Discussion
Overall AF following cardiac surgery was detected in 24% of patients.
POAF (AF following cardiac surgery without history of AF) was detected
in 15.5% of patients without history of AF prior to surgery. Among
patients with history of AF, AF following surgery was detected in 70%.
History of AF and age were independent predictors of AF following
cardiac surgery.
The true incidence of POAF following cardiac surgery remains unclear due
to variability in methods of detection and definitions of POAF [12].
The majority of studies reported POAF rates between 20-40% following
CABG, 40-50% after valve surgery, up to 60% following combined valve
and CABG surgery, and as high as 80% following multiple valve surgery
[11]. Mariscalco et al. reported that among 17,262 cardiac surgery
patients, 4,561 (26.4%) developed POAF, primarily within 2 days of
surgery [13] . Bessissow et
al. reported that the incidence of POAF among adults aged 45+
ranges from 20% to 40% among those undergoing thoracic or cardiac
surgery [14]. In our study,
the overall AF following cardiac surgery was 24%, and POAF was 15.5%.
This rate (15.5%) of POAF seems to be lower than the rate reported in
the literature if we take into account only patients with no history of
AF. The discrepancy could be attributed to differences in definition and
detection of POAF. Part of patients undergoing cardiac surgeries who are
considered to have no history of AF actually have undetected and or
asymptomatic paroxysmal AF before surgery as many of them have risk
factors for AF. Thus, to overcome this limitation, we decided to
investigate the overall AF following cardiac surgery irrespective of
history of AF before surgery.
Many risk factors for POAF were reported in different studies. In
general, older patients and those with more preoperative comorbidities
are more likely to develop POAF. These risk factors were used to create
predictive scoring systems and risk models [2]. Risk models are
based on known risk factors such as age, race, CHF, a high EuroSCORE
rating, COPD, emergency operation, decreased preoperative left
ventricular EF, and decreased estimated glomerular filtration rate
(eGFR) [13, 15-17]. However, Current risk prediction models for POAF
are derived from epidemiological studies and are not based on
pathophysiologic mechanisms. Due to that they are moderately accurate at
best, these models are infrequently used in clinical settings [9].
Currently, no validated, evidence-based threshold exists to stratify
patients according to risk of developing POAF, and there are no
published studies that delineate risk factors for POAF based on
significantly differentiating factors.
In general, the major risk factors for POAF among both non-cardiac
surgery and cardiac surgery patients are male sex, advancing age, CHF
history, and hypertension [14,18]. Among cardiac surgery patients,
specifically, history of arrhythmias and AF, history of vascular and
coronary artery diseases, valvular heart disease, decreased preoperative
kidney function, and type of surgery are also implicated
[11,13,14,16,19-23]. Our results are consistent with the previous
reports in some aspects. In univariate Cox regression analysis, age and
history of AF were found to be predictors of AF post-surgery. Type of
surgery and hypertension tended to predict AF following cardiac surgery.
In multivariate Cox regression analysis, age and history of preoperative
AF were independent predictors of AF following cardiac surgery. Indeed,
history of AF was previously reported to be strongly associated with
POAF complicating cardiac surgery [24]. However, this report
emphasizes the importance of cautious interpretation of the data from
different studies as some studies included patients with history of
arrhythmias and AF. The risk of POAF increases non-linearly with age,
and a large retrospective study of nearly 15000 patients who have
undergone cardiac surgery showed that POAF incidence increases at higher
rates over the age of 55 years [25]. Recently, Eikelboom et
al. reported in systemic review and meta-analysis that POAF occurred in
36,988 (23.7%) out of 155,575 patients [9]. Patients with POAF were
older than those without it (mean, 68.7 vs 63.7 years). There were no
sex differences between the groups. Hypertension, dyslipidemia,
diabetes, and smoking occurred equivalently in patients who did and did
not develop POAF [9].With respect to intraoperative factors, there
was no difference between patients with and without AF post cardiac
surgery, except for aortic clamp time which tended to be longer among
patients with AF post cardiac surgery (p=0.07). In some studies,
procedural factors such as the duration of the aortic cross-clamp time,
location of the venous cannulation, and duration of cardiopulmonary
bypass have been shown to affect the rates of POAF [4].
Finally, POAF after cardiac surgery was reported to be associated with
increased short-term and long-term morbidity and mortality, including an
eightfold increase in the risk of subsequent AF, as well as a higher
rate of stroke and cardiovascular death [3,7,9,26,27]. In our study,
there was no difference in complications between the two groups, except
for readmission within 30 days, which tended to be more frequent among
patients with AF following cardiac surgery.