dispersion of repolarization, which facilitates reentry. Most of the studies have been done in animals, and the mechanism underlying the generation and termination of VF in humans is speculative and remains to be determined. METHODS: Monophasic action potentials (MAPs) were recorded simultaneously from the right ventricular outflow tract (RVOT) and the right ventricular apex (RVA) in 27 patients who underwent implantation and testing of an ICD. T wave shocks were used to induce VF while the termination was attempted using internal defibrillator shocks. The post-shock repolarization time (PSRT) was measured in both the RVA and RVOT MAPs, and the difference between the two recordings was defined as the PSDR. The averages of PSDR were compared between the successful and unsuccessful inductions and terminations of VF. RESULTS: T wave shocks that induced VF generated a greater PSDR (93.4 +/- 85.1 ms) than the unsuccessful ones (45.1 +/- 55.9 ms, p < 0.001). On the other hand, shocks that failed to terminate VF were associated with a greater PSDR (59.9 +/- 41.2 ms) than shocks that terminated VF (21.1 +/- 20.1 ms), p < 0.001. CONCLUSIONS: A high PSDR following a T wave shock is associated with induction of VF; while following a defibrillating shock, it is associated with its failure and the continuation of VF. Conversely, a low PSDR is associated with failure of a T wave shock to induce VF and successful termination of VF by a defibrillating shock.

Action Potentials↗
PubMed2003

A randomized prospective study of single coil versus dual coil defibrillation in patients with ventricular arrhythmias undergoing implantable cardioverter defibrillator therapy.

ICD implantation is standard therapy for malignant ventricular arrhythmias. The advantage of dual and single coil defibrillator leads in the successful conversion of arrhythmias is unclear. This study compared the effectiveness of dual versus single coil defibrillation leads. The study was a prospective, multicenter, randomized study comparing a dual with a single coil defibrillation system as part of an ICD using an active pectoral electrode. Seventy-six patients (64 men, 12 women; age 61 +/- 11 years) were implanted with a dual (group 1, n = 38) or single coil lead system (group 2,n = 38). The patients represented a typical ICD cohort: 60% presented with ischemic cardiomyopathy as their primary cardiac disease, the mean left ventricular ejection fraction was 0.406 +/- 0.158. The primary tachyarrhythmia was monomorphic ventricular tachyarrhythmia in 52.6% patients and ventricular fibrillation in 38.4%. There was no significant difference in terms of P and R wave amplitudes, pacing thresholds, and lead impedance at implantation and follow-up in the two groups. There was similarly no difference in terms of defibrillation thresholds (DFT) at implantation. Patients in group 1 had an average DFT of 10.2 +/- 5.2 J compared to 10.3 +/- 4.1 J in Group 2, P = NS. This study demonstrates no significant advantage of a dual coil lead system over a single coil system in terms of lead values and defibrillation thresholds. This may have important bearing on the choice of lead systems when implanting ICDs.

Chi-Square Distribution↗
PubMed2001

Nonthoracotomy implantable cardioverter defibrillator placement in children: use of subcutaneous array leads and abdominally placed implantable cardioverter defibrillators in children.

INTRODUCTION: The need to access the right ventricle might preclude transvenous placement of a defibrillation lead at implantable cardioverter defibrillator (ICD) placement, especially in small children or children with complex congenital heart defects. We investigated a subcutaneous array lead in addition to an abdominally placed "active can" ICD device in two children to avoid a thoracotomy. METHODS AND RESULTS: The first child (age 12 years, 138 cm, 41 kg) had transposition of the great arteries with a subsequent surgical intra-atrial correction by the Mustard technique. The second child (age 14 years, 161 cm, 54 kg) had a single atrium and a single ventricle, d-transposition of the aorta, and atresia of the main pulmonary artery with a surgical anastomosis between the aorta and the right pulmonary artery by the Cooley technique. The defibrillation threshold was 18 J and <20 J at initial implantation and at generator replacement in the first patient and 20 J in the second patient. During follow-up of 6 years and 1 month, respectively, no ICD-related complications occurred. CONCLUSION: In children in whom endocardial, right ventricular placement of a defibrillation lead is precluded, defibrillation is possible and safe between an abdominally placed "active can" ICD device and a subcutaneous array lead. This approach may avoid a thoracotomy in children with no possibility for transvenous ICD placement.

Abdomen↗
PubMed1992

Failure of defibrillator paddle as mimic for subcutaneous patch lead during nonthoracotomy implantable cardioverter defibrillator lead configuration assessment.

It is a common, although virtually unsubstantiated, practice to assess the efficacy of nonthoracotomy lead systems for implantable cardioverter defibrillators using a defibrillator paddle as mimic for the subcutaneous patch lead. We report a case in which an adequate defibrillation threshold was documented with the nonthoracotomy lead system using a defibrillator paddle but not following implantation of the true subcutaneous patch lead. This case suggests that the substitution of a defibrillator paddle for the subcutaneous patch lead during nonthoracotomy lead system evaluation may have significant limitations in assessing lead configuration efficacy.

Adult↗
PubMed1993

Intracardiac emergency defibrillation for refractory ventricular fibrillation during implantation of cardioverter defibrillators with nonthoracotomy lead systems.

Implantable cardioverter defibrillators (ICDs) are being implanted in increasing numbers. At intraoperative defibrillation threshold tests refractory ventricular fibrillation (VF) requiring emergency open chest resuscitation is a major concern during implantation of nonthoracotomy ICD lead systems. A new method of high energy endocardial/extrathoracic defibrillation via the implanted ICD transvenous defibrillation electrode (TDE) was used to terminate refractory VF. During implantation of ICD with TDE in 20 patients refractory VF occurred in two patients. The arrhythmia was terminated with endocardial/extrathoracic defibrillation in both cases, and no complications were observed.

Aged↗
PubMed2004

Addition of a defibrillation electrode in the low right atrium to a right ventricular lead does not reduce ventricular defibrillation thresholds.

Transvenous unipolar active can defibrillation systems have proven to be effective in treating ventricular tachyarrhythmias. However, a further reduction of ventricular defibrillation thresholds (V-DFT) would increase the longevity, reduce the size of pulse generators, and help to avoid additional leads in patients with inacceptable high V-DFTs. In a finite difference computer model, the extension of the right ventricular (RV) defibrillation coil into the low right atrium led to a 40% reduction of unipolar V-DFT. To evaluate this finding, we conducted a prospective, randomized study in 11 patients receiving an ICD. Extension of the RV electrode was simulated by adding a second coil placed in the low right atrium with the same polarity. Using a binary search protocol, V-DFT was determined with and without the additional electrode in each patient. Total shock impedance was significantly lower in the two coil (low RA) configuration, compared to the single coil (RV) configuration. Corresponding values were 49.9 +/- 6.7 Ohm and 61.1 +/- 9.3 Ohm, respectively (P < 0.01, paired t-test). However, there was no reduction, but even a nonsignificant increase in V-DFTs. Mean V-DFT in the RV configuration was 12.0 +/- 5.6 J and 16.3 +/- 7.8 J in the low RA configuration (P = 0.09, paired t-test). Despite a reduction in total impedance, the addition of a defibrillation coil in the low right atrium does not reduce ventricular defibrillation thresholds.

Aged↗
PubMed2005

Lay rescuer automated external defibrillator ("public access defibrillation") programs: lessons learned from an international multicenter trial: advisory statement from the American Heart Association Emergency Cardiovascular Committee; the Council on Cardiopulmonary, Perioperative, and Critical Care; and the Council on Clinical Cardiology.

Lay rescuer automated external defibrillator (AED) programs may increase the number of people experiencing sudden cardiac arrest who receive bystander cardiopulmonary resuscitation (CPR), can reduce time to defibrillation, and may improve survival from sudden cardiac arrest. These programs require an organized and practiced response, with rescuers trained and equipped to recognize emergencies, activate the emergency medical services system, provide CPR, and provide defibrillation. To determine the effect of public access defibrillation (PAD) programs on survival and other outcomes after SCA, the National Heart, Lung, and Blood Institute, the American Heart Association (AHA), and others funded a large prospective randomized trial. The results of this study were recently published in The New England Journal of Medicine and support current AHA recommendations for lay rescuer AED programs and emphasis on planning, training, and practice of CPR and use of AEDs. The purpose of this statement is to highlight important findings of the Public Access Defibrillation Trial and summarize implications of these findings for healthcare providers, healthcare policy advocates, and the AHA training network.

American Heart Association↗
PubMed1963

SUCCESSFUL USE OF THE DC EXTERNAL DEFIBRILLATOR AFTER FAILURE OF AN AC EXTERNAL DEFIBRILLATOR.

The opportunity for a clinical comparison of the effectiveness of AC and DC types of external defibrillators in the same patient rarely presents. A postoperative patient developed ventricular fibrillation and was successfully resuscitated by means of closed chest cardiac massage and positive pressure ventilation. Three shocks using an AC external defibrillator did not interrupt the arrhythmia, whereas one shock (150 Wsec.) delivered from a DC external defibrillator resulted in immediate interruption of the ventricular fibrillation. This case lends support to the clinical impression gained in the Vancouver General Hospital that the DC external defibrillator is superior to the AC defibrillator.

Defibrillators↗
PubMed2005

Clinical predictors of defibrillation threshold in patients with implantable cardioverter-defibrillators.

BACKGROUND: Safety of patients with malignant ventricular arrhythmias, treated with implantable cardioverter defibrillators (ICD), depends on the possibility of immediate and effective intracardiac defibrillation. It is especially important in those patients in whom there is a risk of increased defibrillation threshold (DFT) of ventricular fibrillation (VF). Thus, it is important to know whether some clinical parameters may predict a high DFT. AIM: To assess the relationship between DFT and clinical, demographic and anthropometric parameters, type and progression of underlying disease as well as antiarrhythmic therapy used in ICD recipients. METHODS: The study group consisted of 168 patients (47 females, 121 males, mean age 55+/-15 years, range 15-82 years) who were selected to receive an ICD. DFT was systematically tested during ICD implantation in all patients. Various clinical, demographic, anthropometric and echocardiographic parameters were analysed as the function of DFT value, examining their accuracy in predicting a high (> or =15 J) or a low (<15 J) DFT, using logistic regression model. RESULTS: Univariate analysis revealed that DFT value was significantly related to the following parameters: idiopathic VF, dilated cardiomyopathy, amiodarone therapy and the use of beta blockers. There was a significant correlation between DFT and LVEDD, height, LVEF and impedance of defibrillating system. Multivariate analysis showed that amiodarone therapy, height, impedance of defibrillating system and LVEDD were independently related to the DFT value. Parameters which predicted a high (> or =15 J) DFT, consisted of amiodarone therapy (p=0.005), height (p=0.01), LVEDD (p=0.01), LVEF (p=0.03), dilated cardiomyopathy (p=0.01) and body surface area (p=0.049). Amiodarone therapy occurred to be the only parameter which independently predicted a high DFT (odds ratio 2.78; 95% confidence interval 1.19-6.5). CONCLUSIONS: Tall stature, enhanced LVEDD, decreased LVEF and amiodarone therapy increase the risk of a high DFT in ICD recipients. Chronic amiodarone therapy increases three times the risk of elevated DFT. In patients with already implanted ICD in whom amiodarone is started, reassessment of DFT following administration of a loading dose of the drug is required.

Adolescent↗
PubMed1987

The relationship between successful defibrillation and delivered energy in open-chest dogs: reappraisal of the "defibrillation threshold" concept.

The traditional assessment of the energy required for successful ventricular defibrillation involves the measurement of a "defibrillation threshold" (DFT), implying a clear-cut distinction between effective and ineffective energies. We examined the relationship between delivered energy and the likelihood of successful defibrillation in 10 open-chest pentobarbital anesthetized dogs, with the use of an internal spring/patch electrode system. An initial DFT was determined by decreasing the energy discharged until a failure first occurred (10.3 +/- 3.4 J). Six energy levels in 1 to 2 J increments were then selected surrounding this value and each was administered eight times in balanced random order (total 48 trials). The relationship between energy and percent success in defibrillation exhibited a shallow slope, with a gradual increase in success from 0% to 100% over several energy increments. The initial DFTs showed actual success rates varying from 25% to 87.5% (mean 71 +/- 26%). The results were fitted to a sigmoidal dose-response curve by logistic regression analysis and the energy associated with 50% success (E50) and 80% success (E80) was determined, as no single value for DFT could be defined in any animal. In 12 other dogs, a defibrillation curve was similarly constructed at baseline and was repeated after 90 minutes. No significant change in E50 (5.0 +/- 2.1 J vs 5.2 +/- 2.7 J) or E80 (6.3 +/- 2.5 J vs 6.6 +/- 3.2 J) was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Determination of patch electrode position for the internal cardioverter-defibrillator by cine computed tomography and its relation to the defibrillation threshold.

Cardioverter-defibrillator implantation in 22 consecutive patients after aborted sudden cardiac death was followed by prospective determination of the correct anatomic position of epicardial patch electrodes by chest X-ray study and cine computed tomography; the data were compared with the defibrillation threshold obtained intraoperatively. Patch electrode position was qualitatively graded. Computed tomography improved the assessment as compared with X-ray study in 13 patients (59%), visualizing electrodes in relation to the underlying myocardial and vascular structures. Although the computed tomographic technique provided more precise visualization, its grading of patch position correlated as poorly as that of the X-ray study with the measured acute defibrillation threshold. Three-dimensional reconstruction by computed tomography made it possible to determine quantitatively left ventricular mass (free wall and septum) and the mass encompassed by the patch electrodes. The 34.6 +/- 13.7% (range 12.6 to 61.1%) of the left ventricular mass encompassed by both patch electrodes showed a linear relation to the defibrillation threshold (r = 0.64, p = 0.01). Differentiation of free wall and septal mass in these measurements revealed that the proportion of septal mass encompassed by patch electrodes correlated closely with the defibrillation threshold (r = -0.6, p = 0.019), whereas that of the free wall mass, although significantly larger (35.4 +/- 15.8 vs. 20.6 +/- 15.4 g, p = 0.007), did not. Thus, the position of epicardial patch electrodes could be reliably determined by computed tomography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

The effects of cardiovascular drugs on the defibrillation threshold and the pathological effects on the heart using an automatic implantable defibrillator.

Internal defibrillating leads were implanted in 6 dogs through a left thoracotomy and in 6 pigs through a subxiphoid approach. The effects of digoxin (0.04 mg per kilogram of body weight), procainamide (15 mg per kilogram), and propranolol (0.2 mg per kilogram) on the defibrillation threshold was determined 30 to 60 minutes following intravenous administration. Resultant blood levels were equal to or greater than therapeutic levels. Individually these drugs resulted in no appreciable change in the defibrillation threshold from baseline. Pathological study of the myocardium obtained from 6 dogs that underwent more than two hundred shocks each did not demonstrate any abnormality. The 6 pigs were reliably defibrillated, this indicating that thoracotomy is not required for successful implantation. The automatic implantable defibrillator is not the definitive treatment for recurrent ventricular arrhythmias, but is a practical regimen of therapy for a select group of high-risk, out-of-hospital patients. These observations advance our knowledge of the use of this device and give more assurance for future implantation in this select group of patients.

Animals↗
PubMed2000

Outcomes of out-of-hospital ventricular fibrillation: their association with time to defibrillation and related issues in the defibrillation program in Japan.

The aim of this study was to provide data on the outcomes of out-of-hospital cardiac arrest caused by ventricular fibrillation (VFOHCA) and analyze factors influencing patient outcomes in order to further improve EMS system performance in the resuscitation of VFOHCA patients in Japan. A datasheet was mailed to the fire defense headquarters throughout Japan, and returned data were analyzed for 614 cases of VFOHCA that occurred from January 1 through December 31, 1996. In relation to the time interval from receipt of emergency call to defibrillation, the subjects were stratified into five groups: 0-8 (n = 39), 9-12 (n = 87), 13-16 (n = 154), 17-20 (n = 118) and more than 21 min (n = 216). The discharge survival rates were 18*, 13.8*, 5.2, 4.2 and 4.2%, respectively (*P < 0.05). When defibrillation was delivered within 12 min after a call, 30.2% (38/126) converted to pulse-generating rhythm (PGR) after defibrillation and 43.6% (17/39) of patients with PGR on arrival at the hospital survived to discharge. In spite of these findings, a marked delay to defibrillation (more than 13 min) was observed in the majority (79.5%). The data shown in this study demonstrated that important issues that limit the benefits of an early defibrillation program reside in the EMS system.

Adult↗
PubMed2003

Is the orientation of the apical defibrillation paddle of importance during manual external defibrillation?

OBJECTIVE: Transthoracic impedance (TTI) is a factor determining the magnitude of the transmyocardial current during external defibrillation. Minimising TTI increases the chances of successful defibrillation. Most external defibrillation paddles are rectangular in shape and can, therefore, be placed in a transverse or longitudinal orientation. The apical paddle is often placed in a transverse orientation. This may theoretically result in a higher TTI than a longitudinal orientation because of poorer contact at the lateral paddle edges. We compared TTI with the apical paddle in both a transverse and longitudinal orientation. MATERIALS AND METHODS: Twenty sequential anaesthetised patients were studied. A pair of defibrillator paddles were instrumented to measure paddle force. TTI was recorded pre-operatively at end-expiration with the apical paddle in both longitudinal and transverse orientations. The sternal paddle was placed in a longitudinal orientation for all measurements. RESULTS: TTI decreased in both transverse and longitudinal orientations as paddle force increased. Transverse paddle orientation resulted in a significantly (P<0.01) higher TTI than longitudinal orientation at all paddle forces below 12 kg force. CONCLUSION: The longitudinal orientation of a rectangular defibrillation paddle provides a lower TTI than orientation horizontally.

Electric Countershock↗
PubMed2004

Body weight does not affect defibrillation, resuscitation, or survival in patients with out-of-hospital cardiac arrest treated with a nonescalating biphasic waveform defibrillator.

BACKGROUND: This is a study of the influence of body weight on defibrillation, resuscitation, and survival in patients with out-of-hospital cardiac arrest treated with a nonescalating impedance-compensating 150-J biphasic waveform defibrillator. METHODS: Cardiac arrest data from Rochester, MN, emergency medical services over a 6-yr period was retrospectively analyzed. Patient weight data were available for 62 of the 68 patients who were treated initially by basic life support personnel and who presented with a shockable rhythm. For each defibrillation and resuscitation outcome variable, we tested for differences in body weight for successful vs. unsuccessful outcome. RESULTS: Initial shocks defibrillated 92% (83% to 97%) of patients. Cumulative success with two shocks was 98% (confidence interval, 92% to 100%) and with three shocks was 100% (confidence interval, 95% to 100%). The mean shock impedance was 90 +/- 21 ohms. The average body weight was 84 +/- 17 kg (minimum, 53 kg; maximum, 135 kg) and was normally distributed. Based on the body mass index for 46 patients, approximately 41% were classified as overweight (body mass index, > or = 25), 24% obese (body mass index, > or = 30), and 4% extremely obese (body mass index, > or = 40). The remaining 31% were classified as normal or underweight. First-shock success, cumulative success through two shocks, and cumulative success through the first-shock series were unrelated to body weight, as were basic life support restoration of spontaneous circulation, prehospital restoration of spontaneous circulation, hospital admission, and discharge. CONCLUSIONS: Overweight patients were defibrillated by the biphasic waveform used in this study at high rates, with a fixed energy of 150 J, and without energy escalation.

Aged↗
PubMed1988

Defibrillation current and impedance are determinants of defibrillation energy requirements.

The relationship between various electrical descriptors of shocks for cardiac defibrillation is incompletely understood. Defibrillating energy, current, impedance and pulse duration were measured in 18 dogs. They were subject to repeated fibrillation--defibrillation through epicardial patches, with shocks of preset energy and voltage and variable pulse duration, impedance and peak current. Current and energy requirements for defibrillation were calculated. Energy requirements were positively correlated with pulse duration and interelectrode impedance (r = .70, P less than 0.01). Correcting for heart weight, these correlations were no longer present. However, peak current was correlated with energy requirements both before (r = -0.62, P less than 0.05) and after (r = 0.76, P less than 0.01) correcting for heart weight, with energy requirement decreasing as peak current/g heart increased. Current requirements were significantly less variable between animals than energy requirements (.027 +/- .012 joules/g vs .016 +/- .003 Amps/g), suggesting that current per unit heart weight may be a better descriptor than energy for the ability to defibrillate.

Animals↗
PubMed2006

Automated external defibrillator program does not impair cardiopulmonary resuscitation initiation in the public access defibrillation trial.

OBJECTIVES: To evaluate whether automated external defibrillator (AED) training and AED availability affected the response of volunteer rescuers and performance of cardiopulmonary resuscitation (CPR) in presumed out-of-hospital cardiac arrest (OOH-CA) during the multicenter Public Access Defibrillation Trial. METHODS: The Public Access Defibrillation Trial recruited 1,260 facilities in 24 North American regional sites to participate in a trial addressing survival from OOH-CA when AED training and availability were added to a volunteer-based emergency response team. Volunteers at each facility were trained to perform either CPR alone (CPR) or CPR in conjunction with AED use (CPR+AED) according to randomized assignments. This study reports the frequency of response and initiation of CPR actions (chest compressions and/or ventilations) by volunteers in the CPR and CPR+AED study groups. RESULTS: A total of 314 presumed OOH-CA episodes occurred in CPR facilities, and 308 occurred in CPR+AED facilities. The volunteers were matched well for age, gender, and other features. Overall, ventilations (23.1% vs. 13.1%), chest compressions (24.4% vs. 12.1%), and both actions (19.8% vs. 10.5%; all p < 0.05) were more commonly performed in OOH-CA cases in the CPR+AED group. However, when only OOH-CA cases with volunteers responding were analyzed, the rates of CPR actions were similar. In the subgroup of CPR+AED cases with a responding volunteer, the AED was turned on for only 47% of cases. Volunteers initiated a CPR action more commonly when the AED was turned on (60.7% vs. 39.3%; p = 0.003). CONCLUSIONS: In the Public Access Defibrillation Trial, rates of CPR actions for presumed OOH-CA victims were low but similar for CPR and CPR+AED responding volunteer rescuers. Factors associated with volunteer response, CPR action initiation, and AED activation warrant further investigation.

Adult↗