DC CARDIOVERSION
Four years experience of a nurse-led elective cardioversion service within a district general hospital setting
Department of Cardiology, Castle Hill Hospital Cottingham, Kingston-upon-Hull HU16 5JQ UK ; Department of Anaesthetics, Castle Hill Hospital Kingston-upon-Hull UK
Manuscript submitted 7 February 2005. Accepted after revision 9 September 2005.
Corresponding author. Tel: +44 1482 624073; fax: +44 7092 840055. E-mail address: rhidianshelton{at}btopenworld.com
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Abstract |
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Aims External direct current cardioversion is an effective method of restoring sinus rhythm (SR) in patients with persistent atrial arrhythmias. Increasing demand for hospital beds, together with a reduction in junior doctors' hours, has adversely affected cardioversion provision. A regular nurse-led cardioversion service conducted in a dedicated hospital day-unit was introduced to resolve these constraints. There are limited data on the safety or efficacy of such a service.
Methods and results All cardioversions between October 2000 and October 2004 were performed by an appropriately trained specialist nurse, under general anaesthesia. Patients attended a pre-assessment clinic. Energy requirements for initial and subsequent defibrillations were guided by a local protocol in accordance with the guidelines from American Heart Association, American College of Cardiology, and the European Society of Cardiology. Rectilinear biphasic defibrillation was introduced in January 2004 with an appropriate protocol amendment. In the absence of complications, the aim was to discharge patients the same day. A total of 578 cardioversions (475 monophasic; 103 biphasic) were performed on 464 patients [72.1% male, mean (±SD) age 67.8±9.4 years] with atrial fibrillation (AF) (89.7%) and atrial flutter (10.3%). SR was restored in 84.0 and 100% of patients with AF and atrial flutter, respectively, which increased to 90.2 and 100% following the introduction of biphasic defibrillation. Biphasic shocks cardioverted AF with less energy (163±22 vs. 289±81 J) and less cumulative energy (230±139 vs. 455±255 J) than monophasic (P<0.001 for both), despite no difference in the duration of AF (P=0.26) or patient age (P=0.78). Two patients required hospital admission due to transient bradycardia; both were discharged within 72 h, without the need for permanent pacing. A total of 99.6% of patients was discharged home the same day; there were no deaths.
Conclusion The provision of a nurse-led elective cardioversion service is feasible and effective, without compromising safety.
Key Words: Atrial fibrillation, Atrial flutter, Cardioversion
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Introduction |
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Atrial fibrillation (AF) and atrial flutter are common arrhythmias,1
,2 associated with significant morbidity and mortality.3,4 Transthoracic or ‘external’ direct current (DC) cardioversion, a procedure traditionally performed by junior doctors, is an effective method of restoring sinus rhythm (SR).5
The provision of an elective cardioversion service within the UK has been compromised by an increasing demand for hospital beds together with a reduction in junior doctor working hours. Strategies to counteract these constraints include further expansion of the role of nurse specialists to include elective cardioversion. Recently, published data suggest that a cardioversion service (performed under deep sedation) provided by specialist nurses without direct physician supervision is effective in addressing these issues.6,7
Nurse-led cardioversion performed under general anaesthesia was introduced to relieve the pressures imposed by limited resources without compromising patient care and cardioversion efficacy, and to provide patients with an effective and efficient service operated by highly trained nurse specialists.
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Methods |
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We report our experience of 464 consecutive patients undergoing elective DC cardioversion between October 2000 and October 2004. All cardioversions were performed by a nurse specialist. No patients were selected or deemed unsuitable to proceed solely on the basis of the health professional performing the procedure.
Two experienced senior nurses (with Advanced Life Support certification) were identified to undertake training in external cardioversion. An initial period of physician supervised cardioversions was required prior to becoming an independent operator.
Patients attended a pre-assessment clinic 4 days prior to the procedure. Blood was taken for international normalized ratio (INR) and serum potassium analysis. Cardiac rhythm was confirmed by electrocardiography and at least 6 weeks anticoagulation adequacy (INR 
2.0 and 
4.0) assessed. All patients were anticoagulated using warfarin. A preliminary anaesthetic assessment was undertaken by the specialist nurse. Medical history and current medication was documented. Written informed consent was taken in all cases. Cardioversion was postponed in patients with suboptimal anticoagulation (INR <2.0), low serum potassium (<3.5 mmol/L), or intercurrent illness. Patients were advised to discontinue digoxin 3 days prior to cardioversion and beta-blockers 1 day prior.
A short period of general anaesthesia was achieved using standard recommended techniques by an anaesthetist; the anaesthetic agent of choice was propofol. Owing to the regular nature of the cardioversion service, a dedicated anaesthetist was available to cover all sessions.
All cardioversions conducted prior to January 2004 used damped sine wave monophasic DC defibrillation (Zoll Medical, USA). Subsequent defibrillations were performed using rectilinear biphasic DC defibrillation (Agilent Technologies Inc., USA). All defibrillations were ‘R-wave’ synchronized, with energy levels being protocol guided, in accordance with joint guidelines from American Heart Association (AHA), American College of Cardiology (ACC), and the European Society of Cardiology (ESC).8 For AF, a monophasic defibrillation regime of 200, 360, and 360 J; and biphasic regime of 150, 200, and 200 J was used. The regime for atrial flutter was 50, 100, 200, and 360 J using monophasic defibrillation, and 20, 50, 100, and 150 J using biphasic. Cardioversion was conducted using adhesive electrode pads (3M Healthcare, Minnesota, USA) with paddles placed in the anterolateral position in all patients. Continuous ECG monitoring was used throughout the procedure with the decision for further defibrillation based on single lead rhythm strip analysis.
Successful defibrillation was defined as the continued presence of SR for at least 60 min following cardioversion. SR was confirmed by performing a 12-lead ECG on return to the day-unit and prior to discharge (1–2 h following the procedure). The decision to discharge was taken by the nurse specialist responsible for performing the cardioversion. Any decision to alter medication (e.g. discontinuation of digoxin) was made following a discussion with the responsible physician.
Guidelines were in place for the management of an adverse event while under anaesthesia or following return to the day-unit. In the event of a cardiac arrest or peri-arrest situation, the cardiac arrest team were to be contacted. The responsible physician would be contacted for all other events. Specialist nurses and anaesthetists were trained in advanced cardiac life support.
Statistical analysis
Discrete variables are expressed as frequency counts and percentages while continuous variables are expressed as means and standard deviations (±SD). Standard descriptive statistics including frequency distributions are used when summarizing group characteristics. Student's t-test and 
2 test were used to determine differences between patient groups with respect to defibrillation type and cardiac rhythm. A probability value of P<0.05 was considered significant.
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Results |
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A total of 578 cardioversions was performed on 464 patients over a 4-year period. Most patients were white males, with arrhythmia duration ranging from 1 month to 20 years. Clinical characteristics are shown in Table 1.
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Efficacy
A total of 475 cardioversions was performed using a monophasic defibrillator and 103 using a biphasic defibrillator. For monophasic defibrillation, cardioversion was successful in 83.7 and 100% of patients with AF and atrial flutter, respectively. This improved to 90.0 and 100%, respectively, following the introduction of biphasic defibrillation (Table 2). There was no statistical difference in rates of success between monophasic and biphasic cardioversion (P=0.18; OR 1.8, 95% CI 0.8–3.9).
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The mean number of shocks required for success was 1.7 (±0.7) and 1.4 (±0.7) (monophasic and biphasic, respectively) for AF, plus 1.8 (±1.2) and 1.9 (±1.0) shocks, respectively, for atrial flutter. Mean energy requirements for successful cardioversion of AF were less for biphasic defibrillation than monophasic (163±22 vs. 289±80 J, P<0.001). Similarly, less energy was required to convert atrial flutter to SR (72±56 vs. 139±111 J, P=0.003) using biphasic defibrillation. Cumulative energy requirements were also reduced by biphasic defibrillation (230±139 vs. 455±255 J, P<0.001) and (115±107 vs. 250±268 J, P=0.008) for AF and atrial flutter, respectively (Table 3).
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The reduction in energy required for cardioversion of AF using biphasic defibrillation was achieved despite no difference in success rates (83.7 vs. 90.0%, P=0.18; OR 1.8, 95% CI 0.8–3.9); patient age (68.5±9.2 vs. 68.2±9.4 years, P=0.78), or AF duration (15.7±36.2 vs. 12.2±16.3, P=0.39); monophasic vs. biphasic, respectively.
Overview of defibrillation outcomes (AF)
Figures 1 and 2 show the outcome of cardioversion at increasing energy levels, for monophasic and biphasic defibrillation. Altogether 158 (36%) patients cardioverted with an initial 200 J monophasic shock compared with 53 (65%) patients with a 150 J biphasic shock. A total of 354 patients required at least two shocks. Of the 278 unsuccessful initial 200 J monophasic shocks, 207 (74%) were subsequently successful using 360 J. Similarly, 21 (72%) patients successfully cardioverted with at least one 200 J biphasic shock following an unsuccessful initial attempt with 150 J. There seemed little benefit in performing more than two monophasic defibrillations at 360 J.
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Predictors of success (AF)
Table 4 shows the relationships between several variables and successful cardioversion of AF. The calculated unadjusted odds ratios show a trend towards unsuccessful cardioversion for patients of male sex with hypertension, AF of longer duration, mitral valve disease, and heart failure. However, the odds ratios for these were not significant. On univariate analysis, left atrial size was significantly greater in patients with AF whose cardioversion was unsuccessful (5.1±0.7 vs. 4.7±0.6 cm, P<0.001).
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Safety and complications
A total of 99.6% of patients was discharged home from the day-unit on the same day as the procedure. Only two patients suffered an adverse event requiring hospitalization. Both suffered a prolonged period of bradycardia associated with hypotension following cardioversion. Intravenous fluids and drug treatment were successful in restoring adequate haemodynamics in both cases. Neither patient required temporary or permanent pacing. Both patients were discharged from hospital within 72 h of undergoing cardioversion.
There were no complications associated with short-acting general anaesthesia, and no reported thromboembolic events at the time of, or following the procedure. No deaths resulted from elective DC cardioversion. However, these data may be incomplete because patients were not routinely followed after cardioversion.
Adjuvant antiarrhythmic medication
Antiarrythmic medication consisted of amiodarone, sotalol, flecanide, beta-blockers, and calcium antagonists. One hundred and eight (23.3%) patients were not prescribed either an antiarrhythmic or rate controlling medication at the time of cardioversion. A total of 154 (26.6%) and 167 (28.9%) patients were prescribed digoxin and beta-blockers (excluding sotalol), respectively. Further antiarrythmic medication data are shown in Table 5.
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Procedure waiting time
It is difficult to assess the impact of nurse-led cardioversion upon procedure waiting time due to the influence of several confounding factors. Analysis takes into account an initial period of administrative improvement together with the later impact of several randomized trials of rate vs. rhythm control upon cardioversion referrals. Patient waiting time (assessed using twenty randomly selected patients within a 3-month period) prior to the introduction of nurse-led cardioversion (September 2000) was 21.4 (±6.6) weeks. This fell to 13.6 (±5.5) weeks in December 2002 (prior to publication of the AFFIRM trial9
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Discussion |
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Our experience of nurse-led elective cardioversion performed under general anaesthesia has shown it to be feasible, safe, and effective. As expected, a regular dedicated service provided by specialist nurses and performed in a proficient day-unit reduces patient waiting time; which previously suffered from the provision of junior doctors on an ad hoc basis.
Concerns that cardioversion performed by highly trained nurses (in the presence of an anaesthetist) would compromise safety are unfounded. Less than 0.5% of patients suffered an adverse event, which compares favourably with previously published data.6,10 Transient bradycardia was the predominant complication; however, data regarding delayed thrombo-embolic events may not be complete due to inconsistent patient follow-up. It should be stressed that care was taken to ensure that all patients attended a pre-assessment clinic and staff strictly adhered to protocols.
It is widely accepted that cardioversion should be performed under a brief period of general anaesthesia or deep sedation. In order not to compromise safety, this should be performed by a suitably qualified physician with advanced airway management skills i.e. an anaesthetist.11 Our hospital protocol for cardioversion requires the use of general anaesthesia. General anaesthesia has several advantages over deep sedation including a proven safety and tolerability record.12 Its effects are more predictable compared with intravenous benzodiazepines. Current guidelines recommend an anaesthetist be present for procedures involving deep sedation in case of airway complications (Royal College of Anaesthetists).13 In addition, many patients with AF have co-existing cardio-respiratory disease, and may be subjected to an increased and unnecessary risk if deep sedation is used.
Although cardioversion under ‘deep’ sedation seems an attractive option, concern will remain regarding its safety.14 Cardioversion performed under general anaesthesia, may be more practical, more feasible, and ultimately safer, although more expensive. In addition, nurse-led cardioversion under general anaesthesia may prove easier to implement than a service using deep sedation, with further training of nurse specialists in the technique of sedation being not necessary. A process of regular audit, assessment, and training will be required for nurses to perform cardioversions, whichever anaesthetic method is used. Whether nurses will deem the increased responsibility of cardioversion plus sedation to be excessive and unacceptable is not yet known.
Cardioversion, whether performed using monophasic or biphasic defibrillation, is highly effective at restoring SR. The benefits of biphasic cardioversion relate to its reduction in number of shocks delivered, energy requirement, and less dermal injury, with equivocal or superior efficacy.15–17 Evidence is accumulating to support the theoretical reduction in myocardial stunning or damage with biphasic defibrillation,18–20 whether this translates into clinical benefit remains to be seen.
The efficient provision of an elective outpatient cardioversion service is dependent upon the majority of patients being discharged promptly from hospital, without compromising safety. In our experience, over 99% of patients were discharged home the same day as the procedure. Despite the improvements in service delivery afforded by a nurse-led service, several barriers to further reduction of procedure waiting time remain, including the regular provision of an anaesthetist and a significant administrative component necessary to optimize service efficacy. These factors may explain why the waiting times reported did not fall to the levels seen in other similar studies.6
Limitations
Although external cardioversion appears to be a very safe procedure, patients in our report were not routinely followed following cardioversion. As a result, we are unable to comment on the medium to long-term safety of nurse-led cardioversion.
Patients were not randomly assigned to receive monophasic or biphasic defibrillation. Rather, the first 475 patients were treated with monophasic defibrillation; the subsequent 103 patients received biphasic defibrillation. However, comparison of clinical characteristics in these patients did not reveal statistically significant differences. Moreover, as patients in this report represent a consecutive series over a 4-year period, selection bias is eliminated.
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Conclusion |
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Nurse-led cardioversion under general anaesthesia offers a practical and safe solution to the constraints imposed upon an elective cardioversion service by insufficient resources.
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References |
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