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PubMed2000

Clinical experience with implantable atrial and combined atrioventricular defibrillators.

UNLABELLED: The high prevalence of atrial fibrillation (AF) and its clinical complications, the poor efficacy of medical therapy for preventing recurrences, and dissatisfaction with alternative modes of therapy stimulated interest in implantable atrial and combined atrioventricular defibrillators. In a multicenter study, the safety and efficacy of a stand alone implantable atrial defibrillator, the Metrix system, were evaluated. The device was implanted in 51 patients with highly symptomatic episodes of AF refractory to pharmacological treatment. During a follow-up of 9 months, 96% of 227 spontaneous AF episodes were successfully converted to sinus rhythm in 41 patients. In 62 episodes (27%), several shocks and/or additional drug treatment were required to maintain stable sinus rhythm because of early recurrences of AF. A total of 3719 shocks were delivered and no induction of ventricular proarrhythmia or inaccurately synchronized shocks occurred. The AF detection algorithm exhibited a 100% specificity for the recognition of sinus rhythm and a 92.3% sensitivity for the detection of AF. The combined atrioventricular defibrillator, Jewel AF 7250, was evaluated in a multicenter, randomized, cross-over trial. The primary study objectives included: overall safety as determined by complications-free survival at 6 months, efficacy of tiered atrial pacing and defibrillation therapies for termination of spontaneous atrial tachycardias (AT) and AF, and relative sensitivity of a new dual-chamber detection algorithm. The device was implanted in 211 patients with either a history of ventricular tachyarrhythmias (VT/VF) alone or with a history of both AT/AF and VT/VF. During a mean follow-up of 4.5 months, it has been shown that the Jewel AF is safe and effective in treating atrial and ventricular tachyarrhythmias. Pace termination of 85% of AT episodes were achieved with painless delivery of antitachycardia pacing; additional 35% of AT episodes were terminated by high frequency burst pacing. CONCLUSIONS: The stand alone implantable atrial defibrillator may be safe and clinically useful in selected patients for the treatment of highly symptomatic, drug resistant recurrences of AF. The combined atrioventricular defibrillator may be particularly indicated in patients presenting with both a history of atrial and ventricular tachyarrhythmias.

Aged↗
PubMed2000

Effects of a thin-sized lead body of a transvenous single coil defibrillation lead on ICD implantation. Kainox RV Study Group.

In the interest of patients receiving implantable cardioverter defibrillators (ICDs), the clinical benefits of newer and thinner transvenous defibrillation leads have to be determined. The aims of this study were to evaluate the ICD procedure duration and the frequency of lead dislocation at the 3-month follow-up of a new defibrillation lead with a thin-sized lead body and its conventional-sized predecessor. The thin-sized single coil defibrillation lead (Kainox RV, Biotronik; lead body 6.7 Fr) was implanted in 61 patients and the conventional-sized defibrillation lead (SPS, Biotronik; lead body 7.8 Fr) in 60 patients. Both leads were connected to a left-sided, prepectorally implanted Phylax ICD (Biotronik) with active housing. The lead implantation time and total procedure duration were determined. Lead implantation time was defined as the time from lead insertion to the end of the pacing measurements. The total procedure duration spanned skin incision to closure. The incidence of lead repositioning during the lead implantation time and during ventricular fibrillation conversion testing was also assessed. The frequency of lead dislocations was recorded at the 3-month follow-up. Mean lead implantation time and total procedure duration of the thin-sized lead (23 +/- 22 minutes 76 +/- 37 minutes) were not statistically different from the time needed for the conventional-sized lead (22 +/- 20 minutes 81 +/- 34 minutes). The number of lead repositionings during the lead implantation time was similar (thin-sized lead: 1.4 +/- 2.4; conventional-sized lead: 1.1 +/- 1.9). An additional lead repositioning was not necessary during ventricular fibrillation conversion testing in 93.4% of the patients with thin-sized and in 94.4% with conventional-sized leads (not significant). At the 3-month follow-up, there were four (6.6%) lead dislocations in the thin-sized and four (6.7%) in the conventional-sized lead group. In conclusion, the down-sized lead body of the new defibrillation lead influenced neither ICD procedure duration nor the incidence of lead dislocation during follow-up.

Case-Control Studies↗
PubMed2001

Electrogram width parameter analysis in implantable cardioverter defibrillators: Influence of body position and electrode configuration.

The "EGM width criterion" is a discrimination algorithm that was available in the last generation ICDs. It improved ventricular tachycardia detection by withholding inappropriate therapy deliveries in the presence of narrow QRS tachycardias. The accuracy of the algorithm depends on the optimal settings of the intracardiac EGM source, the "slew thresholds," and the "width threshold." The possible dependence of these parameters on body position may affect the detection efficacy. Whether these effects can be minimized by a proper choice of the electrode configuration used for signal analysis is still to be investigated. This study aimed to evaluate the stability of the slew threshold and width threshold obtained in the supine and orthostatic positions detected by the tip-to-ventricular coil and can-to-ventricular coil electrode configurations. Their time dependence was also evaluated at the 6-month follow-up. Fifty-eight patients who were recipients of an ICD (model Medtronic 7223cx and 7227cx) were included in the study. Changing from supine to orthostatic position caused a marked variation of slew and width thresholds (21.0 +/- 13.9 V/s and 10.1 +/- 9.6 ms, respectively) in 36% of patients with tip-to-ventricular coil and in 44% of patients with can-to-defibrillating coil (the mean slew threshold variation was in this case 17.6 +/- 15.8 V/s, while the mean width threshold variation was 18.8 +/- 21.0 ms). Width threshold variation was statistically significant (P < 0.02) with the latter electrode configuration. Slew thresholds settings changed between the 1- and 6-month follow-ups in the 75% of patients with can-to-defibrillating coil configuration and in 50% with tip-to-defibrillating coil. These time related variations were significantly larger with the tip-to-defibrillating coil configuration (P < 0.01). In conclusion, EGM width parameters may change between supine and orthostatic position and over time with tip-to-defibrillating coil configuration and can-to-defibrillating coil configuration. The former configuration was less sensitive to body position changes, but more sensitive to time related variations. These findings may be useful for optimal programming of the EGM width criterion, but if parameter programming based on these results can improve the discrimination specificity still needs to be investigated.

Aged↗
PubMed2002

The effects of reverse atrial electrical remodeling on atrial defibrillation thresholds.

The implantable atrial defibrillator is a developing therapeutic option for paroxysmal atrial fibrillation, but shock related discomfort continues to be a limiting factor. To further characterize successful defibrillation, the relationship between reverse atrial electrical remodeling and internal atrial defibrillation thresholds in canines with chronic atrial fibrillation was examined. Testing was performed in 21 dogs. Chronic atrial fibrillation was induced in eight dogs by creating moderate mitral regurgitation and rapidly pacing the right atrium for > or = 6 weeks. The atrial fibrillation cycle length, atrial effective refractory period, refractory period dispersion, and internal atrial defibrillation thresholds were determined after establishment of chronic atrial fibrillation after 4 hours of sinus rhythm postcardioversion and 7 days of sinus rhythm postcardioversion. These measurements were then compared to a normal population of 13 dogs. The atrial defibrillation thresholds were 6.6 J (1.9-10.1 J) initially, 2.9 J (1.5-3.7 J) after 4 hours of sinus rhythm, and 0.9 J (0.4-1.3 J) after 7 days of sinus rhythm (P = 0.04). This decrease was associated inversely with the atrial effective refractory period (P < 0.03), and atrial fibrillation cycle length (P < 0.05), and with a decrease in atrial refractory period dispersion after 7 days of sinus rhythm (P = 0.04). These electrophysiological measurements reached normal population levels by 7 days. Atrial defibrillation thresholds decrease as atrial reverse electrical remodeling occurs and this reduction corresponds to increased atrial fibrillation cycle length, increased atrial refractoriness, and decreased refractory period dispersion.

Animals↗
PubMed2005

Unsuccessful internal defibrillation in Brugada syndrome: focus on refractoriness and ventricular fibrillation cycle length.

INTRODUCTION: In patients with Brugada syndrome, implantable cardioverter defibrillator (ICD) is the only reliable treatment to prevent sudden death though, in some cases, internal defibrillation may be unsuccessful. The aim of this study was to examine the determinants of defibrillation failure, with a focus on electrophysiologic characteristics. METHODS: The study included 51 patients treated with ICD: 22 with Brugada syndrome and 29 with structural heart disease (SHD). The prevalence of defibrillation energy requirement precluding the programming of a 10-J safety margin, the mean right ventricular effective refractory period (ERP), and mean induced ventricular fibrillation cycle length (VFCL) from the stored ICD electrograms, were compared between the two patient groups. RESULTS: High defibrillation requirements were observed in 18% of patients with Brugada syndrome versus 0% of patients with SHD. However, the patients with SHD had larger heart size than those with Brugada syndrome. Mean VFCL and mean ERP were both significantly shorter in patients with Brugada syndrome than in patients with SHD, and ERP and VFCL were significantly correlated. CONCLUSION: Patients with Brugada syndrome have a high prevalence of high defibrillation energy requirement, and short ventricular ERP and VFCL.

Bundle-Branch Block↗
PubMedDate not supplied

I-123 MIBG imaging and heart rate variability analysis to predict the need for an implantable cardioverter defibrillator.

BACKGROUND: Iodine 123 metaiodobenzylguanidine (MIBG) imaging and heart rate variability (HRV) analysis were compared in patients with an implantable cardioverter defibrillator (ICD) who did and did not receive defibrillator discharges. Although the ICD has been shown to abort potentially fatal ventricular arrhythmias, identification of patients who most benefit from this device remains difficult. As the autonomic nervous system has been implicated in the genesis of these arrhythmias, we undertook a pilot study to evaluate local myocardial sympathetic innervation with the use of I-123 MIBG myocardial imaging, as well as central autonomic tone with the use of HRV, in patients with implantable defibrillators. Test results were correlated with the occurrence of ICD discharges. METHODS AND RESULTS: Seventeen patients with previously implanted defibrillators were studied. Of these, 10 had at least 1 appropriate device discharge for ventricular tachyarrhythmias, whereas 7 had no discharge. Patients with a discharge had a significantly lower I-123 MIBG heart-mediastinal tracer uptake ratio, higher I-123 MIBG defect scores, more extensive sympathetic denervation, and significantly reduced values for several HRV parameters, particularly those in the frequency domain. When combined, the I-123 MIBG heart-mediastinal ratio and HRV 5-minute low-frequency variables were highly predictive of defibrillator discharges. All patients with a heart-mediastinal ratio lower than 1.54 and 5-minute low frequency lower than 443 ms(2) had an ICD discharge (4/4), whereas no patient with an uptake ratio greater than 1.54 and 5-minute low frequency greater than 443 ms(2) did (0/3, P =.03). CONCLUSIONS: Cardiac autonomic assessment using a combination of myocardial scintigraphic and neurophysiologic techniques may help select patients who would most benefit from an implantable defibrillator by identifying those at increased risk for potentially fatal arrhythmias.

3-Iodobenzylguanidine↗
PubMed1997

The future role of defibrillators in the management of atrial fibrillation.

Episodes of sustained atrial fibrillation have long been effectively treated with external, transthoracic defibrillation. Despite concomitant, postcardioversion therapy with antiarrhythmic agents, patients will frequently have additional episodes of atrial fibrillation requiring either repeat external cardioversion or treatment with either pharmacologic or additional nonpharmacologic therapies. The limited long-term efficacy of different treatment regimens has resulted in the development and evaluation of newer, nonpharmacologic therapeutic options including the implantable atrial defibrillator. The feasibility of an implantable atrial defibrillator has been supported by recent advances in the areas of implantable ventricular defibrillators, including device size and transvenous lead systems. The concept is also supported by the demonstration in recent studies that transvenous, internal cardioversion of atrial fibrillation is possible using low energy shocks. Preliminary data suggest that low-energy atrial defibrillation shocks synchronized to an R wave with a relatively long coupling interval does not result in potentially lethal ventricular arrhythmias. Patient tolerance, and therefore acceptance of therapy, is presently a topic of significant concern and evaluation. Although present data suggest that the concept of an implantable atrial defibrillator is a potential treatment option for recurrent, persistent atrial fibrillation, significant clinical evaluation is required to define the patient population and overall clinical use of this type of device, either as a stand-alone therapy or in combination with other pharmacologic and nonpharmacologic therapies.

Animals↗
PubMed2006

Recent primary prevention implantable cardioverter defibrillator trials.

PURPOSE OF THE REVIEW: The aim of this article is to summarize the most relevant findings of recently published trials on prophylactic implantable cardioverter defibrillator therapy. RECENT FINDINGS: A number of important randomized clinical trials on the efficacy of prophylactic implantable cardioverter defibrillator therapy in patients deemed to be at high risk for ventricular tachyarrhythmias have recently reported their results. Patients with chronic ischemic cardiomyopathy, a long history of heart failure, and an ejection fraction of 0.30 or below benefit from preventive device therapy and are thus candidates for prophylactic defibrillator implantation. For this purpose, a single chamber device appears to be appropriate since there have been no prospective studies showing convincing clinical benefit by adding an atrial lead. Prophylactic implantable cardioverter defibrillator therapy should not be used in patients with recent myocardial infarction. There is convincing evidence from one trial that benefit from the defibrillator in coronary patients accrue after a considerable time has elapsed from the most recent infarct, presumably at least 6 months or perhaps longer. Finally, in patients with chronic dilated non-ischemic cardiomyopathy and a left ventricular ejection fraction of 0.35 or below, there is also benefit from prophylactic implantable cardioverter defibrillator therapy. SUMMARY: Taken together, these trials allow an evidence-based approach to primary prevention of sudden cardiac death in patients with both ischemic and non-ischemic cardiomyopathy.

Cardiomyopathy, Dilated↗
PubMed1994

Integration of absolute ventricular fibrillation voltage correlates with successful defibrillation.

Previous work has suggested that at higher absolute ventricular fibrillation voltages (AVFV), the heart is more amenable to defibrillation. This study investigated in a canine model whether voltage integration of the AVFV is associated with the defibrillation success rate. The moving-average filter was used to process the ventricular fibrillation (VF) waveform recorded from Lead II of the electrocardiogram (ECG). In seven animals, defibrillation trials were analyzed using a dc shock (DCS) successful approximately 50% of the time when delivered randomly. For each of a total of 84 DCS (40% successes, 60% failures), the fibrillation waveform just prior to DCS was analyzed. The integration of the AVFV waveform was performed over various sample sizes including 1, 4, 8, 16, 64, and 128 ms, as well as the time equal to the mean VF cycle length. The results suggest that dc shocks delivered at instants of higher values of integrated AVFV over the various window sizes are associated with successful defibrillation. Window sizes less than 16 ms appeared to offer the best discrimination. The integration of AVFV over the entire VF cycle length was significantly higher for successful rather than unsuccessful DCS. This interesting observation is consistent with the clinical observation that "coarse" VF (high AVFV) is easier to defibrillate than "fine" VF (low AVFV). The use of voltage integration of AVFV may have potential implications in the improvement of defibrillation success in implantable devices.

Analysis of Variance↗
PubMed1993

The rationale for prophylactic implantation of a defibrillator in "high risk" patients.

The increasing technological developments have made it possible to have implantable defibrillators with a wide range of diagnostic and therapeutic capabilities, which can be implanted without the need for a thoracotomy. It is not surprising, therefore, that the indications for implantation of a defibrillator have rapidly evolved. Defining populations of patients in whom a true "prophylactic" implantation (before the first episode of ventricular tachycardia or ventricular fibrillation) may be justified is still difficult. However, the time has certainly come to provide a cardioverter defibrillator to all patients who have suffered from one episode of ventricular tachycardia or ventricular fibrillation and who are at real risk of sudden arrhythmic death. Identification of these patients is relatively easy. It can be done using simple variables from the clinical history. Results from an ongoing multicenter trial testing the hypothesis that clinical variables can indeed be used to stratify the risk of sudden death and to select candidates for a defibrillator have proven the validity of this approach. There is no medical justification to withhold implantation of a cardioverter defibrillator in the truly "high risk" patient. One has to realize, however, that the concept of "high risk" is relative, and that the indications for the implantable defibrillator will continue to broaden.

Death, Sudden, Cardiac↗
PubMed1994

Comparison of simultaneous versus sequential defibrillation pulsing techniques using a nonthoracotomy system.

The defibrillation threshold (DFT) using simultaneous (SIML) versus sequential (SEQ) pathways for shock delivery was compared in 16 patients with an implanted cardioverter defibrillator. All patients had three-lead nonthoracotomy systems (NTL) using a left chest subcutaneous patch, a right ventricular endocardial lead, and a lead in the coronary sinus (n = 5) or superior vena cava (n = 11). The DFT were determined 2-44 days (17 +/- 17 days) after implantation. The DFT was defined as the lowest energy shock that resulted in successful defibrillation. The first pathway tested was SIML in 12 and SEQ in 4 patients with output beginning at or above the intraoperative DFT, routinely 18 J. The second pathway was tested beginning 2-4 J above the DFT of the first tested pathway. All shocks were delivered in 2-4 J decrement or increment steps. The SEQ pathway shocks resulted in a significantly lower DFT than SIML pathway shocks (14 +/- 6 vs 18 +/- 6 J; P < 0.01). There was no difference in the time delay after ventricular fibrillation initiation before shock delivery for the successful defibrillation between SIML versus SEQ pathways (7 +/- 2 secs for both pathways). In 7 of 16 patients, defibrillation using SEQ pathway resulted in a > 5 J lowering of DFT, while only one patient had > 5 J lowering of DFT using SIML shocks (P < 0.05). These results have important implications for selecting the optimal pathway for implantable cardioverter defibrillator therapy with a multilead NTL system.

Adult↗
PubMed1995

Echocardiographic assessment of epicardial defibrillator patch electrodes.

We performed a blinded controlled analysis of transthoracic echocardiograms on 18 patients before and after epicardial defibrillator patch electrode placement to determine the accuracy of echocardiography in identifying defibrillator patches and to determine possible echocardiographic findings that may correlate with defibrillator function or perioperative complications. The sensitivity of two-dimensional echocardiography in detecting defibrillator electrodes was 72% by one observer and 39% by a second observer. Corresponding specificities were 67% and 83%, respectively. The discordance rate was 27%. The echocardiographic finding of patch buckling was not observed and echocardiographic estimates of the distance from patch to epicardium did not correlate with defibrillator threshold at the time of surgery. We conclude that: echocardiography is only moderately sensitive and specific in identifying epicardial defibrillator electrodes; significant interobserver variability does exist; and echocardiography therefore cannot be used reliably to assess for pericardial changes or possible complications of patch electrode placement.

Adolescent↗
PubMed1996

Biphasic defibrillation using a single capacitor with large capacitance: reduction of peak voltages and ICD device size.

The volume of current implantable cardioverter defibrillators (ICD) is not convenient for pectoral implantation. One way to reduce the size of the pulse generator is to find a more effective defibrillation pulse waveform generated from smaller volume capacitors. In a prospective randomized crossover study we compared the step-down defibrillation threshold (DFT) of a standard biphasic waveform (STD), delivered by two 250-microF capacitors connected in series with an 80% tilt, to an experimental biphasic waveform delivered by a single 450-microF capacitor with a 60% tilt. The experimental waveform delivered the same energy with a lower peak voltage and a longer duration (LVLD). Intraoperatively, in 25 patients receiving endocardial (n = 12) or endocardial-subcutaneous array (n = 13) defibrillation leads, the DFT was determined for both waveforms. Energy requirements did not differ at DFT for the STD and LVLD waveforms with the low impedance (32 +/- 4 omega) endocardial-subcutaneous array defibrillation lead system (6.4 +/- 4.4 J and 5.9 +/- 4.2 J, respectively) or increased slightly (P = 0.06) with the higher impedance (42 +/- 4 omega) endocardial lead system (10.4 +/- 4.6 J and 12.7 +/- 5.7 J, respectively). However, the voltage needed at DFT was one-third lower with the LVLD waveform than with the STD waveform for both lead systems (256 +/- 85 V vs 154 +/- 51 V and 348 +/- 76 V vs 232 +/- 54 V, respectively). Thus, a single capacitor with a large capacitance can generate a defibrillation pulse with a substantial lower peak voltage requirement without significantly increasing the energy requirements. The volume reduction in using a single capacitor can decrease ICD device size.

Adult↗
PubMed1997

Influence of anodal electrode position on transvenous defibrillation efficacy in humans: a prospective randomized comparison.

Nonthoracotomy lead systems for implantable cardioverter defibrillators (ICDs) have reduced operative mortality and morbidity as compared to epicardial lead systems but are usually associated with higher defibrillation thresholds (DFTs). The purpose of this prospective randomized trial was to investigate if the second defibrillation electrode in the left subclavian vein can increase defibrillation efficacy and decrease DFT as compared to the superior vena cava (SVC) position in nonthoracotomy lead systems for ICDs. Seventeen patients (mean age: 49.9 +/- 11.3 years, mean ejection fraction: 46.1% +/- 15.8%) were implanted with an investigational unipolar electrode (Medtronic 13001) used as the defibrillation anode. DFT testing was started in the SVC (n = 10, group A) or the left subclavian vein (n = 7, group B), and repeated in the alternative position starting at the DFT of the initial position. Fifteen patients were eligible for analysis (group A: n = 9, group B: n = 6). With the electrode in the SVC, ventricular fibrillation could be successfully terminated in 9 out of 15 patients (60%). In the left subclavian vein the success rate was 100% (P < 0.01). Mean DFT in the SVC was 13.0 +/- 5.2 J and in the left subclavian vein 10.2 +/- 4.9 J. DFTs in the left subclavian vein were either lower (group A: n = 5/9, group B: n = 5/6) or equal to the results in the SVC position (P < 0.001). Thus, the left subclavian vein appears to be a superior alternative for positioning of the defibrillation anode as compared to the SVC for nonthoracotomy lead systems using two separate leads.

Defibrillators, Implantable↗
PubMed1997

Temporary transvenous cardioversion and defibrillation: a new method for practical tachyarrhythmia management.

The use of transvenous ICD systems and the recent advances in atrial defibrillation techniques have heightened interest in internal defibrillation. However, most shocks for induced or spontaneous arrhythmias in patients without devices are still delivered transthoracically using high energy. We describe the history of temporary internal defibrillation techniques and report the initial clinical results with a custom built disposable catheter for internal cardioversion and defibrillation. This prototype successfully converted more than 95% of 109 episodes of VT or VF in 28 patients, with biphasic energies < or = 20 J. A newer disposable catheter, using 40-wire Matrix technology as the defibrillating electrode, has design features that provide high surface area, low impedance, and low current density when compared to other leads used for similar purposes. Temporary internal cardioversion-defibrillation of induced and spontaneous arrhythmias using such catheter designs is likely to be widely applicable to patients undergoing electrophysiology procedures and to those in critical care units prone to tachyarrhythmias.

Arrhythmias, Cardiac↗
PubMed1999

Coronary artery bypass grafting and defibrillator implantation in patients with ventricular tachyarrhythmias and ischemic heart disease.

In patients with sustained ventricular tachyarrhythmias and myocardial ischemia due to multivessel coronary artery disease, it remains unclear whether revascularization is enough to control the arrhythmias or whether additional implantation of a defibrillator is indicated. We therefore reviewed our clinical strategy of performing both bypass surgery and implantation of a defibrillator in patients with syncopal ventricular tachycardia or fibrillation and significant multivessel coronary artery disease. We retrospectively reviewed the outcome of 18 patients with malignant ventricular tachyarrhythmias, significant multivessel coronary artery disease, and signs of myocardial ischemia who underwent both bypass surgery and defibrillator implantation. Data on these patients were compared to data from 232 other defibrillator patients with respect to baseline clinical variables, cardiac events, and mortality during follow-up. Except for underlying pathology, no other important differences in baseline characteristics were noted between the study patients and the other defibrillator patients. The cumulative occurrence of shocks during follow-up was comparable in both groups (66% vs 67%). The cumulative survival from all-cause mortality was 94% in the study patients and 78% in the others (P = NS). Pre- and postoperative electrophysiological testing was not useful to predict arrhythmia recurrences. In this population of patients with ventricular tachyarrhythmias and ischemia due to multivessel coronary artery disease, bypass surgery alone would not have prevented recurrences of arrhythmias. An excellent survival and a high incidence of shocks after both bypass surgery and defibrillator implantation were observed.

Aged↗
PubMed2006

Present understanding of shock polarity for internal defibrillation: the obvious and non-obvious clinical implications.

BACKGROUND: Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter-defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation. METHOD: A meta-analysis of the clinical studies on ICD shock polarity was performed. Subgroup analyses were also performed to test the impact of high DFTs, various tilts, and the use of the hot can electrode. A review of the basic research surrounding the effects of polarity in defibrillation is also presented. RESULTS: A total of 224 patients were studied. The use of an anodal right ventricular (RV) coil lowers the mean DFT by 14.8% (P = 0.00001). It provides thresholds equal to or lower than cathodal defibrillation in 83% of patients. The fraction of patients with lower anodal DFTs was 94/224 versus 38/224 for cathodal polarity. This phenomenon may be explained by virtual electrode effects. In particular, anodal electrodes tend to produce collapsing wavefronts while cathodal electrodes tend to produce expanding proarrhythmic wavefronts. CONCLUSION: In an ICD implant, the RV coil should be the anode. Furthermore, DFT testing beginning with cathodal defibrillation is most likely unnecessary and needlessly extends the procedure's duration and increases the risks for the patient.

Clinical Trials as Topic↗
PubMed1994

Is there any indication for an intracardiac defibrillator for the treatment of atrial fibrillation?

The experience gained using intracardiac cardioverter defibrillators for the treatment of ventricular arrhythmias has prompted the development of an automatic atrial defibrillator capable of detecting and automatically terminating atrial fibrillation (AF). Experimental studies in sheep have shown that it is possible to terminate AF with energies ranging from < 1 to 7 joules [J], using biphasic shocks. The best electrode configuration using intracardiac catheters and/or a subcutaneous patch was two catheters, one in the right atrium and the other in the coronary sinus. Current studies in man focus on the answers to three questions. First, can the experimental results of atrial defibrillation derived from healthy anesthetized sheep without spontaneous AF be extrapolated to AF in man with areas of fibrosis within the atria and/or underlying heart disease in 80% of cases? Preliminary studies in man suggest that cardioversion of AF of short duration is feasible using a mean energy of 2 J. Second, are these energies well tolerated in an awake nonsedated patient? Energies < 1 J were well tolerated, but pain resulting from higher energies needs further investigation. Third, is low-energy atrial defibrillation safe, i.e., is there a risk of ventricular arrhythmias induced by an atrial shock? Experimental results in sheep have shown that the risk of R wave synchronized shock to induce ventricular arrhythmias was only present when the preceding RR interval was shorter than 300 msec. The risk of proarrhythmia in man is undergoing evaluation and must be sufficiently low (< 0.1) before sanctioning implantation of a stand-alone (without associated ventricular defibrillator) automatic atrial defibrillator. Preliminary data on 1212 shocks showed no proarrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗