Impact of pulse characteristics on atrial defibrillation energy requirements

Improving the acceptability of the atrial defibrillator for the treatment of persistent atrial fibrillation: the atrial defibrillator sedation assessment study (ADSAS)

BACKGROUND

To compare the acceptability and effectiveness of three pre-medication regimens for manually activated cardioversion of recurrent persistent atrial fibrillation.

METHODS

Eighteen patients implanted with the Jewel AF atrial defibrillator for drug-resistant persistent atrial fibrillation only were studied in an open-labelled randomised crossover study. Patients were assigned to sedation (S) with midazolam elixir, analgesia (A) with morphine sulphate or combination therapy (C) with dextromoramide and lorazepam. Pre-medication was taken up to 1 h before cardioversion. Patients rotated through each type of medication after undertaking at least one cardioversion. Visual analogue scales were completed immediately post-cardioversion and 24 h later for pain, anxiety and 'unpleasantness'. Higher scores represented a worse outcome.

RESULTS

After 2 years' follow-up, 238 cardioversions were performed with S, 17 with A and 35 with C. The mean immediate combined score for S (10.9, 95% confidence interval (CI) 8.2-13.6) was significantly lower than for A (17.3, 95% CI 15.1-19.5, P = 0.01) and for C (15.9, 95% CI 12.3-19.6, P = 0.02). All patients who used S chose it as the most favourable pre-medicant. All patients who used A found it the least acceptable.

CONCLUSION

Sedation rather than analgesia enhanced the acceptability of manually activated atrial defibrillation.

Novel passive implantable atrial defibrillator using transcutaneous radiofrequency energy transmission successfully cardioverts atrial fibrillation

BACKGROUND

Conventional methods for cardioversion of atrial fibrillation (AF) to sinus rhythm have numerous difficulties. A novel method for cardioversion using the passive implantable atrial defibrillator (PIAD) was tested in acute animal models. This device does not have a battery or a capacitor to store energy and is activated by transferring RF energy across the skin from an external transmitter to the subcutaneously implanted defibrillator. On activation, a novel monophasic shock waveform with 5% tilt is delivered to the heart via 2 intracardiac defibrillation leads.

METHODS AND RESULTS

Cardioversion attempts with the device were assessed in 2 phases: a feasibility and efficacy study and randomized comparison against standard waveforms. Defibrillation leads were placed transvenously into the distal coronary sinus and the right atrial appendage. These were connected to the subcutaneously implanted PIAD. Sustained AF was induced by rapid atrial pacing. The transmitter coil was placed on the skin overlying the defibrillator, and defibrillation synchronized to the R wave was attempted. The method was found to be efficacious at very low voltage and energy, with 100% cardioversion success observed for 10-ms 100-V shocks (mean energy, 1.54+/-0.02 J). The PIAD waveform had a higher cardioversion success rate than a truncated, 70% tilt monophasic exponential pulse (100 V, 100% versus 78.0+/-7.57%; P=0.001). There were no postshock complications.

CONCLUSIONS

Considering these animal results, this method is promising for cardioverting AF in symptomatic patients.

Defibrillation efficacy and pain perception of two biphasic waveforms for internal cardioversion of atrial fibrillation

Efficacy and Pain Perception of Two Biphasic Waveforms.

INTRODUCTION

We evaluated the influence of the peak voltage of waveforms used for internal cardioversion of atrial fibrillation on defibrillation efficacy and pain perception. A low peak voltage biphasic waveform generated by a 500-microF capacitor with 40% tilt was compared to a standard biphasic waveform generated by a 60-microF capacitor with 80% tilt.

METHODS AND RESULTS

In 19 patients with paroxysmal atrial fibrillation (79% male, age 55 +/- 11 years, 21% with heart disease), the atrial defibrillation threshold (ADFT) was determined during deep sedation with midazolam for both waveforms in a randomized fashion using a step-up protocol. Internal cardioversion with a single lead (shock vector: coronary sinus to right atrium) was successful in 18 (95%) of 19 patients. ADFT energy and peak voltage were significantly lower for the low-voltage waveform (2.1 +/- 2.4 J vs 3.5 +/- 3.9 J, P < 0.01; 100 +/- 53 V vs 290 +/- 149 V, P < 0.01). Sedation then was reversed with flumazenil after ADFT testing. Two shocks at the ADFT (or a 3-J shock if ADFT >3 J) were administered to the patient using each waveform in random order. Pain perception was assessed using both a visual scale and a numerical score. ADFTs were above the pain threshold in 17 (94%) of 18 patients, even though the ADFT with the 500-microF waveform was <100 V in 63% of the patients. Pain perception was comparable for both waveforms (numerical score: 6.5 +/- 2.4 vs 6.3 +/- 2.6; visual scale: 5.4 +/- 2.6 vs 5.2 +/- 3.1; P = NS, 500-microF vs 60-microF). The second shock was perceived as more painful in 88% of the patients, independent of the waveform used.

CONCLUSION

Despite a 66% lower peak voltage and a 40% lower energy, the 40% tilt, 500-microF capacitor biphasic waveform did not change the pain perceived by the patient during delivery of internal cardioversion shocks. Pain perception for internal cardioversion probably is not influenced by peak voltage alone and increases with the number of applied shocks.

Transvenous internal cardioversion for atrial fibrillation: a randomized comparison between catheters with different coil 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.

Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion

OBJECTIVES

This study was performed to assess the atrial defibrillation threshold in patients with recurrent atrial fibrillation (AF) using repeated internal cardioversion.

BACKGROUND

Previous studies in patients with chronic AF undergoing internal cardioversion have shown this method to be effective and safe. However, current energy requirements might preclude patients with longer-lasting AF from being eligible for an implantable atrial defibrillator.

METHODS

Internal shocks were delivered via defibrillation electrodes placed in the right atrium (cathode) and the coronary sinus (anode) or the right atrium (cathode) and the left pulmonary artery. After cardioversion, patients were orally treated with sotalol (mean 189 +/- 63 mg/day). Eighty consecutive patients with chronic AF (mean duration 291 +/- 237 days) underwent internal cardioversion, and sinus rhythm was restored in 74 patients. Eighteen patients underwent repeated internal cardioversion using the same electrode position and shock configuration after recurrence of AF (mean duration 34 +/- 25 days).

RESULTS

In these 18 patients, the overall mean defibrillation threshold was 6.67 +/- 3.09 J for the first cardioversion and 3.83 +/- 2.62 J for the second (p = 0.003). Mean lead impedance was 55.6 +/- 5.1 ohms and 57.1 +/- 3.7 ohms, respectively (not significant). For sedation, 6.7 +/- 2.9 mg and 3.9 +/- 2.2 mg midazolam were administered intravenously (p = 0.003), and the pain score (0 = not felt, 10 = intolerable) was 5.1 +/- 1.9 and 2.7 +/- 1.8 (p = 0.001). Uni- and multivariate analyses revealed only the duration of AF before cardioversion to be of relevance, lasting 175 +/- 113 days before the first and 34 +/- 25 days before the second cardioversion in these 18 patients (p = 0.002).

CONCLUSIONS

If the duration of AF is reduced, a significant reduction in defibrillation energy requirements for internal cardioversion ensues. This might extend the group of patients eligible for an implantable atrial defibrillator despite relatively high initial defibrillation thresholds.

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.

The atrial defibrillator: a stand-alone device or part of a combined dual-chamber system?

Atrial fibrillation (AF) is an extremely common arrhythmia seen in clinical practice. Because of the limited efficacy of traditional therapeutic strategies to restore and maintain normal sinus rhythm, several nonpharmacologic options have evolved. The promising results achieved with internal atrial defibrillation have facilitated the development of an implantable atrial defibrilator. Preliminary results obtained from an initial study on a small number of highly selected patients with refractory AF suggest that atrial defibrillation can be performed effectively and safely with adequate patient tolerance by using a stand-alone device. The extension of this therapy will depend on the results of well-designed prospective studies comparing this new therapeutic option with traditional methods. Several acute studies have shown that internal conversion of AF is feasible at low energies with current endocardial transvenous lead configurations primarily designed for ventricular defibrillation, but long-term efficacy has, to date, only been demonstrated with atrial implantable defibrillator lead systems. As AF is a frequent arrhythmia in implantable cardioverter defibrillator (ICD) recipients, it would seem desirable to incorporate the capability for atrial defibrillation into an ICD. Clinical studies have shown that an atrial defibrillator, as part of a combined dual-chamber ICD system, may not require a potentially complicated switching network for establishing different electrode configurations for atrial and ventricular tachyarrhythmia. The efficacy in atrial cardioversion of such a combined, less complex device seems to be as high as reported for a pure atrial defibrillator, but generally at somewhat higher energy requirements. The results of further investigations will show whether a dual-chamber cardioverter defibrillator would be of clinical relevance in patients with ventricular and supraventricular tachyarrhythmia.

Optimization of shocking lead configuration for transvenous atrial defibrillation

INTRODUCTION

High atrial defibrillation energy requirements (ADER) in patients with chronic atrial fibrillation (AF) may limit the acceptance of transvenous atrial defibrillation. We evaluated an optimized defibrillation electrode configuration that could help to reduce the ADER in patients with AF.

METHODS AND RESULTS

We tested ten different configurations in nine dogs with AF (3.33+/-2.92 days) induced by rapid atrial pacing. The configurations were: right atrial (RA) appendage as anode and coronary sinus (CS) as cathode; RA and innominate vein (I) as anode to CS (cathode); RA-CS (anode) to I (cathode); I-CS (anode) to RA (cathode); RA and left lateral subcutaneous patch (P) as anode to CS (cathode); RA-CS (anode) to P (cathode); P-CS (anode) to RA (cathode); superior vena cava (SVC) and CS (anode) to RA (cathode); RA-CS (anode) to SVC (cathode); and RA-SVC (anode) to CS (cathode). ADER was defined as the voltage needed to defibrillate the atria in 10% to 90% of 20 consecutive shocks. Three lead systems had ADER lower than the RA (anode) to CS (cathode) configuration, which required a mean of 143+/-58 volts. These three were: RA-SVC (anode) to CS (cathode) 103+/-29 V; I-CS (anode) to RA (cathode) 129+/-39 V; and P-CS (anode) to RA (cathode) 130+/-38 V. The remaining configurations had ADER higher than the RA (anode) to CS (cathode) configuration.

CONCLUSION

Adding an additional shocking electrode may reduce ADER when compared with the RA (anode) to CS (cathode) configuration. This concept could be incorporated into future implantable atrial defibrillators or used for refractory patients undergoing temporary transvenous cardioversion.

Marked reduction in internal atrial defibrillation thresholds with dual-current pathways and sequential shocks in humans

BACKGROUND

This study tested the ability of sequential shocks delivered through dual-current pathways to lower the atrial defibrillation threshold (ADFT) compared with a biphasic shock through a standard single-current pathway.

METHODS AND RESULTS

Electrodes were positioned in the right atrial appendage (RA), left subclavian vein (LSV), proximal coronary sinus (CSos), and distal coronary sinus (DCS) in 14 patients with chronic atrial fibrillation (170+/-185 days). Using a step-up protocol, we compared ADFTs for a single-current pathway (RA-->DCS) that used a single 7.5/2.5-ms biphasic shock from a 150-microF capacitor with those for a dual-current pathway system (RA-->DCS followed by CSos-->LSV) using sequential 7.5/2.5-ms biphasic shocks with capacitor discharge waveforms for 150-microF and 600-microF capacitors. Both dual-current pathway configurations (2.0+/-0.4 J for 150-microF capacitance, 2.4+/-0.5 J for 600-microF capacitance) had a significantly lower ADFT than the single-current pathway (5.1+/-1.8 J). Whereas the dual-current pathway with 150-microF capacitor shocks had a significantly lower energy threshold, there was no statistical difference in terms of leading-edge voltage compared with the dual-current pathway with 600-microF capacitance shocks. There were no ventricular arrhythmias induced with appropriately synchronized shocks.

CONCLUSIONS

For internal atrial defibrillation in humans, sequential biphasic waveforms delivered over dual-current pathways resulted in a markedly reduced (>50% reduction) ADFT compared with a single shock over a single-current pathway.

Nonpharmacologic therapies for atrial fibrillation

The limited efficacy and proarrhythmic risks of antiarrhythmic drug therapies for atrial fibrillation have led to the exploration of a wide spectrum of alternative therapeutic approaches. The diversity of the approaches is warranted by the current absence of a single procedure that can safely and effectively cure atrial fibrillation. The interventional therapies that are currently under most active development include implantable atrial defibrillator therapy, prophylactic atrial pacing in combination with drug therapy, multisite regional pace-entrainment of atrial fibrillation by rapid pacing, atrial surgery, and catheter ablation for atrial fibrillation. The current limitations of these procedures include: (1) for the implantable atrial defibrillator--patient tolerance of low energy shocks and early recurrence of atrial fibrillation; (2) for prophylactic pacing-limited efficacy in a small proportion of the total atrial fibrillation population; (3) for multisite regional pace-entrainment--lack of proved efficacy and difficulty in the expansion and merging of the entrained regions; (4) for atrial surgery--highly invasive as a stand-alone procedure; and (5) for catheter ablation-lack of proved long-term efficacy, shortcomings of currently available technology, and risk of thromboembolic stroke. It is evident that more basic and clinical research as well as technologic innovation are needed. However, it is likely that some of these new therapies, possibly in combination with antiarrhythmic drug therapy, will offer considerable clinical benefit to selected patients with symptomatic atrial fibrillation.

Induction of atrial fibrillation with low-energy defibrillator shocks in patients with implantable cardioverter defibrillators

In a population of 151 consecutive patients who received an implantable cardioverter defibrillator, we found that atrial fibrillation was induced by low-energy shocks in 19% and was most common in patients with lead systems that included a right atrial electrode. Our finding that there was a fixed relation between the energy required to fibrillate (< or = 3 J) and defibrillate (> 3 J) suggests the presence of an upper limit of vulnerability in the human atrium.

Low-energy transvenous cardioversion of atrial fibrillation using a single atrial lead system

INTRODUCTION

Clinical studies have shown that electrical conversion of atrial fibrillation (AF) is feasible with transvenous catheter electrodes at low energies. We developed a single atrial lead system that allows atrial pacing, sensing, and defibrillation to improve and facilitate this new therapeutic option.

METHODS AND RESULTS

The lead consists of a tripolar sensing, pacing, and defibrillation system. Two defibrillation coil electrodes are positioned on a stylet-guided lead. A ring electrode located between the two coils serves as the cathode for atrial sensing and pacing. We used this lead to cardiovert patients with acute or chronic AF. The distal coil was positioned in the coronary sinus, and the proximal coil and the ring electrode in the right atrium. R wave synchronized biphasic shocks were delivered between the two coils. Atrial signal detection and pacing were performed using the proximal coil and the ring electrode. Eight patients with acute AF (38 +/- 9 min) and eight patients with chronic AF (6.6 +/- 5 months) were included. The fluoroscopy time for lead placement was 3.5 +/- 4.3 minutes. The atrial defibrillation threshold was 2.0 +/- 1.4 J for patients with acute AF and 9.2 +/- 5.9 J for patients with chronic AF (P < 0.01). The signal amplitude detected was 1.7 +/- 1.1 mV during AF and 4.0 +/- 2.9 mV after restoration of sinus rhythm (P < 0.001). Atrial pacing was feasible at a threshold of 4.4 +/- 3.3 V (0.5-msec pulse width).

CONCLUSIONS

Atrial signal detection, atrial pacing, and low-energy atrial defibrillation using this single atrial lead system is feasible in various clinical settings. This system might lead to a simpler, less invasive approach for internal atrial cardioversion.

Testing different biphasic waveforms and capacitances: effect on atrial defibrillation threshold and pain perception

OBJECTIVES

The goal of this study was to compare the effect of different tilts and capacitances for biphasic shocks on atrial defibrillation efficacy and pain threshold.

BACKGROUND

Although biphasic shocks have been shown to be superior to monophasic shocks, the effect of tilt and capacitance on atrial defibrillation success and pain perception has not been studied in patients.

METHODS

Atrial defibrillation threshold (DFT) testing was performed using a right atrial appendage/coronary sinus lead configuration in 38 patients with a history of paroxysmal atrial fibrillation undergoing an invasive electrophysiologic study. Biphasic waveforms with 40%, 50%, 65%, 80%, 30%/50% and 40%/50% were tested randomly in 22 patients (Group 1). In 16 patients (Group 2), a 65% tilt waveform with 50- and 120-microF capacitance was tested. Before sedation, pain sensation was graded by 15 patients in Group 1 after delivery of a 0.5-J shock and by 10 patients in Group 2 after two 1.5-J shocks with 50- and 120-microF capacitance were delivered.

RESULTS

The DFT energy for the 50% tilt waveform was significantly lower than the 65%, 80% and 30%/50% tilt waveforms. The 40%/50% tilt waveform provided slightly lower energy requirements than the 50% tilt waveform. Nine patients (60%) described the 0.5-J shock as very painful, and four (26.6%) complained of slight pain. The 50-microF capacitor lowered energy requirements compared with the 120-microF capacitor. Six patients (60%) perceived the 1.5-J 50-microF capacitor shock as more painful, whereas three (30%) perceived both shocks as equally painful.

CONCLUSIONS

Biphasic waveforms with 50% tilt in both phases and a smaller tilt in the positive phase than that in the negative phase (40%/50%) provided a decrease in energy requirements at atrial DFT. In addition, stored energy was reduced by biphasic shocks with 50-microF capacitance compared with 120-microF capacitance. Despite the reduction in energy requirements, shocks < 1 J continued to be perceived as painful in the majority of patients.