Internal Atrial Defibrillation Research Articles

High Internal Atrial Defibrillation Threshold Is Related to a High Risk of Recurrence After Catheter Ablation for Long-Standing Persistent Atrial Fibrillation But Not for Persistent Atrial Fibrillation.

The atrial defibrillation threshold (ADFT) for internal cardioversion is theoretically related to the critical mass for sustaining atrial fibrillation (AF). This study aimed to investigate the association of ADFT for internal cardioversion with the outcome of catheter ablation for non-paroxysmal AF (non-PAF). We included 368 consecutive patients who underwent first-time catheter ablation for non-PAF. Based on the degree of ADFT recorded by the internal cardioversion before pulmonary vein isolation, we divided the patients into low ADFT (<20 J) and high ADFT (≥20 J) groups and analysed the association between ADFT and atrial tachyarrhythmia recurrence. There were 234 and 134 patients in the low and high ADFT groups, respectively. Of these, 39 patients (16.7%) and 41 (30.6%) patients, respectively, had atrial tachyarrhythmia recurrence during the 2.6±1.0 year follow-up. The high ADFT group showed a significantly higher atrial tachyarrhythmia recurrence than the low ADFT group (p=0.002). This finding was also noted in patients with long-standing persistent AF (p=0.032) but not in patients with persistent AF (p=0.159). The significant predictors of arrhythmia recurrence on multivariate analysis were high ADFT (p=0.004) and long-standing persistent AF (p=0.011). In multivariate analysis within the long-standing persistent AF group, only ADFT remained a significant risk factor for AF recurrence (p=0.035). The high ADFT of internal cardioversion was found to be a risk factor for post-catheter ablation recurrence in patients with long-standing persistent AF but not in those with persistent AF.

Towards Low Energy Atrial Defibrillation.

A wireless powered implantable atrial defibrillator consisting of a battery driven hand-held radio frequency (RF) power transmitter (ex vivo) and a passive (battery free) implantable power receiver (in vivo) that enables measurement of the intracardiacimpedance (ICI) during internal atrial defibrillation is reported. The architecture is designed to operate in two modes: Cardiac sense mode (power-up, measure the impedance of the cardiac substrate and communicate data to the ex vivo power transmitter) and cardiac shock mode (delivery of a synchronised very low tilt rectilinear electrical shock waveform). An initial prototype was implemented and tested. In low-power (sense) mode, >5 W was delivered across a 2.5 cm air-skin gap to facilitate measurement of the impedance of the cardiac substrate. In high-power (shock) mode, >180 W (delivered as a 12 ms monophasic very-low-tilt-rectilinear (M-VLTR) or as a 12 ms biphasic very-low-tilt-rectilinear (B-VLTR) chronosymmetric (6ms/6ms) amplitude asymmetric (negative phase at 50% magnitude) shock was reliably and repeatedly delivered across the same interface; with >47% DC-to-DC (direct current to direct current) power transfer efficiency at a switching frequency of 185 kHz achieved. In an initial trial of the RF architecture developed, 30 patients with AF were randomised to therapy with an RF generated M-VLTR or B-VLTR shock using a step-up voltage protocol (50–300 V). Mean energy for successful cardioversion was 8.51 J ± 3.16 J. Subsequent analysis revealed that all patients who cardioverted exhibited a significant decrease in ICI between the first and third shocks (5.00 Ω (SD(σ) = 1.62 Ω), p < 0.01) while spectral analysis across frequency also revealed a significant variation in the impedance-amplitude-spectrum-area (IAMSA) within the same patient group (|∆(IAMSAS1-IAMSAS3)[1 Hz − 20 kHz] = 20.82 Ω-Hz (SD(σ) = 10.77 Ω-Hz), p < 0.01); both trends being absent in all patients that failed to cardiovert. Efficient transcutaneous power transfer and sensing of ICI during cardioversion are evidenced as key to the advancement of low-energy atrial defibrillation.

Effects of intravenous amiodarone and ibutilide on action potential duration and atrial conduction kinetics in patients with persistent atrial fibrillation.

Class III antiarrhythmic drugs have been shown to be effective for termination of atrial fibrillation (AF). The aim of this study was to determine the steady state and non-steady state effects of amiodarone and ibutilide on the atrial monophasic action potential (MAP) duration (MAPD), effective refractory period (ERP), and intra-atrial conduction time (IACT) in human persistent AF.Fourteen patients with persistent AF who underwent internal atrial defibrillation were included in the study. The atrial MAP was recorded at the high right atrium. IACT was measured from the pacing spike to the distal coronary sinus. MAPD and IACT were assessed during the steady state and at the shortest diastolic interval (DI) at a basic cycle length (CL) of 600 msec and after a premature stimulus. Amiodarone did not affect MAPD or the ERP at the basic CL, but it increased MAPD at the shortest DI. Amiodarone increased IACT at both the basic CL and the shortest DI. Ibutilide increased the MAPD and ERP at the basic CL and at the shortest DI. Ibutilide did not affect IACT at the basic CL or the shortest DI.Ibutilide increases atrial MAPD not only in the steady state but also at the shortest DI, but it does not affect IACT in patients with persistent AF. Amiodarone does not affect MAPD or ERP, but it increases IACT in the steady state, and it increases MAPD and IACT at the shortest DI.

Monophasic action potential duration alternans after abrupt shortening of the cardiac cycle in humans

BackgroundAction potential alternans may be important in causing ventricular arrhythmias. Methods and resultsWe recorded monophasic action potentials from the right ventricular endocardium in patients with persistent atrial fibrillation who underwent internal atrial defibrillation during rapid ventricular pacing. In 3 of 45 patients, monophasic action potential duration alternans was observed at a pacing cycle length ≤350ms. ConclusionAction potential alternans is not a rare phenomenon (6.6%) in humans.

Inter-catheter impedance variation during internal atrial defibrillation

Introduction: According to the European Society of Cardiology, atrial fibrillation (AF) has a prevalence of 1–2% in the general population, rising to over 5.5% in individuals over 55 years of age and accounts for in excess of 30% of all arrhythmia related hospital admissions. For chronic AF sufferers (where all other therapies have proved ineffective), restoration of sinus rhythm through electrical shock remains the treatment of choice. Internal atrial defibrillation thresholds as low as 1.27 joules have been reported. However, at low energies, complex electro-mechanical interac- tions at the catheter-tissue interface have long been suspected as a major source of variation in the amount of electrical energy required to terminate this arrhythmia. The objective of this work was to characterise the variation of inter-catheter impedance during internal atrial defibrillation.Methods: For this study, a custom low-power programmable impedance spectrometer was built to deliver a sinusoidal current of ± 200 μA in magnitude from 1–100 kHz in frequency. Using this system, the complex impedance between a pair of defibrillation electrode poles (placed in the distal coronary sinus and wall of the right atrium) was recorded between successive atrial defibrillation attempts.Results: A total of ten porcine models were investigated. Measurements detected inter-catheter impedance variations ranging from 15.5% to 28.9%. Subsequent data analysis revealed a mean inter-catheter impedance of 43.9 Ω with a variance of approximately 20.1% recorded.Conclusions: Complex electro-mechanical interactions at the catheter-tissue interface have been identified as a cause of significant variation in inter-catheter impedance; which alters the associated cardioversion threshold during internal atrial defibrillation. Further research will be required to fully understand and mitigate adverse effects of the physical mechanisms involved.

Internal Defibrillation: Where we Have Been and Where we Should be Going?

Internal cardioversion has been developed as an alternative technique for patients who are resistant to external DC cardioversion of atrial fibrillation (AF) and was found to be associated with higher success rates. It used initially high energies (200-300 J) delivered between an intracardiac catheter and a backplate. Subsequent studies have shown that it is possible to terminate with energies of 1 to 6 Joules, paroxysmal or induced AF in 90 percent of patients and persistent AF in 75 percent of patients, using biphasic shocks delivered between a right atrium-coronary sinus vectors. Consequently, internal atrial defibrillation can be performed under sedation only without the need for general anesthesia. Recently developed external defibrillators, capable of delivering biphasic shocks, have increased the success rates of external cardioversion and reduced the need for internal cardioversion. However, internal defibrillation is still useful in overweight or obese patients, in patients with chronic obstructive pulmonary disease or asthma who are more difficult to defibrillate, and in patients with implanted devices which may be injured by high energy shocks. Low energy internal defibrillation has also proven to be safe and this has prompted the development of implantable devices for terminating AF. The first device used was the Metrix system, a stand-alone atrial defibrillator (without ventricular defibrillation) which was found to be safe and effective in selected groups of patients. Unfortunately, this device is no longer being marketed. Only double chamber defibrillators with pacing capabilities are presently available: the Medtronic GEM III AT, an updated version of the Jewel AF and the Guidant PRIZM AVT. These devices can be patient-activated or programmed to deliver automatically ounce atrial tachyarrhythmias are detected, therapies including pacing or/and shocks. Attempts to define the group of patients who might benefit from these devices are described but the respective role of atrial defibrillators versus other non-pharmacologic therapies for AF, such as surgery and radiofrequency catheter ablation, remains to be determined. Advantages and limitations or atrial defibrillators and approaches to reduce shock related discomfort which may be a concern in some patients, are reviewed. Studies have shown that despite shock discomfort, quality of life was improved in patients with atrial defibrillators and the need for repeated hospitalizations was reduced. The cost of these devices remains a concern for the treatment of a non-lethal arrhythmia. Attention that atrial defibrillators will receive from cardiologists and from the industry in the future, will depend of the long-term results of other non-pharmacological options and of the identification of the group of AF patients which will require restoration and maintenance of sinus rhythm. But there is no doubt that selected subsets of patients with AF could benefit from atrial defibrillation.

Internal Atrial and Ventricular Defibrillation During Electrophysiology Procedures

Over the last twenty years internal defibrillation has evolved from an experimental technique into an important adjunctive procedure in the electrophysiology laboratory. Internal deflbrillation is used for treating persistent atrial fibrillation and refractory ventricular arrhythmias. Atrial defibrillation can be performed with several electrode configurations but generally shocks from 1 to 50 joules are delivered between electrodes placed in the coronary sinus and lateral wall of the right atrium. Ventricular defibrillation is usually performed with electrodes in the right ventricle and superior vena cava, although "unipolar" configurations with an internal ventricular electrode and a skin electrode can be used. Currently, internal deflbrillation can be required in 5-10% of cases within the electrophysiology laboratory and will become more commonly used as electrophysiologists perform more complex catheter ablation procedures.

Myocardial injury, neurohormonal activation and inflammation after internal atrial defibrillation

Background The effects of patient-activated atrial defibrillation on subclinical myocardial injury are unknown. Using biochemical markers, this study assessed the effect of a single internal atrial shock delivered by the implantable atrial defibrillator on myocardial damage, neurohormonal activation and inflammation. Methods Twelve patients were implanted with a dual chamber defibrillator for the sole indication of drug refractory symptomatic persistent atrial fibrillation (AF). All had maximum defibrillation energy programmed to maximise the first shock success rate. Creatine kinase isoenzyme, troponin T, cortisol, catecholamines, C-reactive protein and brain natriuretic peptide were measured (i) during sinus rhythm, (ii) 8 h after onset of spontaneously occurring AF (before cardioversion) and (iii) 8 h following successful patient activated cardioversion. Results There was no change in creatine kinase, troponin T, cortisol or C-reactive protein during AF or following internal cardioversion. Brain natriuretic peptide levels rose from a median value of 56 pg/ml during sinus rhythm (inter-quartile range 14–92 pg/ml) to 133 pg/ml during AF (30–262 pg/ml), p=0.002. There was a decrease 8 h after cardioversion to baseline (52 and 40–189 pg/ml), p=0.01. There were increases in serum adrenaline and noradrenaline levels during AF from 0.43 (0.12–0.61) to 0.58 pg/ml (0.39–0.80 pg/ml), p=0.002 and from 2.06 (1.61–2.59) to 2.83 nmol/l (2.43–3.46 nmol/l), p=0.02, respectively. These figures reverted to baseline levels 8 h post-cardioversion. Conclusions Internal atrial defibrillation does not result in myocardial injury. The onset of AF results in sympathetic activation and increased brain natriuretic peptide levels, which resolve following restoration of sinus rhythm.

Reproducibility of internal atrial defibrillation threshold in paroxysmal and persistent atrial fibrillation.

Several pharmacological or technical factors may affect atrial defibrillation threshold (ADFT) for internal cardioversion (ICV) in the treatment of atrial fibrillation (AF). We evaluated the reproducibility of ADFT in lone paroxysmal (electrically induced AF, 10 pts, 51+/-4 years) or persistent AF (15 pts, 64+/-7 years). The AF pattern (F-F interval) was characterised before each ICV attempt. A first step-up synchronised ICV test (ICV1, biphasic shock waveform 6 ms/6 ms) with increasing energy levels from 0.2 to 20 J was performed by a dual-lead defibrillation system (right atrium-coronary sinus configuration) connected to an external cardioverter defibrillator. After 30 min of stable sinus rhythm, a new sustained AF was induced (>20 min duration) and ICV protocol was repeated (ICV2). The AF cycle length was recorded for 30 s from the lateral wall of right atrium in basal condition and before each cardioversion attempt. The mean values of AF cycle length before a successful shock were similar in both AF populations (paroxysmal AF: pre-ICV1 175+/-21 ms vs pre-ICV2 181+/-20 ms (p=NS); persistent AF pre-ICV1 194+/-25 ms vs pre-ICV2 202+/-15 ms (p=NS)). No significant differences were observed between the two successful ICV tests concerning intensity, energy and impedance levels. The value of ADFT energy was reproducible in paroxysmal AF population (SD differences 1.2, coefficient of variability 9.6%). In persistent AF group only the impedance was reproducible (SD differences 2.6 Omega, coefficient of variability 4.5%), but not the energy requirements (SD differences 9.6, coefficient of variability 44.3%). ADFT is reproducible in paroxysmal AF patients, while a high coefficient of variability is present in persistent AF, possibly related to different patterns of re-entrant circuits in the reinduced AF. This observation is important in order to evaluate factors influencing ICV-ADFT correctly in AF patients.

P-297 Internal atrial defibrillation and early reinitiation of atrial fibrillation guiding ablation of focal atrial fibrillation

P-297 Internal atrial defibrillation and early reinitiation of atrial fibrillation guiding ablation of focal atrial fibrillation

P-297 Internal atrial defibrillation and early reinitiation of atrial fibrillation guiding ablation of focal atrial fibrillation

P-297 Internal atrial defibrillation and early reinitiation of atrial fibrillation guiding ablation of focal atrial fibrillation

Dose-response relationship for successful internal atrial defibrillation.

The dose-response relationship for successful defibrillation has been determined in man for the ventricle but not for the atrium. The purpose of this study was to determine the dose-response relationship for internal atrial defibrillation in humans. Seventy-seven consecutive patients underwent internal atrial defibrillation for acute (n = 14) or chronic AF (n = 63). Shocks were delivered in 40-V increments between electrodes positioned in the coronary sinus and the right atrium until successful conversion or a maximum of 400 V was reached. The shock strength versus success of shock data were subjected to a Kaplan-Meier survival analysis combined with a nonparametric probability analysis to arrive at the dose-response relationship. Using this relationship, comparisons were made between acute and chronic AF and clinical relevant conversion percentages (20, 50, 80 and 95%) were estimated and were compared with the conventional mean threshold. There were significant dose-response relationships in both patients groups (P < 0.05). The Kaplan-Meier analysis comparing patients with chronic and acute AF showed significant differences in their dose-response relationships (P < 0.001). The estimated shock intensity for 95% conversion in patients with acute and chronic AF was 279 V (2.9 J) and 433 V (6.6 J), respectively (P < 0.001). The conventional mean defibrillation threshold in patients with acute (192 +/- 15 V. 1.4 +/- 0.2 J) and chronic AF (343 +/- 8 V, 4.4 +/- 0.2 J) predicted the 60% and 45% chance of successful conversion, respectively. In conclusion, this study demonstrates that single shock conversion data can be used to determine a dose-response relationship, which can be used to estimate the shock intensity required for specific successful atrial defibrillation efficacy and to compare different clinical factors that affect defibrillation efficacy.

P1534 Evaluation of myocardial damage, neurohormonal activation, inflammation and ventricular dysfunction prior to, and following internal atrial defibrillation

P1534 Evaluation of myocardial damage, neurohormonal activation, inflammation and ventricular dysfunction prior to, and following internal atrial defibrillation

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.

Internal atrial defibrillation during electrophysiological studies and focal atrial fibrillation ablation procedures.

Induction of sustained AF during electrophysiological studies requires electrical cardioversion to restore sinus rhythm for continuation of the electrophysiological study and mapping procedure. The study included 104 consecutive patients (age 59 +/- 12 years, 74 men), who were in stable sinus rhythm at the beginning of the electrophysiological study, underwent internal atrial defibrillation (IAD) of AF (> 15 minutes) that was induced during electrophysiological study. In 21 patients, AF was regarded to be the clinical problem (group I), and in the remaining 83 patients other arrhythmias represented the primary target of the electrophysiological study (group II). A 7.5 Fr cardioversion catheter (EP Medical) equipped with a distal array was used and placed in the left pulmonary artery and a proximal array of the same size was located along the lateral right atrial wall. All patients were successfully cardioverted with a mean energy of 6.2 +/- 4.0 1. In 18 (78%) of 21 group I patients and in 12 (14%) of 81 group II patients, AF recurred 3.7 +/- 3.4 and 2.4 +/- 1.4 times during electrophysiological study, respectively. The IAD shock did not suppress focal activity, thus the mapping of atrial foci responsible for AF could be continued even after several IADs. No IAD related complications occurred during the study. In conclusion, (1) IAD can be safely and successfully performed during electrophysiological study without using narcotic drugs or high electric energies; (2) IAD does not suppress focal activity; and (3) even if AF recurs frequently during the electrophysiological study, IAD can be performed several times without significant time delay.

Waveform Optimization for Internal Atrial Defibrillation: Effects of Waveform Rounding, Phase Duration, and Voltage Swing

The aim of this study was to compare the efficacy of internal atrial defibrillation by conventional truncated exponential biphasic waveforms with and without waveform rounding (1-2 phases) and to determine optimal duration for this novel double rounded waveform. Atrial fibrillation, induced by rapid electrical stimulation, was converted by internal shocks through defibrillation catheters (lateral right atrium and coronary sinus) in anesthetised sheep. Rounding the leading edges of the conventional biphasic waveform (Ventritex HVS-02; settings 100/-50 V, 150/-70 V, and 200/-100 V; n = 8) reduced delivered peak and trough voltages, currents, and energy (by > or = 21 %, P < 0.001; for double (both phases) rounded) without decreasing cardioversion success. At 100/-50 V the efficacy of single (first phase) rounded (53 +/- 13%; mean +/- SEM) and double rounded (59 +/- 11%) shocks was similar to the conventional waveform (56 +/- 14%). Double rounded waveform (phase durations 1-20 ms) efficacy was optimum at 6-10 ms phase duration (100% success at 10-ms phase duration; 1.52 +/- 0.04 J delivered energy; n = 6). Successful cardioversion by conventional, single rounded, and double rounded biphasic waveforms (duration 6 ms each phase), conventional monophasic, rounded monophasic (duration 12 ms), and a damped sine waveform correlated strongly with peak-to-trough voltage swing within the waveform (r = 0.882; P < 0.01; n = 8). For internal atrial defibrillation, rounding both phases of the conventional biphasic waveforms, the double rounded waveform, permits similar efficacy to the conventional truncated exponential biphasic waveform at reduced peak voltage, current, and delivered energy. Optimum phase duration is 6-10 ms (tested range 1-20 ms).

Internal Cardioversion of Atrial Fibrillation: New Information

For more than 30 years transthoracic external cardioversion has been an established method for the restoration of sinus rhythm in patients with persistent atrial fibrillation. It was first described by Lown in 1963 [1]. Though the success rate for external cardioversion ranges from 60–90% [2–4], there is reduced efficacy in those patients with a high body-mass index and an increased transthoracic diameter [5]. The method of internal cardioversion for restoration of sinus rhythm using transvenous electrodes has been reported in several animal [6,7] and human studies [8–15]. Cooper et al. [6] tested multiple electrode configurations in a sheep model of atrial fibrillation. They demonstrated that the optimal single current pathway for internal atrial defibrillation employed two electrodes that surrounded both atria (e.g., right atrial appendage and distal coronary sinus). Similar results have been reported in several human studies [12–14]. Internal cardioversion has been shown to be superior to conventional external cardioversion in terms of primary success rate, energy requirements and the need for sedation; this superiority holds especially true for patients with a high body mass index of >25 kg/m2 and increased transthoracic diameter [15]. The initial human data has been collected using two separate catheter for internal cardioversion. Though this approach demonstrated some advantages, there are also clear disadvantages, such as lack of ventricular backup stimulation in cases of post shock bradycardia, prolonged fluoroscopy time and the need for venous access via primarily the lower limb. These disadvantages increase the risk of bleeding complications, especially in patients with anticoagulation. Recently published data have demonstrated the benefit of a single lead catheter with two shock arrays on a balloon guided pulmonary artery catheter, when compared to the previous two catheter technique [12]. Optional ventricular backup pacing, preferable venous access via the upper limb, reduced procedural and fluoroscopy time are the major advantages. This new balloon-tipped cardioversion catheter (Figures 1 and 2) resembles a regular Swan-Ganz catheter. A guide-wire introduced via a central lumen allows facilitated searing and positioning of this device. The central lumen also provides means to draw blood samples, infuse drugs or perform haemodynamic measurements (pulmonary artery and wedge pressure). The proximal and distal high-energy electrode arrays for internal defibrillation consist of six 0.5 cm long platinum rings with a total surface area of 2.4 cm2 for each array. The middle ring of the proximal array is connected individually for atrial sensing and pacing, while the others are connected in parallel (atrial array). One pole located in the right ventricular outflow tract—between both arrays— serves for ventricular pacing and sensing. The six distal pulmonary rings are connected in parallel for internal cadioversion shock delivery. For cardioversion with this new device an electrode configuration in the right atrium and left pulmonary artery is suggested. A randomized trial could demonstrate that this configuration provides a homogeneous electrical field for effective cardioversion, and slightly higher energy requirements compared to a lead position in the right atrium and distal coronary sinus [12], as described earlier. However, the use of single lead catheters with a shock array position proximal in the right atrium and distal in the left pulmonary artery has contributed to facilitate the procedure of internal cardioversion of atrial fibrillation considerably. Ventricular backup pacing is an important safety tool, not only for a subgroup of patients with post shock bradycardia, but also for bradycardia after the administration of antiarrhythmic drugs or beta-blockers. The possibility of post shock atrial pacing also offers new therapeutic options in preventing the early recurrence of atrial fibrillation. Immediately after cardioversion 60% of all patients develop premature atrial contractions [16]. Recently published data suggest that short coupling intervals of the premature atrial beat predict an early relapse of atrial fibrillation [16]. Heterogeneity of refractoriness and conduction give way for a premature stimulus to reinduce atrial fibrillation. Immediately after cardioversion, electrical remodeling has shortened the

Reduction of atrial defibrillation threshold with an interatrial septal electrode.

The standard lead configuration for internal atrial defibrillation consists of a shock between electrodes in the right atrial appendage (RAA) and coronary sinus (CS). We tested the hypothesis that the atrial defibrillation threshold (ADFT) of this RAA-->CS configuration would be lowered with use of an additional electrode at the atrial septum (SP). Sustained atrial fibrillation was induced in 8 closed-chest sheep with burst pacing and continuous pericardial infusion of acetyl-ss-methylcholine. Defibrillation electrodes were situated in the RAA, CS, pulmonary artery (PA), low right atrium (LRA), and across the SP. ADFTs of RAA-->CS and 4 other lead configurations were determined in random order by use of a multiple-reversal protocol. Biphasic waveforms of 3/1-ms duration were used for all single and sequential shocks. The ADFT delivered energies for the single-shock configurations were 1.27+/-0.67 J for RAA-->CS and 0. 86+/-0.59 J for RAA+CS-->SP; the ADFTs for the sequential-shock configurations were 0.39+/-0.18 J for RAA-->SP/CS-->SP, 1.16+/-0.72 J for CS-->SP/RAA-->SP, and 0.68+/-0.46 J for RAA-->CS/LRA-->PA. Except for CS-->SP/RAA-->SP versus RAA-->CS and RAA-->CS/LRA-->PA versus RAA+CS-->SP, the ADFT delivered energies of all of the configurations were significantly different from each other (P:<0. 05). The ADFT of the standard RAA-->CS configuration is markedly reduced with an additional electrode at the atrial SP.

A New Beat on an Old Rhythm

* Age. More than 84% of people with AF are over age 65 (with a roughly equal incidence among men and women). * Mortality. Findings from several epidemiologic studies have shown increased morbidity and mortality.'-5 Most notably, 1998 data from the Framingham Heart Study indicate that AF is independently associated with a substantially increased risk for death (1.5-fold for men and 1.9-fold for women), even after adjustment for age and associated factors such as hypertension, congestive heart failure, and stroke. * Cost. In 1998, the estimated increase in cost of treating AF and its sequelae (thromboembolic stroke and heart failure) for patients over age 75 was $2,500 for men and $1,700 for women.6 * Sequelae. Findings from randomized clinical trials have demonstrated that anticoagulants markedly reduce the risk of thromboembolic stroke, one of AF's major sequelae.--12 Treatment options have broadened during the past decade as well, owing in part to recent data on the electrophysiologic mechanisms underlying AE'26 The two standard treatments-restoration and maintenance of normal sinus rhythm (NSR), and ventricular rate control-can involve both electrical and pharmacologic means. Many innovative therapies have shown success-radiofrequency catheter ablation, cardiac pacing, internal atrial defibrillation, and surgery-though the debate continues over whether maintenance of sinus rhythm (rhythm control) or ventricular rate control provides better long-term results. Researchers hope to

Use of sedation during cardioversion with the implantable atrial defibrillator.

The low shock energy used during internal atrial defibrillation may decrease the need for sedation during defibrillation with an implantable atrial defibrillator. The atrial defibrillator (Metrix Atrioverter) was implanted in 12 patients. During the in-hospital treatment of atrial fibrillation (AF) episodes, intravenous sedation was given only on patient request. The Atrioverter was programmed for ambulatory therapy in 4 patients. Efficacy, number of shocks delivered, and sedation requirements were recorded. A total of 393 shocks (1.8+/-1. 6 shocks/AF episode) were delivered to treat 213 AF episodes; 85 of 213 AF episodes (40%) were treated away from the hospital. Sinus rhythm was restored in 195 AF episodes (92%). Five patients never requested sedation. No sedation was needed for ambulatory-treated AF episodes. During the treatment of 26 of 213 AF episodes (12%), 75 shocks were delivered after patients received sedation. The number of shocks required to treat an AF episode determined the need for sedation (4.3+/-2.1 shocks for AF episodes requiring sedation versus 2+/-1 shocks for AF episodes requiring no sedation; P<0.001). These additional shocks were needed to treat immediate reinitiation of AF (14 episodes) or initial failure to cardiovert (4 episodes). For 8 AF episodes, sedation was requested before the first shock. This study suggests that, in a selected group of patients, AF can be treated with Atrioverter therapy without sedation. Successful ambulatory treatment of AF episodes with the Atrioverter, programmed to deliver </=2 shocks, did not require sedation. When multiple shocks were required to treat an AF episode, the need for sedation increased and included patients initially not requesting sedation.