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PubMed1998

[Atrial defibrillators or implantable atrioverters. Initial results].

The atrial defibrillator is a new non-pharmacological treatment of atrial fibrillation (AF) for restoration of sinus rhythm. This device has two programmable modes: automatic or activated by the physician or patient. In the automatic mode, the device delivers a shock synchronous with the R wave to restore sinus rhythm when AF is detected. Two patients with paroxysmal AF resistant to pharmacological therapy were included in a study to assess the efficacy and safety of the atrial defibrillator in the mode activated by the physician. The device implanted in the pectoral region is connected to 3 electrodes, two for atrial defibrillation and sensing positioned in the coronary sinus and right atrium respectively and a sensing and pacing electrode in the right ventricle. The right ventricle is paced if a post-shock pause is detected. It is possible to interrogate the device with a programmer using its Holter function and so determine the number of episodes of AF sensed and treated. The number, intensity and energy of the shocks and the parameters of ventricular stimulation are programmable. In these two patients, the atrial defibrillator effectively reduced prolonged episodes of AF with a follow-up of 12 and 7 months. No pro-arrhythmic effects were observed. Further clinical evaluation is under way to assess this new mode of treatment, including the mode activated by the patient, safety and tolerance of the shocks. In our two patients, the treatment of prolonged episodes of AF was followed by reduction of many short or asymptomatic episodes.

Aged↗
PubMed1998

[Implantable defibrillators in the management of malignant ventricular tachyarrhythmias. Experience at the Arrhythmia National Center].

BACKGROUND: Implantable defibrillators are the most effective means to prevent sudden death in patients with malignant ventricular tachyarrhythmias. The availability of this type of devices is limited in Chile, due to their high price. AIM: To report the first patients treated with implantable defibrillators in our hospital. PATIENTS AND METHODS: Nine males and one female aged 13 to 65 years old are reported. Three presented with ventricular fibrillation (presenting out of the hospital in three) and the rest had ventricular tachycardia resistant to drugs or radiofrequency ablation. RESULTS: All implants were performed using intracardiac electrodes. The generator was implanted in the pectoral region in nine and in the abdomen in one. A successful defibrillation was obtained with less than 15 J in four patients, with 20 J in three and with 24 J in three. There were no complications during the procedure. After a 12 months follow up, four patients have been treated by the implantable device. One of these subjects had a ventricular fibrillation in two occasions. One patient died of a bronchopneumonia two years after the implant. CONCLUSIONS: Implantable defibrillators are an effective therapy for the treatment of malignant ventricular arrhythmias with a high risk of sudden death.

Adolescent↗
PubMed1991

Lateral thoracotomy for the automatic implantable defibrillator.

In 51 patients who required automatic implantable cardioverter defibrillator implantation without additional cardiac procedures, the lead system was implanted using a lateral thoracotomy approach, with complete muscle sparing in the last 24 patients. Exposure was excellent and allowed repositioning of leads for optimal defibrillation thresholds in 18 patients. Five of 19 patients who had previously undergone intrapericardial procedures required intrapericardial dissection for lead placement to provide satisfactory defibrillation thresholds. There were no intraoperative deaths or infarctions. The 30-day mortality rate of 3.9% was comparable with those in other series, and the use of muscle-sparing techniques and supplemental epidural anesthesia prevented pulmonary complications or the need for prolonged ventilatory support. We favor a muscle-sparing lateral thoracotomy incision for automatic implantable cardioverter defibrillator insertion, particularly in patients with a history of previous intrapericardial procedures.

Adult↗
PubMed1984

Treatment of ventricular fibrillation. Emergency medical technician defibrillation and paramedic services.

We compared the effect of rapid defibrillation by emergency medical technicians (EMTs) combined with paramedic care with that of standard EMT and paramedic care on survival from 540 witnessed episodes of out-of-hospital cardiac arrest caused by ventricular fibrillation. More than 400 EMTs were trained in the recognition of ventricular fibrillation and operation of a defibrillator. For a portion of the three-year study, emergency care for 179 cases was randomized between the two types of services. For randomized cases, when the time interval between EMT and paramedic arrival was greater than four minutes there was significantly improved survival with EMT defibrillation and paramedic care (42%) compared with basic EMT and paramedic care (19%). Similar findings occurred when all cases were considered (38% v 18%). Defibrillation by EMTs combined with paramedic services can enhance survival from ventricular fibrillation, compared with basic EMT and paramedic care.

Aged↗
PubMed1983

Safety and effectiveness of a portable external automatic defibrillator-pacemaker.

Sudden cardiac death in the community can be reduced by early resuscitation. The commonest arrhythmia encountered in this setting is ventricular fibrillation. A portable external automatic defibrillator-pacing machine for use by emergency services and laymen after basic training, has recently been introduced. This device has a tongue-abdominal pathway for sensing the electrocardiogram and respiration, as well as delivery of current. In its automatic mode, the machine cannot defibrillate unless the patient's breathing and gag reflex are virtually absent. The decision-making characteristics of the machine were defined in isolation from the patient using simulated ECG signals and recordings of arrhythmias obtained during cardiac surgery and during electrophysiological studies. The pathway was evaluated separately by attaching it to a conventional defibrillator and using it in the elective cardioversion of 15 patients. Electrode sites were examined and creatine phosphokinase (CPK) and creatinine phosphokinase isoenzyme (CPKMB) release determined following conversion. Repeated playback of the same 34 minutes of selected recordings showed that decisions were consistent 95% of the time. Automatic pacing always occurred with asystole. ECG signals less than 0.35 mV in amplitude were not recognized, but a manual override switch could be operated in those circumstances where there was failure to act upon fine ventricular fibrillation. Defibrillation of 50% of the recordings of supraventricular and ventricular tachycardia did occur, but this could not have happened in practice unless the patient was unconscious, and in addition, the operator failed to countermand this decision. The tongue-abdominal pathway yielded good recordings of the ECG.(ABSTRACT TRUNCATED AT 250 WORDS)

Creatine Kinase↗
PubMed1992

Test of four defibrillation dosing strategies using a two-dimensional finite-element model.

The most widely used defibrillation dosing strategy is that adopted by the American Heart Association in 1986. However, several alternative dosing strategies have been proposed to match delivered energy to the individual requirements of defibrillation subjects. In this study, two-dimensional finite element methods are used to investigate the performance of four of these dosing strategies applied to three thoracic models representative of men and women of different thoracic aspect ratios. From the resulting current density distributions, the relative effectiveness of the following dosing strategies are evaluated and compared: constant current; current proportional to body weight; constant energy; energy proportional to body weight. Our results show that the strategy of applying current proportional to subject body weight with a current dose of 0.58 A kg-1 was able to defibrillate all three subjects with only minimal overexposure of any one of them. None of the other dosing strategies examined could be made to successfully defibrillate all three subjects without significantly overexposing at least one.

Adult↗
PubMed2004

Acute effects of adrenergic agents on post-defibrillation arrest time in a cultured heart model.

Possible drug interactions with electrical defibrillation were examined. We tested the hypothesis that adrenergic agents (epinephrine, norepinephrine, isoproterenol) and a calcium channel blocker (verapamil), when applied acutely, alter the duration of arrest following a defibrillator shock. A secondary hypothesis (based on observations) was that the drugs alter the occurrence of changes to normal rhythms following the shock. Dissociated heart cells from 10-day chicken embryos were cultured to form spherical aggregates and plated in petri dishes. In the experiments, the spheres were paced at 0.75 V/cm above contraction threshold, and a biphasic defibrillator shock was applied for 1 ms at 46 V/cm. The arrest time and occurrence of rhythm changes were recorded. The adrenergic agents shortened the duration of arrest following a defibrillator shock, while the calcium channel blocker lengthened the arrest time. Comparisons with the control proportion of double beats showed no significant change with the adrenergic agents and a decrease with verapamil.

Adrenergic Agents↗
PubMed2001

Effects of bystander first aid, defibrillation and advanced life support on neurologic outcome and hospital costs in patients after ventricular fibrillation cardiac arrest.

OBJECTIVE: To evaluate the effects of basic life support, time to first defibrillation and emergency medical service arrival time on neurologic outcome and expenses for hospital care in patients after cardiac arrest. SETTING: Large urban emergency medical services system and emergency department in a 2000-bed university hospital. DESIGN: Outcome and cost benefit analysis of patients admitted to the hospital after witnessed, out-of-hospital, ventricular fibrillation cardiac arrest from October 1, 1991, until December 31, 1997. PATIENTS: Out of 1054 patients with out-of-hospital cardiac arrest, 276 were eligible. MEASUREMENTS AND RESULTS: The effects of basic and advanced life support measures on neurologic outcome and hospital expenses were evaluated. In contrast to intubation (odds ratio 1.08; 95% CI: 0.51-2.31; p=0.84), basic life support (odds ratio 0.44; 95% CI: 0.24-0.77; p=0.004) and time to first defibrillation (odds ratio 1.08; 95% CI: 1.03-1.13; p=0.001) were significantly correlated with good neurologic outcome. Among the patients who did not receive basic life support, the average cost per patient with good neurologic outcome significantly increased with the delay of the first defibrillation (p<0.001). CONCLUSIONS: In contrast to intubation, bystander basic life support and time to first defibrillation were significantly associated with good neurologic outcome and resulted in fewer expenses spent on in-hospital efforts.

Adolescent↗
PubMed1983

Arrhythmias and left ventricular function after defibrillation during acute myocardial infarction in the intact dog.

The purpose of this study was to assess the recovery of the left ventricular pressure (PLV), and the incidence and type of arrhythmias after effective low-dose defibrillation (Imax = 18-70 A) in healthy hearts and in hearts with acute myocardial infarction (AMI) in the intact dog. In fifteen dogs 84 episodes of fibrillation-defibrillation were studied in the healthy heart and 53 episodes were studied in the acute phase of myocardial infarction 1/2 to 3 hours after occlusion of a part of the left anterior descending artery by a catheter technique. Time to recovery of PLV depended on duration of fibrillation (tF) and cumulative defibrillation current (I 1/2), and became critical at tF greater than 45 seconds and I 1/2 greater than 45 A. Total duration of arrhythmias due to defibrillation increased with increasing tF and I 1/2. Arrhythmias which have a relative greater chance of resulting in refibrillation or which may seriously decrease the cardiac output occurred more often with I 1/2 greater than 55 A (p less than 0.001), when 50% of episodes were followed by these arrhythmias. No differences were found in responses between the healthy heart and the heart with AMI.

Animals↗
PubMed1989

Effect of calcium channel blockers on hemodynamic responses to defibrillation.

The hemodynamic response to sequences of ventricular fibrillation and defibrillation includes an adrenergic component that is important for the maintenance of blood pressure after successful defibrillation. Because calcium channel blocking drugs have antiadrenergic effects, we hypothesized that they might blunt the adrenergic response to defibrillation. Ventricular fibrillation was induced in 35 closed-chest dogs. Each received 4 to 7 direct current transthoracic shocks at three energy levels to determine defibrillation energy requirements. Heart rate and blood pressure were recorded. Energy sequences were repeated after 45 minutes of no intervention (control, n = 5) or after 45-minute infusions of diltiazem (0.1 mg/kg/min, n = 10), verapamil (0.1 mg/kg bolus plus 0.01 mg/kg/min, n = 10), or nifedipine (40 micrograms/min for 3 minutes plus 2 to 20 micrograms/min adjusted to maintain a 10 mm Hg drop in mean arterial pressure, n = 10). Our results show that the normal post-shock rise in mean arterial pressure was blunted by the calcium channel blockers diltiazem (systolic arterial pressure at 15 and 60 seconds post-shock, pre-drug versus post-drug: 102 +/- 9 versus 64 +/- 9 mm Hg and 113 +/- 10 versus 87 +/- 6 mm Hg; p less than 0.05) and verapamil (108 +/- 9 versus 78 +/- 12 mm Hg and 113 +/- 7 versus 90 +/- 10 mm Hg, p less than 0.05). There were no differences in blood pressure responses after nifedipine treatment or no drug. Heart rate responses were not altered by diltiazem or verapamil; after nifedipine administration, post-shock heart rates were slower.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Electrode pad size, transthoracic impedance and success of external ventricular defibrillation.

Electrode pad size is an important determinant of transthoracic current flow during external countershock. Self-adhesive, dual function electrocardiogram/defibrillator pads were used to assess the effect of electrode pad size on defibrillation success with low energy (200 J) shocks. The study analyzed 123 cardiac arrests due to primary ventricular fibrillation (VF) in 105 patients (74 men, 31 women) ages 40 to 84 years (mean 64). Transthoracic impedance was measured before defibrillation using a low amplitude 30-kHz current passed through the chest by way of the electrocardiogram/defibrillator pads applied anteroanteriorly. Pad diameters were small (8/8 cm) in 26 cardiac arrests, intermediate (8/12 cm) in 63 arrests and large (12/12 cm) in 34 cardiac arrests. Transthoracic impedance decreased with increasing pad size (112 +/- 17 vs 92 +/- 22 vs 72 +/- 14 omega, respectively, p = 0.0001). Only the first episode of primary VF during a cardiac arrest was analyzed. A single shock of 200 J (delivered energy) was successful in 8 of 26 (31%) arrests using small pads, in 40 of 63 (63%) with intermediate pads and in 28 of 34 (82%) with large pads (p = 0.0003). A second 200-J shock increased the cumulative defibrillation rates to 12 of 26 (46%), 50 of 63 (79%) and 33 of 34 (97%), respectively (p less than 0.0001). In primary VF, larger self-adhesive electrocardiogram/defibrillator pads are associated with a lower transthoracic impedance and improved defibrillation success rates with low energy shocks.

Adhesives↗
PubMed1991

Experience with a third-generation implantable cardioverter-defibrillator.

A Medtronic 7216A pacemaker cardioverter-defibrillator was implanted in 16 patients (mean age 56 years) with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) and organic heart disease with a mean left ventricular ejection fraction of 33%. Endocardial and epicardial defibrillation shock efficacy was evaluated before or at implant using 1 to 3 shock patterns, i.e., monophasic single, sequential or simultaneous shocks with dual and triple electrode configurations. Endocardial leads used a common right ventricular cathode and dual anodes, whereas epicardial leads used 2 or 3 helical coil patches. VT termination was evaluated using pacing or shock therapy, or both, whereas only shocks were used in VF. Programmable bradycardia pacing, individual zones for VT and VF detection and individualized pacing and shock therapy for VT and VF were used. Monophasic shocks had epicardial defibrillation thresholds ranging from 3 to 18 (mean 10) J and were comparable for sequential and simultaneous shocks (p greater than 0.2). VT detection rates ranged from 340 to 470 ms and VF detection rates from 270 to 330 ms. VT or VF induction, or both, was performed noninvasively in 13 patients after implant and was reproducibly terminated by rapid pacing alone (5 patients), low-energy shocks (2 patients), high-energy shocks (3 patients) and combined therapy (3 patients). Intermediate or high-energy shocks terminated all induced VF episodes. During follow-up (2 to 12 months), there have been 2 noncardiac deaths. Electrical therapy was delivered in 7 patients, for VT (3 patients), VT and VF (3 patients) and indeterminate tachyarrhythmia (1 patient). All VT/VF episodes were successfully terminated, with 78 of 96 (81%) spontaneous VT episodes terminated by pacing. Follow-up reprogramming was required in 5 patients. It is concluded that successful application of individualized electrical therapy prescriptions in patients with VT/VF is feasible. Pacing therapies, which are effective for induced VT, can be reliably used for effective long-term spontaneous VT termination in conjunction with shock therapy and can permit reduced patient exposure to shock therapy. Thus, a programmable hybrid pacemaker cardioverter-defibrillator system provides nonthoracotomy implantation, effective VT/VF termination, demand ventricular pacing and noninvasive modes for arrhythmia induction, event monitoring and clinical trouble-shooting.

Adult↗
PubMed1991

Silicone pouch for protection of automatic implantable cardioverter-defibrillator leads.

Automatic implantable cardioverter-defibrillator has become routine treatment for recurrent, drug-resistant ventricular tachycardia. Although there is documentation regarding clinical experience and device performance, there is little information on how to avoid complications related to the retrieval of sensing and defibrillation leads from the subcutaneous space. We are reporting our experience with a silicone pouch for protection of automatic implantable cardioverter-defibrillator leads that allows immediate and simple retrieval of the leads in case an automatic implantable cardioverter-defibrillator generator is needed.

Adult↗
PubMed1984

Transventricular simple-capacitor discharge defibrillation thresholds after coronary ligation and body hypothermia.

Peak current defibrillation thresholds (PCDT), i.e., values with 50% probability of success, were determined after ligation of the left anterior descending coronary artery (LADCA) while, simultaneously, body temperature was slowly decreased until central venous temperature reached an average minimum of 22.8 degrees C (s.d. 3.1). In 14 dogs with over 166 successful defibrillations, the average time elapsed between the moment of ligation and the last defibrillation was 179.1 min. (s.d. 31.9), with an average PCDT of 53.6 mA g-1 of heart (s.d. 20.5). This value was compared by means of the unpaired Student's t test with three previous values obtained, respectively, under hypothermia with no occlusion (HNO), normo-thermia with coronary occlusion (NCO), and normothermia with no occlusion (NNO), that is, HNO 69.5 (s.d. 30.4), NCO 81.1 (s.d. 29.3), and NNO 89.5 (s.d. 32.8), all expressed in mA g-1 of heart. All three differences even after Bonferroni's correction, were statistically significant (P less than 0.3%). We concluded that, (1) defibrillation thresholds were decreased by coronary occlusion and by hypothermia, (2) the decrease due to hypothermia was greater than that due to coronary occlusion, (3) both decrements appeared as additive.

Animals↗
PubMed1985

Experimental evaluation and initial clinical application of new self-adhesive defibrillation electrodes.

We evaluated the efficacy of self-adhesive electrode pads for defibrillation and cardioversion in animals and patients. In 11 anesthetized dogs, the success rate of shocks given to terminate electrically-induced ventricular fibrillation was similar for both self-adhesive electrode pads and hand-held electrode paddles; success rate approached 100% at energies of 125-150 joules. Eighty patients undergoing defibrillation or elective cardioversion received shocks from self-adhesive pads. In all but 2 patients defibrillation or cardioversion was achieved at least once using these pads. The pads were equally effective from either apex-anterior or apex-posterior positions. The transthoracic impedance using self-adhesive pads was 75 +/- 21 ohms, similar to transthoracic impedance we previously reported when using standard hand-held paddles. No complications occurred with the use of the pads. We conclude that self-adhesive electrode pads are effective for defibrillation and cardioversion.

Animals↗
PubMed1988

Ventricular fibrillation-defibrillation in the toad Bufo paracnemis.

Fibrillation is more likely to occur in animals showing a high degree of cellular differentiation. Lower species, with cardiac tissue histologically and electrophysiologically more uniform, very rarely, if ever, can fall into this uncoordinated activity. We describe experiments during which two specimens of the South American toad, Bufo paracnemis (body weights, 363 g and 297 g; ventricular weights, 1.8 g and 1.4 g, respectively), were repeatedly fibrillated and defibrillated almost at will. However, we failed when we tried a series of experiments in a given number of animals. Over a total of 16 fibrillation-defibrillation episodes, a fibrillation threshold of about 3.8 mA/g was estimated. The lowest defibrillation values were, respectively, 43 mA/g and 507 mA/g, using rectangular pulses (less than 7 msec pulses width). There were also a few spontaneous reversals before and after defibrillation shocks. These cases point to our still poor understanding of the mechanisms involved in the process. It is suggested that reentry or multiple ectopic foci might not be the basic mechanisms, as traditionally accepted. Rather, it might well be a new behavior of the cells or group of cells like that predicted by the theory of deterministic chaos.

Animals↗
PubMed1994

Early defibrillation by EMTs: the Brussels experience.

Considering that in Brussels the first-aid ambulance team reaches the patient in cardiac arrest 10 min before the physician-manned ambulance, we instituted a feasibility study of early defibrillation by emergency medical technicians (EMTs). Three hundred EMTs received a 20-h automatic external defibrillation (AED) training course followed by a refresher course every 6 months. Of 316 cardiac arrests included in this study, asystole was encountered in 53% and ventricular fibrillation/ventricular tachycardia (VF/VT) in 33% of the cases on arrival of the EMTs. In the VF/VT group, defibrillation was performed by EMTs with a Laerdal Heartstart 7-9 min before the medical team arrived. The overall cardiac arrest survival rate improved from 7% in 1989 to 19% in 1992. However, the long-term survival rate (14/105) of ventricular fibrillation remained low because of excessive delays in emergency medical service (EMS) access and in early ACLS. In conclusion, this work shows that in Brussels: (1) early defibrillation of cardiac arrest victims in VF is feasible by EMTs when a training and a follow-up program are implemented; (2) the weakest link of the chain of survival is the early EMS access, and the early ACLS; and (3) AED program increases the interest and the efficacy of EMTs and medical teams in the management of cardiac arrests.

Aged↗
PubMed1995

Semi-automatic external defibrillation and implanted cardiac pacemakers: understanding the interactions during resuscitation.

Many emergency medical service (EMS) systems are currently implementing semi-automatic external defibrillation (AED) by emergency medical technicians. Surprisingly little information is available on the possible interactions between AEDs and implanted cardiac pacemakers. Therefore, at present there are no clear guidelines for the use of AEDs on patients having a cardiac pacemaker. During resuscitation, multiple interactions between pacemakers and AEDs are possible. External defibrillation can cause damage to several functions of the pacemaker. On the other hand, the presence of pacemaker spikes during cardiac arrest might prohibit recognition of the ventricular fibrillation by the AED. We report on two resuscitation attempts in which the interaction between the ventricular fibrillation, an implanted dual chamber pacemaker and the AED was decisive for the defibrillation success. A clear understanding of these possible interactions is necessary for the further refining of diagnostic algorithms and clinical strategies of prehospital defibrillation.

Adult↗