Discussion
Port-access MV surgery is nowadays a valid approach to treat all kinds
of MV disease according to contemporary techniques, resulting in a
clinical outcome equal to the conventional sternotomy approach. This
technique has been implemented in our department since more than 10
years now for the surgical management of most MV pathologies, with or
without the need for additional treatment of associated lesions as
atrial fibrillation and tricuspid valve dysfunction. Even after
including the obligatory learning phase, the clinical outcome as well as
the quality of MV procedure itself appeared to be non-inferior to that
of the standard MV surgery. Hence, the effect of the learning period
during the adoption of a new approach is not negligible. In a large
volume center, Holzhey et al. demonstrated that approximately 75 to 125
operations are required to achieve optimal results with MIVT,
characterized by a net decrease of bleeding complications, reoperation
for early valve failure and a nearly obsolete conversion
rate12.
Moreover, some complications are typically related to the surgical
approach. The risk of stroke is often estimated to be increased due to
the retrograde systemic perfusion and the potential risk for aortic
dissection, inadequate aortic de-airing and the deficient tactile
manipulation of the ascending aorta, regardless of the mode of aortic
clamping13-14. The incidence of major neurological
injury in our study was similar to others, revealing only one case of
retrograde aortic dissection. Here, we underscore the importance of
examining the vascular access – specifically the arterial side –
rigorously to limit such devastating complication as much as possible.
Considering the lower traumatic impact of a mini-thoracotomy on the
thorax compared to a sternotomy, one would expect a favorable effect on
respiratory dynamics and so, shorter ventilation time. In this
propensity-matched comparison, the ventilation times were identical as
well as the ICU stay duration. In an equivalent study design comparing
350 port-access patients and 365 sternotomy patients, Suri et al. found
a slight decrease of ventilatory support duration despite of
significantly longer procedural times15. However, it
is commonly known that the criteria for extubation may vary in-between
centers, and that even in one single center, the decision for extubation
may vary among ICU physicians, advancing thereby the subjective aspect
of this parameter.
A recurrent finding of many studies on this topic is the notification of
longer aortic cross-clamp and cardiopulmonary bypass
times5-11. The adverse relationship between these
factors and secondary organ dysfunction is well-known in the field of
cardiac surgery16-17. Through analysis of specific
organ function biomarkers, routinely sampled at the postoperative stage,
we found no significantly different effect between both approaches.
Biomarkers of myocardial and liver origin increased similarly in both
groups, but one has to consider that, through lack of specificity, it is
difficult to know what the real impact of each procedure on respectively
myocardial and liver function is. Interestingly, the creatinine-kinase
level was significantly increased after port-access surgery. Bearing in
mind that this count also represents global muscle damage, one can
relate this to a condition of relative limb ischaemia initiated by the
cannulation of the femoral artery and vein. As the duration of
cardiopulmonary bypass is rarely exceeding the critical duration
threshold for irreversible ischemia and rhabdomyolysis, it generally
remains clinically insidious. However, this issue needs to be accounted
for optimization of the peripheral cannulation strategy, by using
specifically designed arterial cannulas allowing distal leg perfusion or
by avoiding combined ipsilateral femoral artery and vein cannulation.
Kidney biomarkers are both specific and sensitive to renal function. Our
study demonstrated a rise of creatinine and ureum level, together with a
decrease of glomerular filtration, during the early postoperative
period, but independent of the used surgical approach. Nevertheless, the
incidence of effective kidney failure, requiring renal replacement
therapy, was low. Data on this organ-specific outcome are controversial,
some showing a clear advantage for the minimally invasive technique,
while others were not able to found any effect15,18.
One part of this confounding is related to the use of different study
designs including selection bias and other statistical methods to
analyze renal outcome.
Regarding the systemic inflammatory reaction, CRP counts remained
largely inferior during the first 48 hours after port-access MV surgery
than after conventional sternotomy. This suggests that the MIVT
technique is associated with a significant trauma reduction to the body,
with less activation of inflammatory mediators. Watt et al. reported
similar results in a systematic review on CRP post-surgery, and
identified that CRP counts were higher after bigger, more invasive
surgical procedures like thoracic surgery compared to smaller surgeries
such as cholecystectomy19. The results of Paparella et
al. confirmed that CRP and interleukine-6 counts were lower after MIVT
compared to sternotomy MV surgery20.
The lack of detrimental effect of longer duration of cardiopulmonary
bypass and cardiac arrest on secondary organ function, as observed after
port-access MV surgery, points to eventual intra-operative measures,
directly related to the management of cardiopulmonary bypass. The
conduct of cardiopulmonary bypass during MIVT surgery is commonly facing
flow restrictions, due to the use of smaller caliber cannulas via
peripheral vascular access, which on top of it, need to be properly
positioned, depending on adequate guidance via intra-operative
transesophageal echocardiography. Using kidney function as most robust
organ function endpoint, our group recently demonstrated that an
equivalent organ-specific as well as clinical outcome between MIVT and
conventional MV surgery is achievable through targeting an minimal
oxygen delivery during the duration of cardiopulmonary bypass. However,
in order to cope with the frequent inferences of intra-operative flow
restrictions over a longer procedural time during MIVT, other means need
to be applied as the tolerance of lower body temperature, the pursuit of
a higher intra-operative hematocrit level and the use of blood
preserving measures21. Moreover, operative times may
probably be less decisive for patient outcomes, as long as they are not
excessively long.