Introduction:

In early 2002, transcatheter aortic valve replacement (TAVR) has been the best option for patients with symptomatic aortic stenosis (AS). Initially, TAVR was limited to patients at high or prohibitive surgical risk patients. Later discovered that it can support both intermediate and selected low-risk patients also. With advancements in technology and technique, TAVR can now be safely performed in an expanding population with aortic valve disease with more complex scenarios.

 

Challenges in Femoral Access

Transfemoral (TF) access is accepted as the gold standard and can be successfully achieved in the vast majority of AS patients. These mainly comprise (a) small native vessel size, (b) severe peripheral artery disease, and (c) extensive vessel and aortic tortuosity. In patients with challenging anatomies for a TF approach and other complex scenarios, the approach should be estimated based on various factors.  Small Native Vessel Size - largely depend on the delivery system and the size of the transcatheter heart valve (THV).

Using contemporary low-profile sheath designs, the minimal vessel size may be as low as 5.0 mm and is mostly used in patients with small vessels. Preprocedural computed tomography (CT) imaging with three-dimensional reconstruction is crucial to correctly determine the luminal diameter. Severe Peripheral Artery Disease - frequently found in AS patients, as both entities share common cardiovascular risk factors such as age, smoking, hypertension, diabetes, and chronic kidney disease.

PAD is associated with increased mortality, bleeding complications, and readmission rates after TAVR due to (a) interfere with adequate vessel puncture, (b) compromise sheath or device passage, and (c) increase the risk of major vascular complications such as dissection, bleeding and plaque disruption with acute limb ischemia. Extensive Vessel and Aortic Tortuosity- may prevent successful TF TAVR and in worst cases associated with increased vascular complications such as dissection, rupture, and life-threatening bleeding.

 

Challenges in Aortic Anatomy

Horizontal aorta and concomitant aortic aneurysm are the challenges and may vary device delivery and accurate implantation of a THV in complex Aortic anatomy. Horizontal aorta- an excessive aortic angulation measured in coronal projection. It was initially defined as angulation of ≥48° between the horizontal plane and the plane of the aortic annulus. In theory, this may be explained by the longer stent frame and the non-steerable delivery catheter which may lead to suboptimal valve positioning compared to devices such as the SAPIEN 3.

However, conflicting results have been published regarding the impact of a horizontal aorta on outcomes and success rates using newer-generation devices, suggesting a comparable safety profile between self-expanding and balloon-expandable prostheses. Concomitant aortic aneurysm- used in patients with dilatation of the ascending aorta (>40 mm) and found mostly in AS patients. Thus, a conservative approach toward aortic dilatation in high-risk TAVR patients seem to be justified. complex aortic root pathology is still considered a relative contraindication to TAVR and should be limited to highly selected patients. In this context, a transapical approach combined with a right subclavian arteriotomy as a backup arterial cannulation site in case of conversion to open-heart surgery has been proposed.

 

Challenges in Bicuspid Aortic Valve

There is a significant risk the factor for premature aortic valve disease a most common cause of isolated AS in patients aged 50–70 years and is present in up to 20% of the AS in Western population over 80 years of age. three-dimensional imaging, mainly ECG-gated CT, is essential in the diagnosis of BAV, as echocardiography detects congenital BAV morphology only in 58–66% of cases. BAV develops due to abnormal vasculogenesis, Failure of adjacent cusps to separate from each other results in the development of an aortic valve with only two cusps, with one cusp usually larger than the other.

In the context of BAV, SAVR remains the treatment of choice, and TAVR can be an alternative to surgery in patients who are at high surgical risk. However, as lower surgical risk trials have recently shown that TAVR is non-inferior or even superior to SAVR in short term outcomes for patients with low surgical risk, the proportion of potential TAVR candidates with BAV is likely to increase in the future.

 

Challenges in Pure Aortic Regurgitation

Efficacy of TAVR in native pure AR (NPAR) has been largely limited by inherent anatomical differences, including the lack of a calcified native valve apparatus to anchor the THV in place, large aortic annuli, and dilation of the left ventricle. Adding to it, advanced age and multiple comorbidities were frequent reasons for conservative treatment. In selected patients with NPAR and high surgical risk, off-label TAVR is technically feasible with acceptable early morbidity and mortality.

The lack of a native valve calcification to anchor the THV in place and the dilated aortic valve annulus represents the main challenges during TAVR in patients with NPAR. a. Non-dedicated THVs was originally developed to be implanted in patients with AS, as fixation of these devices depends on the calcified aortic annulus. b. Dedicated TAVR Devices for NPAR are second-generation TAVR devices that rely on clip-based fixation over the native aortic valve leaflet independent of annular calcification.

 

Challenges in Valve-in-Valve Procedures

Currently available data on ViV TAVR are obtained from retrospective studies, which showed that ViV TAVR is feasible and safe therapeutic option with favorable acute procedural results and low complication rate. Recent studies show a comparison between VIV TAVR to redo SAVR stating VIV TAVR was associated with lower rates of 30-day all-cause death, cardiovascular death and new onset of atrial fibrillation compared to redo SAVR, while permanent pacemaker implantation was less often reported after redo SAVR. However, in a median follow-up of 516 days, no significant difference was observed between the 2 groups in the composite endpoint of cardiovascular death, all-cause stroke, myocardial infarction, and rehospitalization for heart failure.

 

Challenges in Coronary Anatomy

CAD is significantly less prevalent among low-risk patients, challenges in coronary anatomy remain an important issue in the context of TAVR. These include (a) low coronary Ostia, (b) optimal revascularization strategy, and (c) coronary access after TAVR. Low Coronary Ostia- a short distance between the aortic annulus and the coronary Ostia may pose a considerable challenge due to the potential risk of coronary obstruction. Therefore, in the presence of low coronary Ostia, guidelines support the use of SAVR in preference to TAVR.

Optimal Revascularization Strategy- common among elderly AS patients as both entities share common risk factors. Concomitant myocardial revascularization is recommended in patients with significant CAD (≥70% reduction in luminal diameter) and should be considered in patients with moderate-severe CAD (≥50–70% stenosis). Coronary Access After TAVR- With the expansion of TAVR toward a lower-risk population, the need for coronary access after TAVR will continue to rise as underlying CAD progresses over time. Coronary access after TAVR may be challenging due to various factors including STJ diameter, coronary height, type of THV, and valve implantation depth.

 

Conclusions:

For patients with aortic valve disease, TAVR has promising scope in this treatment. In light of the expansion toward a younger, lower-risk group, TAVR will be used in an expanding patient population posing a variety of concomitant anatomical and clinical challenges. On contrary, these difficulties can be overcome with contemporary THVs and techniques. So, TAVR will need to constantly evolve in the future.

Source

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8076502/