Atrial fibrillation is not just an artefact in the ICU

Atrial fibrillation (AF) is common in the intensive care unit (ICU) and is particularly frequent (46%) in septic shock patients. Inflammation favours AF in the general population, and there is a growing body of evidence that inflammation also plays a role in AF occurring after cardiac surgery but also in the general ICU. How such a finding could modify the therapeutic approach remains elusive. The impact of AF on mortality is not clearly demonstrated in the ICU, with AF reflecting essentially the severity of the underlying disease.

failure and valvular heart disease are well recognized as cardiac components of AF, and on the contrary infl ammation, whatever its origin, is now considered an important noncardiac trigger [4]. In this context, it is not surprising that cardiac surgery generates a higher incidence of AF, and several data support this assumption. Eff ectively, in cardiac surgery the risk of AF is common in the fi rst 3 post operative days and a strength correlation has been found between various infl ammatory parameters and post operative arrhythmia [7,10]. In a prospective double-blind study, 236 patients undergoing elective heart surgery were randomized to receive placebo or dexa metha sone after the induction of anaesthesia. Patients who received dexamethasone had signifi cantly less new-onset AF in the 3 postoperative days (18.9% vs. 32.3%, P = 0.027) [11]. In a recent prospective, multicentre, double-blind study performed in cardiac surgery, hydrocortisone administered the day before and during the next 3 postoperative days signifi cantly reduced the occurrence of AF (30% vs. 48%, P = 0.004) [12]. In the same way, it has been showed that nonsteroidal anti-infl ammatory drugs administered in the postoperative course protected patients from AF [7]. Finally, in general ICU patients and in trauma patients requiring admission to the ICU, the presence of a systemic infl ammatory response syndrome was found to be linked to the risk to develop AF [5,13].
We probably better understand why Meierhenrich and colleagues found a 46% incidence of AF in septic shock patients [1]. Septic shock is a severe systemic infl ammatory disease, and the regular and signifi cant increase in C-reactive protein before onset of AF is another factor highlighting the role of infl ammation in the genesis of AF in the ICU. Nevertheless, we have to keep in mind that infl ammation alone is probably insuffi cient to generate such a high AF incidence, and other contributing factors should not be underestimated such as catecholamine use, central venous catheter catheterization and/or fl uid shifts [3,6,9,14]. Finally, it would be interesting to know whether, in the study by Meierhenrich and colleagues, patients received anti-infl ammatory drugs, notably steroids and/or activated protein C, and whether those patients who did receive such therapy experienced less AF.
What is the impact of AF on mortality in ICU patients? Th is is an old debate, and Brathwaite and Weissmann

Abstract
Atrial fi brillation (AF) is common in the intensive care unit (ICU) and is particularly frequent (46%) in septic shock patients. Infl ammation favours AF in the general population, and there is a growing body of evidence that infl ammation also plays a role in AF occurring after cardiac surgery but also in the general ICU. How such a fi nding could modify the therapeutic approach remains elusive. The impact of AF on mortality is not clearly demonstrated in the ICU, with AF refl ecting essentially the severity of the underlying disease.
already clearly discussed this dilemma in 1998 [3]. Most studies concerning AF in the ICU found that this arrhythmia increases ICU and hospital lengths of stay and/or mortality, but these patients were also the most severely ill [3,5,6,8,9]. In a prospective observational study conducted in trauma patients, AF was observed in the most severe patients and carried a higher mortality [13]. Nevertheless, the standardized mortality ratio was similar in patients who had AF and in patients who did not have AF, suggesting AF is rather a marker of severity without major impact on mortality [13]. Moreover, in a larger multicentre study performed in 26 European general ICUs, Annane and colleagues showed that, after adjust ment and propensity score use, supraventricular arrhyth mia did not increase the risk of hospital death [15]. Interestingly, in the study by Meierhenrich and colleagues the mortality in septic shock patients was not infl uenced by the presence of AF despite a higher Sequential Organ Failure Assessment score in AF patients [1].
AF is not just an artefact in the ICU, and the article of Meierhenrich and colleagues contributes to our better understanding of the mechanisms contributing to AF in the ICU. Nevertheless, the impact of such fi ndings remains elusive from a therapeutic point of view.