DISCUSSION
The main finding of this single-centre, retrospective large-cohort study
is that preoperative AF is independently predictive of long-term
all-cause mortality at a median follow-up of 4 years and remained
independently predictive after adjustment for other risk factors and in
propensity score-matched analysis following first-time isolated surgical
AVR.
Our study further lends support to previous studies investigating the
relationship between preoperative AF and mortality after AVR. Ngaage and
colleagues demonstrated an increased risk of major adverse
cardiovascular events with preoperative AF in 381 patients undergoing
surgical AVR, however preoperative AF was not predictive of all-cause
long-term mortality after risk factors adjustment, which was probably
due to the small sample size. Saxena and colleagues showed that
preoperative AF significantly increases the risk of all-cause mortality
by 36% after surgical AVR. However, intraoperative variables such as
bypass time and aortic clamp time were not adjusted for in their
analysis, despite the bypass time being significantly different between
the study groups. These important variables have been shown to affect
clinical outcomes following cardiac surgery. Of note, there was no
significant difference between the bypass time and aortic clamp time
between the two cohorts in our study (Table 1). Levy and colleagues
found that preoperative AF was independently associated with more than
5-fold increase in long-term mortality (HR 5.5, 95% CI, 1.13-26.15;
P=0.03), however, the study involved only 83 patients undergoing
surgical AVR, all with poor left ventricular function. The remarkable
hazard ratio expressed in Levy’s analysis likely reflects the
well-documented fact that AF is poorly tolerated and portends a worse
prognosis in patients with congestive heart failure. Transcatheter
aortic valve implantation (TAVI) is currently the gold standard
intervention for non-surgical candidates with aortic valve stenosis. A
meta-analysis of observational studies found that preoperative AF
significantly increases the risk of long-term all-cause and
cardiovascular mortality after TAVI.
Wang and colleagues demonstrated that preoperative AF was a predictor of
30-day mortality after surgical AVR. In our study, patients who had
preoperative AF were significantly older with more comorbidities such as
hypertension, diabetes, peripheral vascular disease, previous myocardial
infarction, renal disease and left ventricular dysfunction compared with
patients who had preoperative SR. This is probably the reason for the
prolonged in-hospital stay observed in the preoperative AF cohort.
However, we observed no significant difference in the operative or
30-day mortality between the 2 study groups. One plausible explanation
is that our study only included patients undergoing elective surgery
whereas 62% of Wang et al.’s preoperative AF cohort had urgent or
emergency surgery compared with 48% in the preoperative SR cohort
(P=0.008). Urgent or emergency surgery was predictive of morbidity and
mortality during follow-up.
Our results suggest that preoperative AF has no value in formalized
surgical risk-stratifying tools, such as the EuroSCORE, as we did not
find in-hospital mortality to be impacted by preoperative AF.
There is scope, however, for preoperative AF to be incorporated into
long-term surgical risk assessments, or at least to inform
decision-making when counselling patients as to the risk of AVR in the
outpatient setting. Of greater clinical interest is whether restoration
of SR pre- or perioperatively reverses the risk attributable to
preoperative AF. This is yet to be determined and represents a highly
worthwhile area for further studies.