Discussion
Low flow, low gradient aortic stenosis (LFLGAS) is associated with a
higher risk of a cardiac event and heart failure, increasing the rate of
all-cause mortality, cardiovascular- and valvular-related death27. Aortic valve replacement (AVR) is effective in
either classical or paradoxical LFLGAS 28. AVR has
shown to be able to reduce the rate of adverse events and improve left
ventricle ejection fraction (LVEF), enhancing long-term survival when
compared to non-aortic valve replacement (noAVR) approaches. However, in
patients with concomitant coronary artery disease (CAD and reduced
contractile reserve (CR), the preoperative risk is too high to opt for
AVR 29,30. In these cases, medical management is the
recommended alternative approach, despite its reduced long-term survival
rates 31. The aim of techniques alternative to AVR is
to treat patients who are inoperable because of concomitant
life-threatening comorbidities and the reduced life expectancy32. The therapy has more palliative purposes, and it
is per se related to complications such as stroke, aortic regurgitation,
myocardial infarction 33, restenosis, and
deterioration of the aortic valve (AV) 34,35.
The main finding of your meta-analysis is the superiority of AVR over
noAVR in enhancing survival in patients with LFLGAS. Our result is
consistent with studies reporting improved outcomes following AVR rather
than noAVR 36. AVR bears an
elevated preoperative risk, but
its benefits still outweigh the disadvantages when compared to noAVR.
This is attributable to the fact that in high-risk patients with low
life expectancy, medication with or without valvuloplasty represents a
mere palliative cure not aimed at achieving therapeutic responses. NoAVR
approach is mainly oriented towards the management of the cardiovascular
risk factors, which include controlling hypertension and volume status.
Furthermore, the low survival rate in the noAVR group could be the
result of the increased risk of restenosis after valvuloplasty, which
leads to deterioration of the valve already after one year37,38. Indeed, if, on the one hand, valvuloplasty
reduces the transvalvular pressure gradient and improves symptoms, on
the other hand, the post-valvuloplasty AVA does not exceed 1.0
cm2 33,39. Moreover, our result
could have been influenced by the employment of the TAVR technique in
some of the patients included in our analysis, as TAVR has better
survival rates than SAVR as well as better LVEF recovery3,40,41.
The second finding of our meta-analysis was the increased survival at
follow up in patients with reduced LVEF compared to those with preserved
LVEF in the AVR group. Despite this could be initially counterintuitive,
it is critical to acknowledge that it has been widely proved that LV
dysfunction is present even with preserved LVEF. Indeed, studies
employing speckle-tracking echocardiography have shown that in patients
with LFLGAS and normal LVEF, LV systolic longitudinal dysfunction
manifests as a result of the increased afterload 12.
Additionally, in patients with a low LVEF undergoing coronary artery
bypass grafting (CABG) concomitantly to AVR, long-term survival appears
to be enhanced. CABG makes the myocardium in certain areas viable,
increasing LV function, and exerting a protective effect35,42 leading to an improvement in LVEF that was
reduced consequently to CAD.
Being the majority of the patients in our meta-analysis operated on
AVR+CABG, we believe that the simultaneous CABG procedure might have
been beneficial for patients with low LVEF 2.
Furthermore, we found that LVEF does not impact survival in the noAVR
group. We believe that these results are attributable to the fact that
conservative management has palliative purposes, thus not improving
cardiac function but only dealing with symptoms 31.
This is because both classical and paradoxical LFLGAS can induce heart
failure via different mechanisms. Patients with classical LFLGAS have
low survival rates as the cardiac function is severely compromised by
the small LV cavity size due to LV hypertrophy, severe myocardial
fibrosis, and the restrictive pattern of LV filling 2.
On the other hand, some studies suggest that conservative management is
not particularly useful in increasing survival in the case of
paradoxical LFLGAS as a result of the advanced stage of myocardial
fibrosis, the systolic and diastolic dysfunction and the reduced stroke
volume index 2. Moreover, patients with paradoxical
aortic stenosis mostly have diffused atherosclerosis and increased
stiffness of arterial walls, which decreases arterial compliance2. In this situation, medical management is only
useful in treating resulting hypertension rather than affecting the
aortic valve 3.