Atrial Fibrillation in Critical Illness

Atrial fibrillation (AF) presents significant management challenges in the ICU. Pre-existing AF affects 10–20% of ICU patients, while new-onset AF (NOAF) occurs in 5–15% of critically ill individuals and up to 46% in those with septic shock. NOAF may be transient or indicate an underlying predisposition, complicating treatment decisions. 

AF in critical illness is linked to worse outcomes, including longer hospital stays, higher mortality, and increased long-term risks of stroke and heart failure. Current management is hampered by limited high-quality evidence, leading to inconsistent care due to reliance on data from non-critically ill populations. 

A new review aims to synthesise current evidence, contextualise existing guidelines for critical care, and identify research gaps to enhance AF management in ICU settings. NOAF in critically ill patients shares general risk factors with AF in the broader population, such as age, male sex, hypertension, and chronic diseases, but also includes ICU-specific risks like sepsis, shock, organ failure, and major surgery. 

Preventing NOAF in critically ill patients may be possible by modifying known triggers, particularly limiting catecholamine use. Studies show that higher vasopressor doses and elevated blood pressure targets increase NOAF risk, while catecholamine-sparing strategies, such as using vasopressin, are associated with lower incidence. Limited evidence also suggests potential preventive effects from hydrocortisone and dexmedetomidine. Although fluid imbalance is a recognised risk factor, optimal fluid management for NOAF prevention remains unstudied. Similarly, while electrolyte supplementation is common, there's little evidence supporting aggressive supplementation to high-normal levels. Further research is needed to clarify and validate effective preventative strategies.

Both pre-existing AF and NOAF benefit from addressing reversible causes (electrolyte imbalances, fluid shifts, acidosis, adrenergic stimulation). Many NOAF cases resolve spontaneously after treating the underlying issue.

In haemodynamically unstable patients, electrical cardioversion is recommended but has low success in ICU patients. Amiodarone is commonly used for rhythm and rate control; effectiveness is variable and may improve with IV magnesium. Landiolol, a beta-1 selective blocker, achieves rapid rate control with minimal BP effects. Esmolol outperforms amiodarone in rate control without additional BP compromise. Digoxin is inferior to amiodarone for rate control but may be non-inferior for rhythm control and safer in heart failure patients. Propafenone offers faster and more sustained rhythm control than amiodarone in septic shock patients with preserved or mildly reduced LV function. Phenylephrine mildly reduces heart rate versus norepinephrine, with no difference in clinical outcomes.

In haemodynamically stable patients, beta-blockers, diltiazem, verapamil, or digoxin are recommended for rate control in patients with LVEF >40%. Beta-blockers are linked to improved survival in retrospective analyses. Amiodarone is widely used but may be associated with higher mortality and comparable time to rate control as beta-blockers. Diltiazem provides superior rate control compared to amiodarone but is more often stopped due to hypotension. Knowledge gaps include optimal timing, rate vs rhythm control strategies, and defining heart rate targets in the critically ill.

NOAF increases risk of thromboembolic events (e.g., stroke, limb ischaemia, infarctions), especially within 90 days post-ICU. Traditional risk scores like CHA₂DS₂-VASc poorly predict stroke risk in critically ill patients. No validated tools currently guide anticoagulation decisions in this population. Timing and choice of anticoagulant remain uncertain. Early anticoagulation hasn't shown clear benefit. Warfarin use is problematic due to monitoring challenges and suboptimal therapeutic time. DOACs are preferred in non-ICU settings for their safety but lack robust evidence in the ICU. Research is needed to guide anticoagulation timing, choice, and risk stratification.

Echocardiography is the preferred imaging tool in haemodynamically unstable ICU patients and is recommended to guide AF treatment decisions. Transthoracic echocardiography (TTE) helps identify predictors for NOAF, including left ventricular ejection fraction (LVEF) <35%, left atrial (LA) dilatation and diastolic dysfunction LA size correlates with AF burden; larger LA area is associated with higher AF burden. Ventricular function assessment helps tailor therapy; cardiac depressants should be avoided in patients with reduced LVEF. Patients with LV relaxation abnormalities may benefit more from cardioversion than rate control. LA enlargement and impaired atrial function reduce the success rate of maintaining sinus rhythm after cardioversion. Transesophageal echocardiography (TOE) is particularly useful in evaluating the left atrial appendage (LAA), ruling out thrombus before cardioversion and stratifying thromboembolic risk based on atrial size, valve disease, and systolic function

Optimal timing for echocardiographic assessments remains uncertain due to rapid structural changes during critical illness. Best timing for TOE in AF patients is unclear. While recommended before cardioversion in non-critically ill patients with AF >24 h, its role and timing in ICU patients need more study. One study showed delayed thrombus formation detectable by TOE, emphasising the need for repeated assessment. Predictive value of LA size for AF recurrence is established, but exact echocardiographic cut-off values for risk prediction are not well-defined and require further research.

Recurrent AF is common after hospital discharge in patients who developed NOAF during critical illness. These patients have a 4- to 6-fold increased risk of developing chronic AF compared to those without AF during critical illness. 32% of patients with transient AF during non-cardiac hospitalisation experience recurrence within one year. Risks of stroke, heart failure, and recurrent AF are high after NOAF, prompting recommendations for post-discharge follow-up, including cardiology referral or screening. 

NOAF during ICU stays is often missed or under-reported, reducing opportunities for early intervention. In one study, 31.9% of ICU patients with NOAF had recurrent AF after a median follow-up of 413 days. High AF burden (>25% of ICU stay) strongly predicted recurrence. Risk prediction models improve when incorporating ICU-related factors (e.g., infection type, severity scores), not just pre-existing cardiovascular risk. No standardised guidelines exist for post-discharge AF screening in critical illness survivors. Common AF risk reduction strategies (e.g., weight loss, exercise, alcohol/tobacco cessation, hypertension management) are not yet studied in this population. The impact of social determinants of health on NOAF outcomes after critical illness is unknown and needs exploration. Many ICU survivors develop post-intensive care syndrome (PICS), which may influence AF recurrence. Post-ICU clinics could play a role in managing AF recurrence through rehabilitation and psychosocial support, but further study is needed.

Overall, AF is the most common arrhythmia in critically ill patients and is linked to worse short- and long-term outcomes. Its management is complicated by patient heterogeneity and multifactorial pathophysiology. Major knowledge gaps persist, including whether AF causes poor outcomes or merely reflects illness severity and what duration or treatment of AF is clinically meaningful.

To improve care, well-designed studies are needed to explore causal relationships, long-term impacts, and patient-centred outcomes. An individualised, multidisciplinary approach is essential, considering baseline cardiac function, type of critical illness, and patient preferences. Effective communication, continuity of care, and support for ICU survivors are crucial to optimising outcomes.

Source: Intensive Care Medicine

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