Use of Sedation During Cardioversion With the Implantable Atrial Defibrillator
Background—The low shock energy used during internal atrial defibrillation may decrease the need for sedation during defibrillation with an implantable atrial defibrillator.
Methods and Results—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.
Conclusions—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.
Maintaining sinus rhythm is an important goal in the management of atrial fibrillation (AF). Some of the initial skepticism regarding the value of an implantable atrial defibrillator has been answered by a recent multicenter study using the Metrix Atrioverter (InControl Inc).1 This study reported, in a selected group of patients with recurrent AF, accuracy of AF detection, successful cardioversion of AF, and no ventricular proarrhythmia during shock delivery. However, issues such as patient selection, therapy tolerability, effect on patient’s quality of life, and cost effectiveness need to be addressed before determining the true value of this device. The objective of this study was to evaluate the use of sedation during defibrillation with the Atrioverter as a measure of therapy tolerability.
Twelve patients with recurrent symptomatic AF and an estimated AF episode frequency ranging from 1 week to 3 months underwent implantation of the Metrix Atrioverter at a single center (Table 1⇓). In the first 10 patients, the criteria used for Atrioverter implantation were as outlined in the initial Atrioverter trial.1 The device was thereafter implanted in a patient with tachycardia-induced cardiomyopathy and in a patient with a mitral valve replacement.2 Shock discomfort during preimplant evaluation was not an exclusion criteria. After device implantation, the patients continued to receive antiarrhythmic drugs as needed. At the completion of this study in October 1998, the mean follow-up duration was 17.3±6.5 months (range, 5 to 25 months).
Only spontaneous AF episodes for which cardioversion with the Atrioverter was attempted were analyzed. Biphasic shocks with a programmable voltage (200, 240, 260, or 300 V) were delivered to treat AF episodes. Shocks were delivered between coil electrodes, 1 in the right atrium and 1 in the coronary sinus. During at least the first 3 months after implantation, the device was programmed in monitoring mode, and all shocks were delivered in the presence of a physician. Patients were forewarned when the device was activated to deliver therapy. Sedation was not used on a routine basis, but it was provided on patient request; intravenous midazolam, etomidate, or diazepam was used. In cases of failure to restore sinus rhythm or when immediate reinitiation of AF occurred (IRAF),3 intravenous flecainide (50 to 150 mg) or sotalol (40 to 120 mg) was given before the next shock.
The Atrioverter was programmed for out-of-hospital therapy in 4 patients. These 4 patients had frequent episodes of AF (2.7±1.8 AF episodes/month) that were treated initially in-hospital with the Atrioverter. Ambulatory use of the device was considered for the convenience of the patient. The device was programmed to deliver 1 shock of 300 V in 3 patients and 2 shocks of 300 V in the remaining patient. Patients were instructed to come to the hospital for further treatment of an AF episode if the programmed shock(s) failed to restore sinus rhythm.
Results are expressed as mean±SD. Continuous variables were compared using Student’s t test or ANOVA for unpaired samples. All results were considered significant at P<0.05.
During a mean follow-up of 17.3±6.5 months, 12 patients were treated for 213 spontaneous episodes of AF for which 393 shocks were delivered (mean, 1.8±1.6 shocks/AF episode; median, 1 shock/AF episode) by the Atrioverter (Table 2⇓). No differences existed between the patients with respect to the mean number of delivered shocks per AF episode (P=0.25). Overall, the device successfully terminated 195 AF episodes (92%), usually using a single 300-V shock. During ambulatory therapy, the Atrioverter restored sinus rhythm for 66 of the 85 AF episodes (78%). For the remaining 19 episodes, subsequent device therapy successfully restored sinus rhythm when the patients came to the hospital. During the treatment of 45 of 213 AF episodes (21%), IRAF was observed.
Five of the 12 patients did not request sedation during the treatment of any AF episode. Sedation was requested by the remaining 7 patients during the treatment of 26 of 213 AF episodes (12%; 75 of 393 shocks, 19%). No sedation was required during the treatment of 187 AF episodes (88%). Furthermore, for the 85 episodes treated while the patients were away from the hospital, no sedation was required.
Conscious sedation was provided using intravenous midazolam (19 AF episodes), etomidate (5 AF episodes), or diazepam (2 AF episodes), with a mean dose of 5.7±6 (range, 2 to 30), 22±8 (range, 8 to 40), and 10±7 (range, 5 to 15) mg, respectively. In general, sedation was needed only when a greater number of shocks was needed to treat an AF episode (4.3±2.1 shocks for AF episodes requiring sedation versus 2±1 shocks for AF episodes requiring no sedation; P<0.001). As illustrated in the Figure⇓, the percentage of AF episodes requiring sedation increased as the number of shocks delivered per AF episode increased. Sedation was requested during the treatment of 30% of AF episodes requiring >3 shocks.
The most frequent cause for sedation was the delivery of multiple shocks required to treat IRAF (14 of 26 episodes). Other reasons for the use of sedation included a request for sedation before the delivery of the first therapeutic shock (8 of 26 episodes) and initial failure to cardiovert (4 of 26 episodes).
Internal atrial defibrillation was initially considered a method that would diminish the need for sedation by decreasing the shock intensity required for successful cardioversion. However, in an early study of this technique in which defibrillation thresholds were determined using a step-up defibrillation protocol, the majority of the patients required sedation.4 Conversely, other studies have shown that low-energy internal atrial defibrillation can be performed in most cases without sedation.5 6 Lok et al5 suggested that the number of shocks substantially affects discomfort and that 2 to 3 shocks are usually tolerated. Therefore, it is likely that the number of shocks, as much as their individual intensity, affect patient discomfort. In the present study, Atrioverter therapy could be delivered without sedation when 2±1 shocks/AF episode were delivered, but sedation was used when 4.3±2.1 shocks were required per AF episode. As shown in the Figure⇑, the request for sedation increased with the number of shocks delivered to treat an AF episode. Furthermore, sedation was required at one time or another by 7 of the 12 patients, but only during the treatment of 26 of 213 AF episodes (12%). These findings further indicate a relationship between the number of shocks delivered and the need for sedation.
Controlling the reasons for patients to request sedation during Atrioverter therapy will improve the acceptance of the device. Because IRAF was the most frequent cause for the delivery of additional shocks and, consequently, for the use of sedation during Atrioverter therapy, successful management of IRAF could further decrease the need for sedation and improve overall acceptance of the therapy. Suppression or prevention of premature atrial complexes that initiate AF by pharmacological therapy,3 ablation,7 or pacing may preserve sinus rhythm after successful cardioversion without the need for additional shocks. Also, requests for sedation before delivery of the first shock could be decreased by psychologically preparing the patient, early initiation of ambulatory therapy to encourage self-confidence and, when necessary, through the use of anxiolytic drugs. Further improvements in device technology8 and a better understanding of the influence of concomitant therapy may contribute to lowering the defibrillation threshold. Lowering the defibrillation threshold could increase the rate of successful cardioversion at lower energies, which in turn, may reduce the need for sedation during Atrioverter therapy.
Overall patient acceptance of this therapy and individual shock tolerability, as determined by using a questionnaire, were not evaluated during this study. What was measured was the need, on the basis of patient request, for agents intended to relieve the discomfort of the therapy. However, it is important to note that patients continued to desire to receive Atrioverter therapy without sedation, even when sedation may have been required for a prior episode. This finding is indicative of, but not conclusive for, overall Atrioverter patient tolerability.
This study suggests that, in a selected group of patients, AF episodes can be successfully treated with the Atrioverter without the use of sedation. Successful ambulatory treatment of AF episodes with the Atrioverter, programmed to deliver ≤2 shocks, did not require sedation. When multiple shocks are required for the treatment of an AF episode, the need for sedation increases. Reduction in threshold may reduce the discomfort caused by individual shocks; however, future efforts should be focused on reducing the number of shocks. Additionally, future studies are needed to evaluate the patients’ perceived quality of life and overall patient acceptance of therapy.
- Copyright © 1999 by American Heart Association
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