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PubMed1982

The automatic implantable defibrillator. New Modality for treatment of life-threatening ventricular arrhythmias.

The automatic implantable defibrillator continuously monitors cardiac rhythm, identifies ventricular fibrillation and then delivers corrective defibrillatory discharges when indicated; it weighs 250 grams and has a volume of 145 cc. When a suitable arrhythmia is detected, a 25 Joule pulse is delivered through a superior vena cava catheter electrode and another electrode placed over the cardiac apex. As of March 1981, sixteen survivors of multiple cardiac arrests refractory to antiarrhythmic therapy had undergone implantation of the automatic defibrillator. There was no operative mortality and the morbidity was minimal. Electrophysiologic studies were performed before and after surgery to confirm failure of drug therapy and to ensure the device's ability to terminate malignant arrhythmias. Eight spontaneous and fourteen of the seventeen induced malignant arrhythmias were properly recognized and corrected by the device. The discharges were well tolerated by awake patients. A number of problems including recycling delays and spurious discharges have been identified and corrected. There were three late deaths with pulmonary edema noted in two patients, and asystole in one. The autopsies revealed no myocardial damage attributable to the automatic defibrillator. Although the ultimate role of this approach to prevention of sudden arrhythmic death has yet to be determined, the results obtained to date are encouraging and indicate that a useful modality for treating malignant ventricular arrhythmias has been added to our armamentarium.

Adolescent↗

PubMed1984

The automatic implantable cardioverter-defibrillator.

The automatic implantable cardioverter-defibrillator is an electronic device designed to monitor the heart continuously, to identify malignant ventricular tachyarrhythmias, and then to deliver effective countershock to restore normal rhythm. There are two defibrillating electrodes which are also used for waveform analysis; one is located in the superior vena cava, the other is placed over the cardiac apex. A third bipolar right ventricular electrode serves for rate counting and R-wave synchronization. When ventricular fibrillation occurs, a 25 joule pulse is delivered; when ventricular tachycardia faster than a preset rate is detected, the discharge is R-wave synchronized. The device can recycle three times if required. Special batteries can deliver over 100 shocks or provide a 3-year monitoring life. Implantation of the device is made either through a thoracotomy or by a subxiphoid approach. Thus far, the device has been implanted in 160 patients with a follow-up of 42 months. Acceleration of ventricular tachycardia to a faster rhythm or to ventricular fibrillation occurred only rarely and is dealt with most successfully through recycling. Actuarial analysis of the initial 52 patients has indicated 22.9% one-year total mortality, a 52% decrease from the 48% mortality that would be expected in the same group of patients without the device; the mortality attributed to arrhythmias was only 8.5%. In conclusion, the automatic cardioverter-defibrillator can reliably identify and correct potentially lethal ventricular tachyarrhythmias, leading to a substantial increase in survival in properly selected high-risk patients.

Death, Sudden↗

PubMed1984

The potential role of the implantable defibrillator in malignant ventricular arrhythmias.

A malignant arrhythmia is one which threatens life and is difficult to predict, prevent or treat. Any arrhythmia which falls into this category is an indication for the implantable defibrillator. The simplicity of this statement is of course deceiving. Transthoracic defibrillation, which for 20 years has been the therapeutic standard, has provided us with the greatest insight and understanding of cardiac arrhythmias. In the long run, the same information will be acquired with the implanted defibrillator. However, technical, medical and economic factors are more complex and will not be resolved in the near future.

Arrhythmias, Cardiac↗

PubMed1988

Effect of antiarrhythmic drugs on defibrillation threshold: case report of an adverse effect of mexiletine and review of the literature.

Antiarrhythmic agents can influence defibrillation threshold (DFT). Basic research suggests that some class I drugs may have deleterious effects by raising defibrillation energy requirements. Evaluation of this problem in man has been limited to reports of patients who were more difficult to cardiovert or defibrillate after treatment with amiodarone and class IC agents. In the present report, mexiletine appeared to be the probable cause of an important elevation of DFT in a patient undergoing replacement of a malfunctioning automatic implantable cardioverter/defibrillator (AICD). This report and the accompanying literature review suggest that more information at both the basic and clinical levels is required. Retesting of device efficacy in terminating induced arrhythmia in the laboratory appears prudent in patients who require antiarrhythmic drug therapy subsequent to AICD implantation.

Animals↗

PubMed1988

Evaluation of global and regional left ventricular function using two-dimensional and M-mode echocardiography in patients with an automatic implantable cardioverter defibrillator.

The effects of glued epicardial patch electrodes of the automatic implantable cardioverter defibrillator on the left ventricular function was studied by two-dimensional and M-mode echocardiography in 15 patients. Pre- and postoperative end-diastolic and end-systolic left ventricular cross-sectional areas were evaluated using planimetry. Regional left ventricular wall motion at the level of the left ventricular patch electrode was analyzed by two end-diastolic and end-systolic perpendicular axes. Left ventricular end-diastolic and end-systolic diameters as well as E-point-septal-separation and fractional shortening were analyzed using M-mode echocardiography. The mean time interval between preoperative echocardiograms and implantation of the automatic defibrillator was 0.3 X 1.3 (less than 1-2) months. Postoperative echocardiograms were recorded 6.6 +/- 6.9 (0.5-24) months after implantation of the device. There were no significant differences between pre- and postoperative mean values of end-diastolic and end-systolic areas and axes as well as M-mode echocardiographic parameters. Our data show that left ventricular patch electrodes do not significantly alter global or regional left ventricular function in patients after implantation of the automatic defibrillator.

Adult↗

PubMed1989

The use of beep-o-grams in the assessment of automatic implantable cardioverter defibrillator sensing function.

Noninvasive assessment of sensing performance in the automatic implantable cardioverter defibrillator is limited by the absence of telemetry or memory functions. The adaptation of the electrophysiological test mode into a "beep-o-gram" recording, with simultaneous audible tones and a surface electrocardiogram, was used in the confirmation of sensing malfunction. Eleven of 13 recordings in patients with documented or clinically suspected inappropriate defibrillator discharges (group 1) demonstrated evidence of definite oversensing. Nonspecific oversensing or undersensing was present in 77% of 27 randomly selected asymptomatic patients without known sensing malfunction (group 2). The sensitivity and specificity for identifying definite oversensing was 85% and 60%, respectively. The beep-o-gram system is a reliable, noninvasive means of confirming sensing malfunction in the automatic implantable cardioverter defibrillator. Its specificity is limited by the detection of subclinical sensing aberrations, to some degree related to the device's automatic gain control sensing algorithm.

Electric Countershock↗

PubMed1990

Cardiomyopathy and the use of implanted cardio-defibrillators in children.

Children and adults with cardiomyopathy and ventricular dysrhythmias have a uniformly poor prognosis, despite medical therapy. The use of automatic implantable cardio-defibrillators in adult patients with medically resistant ventricular dysrhythmias has resulted in a positive impact on survival. Because of its size and former lack of programmability, the device has been used rarely in children. Four patients with cardiomyopathy, in whom refractory ventricular dysrhythmias were managed with automatic implantable cardio-defibrillators, are presented. Two of these children are the youngest and smallest known in whom the device has been used; one of them received the first programmable model. The use of the automatic implantable cardio-defibrillator may enhance survival in selected young patients.

Adolescent↗

PubMed1991

Ventricular and atrial defibrillation using new transvenous tripolar and bipolar leads with 5 French electrodes and 8 French subcutaneous catheters.

This study evaluated the use of new small transvenous atrial and ventricular leads for converting atrial fibrillation (AF) and ventricular fibrillation (VF) in 10 adult male mongrel dogs. Five dogs (group A) received a right atrial "J" (AJ) and right ventricular (RV) active fixation tripolar lead, each consisting of a platinized platinum pacing tip, anode band, and braided defibrillation electrode. The remaining five dogs (group B) received one bipolar RV lead and one tripolar AJ lead. The RV leads were implanted in the right ventricular apex (RVA) and the AJ leads were placed in the atrial appendage. Additionally all dogs received two 8 French subcutaneous defibrillation catheters in the fifth and seventh intercostal spaces. Twenty asymmetric biphasic shocks consisting of five randomized voltage levels were used to convert VF in groups A and B. The bipolar RV lead (group B) had a significantly higher probability of success in converting VF than the tripolar RV lead (group A). In group A defibrillation thresholds for converting AF were obtained using two electrode configurations. No significant difference was observed between the two electrode configurations used to convert AF. Pacing and sensing thresholds were satisfactory for bipolar and tripolar lead configuration.

Animals↗

PubMed1991

Is defibrillation testing safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillator (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5-35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 +/- 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P less than 0.01) in absolute delta (1.5-3.5 Hz) power persisting for greater than or equal to 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing greater than 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing less than 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.

Electric Countershock↗

PubMed1991

Sudden bradyarrhythmic death in patients with the implantable cardioverter-defibrillator: report of two cases.

Two cases of sudden bradyarrhythmic death necessitating cardiopulmonary resuscitation in patients with the automatic implantable cardioverter-defibrillator are described. One patient had sudden bradyarrhythmic death while being monitored in the hospital. This patient could not be resuscitated and represents the first reported sudden cardiac death secondary to bradyarrhythmia in a patient with the automatic implantable cardioverter-defibrillator. The second patient had an out-of-hospital sudden death followed by probable cardioverter-defibrillator discharge, leading to complete heart block with escape ventricular rhythm necessitating immediate temporary pacemaker insertion. These cases highlight the need for bradycardia back-up pacing and event monitoring in the newer tachyarrhythmia management devices.

Aged↗

PubMed1992

Holter documented sudden death in a patient with an implanted defibrillator.

A 68-year-old man with recurrent attacks of monomorphic ventricular tachycardia (VT) received a pacer cardioverter defibrillator featuring antitachycardia pacing and cardioversion/defibrillation. Over 300 episodes of VT were successfully terminated by antitachycardia pacing. During Holter monitoring the patient experienced supraventricular tachycardia with delivery of multiple antitachycardia pacing, cardioversion, and defibrillation therapies ending with the death of the patient. The following factors played a role in the unfortunate outcome of this patient: 1. triggering of VT therapy by an unexpected high sinus rate; 2. atrial fibrillation induced by cardioversion therapy; 3. a gradual and continuous increase in rate during atrial fibrillation possibly caused by repeated VT and ventricular fibrillation therapies and/or by a thrombus, found at autopsy, in a bypass graft; and 4. the limited ability of presently available defibrillators to distinguish between ventricular and supraventricular arrhythmias.

Aged↗

PubMed1992

Use of event markers during exercise testing to optimize morphology criterion programming of implantable defibrillator.

The present generation implantable defibrillator introduced on-line event markers that can be used to evaluate tachycardia detection in the electrophysiological testing mode. These markers were used to assess the appropriateness of programming the morphology criterion for detection of ventricular tachycardia. Twenty-one consecutive patients (19 men, 2 women) performed 29 bicycle exercise tests with real-time recording of the electrocardiogram and the event markers on a multichannel recorder. Mean ejection fraction was 29% (range 15%-69%). Seven patients were taking antiarrhythmic agents. Twelve patients satisfied the morphology criterion at rest (n = 1) or during exercise (group I), and nine patients did not (group II). One patient was excluded from analysis because of continuous ventricular pacing. Mean peak heart rate was 130 beats/min in group I and 125 beats/min in group II. No statistical differences existed between the groups in relation to cycle length of ventricular tachycardia and mode of induction of arrhythmia, QRS duration on the electrocardiogram, during native rhythm, amplitude and duration of defibrillation patch R wave, calculated duty cycle at peak heart rate, and number of discharges of the automatic implantable cardioverter defibrillator at 2 to 14 months of follow-up time. It is concluded that clinical, electrocardiographic, and implantation data are unreliable in predicting satisfaction of the morphology criterion during high heart rates in native rhythm. Formal exercise testing in the electrophysiological mode enables a rational decision to be made about the appropriateness of the use of probability density function in each patient.

Algorithms↗

PubMed1992

Driving restrictions advised by midwestern cardiologists implanting cardioverter defibrillators: present practices, criteria utilized, and compatibility with existing state laws.

Although some patients remain at risk of losing physical control or collapsing after implantation of a cardioverter defibrillator for sustained ventricular arrhythmias, little is known about restrictions advised by arrhythmia specialists to patients with implanted devices concerning physical activities such as driving. In this study, all of the 58 cardiologists implanting cardioverter defibrillators in three contiguous midwestern states were surveyed to determine present practices and the compatibility of these practices with existing state law. Of the 51 respondents (88%), 27 cardiologists (53%) advised only those implanted patients who had had arrhythmia-induced presyncope or physical collapse to cease driving. Twenty two of the remaining cardiologists (43%) advised all implanted patients to cease driving, whereas two cardiologists (4%) never advised any implanted patient to restrict driving. Permanent driving abstinence was advised by seven of the responding cardiologists (14%), while temporary driving abstinence for periods of 2-12 months (mean 6 +/- 3 months) was recommended by the remaining 42 respondents (82%) who advised against driving. The criteria utilized, driving restrictions advised, and durations advised for driving restrictions were not uniform in any of the 13 surveyed university and nonaffiliated cardiology practices with greater than or equal to 2 implanting cardiologists. Overall, 38 cardiologists (74%) advised against driving and recommended durations that equaled or exceed their state's minimum legal requirements, although only 27 of the 51 cardiologists (53%) based their practice upon knowledge of their state's driving laws. The results of this survey suggest that the majority of cardiologists who implant cardioverter defibrillators advise their patients against driving postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Automobile Driving↗

PubMed1993

The defibrillation threshold: a comparison of anesthetics and measurement methods.

In 18 open-chested mongrel dogs (18.0 +/- 1.7 kg) we compared three anesthetics and three methods for measuring the defibrillation threshold. Six animals were anesthetized with pentobarbital (30 mg/kg) and maintained with a pentobarbital infusion (4 mg/kg per hour). All other animals were anesthetized with sodium brevital (10 mg/kg) and maintained with either halothane gas (1.5%, N = 6) or isoflurane gas (1.8%, N = 6). In each dog, we measured the energy required for 50% successful defibrillation (E50) with: (A) a 3 reversal--up/down method; (B) a 15 shock--up/down method; and (C) a percent success method. Anesthetics and methods were selected in a balanced random order. Ventricular fibrillation was induced with 50 Hz electrical pacing. After 15 seconds, monophasic truncated exponential shocks were delivered by way of a spring-patch electrode configuration. The animal was rescued (if needed) and fibrillation/defibrillation episodes were repeated at 3 minute intervals. After each determination of the E50, the E50 was delivered in ten successive defibrillation trials to determine its actual success rate. We found no significant difference in E50 among anesthetics; a significant difference (P < 0.05) in E50 between method C (9.7 +/- 2.6 joules) and method B (8.2 +/- 1.6 joules); no significant difference among anesthetics or methods for the actual success rate of the E50 (45 +/- 21% successful); and method A required significantly fewer fibrillation episodes and number of shocks and less cumulative energy than the other methods. We concluded that the anesthetics tested had little effect on E50 but that the method used to determine E50 could have an effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics↗

PubMed1996

The influence of sodium channel blockade on the defibrillation energy requirements of biphasic versus monophasic shocks.

The sodium channel-blocking actions of some Class I antiarrhythmic agents can increase the defibrillation energy requirements (DER) of monophasic shock waveforms. The influence of sodium channel blockade on biphasic shocks is less certain. The purpose of this study was to compare, in a randomized, placebo controlled study, the influence of lidocaine on the DER of biphasic and monophasic shock waveforms in a canine model of transvenous internal defibrillation. The DER was determined by the iterative increment-decrement protocol. Monophasic and biphasic shock DERs were tested at baseline and during lidocaine infusion (group A) or saline control (group B). Group A biphasic shock DERs increased significantly from a baseline of 12.1 +/- 3.6 J to 19.1 +/- 9.3 J when compared to group B (P = 0.005). In group A, the mean DER during lidocaine was significantly higher with monophasic shocks than biphasic shocks (29.6 +/- 11.8 J vs 19.1 +/- 9.3 J, respectively; P < 0.003), but the magnitude of change in biphasic versus monophasic shock DERs was not significantly different (F = 1.78; p = 0.193). There was a linear relationship between the baseline DER and the DER during lidocaine (r2 = 0.63, P < 0.0001). Sodium channel blockade with lidocaine increases the DER of both monophasic and biphasic shocks. However, the DER of biphasic shocks during lidocaine are significantly lower than monophasic shock DERs, a finding that can be explained by the linear relationship between the baseline DER and the DER during lidocaine. These results may have favorable implications for the use of Class I antiarrhythmics with biphasic shock defibrillators.

Animals↗

PubMed1997

The effect of biphasic waveform tilt in transvenous atrial defibrillation.

Atrial defibrillation can be accomplished using low energy shocks and transvenous catheters. The biphasic waveform tilt required to achieve optimal atrial defibrillation thresholds (ADFTs) is, however, not known. The effect of single capacitor biphasic waveform tilt modification on ADFT was assessed in 20 patients. Following AF induction the defibrillation pulses were delivered between the catheters positioned in the coronary sinus and the right atrium. The single capacitor biphasic waveform shocks, delivered over the same pathways, consisted of 65% tilt (65/65 biphasic waveform) to produce an overall tilt of 88%, or 50% tilt (50/50 biphasic waveform) to produce an overall tilt of 75%. Although 65/65 biphasic waveform delivers more energy, the shorter duration 50/50 biphasic waveform reduced stored energy ADFT 21%, from 1.34 +/- 0.82 J with 65/65 biphasic to 1.06 +/- 0.81 J. These differences were not statistically significant. Nine patients had lower ADFT with 50/50 biphasic waveform while five patients had lower ADFT with 65/65 biphasic waveform. Equivalent reduction in ADFT was seen in the remaining six patients. The ADFT was 0.83 +/- 0.65 J when both tilts were considered. In conclusion, biphasic waveform tilt modification may affect the ADFT in an individual patient. The optimal biphasic waveform for ADFT is not known.

Adult↗

PubMed1997

Is there an optimal electrode pad size to maximize intracardiac current in transthoracic defibrillation?

Achieving defibrillation depends on adequate intracardiac current. The purpose of this study was to determine, in advance of administering shocks which parameters of body habitus can be used to select the electrode size that maximizes intracardiac current in transthoracic defibrillation. We administered direct current shocks to 18 mongrel dogs over a wide range of weight and size (weight 10-30 kg with chest circumferences 44-77 cm) using a damped sine wave defibrillator and self-adhesive electrode pairs of various diameters (4 cm, 5.8 cm, 8 cm and 10 cm), placed on the right and left lateral chest walls. The energy levels used were 50, 100, and 150 J. Intracardiac voltage gradient, a parameter of intracardiac current, was determined in three orthogonal planes using an intramyocardial electrode array placed in the interventricular septum. The relation between intracardiac voltage gradient magnitude magnitude of VG and various parameters (body weight, chest, circumference, chest volume, chest radius, and heart weight divided by chest radius) was determined. The correlation (r) with the smallest P value was between magnitude of VG and the heart weight divided by chest radius (HW/R) (r = 0.71). Intracardiac current was highest at intermediate pad sizes. The electrode pads that maximized magnitude of VG tended to be large for the larger HW/R dogs, and smaller HW/R dogs. In none of the HW/R groups did the largest electrode pads yield the highest intracardiac voltage gradient. We conclude that there is no simple way to determine in advance an electrode pad size that maximizes intracardiac current. The HW/R ratio influences but does not determine intracardiac intracardiac current.

Animals↗

PubMed2004

Use of a wearable defibrillator in terminating tachyarrhythmias in patients at high risk for sudden death: results of the WEARIT/BIROAD.

The automatic ICD improves survival in patients with a history of sudden cardiac arrest. However, some patients do not meet the guidelines for ICD implantation or are unable to receive an implantable device. This study tested the hypothesis that these patients could benefit from a wearable cardioverter defibrillator. Patients with symptomatic heart failure and an ejection fraction of <0.30 (WEARIT Study) or patients having complications associated with high risk for sudden death after a myocardial infarction or bypass surgery not receiving an ICD for up to 4 months (BIROAD Study) were enrolled into two studies. After a total of 289 patients had been enrolled in the trial (177 in WEARIT and 112 in BIROAD), prespecified safety and effectiveness guidelines had been met. Six (75%) of eight defibrillation attempts were successful. Six inappropriate shock episodes occurred during 901 months of patient use (0.67% unnecessary shocks per month of use). Twelve deaths occurred during the study 6 sudden deaths: 5 not wearing and 1 incorrectly wearing the device). Most patients tolerated the device although 68 patients quit due to comfort issues or adverse reactions. The results of the present study suggest that a wearable defibrillator is beneficial in detecting and effectively treating ventricular tachyarrhythmias in patients at high risk for sudden death who are not clear candidates for an ICD and may be useful as a bridge to transplantation or ICD in some patients.

Death, Sudden, Cardiac↗

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