A stepwise external cardioversion protocol for atrial fibrillation to maximize acute success rate (2024)

Aims

Cardioversion is a very commonly performed procedure for persistent atrial fibrillation (AF). However, there is no well-defined protocol to address failed external electrical direct current cardioversion. The aim of the study is to test the efficacy of a pre-defined stepwise cardioversion protocol for patients with persistent AF of ≤12 months. Success was the achievement of sinus rhythm.

Methods and results

The study population included patients with persistent AF of ≤12 months duration requiring rhythm management. Patients were offered cardioversion using a pre-defined stepwise protocol using different electrode placement locations, applying compression at end of expiration, and higher energy delivered simultaneously through two defibrillators. : A total of 414 patients were included in the study, of which 362 (87.4%) required a single successful cardioversion. The remaining 52 (12.5%) patients required additional cardioversion attempts using the stepwise cardioversion protocol with an overall success rate of 99.3%. Two simultaneous defibrillators were required in 14 patients (3.4%). Patients with multiple cardioversions (13.5%) experienced more local skin irritation and pain compared with patients with single cardioversion (13.5% vs. 3.5%, P = 0.004). The predictor for the need for multiple cardioversion attempts is high body mass index, while high transthoracic impedance is associated with failed cardioversion. No major complications were observed during the study.

Conclusion

The stepwise cardioversion protocol has a high success rate of >99% and can be safely performed in outpatient or inpatient settings.

Keywords: Atrial fibrillation, External direct current cardioversion, Transthoracic impedance

Study cohort and design

All consecutive patients requiring EDCCV as indicated for the rhythm management of pers-AF of ≤12 months duration were offered to participate in this study. These included patients presenting as outpatients for elective cardioversion or inpatients requiring an EDCCV at the University of Kentucky for a 3-year duration (2017–2020). Patients were excluded if they were <18 years old, pregnant, have untreated hyperthyroidism, required emergent cardioversion with unstable haemodynamics, or were unable to consent. In addition, patients with a typical or atypical atrial flutter at the time of EDCCV were not included in the analysis of this study. Data collected include demographic findings, co-morbidities, medication use, and energy/impedance/current used during cardioversion. All patients who participated in the study signed informed consent for the stepwise EDCCV protocol. The study was approved by the institutional review board.

Cardioversion procedure

Patients fasted for at least 6 h; electrolytes (particularly serum potassium) were checked and replaced as needed before cardioversion. Patients with acute congestive heart failure were optimized with medical therapy and diuresis prior to cardioversion. Digoxin was typically not used at our institution,^9,10 but if used, it was discontinued at least 24 h before EDCCV.¹¹ All patients were anticoagulated for at least 3 weeks before the procedure following the guidelines to prevent thromboembolism¹ or had transoesophageal echocardiography before the EDCCV to rule out left atrial appendage thrombus.¹² Synchronized direct current biphasic cardioversion was performed while the patient is under conscious sedation (using intravenous midazolam, fentanyl, or Methohexital) with continuous monitoring of blood pressure, heart rate, heart rhythm, oxygen saturation, and capnography.

Cardioversion protocol

The protocol used the following stepwise approach (Figure 1). Step 1: use of synchronized biphasic shock of 200 J (ZOLL Medical Corporation, Chelmsford, MA, USA) using self-adhesive gel electrodes in the anteroposterior location (anterior location of the pad in left infraclavicular area, posterior pad in the left lower scapular region with the electrode edge left to the spinal column; see Figure 2A). We placed the anterior electrode at least 2 inches away from an implanted pacemaker or defibrillator. We elected to use 200 J rather than escalating energy (100-150-200 J) to maximize the success rate of the first shock.¹³

Step 2: deliver 200 J by exerting compression on the anterior transcutaneous electrode at the time of shock at the end of expiration to decrease TTI. Compression was applied in a standing position by the operator using a force of ∼80 N (8 kg; roughly equivalent to the force of a ‘push up’).^14,15

Step 3: reposition the anterior electrode from the left infraclavicular to the right parasternal area¹⁶ (see Figure 2B) and deliver 200 J with external compression at end-expiration as described in Step 2.

Step 4: use two external defibrillators simultaneously with electrodes placed in the anteroposterior location (one anterior electrode in the right parasternal and the other in the left infraclavicular location with both posterior electrodes in the left parascapular area, vectors of both pairs of electrodes should cross as shown in Figure 2C to deliver a higher total number of joules across the atrial tissue (200 J × 2 with external compression at end-expiration as described above). The energy delivery buttons on both defibrillators were pushed simultaneously by a single operator.

If the above steps fail, the patient is started on anti-arrhythmic therapy (AAD) or changed to amiodarone if already on other AAD and brought back for a second attempt using the above protocol starting at Step 4.

Step 5: If the above steps are unsuccessful, the patient was brought to the EP lab to position the electrodes using fluoroscopy. A metallic marker (quarter coin) is placed on the patient’s chest to determine the best location of the electrodes in relation to the heart border on at least two different views [anterior-posterior (AP) and left anterior oblique] to position the electrodes of both defibrillators. The EDCCV is then performed as described in Step 4.

Endpoints

The primary endpoint is the proportion of patients achieving sinus rhythm of any duration using the stepwise cardioversion protocol. Secondary endpoints included a safety outcome and a skin/pain outcome. The safety outcome is the occurrence of arrhythmic events (asystole > 5 s, transient severe bradycardia defined as a heart rate <40 b.p.m. or sustained ventricular arrhythmia)¹⁷ during or after cardioversion detected within 2 h of monitoring as well as the occurrence of pulmonary oedema, acute coronary event, and cerebrovascular accident within 24 h.

In addition, skin erythema and pain (using a visual analogue pain scale) under the transcutaneous electrodes were estimated by a nurse 2 h after cardioversion and characterized as mild (not requiring additional treatment) or moderate/severe (requiring additional treatment). Treatment included the application of local cream or the administration of an oral analgesic agent.

Statistical analysis

A literature review showed that the cardioversion failure rate for AF is about 10%. We expected that our stepwise cardioversion protocol will reduce the cardioversion failure rate to at least 5% (i.e. 50% reduction). Therefore, we estimated the sample size as 381 patients with an 80% power. Results were expressed as numbers (per cent), mean ± standard deviation, or median (interquartile range). Dichotomous variables were compared with Fisher’s exact test two-tailed; continuous variables normally distributed numeric variables were compared with an unpaired t-test, and non-normally distributed variables with a nonparametric rank-sum test. Multiple logistic regression analysis studied the association of clinical variables with cardioversion success after retaining all variables statistically significant in univariate analysis. A two-sided P-value <0.05 was considered significant. Data analysis was performed using Excel 2013 (Microsoft Corp., Redmond, WA, USA), Version 9.3 of SAS (SAS Institute, Cary, NC, USA), and online applets from GraphPad (GraphPad Software, La Jolla, CA, USA).

Table 1.

Patient baseline and cardioversion characteristics

Table 2.

Patient baseline characteristics comparing one direct current cardioversion (Group A) vs. >1 direct current cardioversion (Group B)

Table 3.

Cardioversion values of the first attempt compared between both groups

Predictors requiring more than one step for successful cardioversion

Patients who required more than a single cardioversion attempt are younger (57.6 ± 10.8 vs. 63.1 ± 12.4, P = 0.0027) and have a higher BMI (41.4 ± 13.2 vs. 32.3 ± 7.6 kg/m², P = 0.0001). Using multivariable logistic regression, BMI is a predictor of cardioversion success (P < 0.001) but age is not (P = 0.88). Also, a BMI of ≥30, ≥35, and ≥40 kg/m² is associated with a 1.87, 2.50, and 4.9 relative risk of requiring more than one cardioversion attempt, respectively.

Secondary endpoints

Safety outcome: There were no significant cases of arrhythmia that required intervention after cardioversion in both groups with the one exception mentioned below. Four patients developed transient bradycardia (0.97%; 2 in Group A and 2 in Group B). One patient developed asystole that responded to atropine (Group A). One patient had worsening heart failure symptoms after the cardioversion (Group B). One patient developed an intracranial haemorrhage in Group B as described above but this happened 2 weeks after the cardioversion, so it is not included as a safety outcome. Overall, there was no statistical difference between Groups A and B. Cutaneous erythema/pain: 19 patients (4.6%) required additional care with medication for skin erythema and pain. Among these, 12 patients (3.3%) were in Group A vs. 7 patients (13.5%) in Group B, P = 0.004.

Main findings

The overall success rate of the stepwise cardioversion protocol to restore sinus rhythm acutely is 99.3% (411/414). About 12.6% (52/414) of patients failed the first cardioversion attempt and required more than one shock to restore sinus rhythm. Two simultaneous defibrillators were required in 3.4% of patients (14/414). Patients with multiple cardioversions 13.5% (7/52) experienced more local skin irritation and pain compared with patients with a single cardioversion 3.3% (12/362), P = 0.004. A high BMI was the only clinical predictor of the need for more than one cardioversion attempt in univariate and multivariate analyses. A BMI of ≥40 kg/m² is associated with a 4.9 relative risk of needing more than one cardioversion.

A systematic approach to cardioversion

The main finding of our study is that a stepwise protocol for EDCVV was able to acutely restore sinus rhythm in >99% of patients. Our protocol incorporates all techniques known to increase the cardioversion success rate. Therefore, the use of this well-defined stepwise protocol is associated with a high success rate and may potentially lead to better clinical outcomes and improved quality of life among pers-AF patients.

Factors influencing cardioversion success

The success of cardioversion depends on multiple factors and can be classified as operator-dependent and patient-related (primarily BMI). The operator-dependent factors include optimal electrode position, use of active compression, delivery of the EDCCV at end of expiration, use of two defibrillators, the addition of AADs, and the use of fluoroscopy to guide cardioversion pads’ position. The position of the transcutaneous electrodes determines TTI which in turn affects the flow of current across atrial tissue during electric shock. TTI was found to be a predictor of cardioversion success, where lower values are associated with a higher success rate.¹⁸ The cardioversion pads’ position is optimal when the shock vector between the pads encompasses the atria (Figure 2). The AP placement of the pads is commonly used, based on previously published data.¹⁹ We did not use an anterior-lateral (AL) placement due to the paucity of data to support the effectiveness of such as approach at the time of designing the protocol. Multiple studies have been conducted to compare the success rate between AP and AL locations, but the results are conflicting.^20,21,22 The RAFF2 (Electrical Versus Pharmacological Cardioversion for Emergency Department Patients with Acute Atrial Fibrillation)²³ found that there was no difference between both locations in achieving cardioversion success. However, a meta-analysis by Zhang et al.²² found that the AP location has higher cardioversion success over AL location in patients with lone AF and LA size of <45 mm. Furthermore, a study showed that TTI was significantly lower with the AP electrode position compared with the AL electrode position, with a higher success of cardioversion in the AP location.²⁴ Therefore, the use of the AP location is a reasonable first attempt approach in cardioversion unless it is not feasible (for example, during a cardiac ablation procedure or with the presence of a cardiac implantable elctronic device).

Another factor for cardioversions’ success is the applying compression on the transcutaneous electrodes during shock delivery.^3,14 The use of active compression during cardioversion decreases TTI by improving contact with skin and decreasing thoracic volume and has been shown to increase the success rate of EDCCV by 12%.¹⁴ In our study, active compression was used and applied at end-expiration to allow energy deliver at the lowest possible thoracic volume which is associated with lower TTI. The use of higher energy with two simultaneous defibrillators can also improve EDDCV success rate, but it may be associated with more cutaneous burns. The patients in Group B experienced more local erythema and discomfort and required additional treatment, but none of the cohort patients developed severe skin lesions. Furthermore, the use of biphasic energy for EDDCV with a maximum of 200 J is associated with less skin injury compared with the use of monophasic energy at 360 J.²⁵

Meanwhile, patient-related factors for successful EDCCV include primarily high BMI and male gender.²⁶ In our study, there was no difference between genders with regards to success rate, but higher BMI was associated with the need for more than one cardioversion attempt. Obesity impedes the delivery of adequate direct current energy to the atrial tissue and increases TTI, which can be overcome by applying additional energy. Dual external cardioversion using biphasic shock is a safe and effective strategy in patients with large body habitus.^7,27 In our study, the mean BMI in a patient that required the use of two simultaneous defibrillators was 56.2 ± 9.51 while the remaining patients in Group B had a mean BMI of 35.9 ± 9.81 (P < 0.0001).

Finally, the use of anti-arrhythmic drugs has been shown to increase the success rate of EDCCV in a recent study.²⁸ In our study, anti-arrhythmic drugs were part of the stepwise protocol if Step 4 failed for patients not already on such medications.

Safety of the stepwise cardioversion protocol

Cardioversion is generally considered a safe procedure. Even the use of multiple shocks in the same session was not associated with increased mortality in an analysis of the AFFIRM study.⁹ However, adverse events may occur after EDCCV. Most are transient such as hypoxia and hypotension related to sedation or are relatively benign such as skin irritation or mild burns. However, there is a small possibility of having ST segment and T wave changes, arrhythmia and conduction abnormalities, significant bradycardia, thromboembolism, myocardial dysfunction, stroke, and pulmonary oedema.²⁹ A total of six adverse events (see above) occurred in the study and only two patients only required intervention, one patient required atropine in Group A for asystole and a patient developed acute congestive heart failure in Group B and required diuresis. Intracranial haemorrhage occurred in a patient 2 weeks after the cardioversion outside the protocol follow-up window.

Practical clinical implications

The findings of this study are important since cardioversion is a very commonly performed procedure but there is no standardized protocol to maximize success. This approach can be used in the outpatient or inpatient setting. Patients with high BMI should be informed that they may require more than one cardioversion attempt. The operator may consider performing the first cardioversion attempt using chest pressure and at the end of expiration in obese patients (Step 2). The highest success of cardioversion is achieved with appropriate electrode location and therefore with the lowest TTI. The use of two simultaneous defibrillator pads in selected patients increases the success rate of conversion to sinus rhythm. The protocol can be utilized at most centres using a defibrillator. The need for fluoroscopy to position electrode patches may be required in a small minority of patients (1.4% of patients) and might require referral to a centre with a higher level of care.

Study limitations

Most patients included in this study are obese and had a mean BMI of 33.5 ± 9.2 (kg/m²) and so the success rate with the first cardioversion attempt might be higher in a population with lower BMI. The occurrence of AF was relatively recent (<12 months) and so our data may not be extrapolated to patients with long-standing persistent AF. The success rate may be different if the study selected a specific subpopulation of patients [e.g. patients with left ventricular assist device (LVAD)]. In our study, we had only two patients with LVAD who required the use of two defibrillators to achieve success. The study is a prospective cohort with potential selection bias. We attempted to reduce selection bias by including all consecutive consented patients in the inpatient and outpatient settings who presented for cardioversion. We only included patients with persistent AF of <1-year duration and excluded paroxysmal AF, long-standing persistent AF, or atrial flutter to select a more homogenous population.

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Data Availability Statement

The data underlying this article will be shared on reasonable request to the corresponding author.