Discussion
To the authors’ knowledge, the herein presented study is the first to
scrutinize differences in outcomes after minimally invasive valve
surgery according to patient obesity class. Our results demonstrate
mini-AVR to be feasible and safe in obese patients irrespective of
obesity class, thus supporting a nondiscriminatory approach to operative
planning for patients with valvular disease. The postoperative lengths
of stay averaged four to five days and total direct costs
$22,000-25,000, both outcomes comparable between patients of any
obesity class. Thirty-day postoperative mortality affected two patients
in the study population, and they were of Class I obesity, notably the
largest patient cohort. Consequently, patients with comorbid obesity and
aortic valve disease should be considered for minimally invasive surgery
without concern for a disproportionately complicated course of recovery.
Performing minimally invasive valve surgery for obese patients has often
been a point of contention due to concerns of adequate surgical field
exposure, single lung ventilation, and the greater frequency of
additional chronic medical conditions in this population. Nevertheless,
studies comparing the outcomes of patients with normal (18.5-25
kg/m2), overweight (25-30 kg/m2),
and obese (> 30 kg/m2) BMI have shown
that experienced centers see comparable rates of postoperative
mortality, reoperation, blood transfusion, wound infection, stroke,
pacemaker implantation, and length of stay after minimally invasive
valve surgery.9 Aljanadi et al. found that
five-year survival between obese and non-obese patients undergoing
minimally invasive mitral valve surgery was similar (95.8% vs 95.5%,
p=0.83).10 In consideration of the patient with
obesity, Santana et al. demonstrated minimally invasive
approaches to be superior to full sternotomy with fewer postoperative
complications (23.5% vs 51.0%, p=0.034) and lower in-hospital
mortality (0% vs 8.3%, p=0.04).4
However, to date, these observations have not been scrutinized between
obesity classes, raising question of the broad application of these
findings across the continuum of higher BMIs. Our study thus builds on
previous work to share multiple important findings. First, we
demonstrated that mini-AVR is feasible in patients of Class I, II, and
III obesity. Second, mini-AVR is safe despite baseline STS PROM scores
that positively correlate with obesity class: patients amongst obesity
classes experience no different lengths of stay, short-term mortality,
hospital readmission rates, or perioperative complications (with the
exception of atrial fibrillation). Third, the cost of performance of
minimally invasive AVR (i.e. , via partial sternotomy or
minithoracotomy) does not differ between patient obesity classes.
Collectively, these observations support the equitable provision of
minimally invasive options to obese patients regardless of obesity class
– options that may in turn minimize perioperative pain, expedite
recovery, and reduce resource utilization without compromising clinical
outcomes.
Additional observations were made regarding the relationships between
select baseline patient characteristics and obesity classes. Common to
the current literature, we observed an association between obesity class
and metabolic comorbidities, namely, diabetes
mellitus;11 while our study found no difference in the
frequency of diabetes between patients with Class I versus Class II
obesity, diabetes was significantly more common amongst patients in the
Class III obesity cohort. The STS PROM score also demonstrated a
stepwise relationship with obesity class. In line with this finding,
Ghanta and colleagues have shown that STS PROM tends toward lower risk
scoring for obese patients (spanning Class I and II BMIs) versus normal
weight, overweight, and morbidly obese (Class III)
patients.12 In contrast to the current literature that
correlates hypertension and obesity class, however, our study found no
such association.12,13 This is due to an exceedingly
high prevalence of hypertension across our study population (affecting
90-95% of patients on average), which would have required a large study
population to differentiate minute differences amongst obesity cohorts.
Upon observation of the primary study outcomes, we found patient obesity
class to have no effect on postoperative length of stay or direct cost
of mini-AVR. Whilst Mariscalco et al. ’s obesity paradox in
cardiac surgery continues to be debated, single center studies have
shown that patients with higher BMI experience longer lengths of stay
and more expensive costs of care after cardiac
surgery.12,14 At our academic medical center,
appropriate operative planning, intraoperative patient positioning, and,
over the study period, a gradual implementation of typical Enhanced
Recovery After Surgery (ERAS) protocol elements (e.g. ,
preoperative conditioning, early extubation) have perhaps prevented BMI
from dictating operative room time and costly resource utilization. With
a multidisciplinary team of cardiac surgery anesthesiologists and
physician assistants, critical care physicians, and nurse practitioners
providing comprehensive perioperative care, our patients are optimized
for discharge within four to five days of their operation, as
demonstrated in this study. Our study also failed to reveal a difference
in 30-day mortality after mini-AVR amongst obesity classes,
complementary to the meta-analysis conducted by Mariscalco et
al. 3 Not only might obese patients experience
paradoxically lower risks of mortality after cardiac surgery, but this
risk may be comparable across all classes of obesity at least in the
population of patient who undergo minimally invasive valve surgery.
Postoperative complications were generally experienced no differently by
patients of any obesity classes. Only new atrial fibrillation was less
frequently encountered by patients of Class I versus those of Class II
and III obesity. With the incidence of onset of this arrhythmia as high
as 20-50% after cardiac surgery, coupled with obesity as a known
independent risk factor for atrial fibrillation, our finding should not
preclude patients with Class II and II obesity from receiving minimally
invasive valve surgery.15,16
There are several limitations to this study. First, bias can be
attributed to its retrospective, observational design due to the lack of
randomization, a control group, and a priori data field
selection. Second, while our results demonstrated no difference in
30-day mortality amongst obesity classes, two patients in the study
population did not survive the duration of the postoperative follow-up
period. While we expect that these deaths occurred in the Class I
obesity population by random chance consistent with its largest cohort
size (total study population: Class I n=106 vs. Class II n=42 vs. Class
III n=34), our study is under-powered to detect significant differences
between such small event rates and thus to arrive at a sound conclusion
regarding 30-day mortality amongst obesity classes. To better elucidate
mortality differences amongst obese patients undergoing mini-AVR, a
large database or multi-center study should be conducted.