Internal Cardioversion Of Atrial Fibrillation Research Articles

External versus internal cardioversion for atrial fibrillation: a meta-analysis of randomized controlled trials.

Patients with atrial fibrillation (AF) often require rhythm control strategy for amelioration of symptoms. It is unclear if there is any difference between external cardioversion (ECV) and internal cardioversion (ICV) for successful conversion of AF to normal sinus rhythm. We performed a meta-analysis of published randomized controlled trials (RCTs) evaluating success of cardioversion using ECV versus ICV. In the pooled analysis of 5 RCTS, there was no difference in success of cardioversion using ECV versus ICV (OR 1.69, 95% CI 0.24-11.83, p = 0.6). In the subgroup analysis, there was no difference between ECV and direct electrode ICV (OR 0.41, 95% CI 0.09-1.83, p = 0.24). However, ECV was significantly better compared with ICV using ICD (OR 11.97, 95% CI 1.87-76.73, p = 0.009). There was no difference between ECV versus ICV in effectiveness for termination of AF. Larger well-designed randomized controlled trials are needed to confirm our findings.

Intracardiac impedance response during acute AF internal cardioversion using novel rectilinear and capacitor-discharge waveforms

Intracardiac impedance (ICI) is a major determinant of success during internal cardioversion of atrial fibrillation (AF). However, there have been few studies that have examined the dynamic behaviour of atrial impedance during internal cardioversion in relation to clinical outcome. In this study, voltage and current waveforms captured during internal cardioversion of acute AF in ovine models using novel radiofrequency (RF) generated low-tilt rectilinear and conventional capacitor-discharge based shock waveforms were retrospectively analysed using a digital signal processing algorithm to investigate the dynamic behaviour of atrial impedance during cardioversion. The algorithm was specifically designed to facilitate the simultaneous analysis of multiple impedance parameters, including: mean intracardiac impedance (ZM), intracardiac impedance variance (ICIV) and impedance amplitude spectrum area (IAMSA) for each cardioversion event. A significant reduction in ICI was observed when comparing two successive shocks of increasing energy where cardioversion outcome was successful. In addition, ICIV and IAMSA variables were found to inversely correlate to the magnitude of energy delivered; with a stronger correlation found to the former parameter. In conclusion, ICIV and IAMSA have been evidenced as two key dynamic intracardiac impedance variables that may prove useful in better understanding of the cardioversion process and that could potentially act as prognostic markers with respect to clinical outcome.

A novel electrode placement strategy for low-energy internal cardioversion of atrial fibrillation: A simulation study

highlights the importance of implementing early general cardiovascular health monitoring. Monitoring and treatment of these risk factors may reduce the incidence of aortic dissection and its consequences, although diagnosis still relies on a high degree of clinical suspicion given the paucity of clinical signs and rapid progression to fatal outcomes. Further, post-menopausal women were noted to have the same risk as age matched males, highlighting the need for similar vigilance in cardiovascular monitoring in this population. Only 11.9% of the cases involved dissection associated with an area of aneurysmal dilatation. Previous clinical studies have demonstrated that aortic diameters are similar when comparing aneurysmal cases with and without dissection, further supporting the theory that aneurysm and dissection develop independently [1]. While current recommendations for aneurysm risk monitoring include annual imaging of the aorta of Marfan patients with an aortic diameter less than 4.5 cm, screening for aortic dissection in high risk demographics is not currently within the scope of published guidelines [3,5]. The diagnosis of aortic dissection remains clinically challenging and the outcomes from this disease are often fatal and in particular can apply to young men, where modifiable risk factors have been identified prematurely. Improved imaging of atherosclerotic changes within the thoracic aorta may have a role in improving diagnosis and management of aortic dissection in the future.

Waveform optimization for internal cardioversion of atrial fibrillation

IntroductionA novel atrial defibrillator was developed at the Royal Victoria Hospital in collaboration with the Nanotechnology and Integrated Bio-Engineering Centre, University of Ulster. This device is powered by an external pulse of radiofrequency energy and designed to cardiovert using low-tilt monophasic waveform (LTMW) and low-tilt biphasic waveform (LTBW), 12 milliseconds pulse width. This study compared the safety and efficacy of LTMW with LTBW for transvenous cardioversion of atrial fibrillation (AF). MethodsPatients were anticoagulated with warfarin to maintain International Normalized Ratio between 2 and 3 for 4 weeks prior cardioversion. Warfarin international normalized ratio level was maintained in between 2 and 3 for 4 weeks prior cardioversion. St Jude's defibrillating catheter was positioned in the distal coronary sinus and right atrium and connected to the defibrillator via a junction box. After a test shock using a dummy load, the patient was cardioverted in a step-up progression from 50 to 300 V. Shock success was defined as return of sinus rhythm for 30 seconds or more. If cardioversion was unsuccessful at peak voltage, the patient was crossed over to the other arm of the waveform type and cardioverted at peak voltage. ResultsThirty patients were randomized equally to LTBW and LTMW (15 each). Seven out of 15 patients (46%) cardioverted to sinus rhythm with LTBW, and 1 (6%) of 15, with LTMW (P = .035). Including crossover patients, 14 patients (46%) converted to sinus rhythm. After crossover, 4 patients were cardioverted with LTBW and 2 with LTMW. Overall mean voltage, current, and energy used for cardioversion were 270.53 ± 35.96 V, 3.68 ± 0.80 A, and 9.12 ± 3.73 J, respectively, and intracardiac impedance was 70.82 ± 13.46 Ω. For patients who were successfully cardioverted, mean voltage, current, energy, and intracardiac impedance were 268.28 ± 42.41 V, 3.52 ± 0.63 A, 8.51 ± 3.16 J, and 73.92 ± 12.01 Ω. There were no major adverse complications during the study. Cardiac markers measured postcardioversion were unremarkable. ConclusionLow-tilt biphasic waveform was more efficacious for low-energy transvenous cardioversion of AF. A significant proportion of patients were successfully cardioverted to sinus rhythm with low energy. Radiofrequency-powered defibrillation can be safely used for transvenous cardioversion of AF.

First clinical experience with internal cardioversion of atrial fibrillation using a new single lumen endocardial defibrillation catheter

First clinical experience with internal cardioversion of atrial fibrillation using a new single lumen endocardial defibrillation catheter

Electrophysiology transvenous internal cardioversion for atrial fibrillation: A randomized comparison between catheters with different Coll length

Objectives The aim of this study was to evaluate the effects of 2 different right atrial electrode coil lengths on energy and voltage requirements for transvenous atrial cardioversion. Methods Twenty-six patients (mean age 61 ± 11 years) with chronic persistent atrial fibrillation (AF) (mean duration 11 ± 10 months) underwent transvenous cardioversion. A 6F catheter with a 5.5-cm coil was positioned in the coronary sinus. Another catheter with either a 5.5-cm or an 8-cm coil was positioned along the lateral wall of the right atrium, according to a randomized allocation. R wave-synchronized biphasic shocks were delivered according to a step-up protocol. After cardioversion of baseline AF, AF was reinduced, the right atrial catheter was substituted, and cardioversion was repeated with the alternative right atrial coil. Results Successful cardioversion was obtained in all of the patients. Leading edge voltage of effective shocks was significantly lower when catheters with an 8-cm coil in right atrium were used compared with the alternative 5-cm coil catheters (301 ± 80 volts vs 340 ± 78 volts, P <.001), and delivered energy (6.75 ± 4.25 joules vs 7.86 ± 4.29 joules, P =.043) and shock impedance (60 ± 9 ohm vs 66 ± 10 ohm, P <.001) were lower. Moreover, shock-induced discomfort, evaluated by assessment of pain score, was reduced (3.69 ± 1.09 vs 4.12 ± 0.99, P =.035). Conclusions The use of a longer right atrial coil results in lower shock impedance, lower energy and voltage requirements, and lower discomfort during transvenous atrial cardioversion. The results of the current study are of value either for transvenous internal cardioversion of chronic persistent AF or for implantable atrial defibrillators. (Am Heart J 2002;144:851-7.)

Internal cardioversion of atrial fibrillation under transesophageal echocardiography guidance without fluoroscopy using single-lead catheter technique

disease. A recent report from the Coronary Artery Risk in Young Adults (CARDIA) population indicated that 18% of young black men aged 18 to 30 years had detectable calcium. Among our study participants (all black adults) who were aged 30 years with no history of cocaine use, 36.4% had detectable coronary calcium. Thus, the proportion of young black adults having detectable coronary calcium is much higher in our study than in the CARDIA report. This suggests that some other unmeasured factors merit investigation.

Significant prolongation of atrial monophasic action potential duration: short-term reverse electrophysiological changes after internal cardioversion of atrial fibrillation.

Since short action potentials and short refractory periods facilitate the induction of atrial reentry, this maladaptation has been proposed as the pathophysiological basis of the frequent immediate recurrences of atrial fibrillation (IRAF) after internal cardioversion. However, short-term reverse electrophysiological changes of the atria after cardioversion have not been studied in humans. Thirty-seven patients with chronic atrial fibrillation of 16+/-19 months and ten patients with an atrial fibrillation duration < or =48 h underwent internal cardioversion. Antiarrhythmic medication was only continued in 10 patients (21%), who were on amiodarone before cardioversion. Atrial monophasic action potential duration at 90% repolarization (APD(90)), sinus rate, P wave duration and interatrial conduction times between high right atrium and coronary sinus were recorded at min 0, 1, 3, 5, 10, 15 and 20 after cardioversion. Internal cardioversion was successful in all patients, but twelve of the patients with chronic AF (32%) and three of the patients with intermittent AF (30%) had one to four episodes of IRAF after 16+/-28 s. There was a significant 52+/-30 ms APD(90) prolongation, 83% of which occurred in min 0-3 (P<0.0001) and 17% in min 3-20 (P<0.05) after internal cardioversion. There was no significant temporal change in sinus rate, P-wave and interatrial conduction time during the time studied. APD(90) prolongation and its time dependence did not show a detectable difference in subgroups with chronic AF, IRAF, left atrial size >40 mm and treatment with amiodarone. There is a significant prolongation of action potential duration in min 0-3 after internal cardioversion of atrial fibrillation, whereas sinus rate and intra- and interatrial conduction time remain unchanged. APD(90) prolongation in min 0-3 shows a temporal relationship to the high rate of immediate recurrences of atrial fibrillation during this time interval. The data imply that there is a transient recovery of atrial refractoriness after cardioversion and suggest a mechanism of the high rate of early recurrences of atrial fibrillation.

Cardioversión eléctrica externa y sistemas de cardioversión interna: evaluación prospectiva y comparativa del daño celular con troponina I

In this study we measured the concentrations of cardiac troponin I (cTnI) and several biochemical markers of myocardial damage after elective external cardioversion or internal cardioversion by specific catheters or automatic defibrillators. Biochemical markers were analyzed prospectively for 30 consecutive patients after electrical cardioversion. Concentrations of cTnI, myoglobin, creatine kinase (CK), CK-MB and the MB/CK ratio were determined in samples before cardioversion and 2, 8 and 24 h later. The shock energy ranged from 50 to 360 joules (235 106 joules) in external cardioversions and from 3 to 37 joules (15 8 joules) in internal cardioversions. We detected abnormal concentrations of CK, myoglobin, CK-MB and MB/CK in 33% of the patients after external cardioversion. The concentrations of cTnI remained within normal limits at all times, with no elevations detected. Whereas no abnormal concentration of any biochemical marker was detected in any patient who required internal cardioversion for atrial fibrillation, two patients who underwent external cardioversion from an automatic defibrillator did have abnormal concentrations of CK-MB, myoglobin, and even of cTnI. The concentration of cTnI remained below the detection limit after external cardioversion, even though the other more non-specific markers changed. No enzyme alteration was detected in patients who underwent internal cardioversion of atrial fibrillation.

Transvenous low energy internal cardioversion for atrial fibrillation: a review of clinical applications and future developments.

Low energy internal atrial cardioversion can be performed by delivering biphasic shocks between transvenous catheters positioned within the cardiac chambers or great vessels. Delivery of shocks results in effective cardioversion at energies < 6-10 J and the procedure can be effective even when external cardioversion has failed. Shock induced discomfort varies from patient to patient, but the procedure can be usually performed without general anesthesia and eventually under mild sedation. Nevertheless, tolerability has to be improved by obtaining a substantial reduction in defibrillating thresholds. With regard to safety, delivery of shocks for defibrillating the atria implies a potential risk of inducing ventricular fibrillation; to minimize this risk, shock delivery must be synchronous to the QRS and should be avoided during rapid RR cycles (< 300 ms). Presently, transvenous low energy cardioversion is an investigational procedure, but a widening of indications is expected in the near future. The cost of the procedure, which remains invasive and requires a brief hospital stay, must be balanced with the benefit of restoring sinus rhythm and the possibility of maintaining sinus rhythm for the medium- to long-term. Experimental and clinical investigations of low energy internal cardioversion have resulted in the development of devices for atrial defibrillation whose clinical role and cost-benefit ratio is currently under evaluation.

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

Safety and efficacy of internal cardioversion of atrial fibrillation in patients with impaired left ventricular systolic function

In patients with structural heart disease and left ventricular ejection fraction <40%, internal cardioversion is a safe and effective method for converting persistent atrial fibrillation. The acute success rate and atrial defibrillation requirement for cardioversion in these patients is comparable to patients with lone atrial fibrillation and structurally normal hearts.

Incidence and modes of onset of early reinitiation of atrial fibrillation after successful internal cardioversion, and its prevention by intravenous sotalol

OBJECTIVESTo study the incidence and mode of onset of early reinitiation of atrial fibrillation (ERAF) following successful internal cardioversion of chronic atrial fibrillation, and to determine the effects of sotalol...

Transvenous internal cardioversion for atrial fibrillation: a randomized study on defibrillation threshold and tolerability of asymmetrical compared with symmetrical shocks

The aim of the study was to compare, according to a randomized cross-over design, two different biphasic waveforms (6.5/2.5 ms and 3.0/3.0 ms phases duration, respectively) for low energy internal atrial cardioversion with regard to energy requirements for cardioversion and shock induced discomfort. Methods: Nineteen patients with chronic persistent atrial fibrillation (AF)(mean duration 16±20 months) were submitted to internal atrial cardioversion (shock delivery between catheters in right atrium and coronary sinus, respectively) and were randomly allocated to baseline cardioversion with an asymmetrical biphasic shock (6.5/2.5 ms) or with a symmetrical biphasic shock (3.0/3.0 ms), according to a step up protocol. After baseline cardioversion, a sustained AF was reinduced and the patients crossed to the alternative waveform. The procedure was performed without routine administration of sedatives and shock induced discomfort was monitored by a subjective score (1 to 5). Sedatives or anesthetics were administered at patient’s request. Results: The procedure was effective in all the patients and was performed without need for sedatives/anesthetics in 17/19 patients (89%). Leading edge voltage of effective shocks resulted lower for asymmetrical shocks compared to symmetrical shocks (290±76 vs. 337±104 V, P<0.001) with no statistically significant differences in delivered energy (7.74±4.25 vs. 8.65±5.94 J). Moreover shock induced discomfort resulted lower for asymmetrical shocks compared to symmetrical (pain score=4.18±0.73 vs. 4.59±0.62, P<0.02). Shock impedence of effective shocks was 59±10 ohms for both waveforms. No significant complications occurred during the procedure and no ventricular arrhythmia was observed after atrial cardioversion. Transient bradycardia requiring support ventricular pacing was observed in one patient. Conclusions: Delivery of biphasic asymmetrical shocks (6.5/2.5 ms) results in lower leading edge voltage of effective shocks and better patients tolerability compared with conventional biphasic symmetrical shocks (3.0/3.0 ms). These findings are of interest both for transvenous internal cardioversion of chronic persistent AF and for implantable atrial defibrillators.

Favorable effects of flecainide in transvenous internal cardioversion of atrial fibrillation

ObjectivesThe aim of the study was to evaluate the effects of intravenous (IV) flecainide on defibrillation energy requirements in patients treated with low-energy internal atrial cardioversion.BackgroundInternal cardioversion of atrial fibrillation is becoming a more widely accepted therapy for acute episode termination and for implantable atrial defibrillators.MethodsTwenty-four patients with atrial fibrillation (19 persistent, 5 paroxysmal) underwent elective transvenous cardioversion according to a step-up protocol. After successful conversion in a drug-free state, atrial fibrillation was induced by atrial pacing; IV flecainide (2 mg/kg) was administered and a second threshold was determined. In patients in whom cardioversion in a drug-free state failed notwithstanding a 400- to 550-V shock, a threshold determination was attempted after flecainide.ResultsChronic persistent atrial fibrillation was converted in 13/19 (68%) patients at baseline and in 16/19 (84%) patients after flecainide. Paroxysmal atrial fibrillation was successfully cardioverted in all the patients. A favorable effect of flecainide was observed either in chronic persistent atrial fibrillation (13 patients) or in paroxysmal atrial fibrillation (5 patients) with significant reductions in energy requirements for effective defibrillation (persistent atrial fibrillation: 4.42 ± 1.37 to 3.50 ± 1.51 J, p < 0.005; paroxysmal atrial fibrillation: 1.68 ± 0.29 to 0.84 ± 0.26 J, p < 0.01). In 14 patients not requiring sedation, the favorable effects of flecainide on defibrillation threshold resulted in a significant reduction in the scores of shock-induced discomfort (3.71 ± 0.83 vs. 4.29 ± 0.61, p < 0.005). No ventricular proarrhythmia was observed for any shock.ConclusionsIntravenous flecainide reduces atrial defibrillation threshold in patients treated with low-energy internal atrial cardioversion. This reduction in threshold results in lower shock-induced discomfort. Additionally, flecainide may increase the procedure success rate in patients with chronic persistent atrial fibrillation.

Internal cardioversion of atrial fibrillation: marked reduction in defibrillation threshold with dual current pathways.

The ultimate acceptance of a fully automatic atrial defibrillator will depend on the reduction of pain to acceptable levels, requiring a marked decrease in defibrillation thresholds. The purpose of this study was to determine whether atrial defibrillation thresholds can be reduced by sequential shocks delivered through two current pathways. Sustained atrial fibrillation was induced with rapid atrial pacing in 12 adult sheep. Defibrillation electrodes were positioned in the right atrial appendage (RAap), distal coronary sinus (DCS), proximal coronary sinus (CSos), main/left pulmonary artery junction (PA), and right ventricular apex (RV). Single-capacitor biphasic waveforms (3/1 ms) were delivered through combinations of these electrodes. Probability-of-success curves were determined for single shocks with a single current pathway and sequential shocks with either single- or dual current pathways. The ED50 for delivered energy for the dual current pathway RAap to DCS then CSos to PA was 0.36+/-0.13 J, which was significantly lower than the ED50 of the standard single current pathway RAap to DCS (1.31+/-0.3 J) and was significantly lower than all other configurations tested. Internal atrial defibrillation thresholds can be markedly reduced with two sequential biphasic shocks delivered over two current pathways compared with the standard single shock delivered over a single current pathway or with sequential shocks delivered over a single current pathway.

Safety of high energy internal cardioversion for atrial fibrillation.

High energy internal cardioversion has been proposed as an alternative method to cardiovert drug refractory or external cardioversion refractory atrial fibrillation. However, the safety of this technique has not been clearly evaluated. We reviewed findings in 53 patients who underwent 55 sessions of high energy internal cardioversion (2 patients underwent 2 sessions) for termination of longstanding atrial fibrillation. Shocks energy varied from 70-270 J. Three patients had 3 shocks during the same session, 5 had 2, and 47 only 1. Success rate was 89% (success was defined as immediate conversion to normal sinus rhythm). Low cardiac output occurred in two patients, and resulted in the death of one of these individuals, a patient with significant hypertrophic cardiomyopathy and heart failure. The other patient recovered completely. In 11% of the cases, shock induced transient atrioventricular block, necessitating ventricular pacing until sinus rhythm was restored. In three patients, a moderate but asymptomatic and uncomplicated pericardial effusion was diagnosed on echocardiogram. Finally, four patients had side effects related to venous puncture, which resolved spontaneously. These results suggest that high energy internal cardioversion is effective for conversion of atrial fibrillation. However, the technique may not be optimal in patients with advanced hypertrophic cardiomyopathy and in such cases the technique should be used carefully and only in the case of failure of external cardioversion; no more than two shocks should be delivered during the same procedure. Temporary ventricular pacing should be provided in all patients and an echocardiogram should be performed before patients are being discharged.

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.

Low energy internal cardioversion of atrial fibrillation resistant to transthoracic shocks.

To investigate the efficacy of internal cardioversion using low energy shocks delivered with a biatrial electrode configuration in chronic atrial fibrillation resistant to transthoracic shocks. Low energy internal cardioversion was attempted in 11 patients who had been in atrial fibrillation for 233 (SD 193) days and had failed to cardiovert with transthoracic shocks of 360 J in both apex-base and anterior-posterior positions. Synchronised biphasic shocks of up to 400 V (approximately 6 J) were delivered, usually with intravenous sedation only, between high surface area electrodes in the right atrium and the left atrium (coronary sinus in nine, left pulmonary artery in one, left atrium via patent foramen ovale in one). Sinus rhythm was restored in 8/11 patients. The mean leading edge voltage of successful shocks was 363 (46) V [4.9 (1.2) J]. Higher energy shocks induced transient bradycardia [time to first R wave 1955 (218) ms]. No proarrhythmia or other acute complications were observed. Low energy internal cardioversion of atrial fibrillation can restore sinus rhythm in patients in whom conventional transthoracic shocks have failed.

Internal cardioversion of atrial fibrillation in sheep.

The cardioversion efficacy of multiple defibrillation waveforms and electrode systems was compared in a sheep model of atrial fibrillation. Sustained atrial fibrillation could be induced with rapid atrial pacing in 23 (55%) of the animals. This study was performed in four parts. Six sheep with sustained atrial fibrillation were used for data analysis for each part, except in part 4 where five sheep without sustained atrial fibrillation were used. In part 1, four lead systems and four single capacitor truncated exponential defibrillation waveforms (two monophasic and two biphasic) were tested. In part 2, two transvenous lead systems were compared; one was a right-to-left system with one electrode located in the right side of the heart and the other electrode located in the left side of the heart, and the other was a totally right-sided system with both electrodes located in the right side of the heart. Eight (four monophasic and four biphasic) waveforms were tested with each lead system. In part 3, eight transvenous lead systems were compared, and two waveforms (one monophasic and one biphasic) were tested with each lead system. For parts 1-3, probability of success curves were determined for each waveform/lead system configuration using an up-down technique with 15 shocks per configuration. In part 4, shocks were synchronized to the QRS and given through two lead configurations during sinus rhythm in 20-V steps starting with 40 and ending with 500 V, and two waveforms were tested with each lead system (one monophasic and one biphasic). Ventricular fibrillation thresholds were determined by giving shocks during the T wave of sinus rhythm. For part 1, the three lead systems that used only intravenous catheter electrodes had significantly lower defibrillation requirements than the catheter-to-chest wall patch system. A 3/3-msec biphasic waveform had significantly lower defibrillation requirements than any of the other three waveforms in part 1. In part 2, the 3/3-msec biphasic waveform with a right-to-left lead system configuration had significantly lower defibrillation requirements than any other waveform lead system combination tested, and for each waveform tested, the right-to-left configuration had significantly lower requirements than the totally right-sided configuration. In part 3, for each waveform the right-to-left configuration had significantly lower voltage and energy requirements than the corresponding totally right-sided configuration. Furthermore, in part 3, waveform/lead configurations that probably generated high potential gradients near the sinoatrial node and near the atrioventricular node resulted in more postshock conduction disturbances. In part 4, there were no episodes of ventricular arrhythmias with shocks synchronized to the QRS. However, with synchronization to the T wave, ventricular fibrillation was induced in all five animals with the minimum tested voltage, which was 40 V. This acute model yielded sustained atrial fibrillation in approximately 55% of the animals. Cardioversion of atrial fibrillation in sheep is possible with very low energy requirements using transvenous electrode systems (50% successful energy of 1.3 +/- 0.4 J for the 3/3-msec biphasic waveform with a right-to-left lead system). The biphasic waveform had the lowest defibrillation requirements of any waveforms tested, and right-to-left lead systems resulted in lower defibrillation requirements than totally right-sided lead systems. Also, lead systems that probably generated high potential gradients near the sinoatrial and atrioventricular node areas resulted in more frequent episodes of postshock conduction disturbances. Furthermore, synchronization of the shock to the QRS was vital to avoid potentially lethal postshock ventricular arrhythmias...