200 J-first, fixed-escalation biphasic electrical cardioversion for atrial fibrillation >48 hours in the emergency department: a single-centre retrospective observational study

Abstract

Background

Guidelines permit up to 360 J for synchronised biphasic electrical cardioversion (ECV) in atrial fibrillation (AF) lasting >48 hours. The CHESS randomised trial reported higher first-shock success with fixed 360 J versus a low-escalation 125–150–200 J sequence. Much of this evidence used adhesive pads without manual pressure and anterior–posterior positioning. We evaluated a 200 J-first, fixed-escalation biphasic ECV protocol delivered with a standardised technique in an emergency department (ED).

Methods

Single-centre retrospective observational study of consecutive adults undergoing elective ECV for symptomatic AF >48 hours (2019–2021). Procedures used hand-held paddles with firm chest pressure in the anterolateral (AL) position under deep sedation. The predefined sequence was 200→300→360 J if needed. The primary outcome was restoration of sinus rhythm (SR) documented on a 12-lead ECG within 120 min. Secondary outcomes were first shock success at 200 J, cumulative efficacy, SR to discharge without post-ECV antiarrhythmics, adverse events and subgroup efficacy. Results were contrasted descriptively with 360 J-first cohorts (CHESS).

Results

Of 451 ECV procedures identified, 374 were eligible. The primary outcome was achieved in 97.3% (364/374; 95% CI 95.5 to 98.7). First-shock success with 200 J was 88.0% (329/374; 95% CI 84.3 to 90.9). Escalation to 300 J and 360 J was required in 44 and 15 patients. SR was maintained to discharge in converted patients. Two minor adverse events occurred (2/374, 0.5%) and no serious adverse events were recorded.

Conclusions

A 200 J-first, fixed-escalation biphasic protocol with a standardised technique (manual paddles, firm pressure, AL placement) achieved high first-shock and excellent cumulative efficacy for AF>48 hours in real-world ED care without routine pharmacologic adjuncts. Findings support considering a 200 J-first approach and motivate pragmatic multicentre randomised controlled trials directly comparing 200 J-first versus 360 J-first under harmonised technique with objective safety endpoints.

WHAT IS ALREADY KNOWN ON THIS TOPIC

• European Society of Cardiology/EACTS guidelines for atrial fibrillation permit up to 360 J for biphasic electrical cardioversion in atrial fibrillation (AF)>48 hours, and the CHESS randomised controlled trial (RCT) reported higher first-shock success with 360 J-first versus a 125–150–200 J low-escalation sequence; however, these data were generated using adhesive pads in the anterior–posterior position without manual pressure, limiting generalisability to a 200 J-first approach performed with an optimised technique in real-world emergency department (ED) practice.

WHAT THIS STUDY ADDS

• In 374 ED patients with AF>48 hours, a 200→300→360 J sequence delivered with manual paddles, firm chest pressure and anterolateral placement achieved 88.0% first-shock efficacy (200 J) and 97.3% cumulative efficacy, with 0 serious adverse events, 0.5% minor events and 99.7% discharged from the ED.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• Findings support considering a 200 J-first strategy with optimised technique as an effective alternative to maximum-fixed energy in the ED and indicate the need for pragmatic multicentre RCTs directly comparing 200 J-first versus 360 J-first under harmonised methods.

Introduction

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in the general population, contributing significantly to morbidity, stroke risk and healthcare resource utilisation.^{1 2} Recent epidemiological data indicate a steady global increase in AF incidence. In Europe alone, more than 9 million individuals over the age of 55 currently live with AF, and this number is projected to more than double by 2060, driven by ageing populations and improved screening and diagnostic methods.^{1 3 4} As new diagnoses continue to rise, AF now accounts for approximately 0.5%–2% of all emergency department (ED) visits.^{5 6} Large observational cohorts report that a majority of ED presentations for AF result in hospital admission, underscoring the burden on acute care systems.^{5 6} In many EDs, increasing patient volumes—combined with limited inpatient bed availability and growing evidence that ED stays beyond 5 hours are associated with increased in-hospital mortality—have prompted a shift towards managing AF more definitively in the ED setting.^{7 8}

Electrical cardioversion (ECV) remains the most commonly used strategy for restoring sinus rhythm (SR) in patients with persistent AF, particularly in emergency settings.^{1 2} It is often favoured over pharmacological cardioversion due to higher immediate efficacy and a shorter time to conversion.⁹ Accordingly, optimisation of ECV protocols—both energy selection and shock delivery technique—has become increasingly relevant to improve first-shock success, reduce repeat shocks and avoid unnecessary hospitalisation.¹⁰,¹² Current guidelines permit biphasic energies up to 360 J for AF lasting >48 hours, but do not mandate a universal ‘360 J-first’ approach for all patients.¹ In the CHESS randomised trial, a maximum-fixed-energy strategy (360–360–360 J) achieved higher first-shock success than a low-escalation sequence (125–150–200 J), although CHESS was performed using self-adhesive electrodes in the anterior–posterior (AP) position without manual pressure augmentation.¹³ Importantly, Bharwani and colleagues synthesised contemporary optimisation strategies and highlighted that, in modern biphasic cardioversion, first-shock efficacy depends not only on the selected energy but also on modifiable procedural factors that reduce transthoracic impedance and improve delivered current.¹⁴ In addition, a systematic review and meta-analysis highlighted that cardioversion success is influenced by modifiable procedural and protocol factors, including energy selection and electrode application techniques.¹³ Taken together, these data support optimising shock delivery particularly by reducing transthoracic impedance through improved electrode contact and pressure augmentation to maximise first-shock success.¹⁴,¹⁶

Notably, key trials informing energy-based strategies (including CHESS) used self-adhesive pads without pressure augmentation, whereas manual pressure augmentation has been shown to improve cardioversion efficacy by lowering transthoracic impedance.¹³ Although high-energy protocols have not consistently demonstrated clinically significant myocardial damage—such as persistent elevation in troponin levels or adverse echocardiographic changes—some animal and clinical studies have reported transient myocardial dysfunction, electrical remodelling or biochemical markers of injury following repeated or cumulative shocks.¹⁷,²¹ Therefore, an approach that achieves high efficacy with an initial energy of 200 J—while applying an impedance-reducing, standardised technique—may represent a pragmatic balance for ED care where safety, comfort and throughput are prioritised.^{10 11 14 22}

Study aim: we evaluated the real-world performance of a 200 J-first, fixed-escalation biphasic ECV protocol (200→300→360 J) delivered with a standardised technique (hand-held paddles, firm pressure, anterolateral (AL) placement) in ED patients with symptomatic AF lasting >48 hours.

Methods

Study design and setting

This single-centre retrospective observational study was conducted at the Department of Emergency Medicine, Dr Jan Biziel University Hospital, Bydgoszcz, Poland. The analysis included all ECV procedures for AF performed between January 2019 and December 2021. The department serves a catchment population of over one million inhabitants and is the only facility in the region offering unscheduled ECV for AF. Scheduled procedures in cardiology clinics often require weeks to months of waiting. The study protocol was approved by the local ethics committee (KB 597/2021) and conducted in accordance with the Declaration of Helsinki.

Data sources and ECG assessment

Standard 12-lead ECGs were obtained before cardioversion and within 120 min after the procedure. The 120 min ECG was selected to confirm short-term rhythm stability during routine postsedation observation prior to ED discharge. ECGs were reviewed by the treating emergency physician and, as part of routine care, discussed with an on-call cardiologist. For this study, ECG assessment was limited to rhythm classification and heart rate.

Study population and eligibility criteria

We analysed all ECV procedures for AF performed between January 2019 and December 2021. Reporting follows the Strengthening the Reporting of Observational Studies in Epidemiology statement for observational studies and the RECORD extension for studies using routinely collected data.

Participants (eligibility and flow)

Participants flow is presented in figure 1.

Figure 1. STROBE participant flow diagram. Flow of procedures/patients through the retrospective cohort of ED electrical cardioversion for atrial fibrillation>48 hours. Of 451 ECV procedures screened, 77 were excluded per prespecified criteria and 374 were included; all received a first 200 J shock, 44 required escalation to 300 J and 15–360 J. ECV, electrical cardioversion; ED, emergency department; STROBE, Strengthening the Reporting of Observational Studies in Epidemiology.

Inclusion criteria:

• adults (≥18 years).

• Symptomatic AF >48 hours.

• Haemodynamically stable.

• Adequately anticoagulated for ≥21 days or status post left atrial appendage closure.

• Written informed consent.

Exclusion criteria:

• AF <48 hours.

• Acute coronary syndrome with ST-segment elevation.

• Active infection (fever, CRP>100 mg/L).

• Unregulated thyroid disease.

• Haemoglobin <8 g/dL.

• Haemodynamic instability.

• AF secondary to acute decompensation (eg, pulmonary oedema).

• Irregular medication history or unknown AF onset.

• Spontaneous reversion to SR before cardioversion.

• Atrial flutter cardioversion.

Patient and public involvement

Patients or members of the public were not involved in the design, conduct, reporting or dissemination plans of this research. This was a retrospective study of routinely collected ED data and electrocardiograms; no additional patient contact was required and all data were anonymised prior to analysis. We plan to involve patient representatives in future work (eg, codeveloping a lay summary and patient-facing materials on ED cardioversion pathways) to support dissemination.

ECV protocol and technique

All procedures were performed using a BeneHeart D3 defibrillator monitor (Shenzhen Mindray BioMedical Electronics, Shenzhen, China). The device delivers a biphasic truncated exponential waveform with automatic impedance compensation according to patient impedance in manual defibrillation and synchronised cardioversion modes, with handheld paddles. Self-adhesive pads were not used. Electrode placement was sternal–midaxillary (AL). A fixed escalation biphasic sequence was employed: 200 J → 300 J → 360 J if needed. Procedures were performed under deep sedation with intravenous fentanyl and propofol per institutional protocol. A standardised impedance-reducing technique was used (firm manual paddle pressure; AL positioning). Transthoracic impedance and applied paddle force were not directly measured. Patients without conversion after all three shocks were discharged for pharmacologic pretreatment (typically amiodarone) and scheduled for delayed cardioversion under cardiology supervision.

Outcomes

The prespecified primary outcome was successful cardioversion. It was defined as SR on a 12-lead ECG within 120 min after the procedure. This timepoint reflects routine ED postsedation monitoring and ECG reassessment. Secondary outcomes were:

• first-shock success (200 J).

• Cumulative success across the fixed escalation sequence (200→300→360 J).

• SR maintained to ED discharge without post-ECV antiarrhythmic therapy.

• Adverse events (AEs) and need for post-ECV antiarrhythmics therapy.

Subgroup analyses

Subgroup analyses were prespecified for first-shock success at 200 J. Subgroups were sex, age (≤ 65 years vs >65 years), prior cardioversion (first vs subsequent) and anticoagulation category (direct oral anticoagulant (DOAC) vs vitamin K antagonist (VKA)).

Safety outcomes and definitions

AEs were captured from the start of procedural sedation until ED discharge and classified a priori as serious AE (SAE) or minor. An SAE was defined as any event resulting in death, cardiac arrest, sustained ventricular arrhythmia requiring resuscitation, stroke or transient ischaemic attack, refractory hypotension requiring vasopressors, bradycardia requiring temporary pacing or ICU admission, anaphylaxis or unplanned hospital admission/prolongation directly attributed to a procedural complication. Minor AEs were events allowing conservative management without vasopressors, pacing, intubation or ICU transfer (eg, transient bradycardia responsive to observation/atropine only; transient hypotension responsive to fluids only; nausea/vomiting; mild skin erythema without blistering). Brief observation unit monitoring without specific therapy was recorded separately and not classified as SAE unless other SAE criteria were met.

Comparative context

No internal control group was used. Results were descriptively contrasted with the CHESS trial (Schmidt et al), which evaluated a maximum-fixed-energy strategy (360–360–360 J) delivered with self-adhesive pads, without manual pressure augmentation, in the AP position. These differences limit direct comparability but contextualise external validity.

Statistical analysis

Continuous variables are summarised as mean ± SD or median (IQR); categorical variables as counts and percentages. Proportions are reported with 95% CIs (Wilson method). First-shock efficacy is expressed as conversions/374 (cohort denominator); per-shock conversion at 300 J (n=44); and 360 J (n=15) uses the number receiving that shock; cumulative efficacy is calculated on 374. No hypothesis testing was performed against external cohorts (eg, CHESS). No formal sample size calculation was performed; all eligible cases were included. Missing data were not imputed.

Patients and public involvement

Patients or the public were not involved in the design, conduct, reporting or dissemination plans of this research.

Results

Study population and baseline characteristics

• A total of 451 biphasic cardioversion procedures were performed between 2019 and 2021. After applying prespecified eligibility criteria, 374 patients with symptomatic AF>48 hours were included (figure 1). In the included cohort (n=374), 197 were men (52.7%) and 177 were women (47.3%). The mean age was 69.5 years (SD 9.5); median 71 (IQR 64–76) and the overall age range was 39–90 years. Baseline characteristics are presented in table 1.

Table 1. Baseline characteristics of the study cohort (N=374).

Variable	Parameter	Total (N=374)
Gender	Man	52.7% (N=197)
	Female	47.3% (N=177)
Age (years)	N	374
	Mean (SD)	69.521 (9.54)
	Median (IQR)	71 (64–76)
	Range	39–90
Medication and dose	Apixaban 5 mg 2×1	17.6% (N=66)
	Dabigatran 150 mg 2×1	29.1% (N=109)
	Rivaroxaban 20 mg	42.5% (N=159)
	VKA	7.2% (N=27)
First cardioversion	43.8% (N=163)
Obesity	15% (N=56)
Arterial hypertension	92.8% (N=347)
Diabetes mellitus	22.5% (N=84)
COPD	3.5% (N=13)
Hypothyroidism	8% (N=30)
Hyperthyroidism	10.7% (N=40)
Prior catheter ablation for AF (pulmonary vein ablation)	5.6% (N=21)
Nicotine use	9.6% (N=36)
Chronic kidney disease	7.8% (N=29)
Hypercholesterolaemia	38.2% (N=143)
Implantable cardioverter-defibrillator	5.9% (N=22)
IHD	15.5% (N=58)
PTCA	13.9% (N=52)
CHF	19.3% (N=72)
Ablation	9.1% (N=34)
Cardiac ablation of pulmonary veins	5.6% (N=21)
CABG	2.7% (N=10)
Myocardial infarction	7% (N=26)
Stroke	10.7% (N=40)
Status post cardiac pacemaker implantation	0.8% (N=3)
Tachy-brady syndrome	1.6% (N=6)
TIA	3.2% (N=12)
Non-ischaemic cardiomyopathies	4.8% (N=18)
Pre-procedure vitals
SBP (mm Hg)	N	374
	Mean (SD)	141.88 (23.556)
	Median (IQR)	141 (124–157)
	Range	70–218
DBP (mm Hg)	N	374
	Mean (SD)	92.214 (17.056)
	Median (IQR)	92 (80–102)
	Range	11–155
HR (beats/min)	N	374
	Mean (SD)	108.527 (25.623)
	Median (IQR)	102 (90–125)
	Range	58–200
Saturation (%)	N	374
	Mean (SD)	0.978 (0.014)
	Median (IQR)	0.98 (0.97–0.99)
	Range	0.92–1

AF, atrial fibrillation; CABG, coronary artery bypass grafting; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; DBP, diastolic blood pressure; HR, heart rate; IHD, ischaemic heart disease; PTCA, percutaneous transluminal coronary angioplasty; SDP, systolic blood pressure; TIA, transient ischaemic attack; VKA, vitamin K antagonist.

Primary and secondary efficacy outcomes

Primary outcome

SR on a 12-lead ECG within 120 min after the procedure was achieved in 364/374 patients (97.3%, 95% CI 95.5 to 98.7). Stepwise and cumulative efficacy by shock energy are summarised in table 2.

Table 2. Stepwise efficacy of biphasic electrical cardioversion by shock energy (200→300→360 J).

Shock energy	Patients receiving shock (n)	Effective conversion (n)	Conversion rate for that shock	Cumulative efficacy rate
First shock (200 J)	374	329	88.0%	88.0%
Second shock (300 J)	44	29/44	65.9%	95.7% (358/374)
Third shock (360 J)	15	6/15	40.0%	97.3% (364/374)

Primary outcome was sinus rhythm (SR) documented on 12-lead ECG within 120 min after the procedure.

First-shock success and cumulative efficacy are reported using the cohort denominator (n=374).

Per-shock conversion rates at 300 J (n=44) and 360 J (n=15) use the number of patients receiving that shock.

Boldface indicates the final cumulative efficacy rate (overall success after up to three shocks).

Secondary outcomes

A single 200 J shock restored SR in 329/374 patients (88.0%, 95% CI 84.3 to 90.9). Among patients not in SR after the first shock (45/374), 44 underwent escalation to 300 J, with SR achieved in 29/44 (65.9%). A third shock at 360 J was delivered in 15 patients, with SR achieved in 6/15 (40.0%). After the second step, cumulative success reached 358/374 (95.7%).

Subgroup analyses

First-shock efficacy with 200 J was comparable across sex and age strata: men 89.3% (176/197; 95% CI 84.3 to 92.9) versus women 86.4% (153/177; 95% CI 80.6 to 90.7); ≤65 years 86.9% (93/107; 95% CI 79.2 to 92.0) vs >65 years 88.4% (236/267; 95% CI 84.0 to 91.7). By anticoagulation category, first-shock success was 88.7% (306/345) for DOAC and 81.5% (22/27) for VKA. No statistically significant differences were observed across prespecified subgroups.

Comparison with maximum-fixed-energy protocols (external comparison)

The efficacy of our protocol, which utilised manual compression via handheld paddles in the AL position, was compared with the efficacy reported in the CHESS trial (Schmidt et al). CHESS used maximum-fixed energy (360–360–360 J), self-adhesive electrodes and the AP position. Key methodological differences between our ED protocol and CHESS (electrode type, position, pressure augmentation and endpoint timing) are summarised in table 3. Therefore, any between-study comparison is descriptive rather than head-to-head

Table 3. External comparison of protocol and outcomes: present ED cohort versus CHESS trial.

Characteristic	Present study (ED cohort, AF>48 hours)	CHESS RCT—maximum-fixed arm	CHESS RCT—low escalation arm
Study design	Single-centre retrospective observational cohort	RCT
Sample size (n)	374	129	147
Population (AF duration)	Symptomatic AF>48 hours	Elective cardioversion of AF (not restricted to>48 hours); AF duration<1 year 70%, >1 year 30%
Age (years)	Mean 69.5 (SD 9.5)	Mean 68 (SD 9)
Male sex	197/374 (52.7%)	72%
Defibrillator/waveform	Biphasic (Mindray BeneHEart D3)	Biphasic truncated exponential waveform (LIFEPACK 20)
Electrodes	Hand-held paddles	Self-adhesive pads
Electrode position	Anterolateral (sternal-midaxillary)	Anterior-posterior
Manual pressure augmentation	Yes (firm paddle pressure)	No (not reported/not used)
Energy protocol	200-300-360	360-360-360	125-150-200
Primary outcome definition	Sinus rhythm on 12-lead ECG within 120 min after procedure	Sinus rhythm on 12-lead ECG within 120 min after procedure
Primary outcome achieved	364/374 (97.3%)	114/129 (88%)	97/147 (66%)
First-shock success	329/374 (88%)	97/129 (75%)	50/147 (34%)
Safety assessment	Adverse events from routine clinical records. High-sensitivity troponin, transthoracic impedance and post-shock ECG parameters beyond rhythm classification were not systematically assessed.	Adverse events from routine clinical records. High-sensitivity troponin, transthoracic impedance and post-shock ECG parameters beyond rhythm classification were not systematically assessed.

Outcome timepoints differed between studies (present cohort: SR within 120 min; CHESS: SR at 1 min), limiting direct comparability.

AF, atrial fibrillation; ED, emergency department; RCT, randomised controlled trial; SR, sinus rhythm.

• Comparison of first-shock efficacy

In our cohort, a single 200 J shock restored sinus rhythm in 329/374 (88.0%; 95% CI 84.3 to 90.9), with rhythm stability confirmed 120 min postcardioversion and at discharge. In CHESS (360–360–360 J; adhesive pads; AP), first‑shock success at 1 min was 75.2%, whereas cumulative success across up to three shocks was 88.4%. Methodological differences (pads without pressure augmentation, AP position, 1 min assessment) limit direct comparison but contextualise our 200 J‑first performance with optimised technique.

• Comparison of secondary efficacy endpoint (discharge/late success)

The success rate at discharge in our cohort was 88.0% (329/374), which appears higher than the CHESS secondary endpoint of SR at 4 hours (75.2%) for the 360 J‑first arm. This contrast is descriptive only and should be interpreted cautiously given differing time points and methods (pads/AP/1 min primary assessment in CHESS).

Safety outcomes

Using prespecified definitions (see the Methods section), no SAEs were recorded. Two minor AEs occurred (0.5%, 2/374): one episode of transient bradycardia managed with observation only and one episode of vomiting responsive to supportive care. One patient underwent brief observation-unit monitoring for bradycardia (0.3%, 1/374) without escalation of care; per protocol, this was recorded separately and not classified as SAE. Overall, 99.7% (373/374) were discharged home from the ED; 8.3% reattended (median 12 days) due to AF recurrence.

Discussion

Contemporary ESC guidance permits biphasic energies up to 360 J for AF lasting >48 hours, and evidence supporting a maximum-fixed-energy strategy derives largely from randomised comparisons such as CHESS.^{1 13} Our real-world, single-centre retrospective study involving 374 patients with persistent AF (>48 hours) suggests that routine 360 J first initiation may not be necessary in all ED patients when shock delivery technique is standardised and escalation is available. We achieved an 88.0% effectiveness rate in restoring SR after the first 200 J shock and our cumulative success rate across the 200 J–300 J–360 J sequence reached 97.3%. Key methodological differences are summarised in table 3. These results suggest that a moderate initial energy level (200 J) can achieve remarkably high conversion rates on first attempt when procedural technique is optimised, suggesting that maximum energy delivery is not necessarily required to initiate the procedure.^{10 11 14 22} In subgroup analyses (see the Results section), first-shock efficacy with 200 J did not materially differ by sex, age, prior cardioversion or anticoagulation regimen; all 95% CIs overlapped the cohort estimate.

Impact of energy

Our study was not designed to quantify subclinical tissue effects (eg, biomarkers or imaging), and high-sensitivity cardiac troponin was not collected routinely; therefore, we cannot directly assess myocardial injury beyond clinically apparent AEs. A 200 J first, fixed escalation strategy is intended to minimise cumulative delivered energy (total joules) by achieving early conversion, and in our cohort, acute efficacy was high.^{11 22} The clinical relevance of reducing cumulative energy exposure should be evaluated prospectively using predefined safety endpoints (eg, biomarkers and systematic skin assessment).^{19 20}

Procedural technique: context from prior evidence

A key difference between our protocol and several pivotal randomised trials (including CHESS) is the technical execution of external cardioversion. Prior studies have shown that lower transthoracic impedance (TTI) and improved electrode–skin contact are associated with higher cardioversion success, and that technique-related manoeuvres can reduce impedance and increase delivered current.^{10 15 23} However, TTI and applied paddle force were not measured in our retrospective dataset; therefore, the mechanistic considerations below should be interpreted as context from prior evidence rather than effects quantified in the present study. This broader context is reflected in the review by Bharwani et al, which emphasises that first-shock success depends on both energy selection and optimisation of technique—particularly manoeuvres that reduce TTI, including pressure augmentation (especially in patients with higher impedance such as those with obesity).¹⁴

Manual paddles and compression

Unlike the CHESS trial, which utilised self-adhesive pads without mechanical pressure augmentation, our study exclusively used hand-held paddles and emphasised the application of adequate pressure on the patient’s chest.¹³ Hand-held paddles facilitate operator-applied pressure augmentation, which can reduce TTI and increase delivered current.^{15 23} Ramirez et al demonstrated that applying force to self-adhesive electrodes lowers TTI.¹⁵ In addition, the PRESSUREAF randomised trial reported improved cardioversion success with manual pressure augmentation.¹⁶ As TTI and applied force were not measured in our cohort, these mechanisms should be interpreted as external context rather than effects quantified in the present study.

Electrode positioning

We utilised the sternal–midaxillary line position (AL). While the optimal electrode position remains a subject of ongoing debate, a meta-analysis involving 1845 patients found a statistically significant association between the AL position and an increased cardioversion rate (OR=1.40).²⁴,²⁶ This effect was particularly pronounced in subgroups such as patients receiving fewer than five shocks. Together with pressure augmentation, AL placement may have contributed to effective current delivery; however, we did not measure impedance, so this remains a plausible explanation rather than a quantified mechanism.²⁷

Challenging the need for routine 360 J: energy thresholds and safety

Available evidence suggests that very low initial energies (<200 J) are associated with lower success, whereas the incremental gain from routinely starting above 200 J may be smaller and context-dependent, particularly when technique is optimised and escalation is immediate.^{10 13 14} Furthermore, the rationale for avoiding routinely starting with maximum energy stems from the principle of minimising the non-neutral effects of the procedure on the patient’s health.^{18 20 21}

Evidence of myocardial harm

Cardioversion, although often perceived as a routine intervention, is not a physiologically neutral procedure. Although the AFFIRM trial demonstrated no association between external cardioversions and long-term mortality, modern imaging provides concerning evidence of injury.¹⁷ Studies utilising cardiovascular MR (CMR) in animal models demonstrate that external cardioversion causes interstitial and cellular oedema along the pulse path, and repeated shocks can cause severe damage to the skeletal muscles and the myocardium. Follow-up CMR in humans observed significant fibrosis and myocardial oedema 6–8 weeks after cardioversion, particularly in patients with pre-existing heart injury or failure.^{18 21}

Minimising cumulative energy

These pathological findings (skeletal muscle oedema, fibrosis and remodelling of the myocardium) and the surge of proinflammatory interleukins and C reactive protein provide a rationale to minimise unnecessary cumulative energy exposure, particularly when high efficacy can be achieved with an initial 200 J setting and rapid escalation. Starting at 200 J reduces the cumulative energy delivered compared with a fixed 3×360 J protocol, thereby potentially reducing the impact on the patient’s health. The clinical importance of this reduction is supported by studies like the PROTOCOLENERGY trial, where the lower initial energy protocol resulted in significantly fewer incidents of skin redness (19.3% vs 36.0%).^{11 13 18 20 22}

Troponin levels

Prior clinical studies report that external cardioversion is not consistently associated with clinically meaningful rises in cardiac biomarkers. However, biomarkers alone may not capture transient or subclinical tissue effects, particularly after repeated or cumulative shocks.¹⁸,²⁰

Clinical implications and future directions

The cumulative efficacy of 97.3% achieved in our cohort demonstrates that the combination of a robust, established energy dose (200 J) and operator-controlled impedance reduction is highly successful in the ‘real-world’ ED setting for patients with AF lasting >48 hours. The high success rate after the initial 200 J shock (88.0%) simplifies ED workflow, supporting the critical objective of emergency medicine rapid, effective treatment with subsequent patient discharge when appropriate, rather than hospitalisation.

Given the confounding impact of patient variables such as obesity, which is strongly associated with higher ECV failure and increased TTI, we suggest that future international efforts should focus on establishing a formula for calculating the optimal shock energy based on patient characteristics. ²⁸ This personalised approach would allow for a significant reduction of unnecessary energy delivery while maintaining high conversion rates with only 200 J for initial shock delivery. Our work suggests that staff performing the procedure should focus on the appropriate placement of paddles and the use of sufficiently strong pressure on the patient’s chest, rather than universally starting with 360 J.

Limitations

We acknowledge several limitations, which temper the interpretation of our findings:

• Design: this was a single-centre, retrospective observational study, meaning it is susceptible to selection and reporting biases and the findings may have limited external validity.

• External comparison: the contrast with published cohorts (including CHESS) is external and non-randomised, based on aggregate data, and is, therefore, descriptive only. Differences in patient selection, electrode type (paddles vs pads), electrode position (AL. vs AP) and outcome assessment timepoints limit interpretability.

• Safety data: we did not collect standardised objective safety measurements such as high-sensitivity troponin, postshock ECG parameter analysis beyond rhythm assessment or systematic skin assessment for erythema/burns. Safety conclusions are limited to AEs documented in routine clinical records. Mechanistic interpretation: TTI was not measured, and, therefore, the impact of impedance reduction cannot be quantified in this dataset. Any discussion of impedance-related mechanisms should be interpreted as context from prior literature rather than evidence generated by this study.

Mechanistic interpretation: TTI was not measured, and, therefore, the impact of impedance reduction cannot be quantified in this dataset. Any discussion of impedance-related mechanisms should be interpreted as context from prior literature rather than evidence generated by this study.

Electrode position: cardioversion was performed using an AL (sternal–midaxillary) configuration. Findings may not be generalisable to AP positioning.

Electrode type: we used handheld paddles and did not use self-adhesive pads. Results may not extrapolate to centres that routinely use adhesive pads.

Manual pressure: the amount of paddle pressure was not measured, which introduces operator-dependent variability and limits reproducibility.

Conclusions

In this single-centre, real-world ED cohort of patients with symptomatic AF lasting >48 hours, a structured biphasic protocol starting at 200 J achieved high first-shock efficacy (88.0%) and excellent cumulative success (97.3%) with sustained SR to discharge and no routine need for post-ECV antiarrhythmic therapy. Given the retrospective observational design and the absence of a concurrent 360 J-first comparator, these findings are hypothesis-generating and do not establish superiority over maximum-energy-first protocols. Pragmatic multicentre RCTs directly comparing 200 J-first versus 360 J-first with harmonised technique and objective safety endpoints (eg, postprocedure biomarkers and skin assessment, and, where feasible, imaging)—are warranted to refine guideline recommendations and personalise initial shock energy selection.

Data availability statement

Data are available upon reasonable request.