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Circulation. 2025;152(suppl 2):S538–S577. DOI: 10.1161/CIR.0000000000001376 October 21, 2025 S569

Wigginton et al Advanced Life Support: 2025 AHA Guidelines for CPR and ECC

While an expeditious trial of medications, intravenous fluids, or both may be appropriate in some cases, unstable patients or patients with ongoing cardiac ischemia caused or exacerbated by atrial fibrillation/flutter require prompt cardioversion.7–9 One should also consider whether the arrhythmia is causative or secondary to a rapid ventricular response driven by underlying factors (eg, sepsis), as this may guide initial pharmacologic strategies for hemodynamic stabilization. Limited data exist on these strategies in hemodynamically unstable patients; however, the hemodynamic benefits of successful cardioversion have been documented.10,11 In addition, risk of hypotension and hypoperfusion with negative inotropes has been demonstrated even in normotensive patients.12–14 Hemodynamically unstable patients and those with ongoing cardiac ischemia are likely to benefit from improved hemodynamic status from immediate restoration of sinus rhythm and avoidance of hypotension caused by pharmacological therapies. Depending on the clinical scenario, patients cardioverted from atrial fibrillation/flutter of greater than 48 hours’ duration are candidates for anticoagulation. Appropriate selection of patients and medications for anticoagulation are addressed elsewhere and beyond the scope of these guidelines.1

3 Guidance for monophasic waveform car-

dioversion of AF/flutter is found in previous guidelines,15 displaced by biphasic waveforms due to their greater efficacy. Given proprietary differences in electrical characteristics, guidelines previously deferred biphasic cardioversion energy settings to manufacturer specifications.16 However, interim randomized head-to-head trials together with a network meta-analysis involving >3000 AF patients found that 200-J shocks achieved greater than 90% cumulative cardioversion success across all 3 biphasic platforms currently available in the United States.6,17–21 Previous guidelines advocated lower energy settings over concerns that higher energies posed greater risk for cardiac injury and complications.18,22–25 Subsequent clinical studies observed no association between starting biphasic shock energies of up to 360 J with energy-associated elevations in cardiac-specific enzymes, postcardioversion arrhythmias, cardiac dysfunction, or other sequelae.26–28 Notably, low-energy monophasic shocks were significantly more likely to provoke VF when cardioverting AF, and AF when cardioverting atrial flutter than a 200-J or greater setting.29 This observation is consistent with the upper limit of vulnerability principle: that an energy threshold exists above which a shock will not induce fibrillation.30,31 A higher starting energy was also found to be more efficient than “starting low, titrating higher” approaches, achieved greater first-shock cardioversion success, required fewer overall shocks, and could shorten the period of anesthesia needed for serial shock attempts.18,22

Considering efficacy, safety, efficiency, simplicity, and consistency with other professional guidelines, evidence supports a starting energy of 200 J.16–21 Regardless of energy setting, appropriate sedation for cardioversion is advisable in awake patients, given shock is a painful procedure. 4.	One approach to synchronized cardiover-

sion is double synchronized cardioversion. Administering 2 simultaneously-synchronized high-energy shocks from separate defibrillators and pads has been described anecdotally, in small case series, and a single randomized trial. As an “initial” cardioversion strategy, a modestly-sized randomized trial comprised of class II obesity patients (39% had prior cardioversion attempts) found first shock efficacy improved with 400 J double synchronized cardioversion versus 200 J synchronized cardioversion (98% versus 87%, p=0.002).32 Although not consistently reported, double synchronized cardioversion has not been associated with proarrhythmia, hemodynamic complications, cardiac-specific enzyme elevation,28 or postprocedure discomfort but has caused defibrillator damage.33 A concern in all studies has been the vagueness of procedural specifications, particularly how 2 independently-initiated shocks from separate defibrillators being reliably simultaneously-synchronized was assured.34 Given the high success of optimal synchronized cardioversion using biphasic waveforms, the incremental benefit from double synchronized cardioversion is modest. 5.	Organized rhythms like atrial flutter, caused by

a discrete reentry circuit, require less energy for termination than AF, whose multiple reentry circuits broadly engulf the atrial myocardium.35 However, periodic transitions between the two arrhythmias are common. Distinguishing AF from flutter in an emergent setting with only single-lead monitoring can be challenging. Studies evaluating rectilinear and truncated exponential biphasic waveforms available in the United States, while indirect and fewer in number than for AF, have shown comparable cumulative

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