The American Heart Association and American College of Cardiology released a comprehensive guideline on the management of atrial fibrillation (AF).¹ Most of the AHA/ACC recommendations are either irrelevant to the general emergency physician or common sense. For example, if a patient has hemodynamic instability attributable to AF, perform immediate electrical cardioversion. That recommendation is not controversial; however, some interesting recommendations within these guidelines may reshape clinician practice, particularly regarding rate control strategies.

Rate Versus Rhythm in the ED

The 2023 AHA/ACC guideline doesn’t give explicit recommendations or preference regarding initial rate or rhythm control strategy for new-onset AF patients who are hemodynamically stable. The guideline states that electrical cardioversion can be performed (Class 1, Level B evidence from randomized trials) and suggests that, if you go this route, you should start with at least 200 joules to increase success (Class 2a, Level B evidence from randomized trials).

The Beta Blocker Versus Calcium Channel Blocker Debate

The ideal control agent for patients with AF with rapid ventricular response (AFRVR) is widely debated in emergency medicine. Often, the best means of rate control is control of the underlying disease process (e.g., antibiotics and fluids or diuresis); however, most emergency clinicians probably have a “favorite” means of rate control for patients with AFRVR. Intravenous (IV) metoprolol and diltiazem are the most commonly administered rate control agents for AFRVR. The current iteration of the guideline does not signal a preference between beta blockers and nondihydropyridine calcium channel blockers (CCBs) for most patients. In fact, few studies compare the two classes.²

Heart failure, however, is a different story. The 2023 AHA/ACC guideline has warned clinicians to essentially toss their IV nondihydropyridine CCBs in the trash for any patient with systolic dysfunction. The panel gave a rare Class 3: harm recommendation for the use of IV nondihydropyridine CCBs in patients with AFRVR and known moderate or severe left ventricular systolic dysfunction with or without decompensated heart failure (HF). This recommendation is a departure from the 2014 guideline iteration that only recommended against CCBs in patients with decompensated heart failure.³ The guideline cites low quality evidence from small studies and fear of negative ionotropic effects. Unfortunately, few studies have directly compared acute management strategies for patients with AFRVR and acute decompensated heart failure, and those that have done so have woefully inadequate sample sizes to detect somewhat uncommon but critical harms.⁴ The 2023 recommendation is based on consensus and two retrospective studies demonstrating some negative outcomes with exposure to diltiazem (acute kidney injury, worsening HF symptoms); however, diltiazem was not associated with mortality and hypotension. The guideline recommends amiodarone for rate control in patients with AFRVR and decompensated heart failure. Although the recommendation against CCBs for acute rate control in patients with any systolic dysfunction is largely consensus based, a paucity of data suggests that beta blockers are any more effective in this subgroup. So, while clinicians can continue to use judgment and the best medications for a given patient, the guideline will likely encourage the use of alternatives in patients with AFRVR and systolic dysfunction.

Magnesium Benefit May Be Overestimated

Much like ketamine and tranexamic acid, magnesium is a darling of emergency medicine. Use of magnesium to augment rate and, to some extent, rhythm control in AFRVR has had some support.⁶ The new AHA/ACC guideline states that in patients with AFRVR, the addition of IV magnesium to standard measures is reasonable to achieve rate control. The committee gave this a class 2A (moderate) recommendation, citing the highest level of evidence (A) from more than one randomized control trial (RCT) or meta-analysis of high quality RCTs. The AHA/ACC cites a meta-analysis including five RCTs of 745 participants. On the surface, this meta-analysis found that the IV magnesium had greater odds of rate control (OR 2.49; 95 percent CI 1.80-3.5) as well as conversion to sinus rhythm (OR 1.75; 95 percent CI 1.08-2.84).7 Digging into the meta-analysis, a few important details emerge. First, a single study by Bouida and colleagues drove the meta-analysis, contributing over 60 percent of patients. The study compared four grams and 9.5 grams of IV magnesium to placebo, doses considerably higher than the two grams of magnesium often administered in the emergency department (ED). Further, the patients in this trial are not representative of U.S.-based care of ED patients with AFRVR. Over one-third of patients in this study received digoxin as their rate control agent, and about half received either diltiazem or a beta blocker. In fact, in the meta-analysis, digoxin was the most commonly administered agent. Consistent with guideline recommendations, digoxin is not commonly administered as a rate control agent in the U.S. due to the lengthy onset of action and higher risk profile compared with CCBs and beta blockers. Second, the outcomes definitions rate and rhythm control at four and 24 hours are far beyond times relevant in emergency medicine in the U.S. The evidence suggests that large doses of magnesium (4.5 g) may improve rate control in patients receiving digoxin.

Summary

The AHA/ACC guideline is a mixed bag, mostly centered on limited data for a bread-and-butter disease process. Cardiovert when it’s indicated or in concordance with patients’ wishes and the AFRVR is the cause. Try to avoid CCBs in patients with systolic dysfunction, understanding that there is limited evidence. And magnesium? Sure, add if you’re giving digoxin and/or failing at other rate control attempts with primary AFRVR.

Dr. Westafer (@Lwestafer) is an attending physician and research fellow at Baystate Medical Center, clinical instructor at the University of Massachusetts Medical School in Worcester, and co-host of FOAMcast.

References

1. Joglar JA, Chung MK, Armbruster AL, et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation: A report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2024;149(1):e1-e156.
2. Fromm C, Suau SJ, Cohen V, et al. Diltiazem vs. metoprolol in the management of atrial fibrillation or flutter with rapid ventricular rate in the emergency department. J Emerg Med. 2015;49(2):175-182.
3. January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation. Circulation. 2014;130(23):e199-267.
4. Niforatos JD, Ehmann MR, Balhara KS, et al. Management of atrial flutter and atrial fibrillation with rapid ventricular response in patients with acute decompensated heart failure: A systematic review. Acad Emerg Med. 2023;30(2):124-132.
5. Jandali MB. Safety of intravenous diltiazem in reduced ejection fraction heart failure with rapid atrial fibrillation. Clin Drug Investig. 2018;38(6):503-508.
6. Bhatt K, Hickey SM, Andreae M. Roadblock: AFib with RVR. Emergency Medical Residents‘ Association. Published July 25, 2023. Accessed July 15, 2024.
7. Ramesh T, Lee PYK, Mitta M, et al. Intravenous magnesium in the management of rapid atrial fibrillation: A systematic review and meta-analysis. J Cardiol. 2021;78(5):375-381.