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Aortic Valve Disease and Transcatheter Aortic Valve Replacement

Non-invasive Imaging: Magnetic Resonance Imaging


Aortic stenosis and transcatheter aortic valve replacement (TAVR) is an exciting topic that has been spreading throughout the cardiology community worldwide.  The development and adoption of the new technique have improved the mortality of inoperable and high risk patients with severe aortic stenosis.  In this session, experts in the field discussed the role of CMR in aortic valvular disease as well as its role in TAVR.

To start, Gerald McCann, MD (University Hospitals Leicester) gave a nice overview of the clinical pathophysiology of aortic stenosis (AS), and the need to identify individuals that would benefit from early intervention. He described the natural course of aortic stenosis, and how 80% of the patients who died from severe aortic stenosis had symptoms.  Aside from the severity of AS, there has not been any specific markers that identify patients that may benefit from aortic valve replacement.  One target, which he proposed, was to look into the myocardial extracellular space.  Fibrosis has been well documented in patients with AS.  It is correlated with worse prognosis, and does not appear to be reversible after valve replacement.  There is variability in the amount of fibrosis in patients who underwent aortic valve replacement. Thus, perhaps novel imaging techniques have the potential to individualize the timing of intervention in severe AS.

This was followed by a presentation by Clerio Azevedo, MD (Clínica de Diagnóstico por Imagem) demonstrating how CMR can provide a thorough assessment of aortic stenosis. CMR is unique in that it can provide a gold standard assessment of biventricular volumes and function, combined with a reproducible quantification of the degree of stenosis, as well as characterization and quantification of myocardial injury (both by late gadolinium enhancement and T1 mapping). The presentation included practical tips from an experienced center in planning the flow sequences to maximize accuracy. However, it is in the quantification of myocardial injury that Dr Azevedo felt CMR had the most potential: both with the role of LGE and its recognized prognostic implications, and in the future with T1 mapping.

Switching from aortic stenosis, Alex Pitcher, PhD (University of Oxford) discussed the role of CMR in the assessment of aortic regurgitation (AR).  Although echocardiography remains the major modality in the identification and qualitative assessment of AR, as well as left ventricular (LV) volume and function, it does have some weaknesses in separating moderate from severe AR, assessment of eccentric jets, and accurate quantitation as it involves many assumptions.  With CMR, phase contrast can be used to directly quantify AR despite eccentric jet, but with care regarding phase contrast background flow offset errors. Aside from the aortic valve, it can also provide accurate LV volume and function, which is highly reproducible. Quoting the work of Dr. Myerson et al, Dr. Pitcher illustrated that in patients with asymptomatic moderate to severe AR, regurgitant fraction was able to risk stratify patients with both echo and CMR, as well as CMR determined LVEDV >246mL portending to poorer prognosis.  The combination of the two parameters was able to identify patients who may require surgery within a few years.  Dr. Pitcher also described the advantage of CMR in the assessment of the aortic root for surgical planning, which included cardioplegia strategies, coronary location and cross clamping sites.  After aortic valve replacement, CMR can remain helpful in assessment of paravalvular leaks.  At the end of the session, Dr. Pitcher brought up what is on the horizon for CMR in AR:

•    Replication of prognostic cut points with CMR
•    Use of CMR to predict likelihood of good outcome after aortic valve replacement and repair (identify patients better)
•    Prospective studies comparing CMR and selective pre-operative transoesophageal echo to routine transoesophageal echo alone.
•    Improved understanding of the role of CMR in TAVI/TAVR and in prosthetic valve leak.

Dr Joao A.C. Lima, MD (Johns Hopkins University) presented on novel mapping techniques in aortic valve disease and highlighted that despite the incredible advances in our understanding and management of aortic stenosis, probably the most important decision in these patients is the optimum timing of valve surgery remains very controversial. However, there are a number of promising imaging features that may in the near future answer this important question. The role of focal scar, extracellular volume, lipid accumulation and myocardial perfusion reserve on prediction adverse features all have the potential to change the way we manage aortic stenosis. However, comparative studies are needed to clarify which novel parameter is the best prognostic marker. Studies, such as RELIEF AS, will hopefully give us confidence in these new methods.

With the rapid adoption of TAVR in the treatment of severe aortic stenosis (AS), the appropriate and accurate assessment of patients with aortic stenosis for TAVR is paramount.  In this session, Matthias Gutberlet, MD PhD (University of Leipzig) discussed the role of CMR in the pre-procedural, post-procedural and intra-procedural assessment.  In regards to pre-operative assessment, CMR is great in the assessment of aortic valve stenosis severity, left ventricular volume, function and mass.  There is also potential for CMR to identify subclinical tissue characteristics with late gadolinium enhancement imaging.  Although CMR has the capabilities to assess annular size, coronary ostial height and vascular access sites, cardiac CT with contrast remains the standard due to the higher spatial resolution, better signal-to-noise and contrast-to-noise as well as shorter acquisition time despite a better temporal resolution.  For post-procedure assessment, CMR can be helpful in the assessment of paravalvular leaks and its severity, left ventricular remodeling by volume, function and mass.  Intra-procedurally, CMR has demonstrated potential in assisting positioning of the catheters and valve; however, this is still investigational (which has only been performed in vitro and in animals only).

The final presentation, by Calvin Chin, MD (University of Edinburgh) explored the future directions of AS imaging by CMR and other modalities. The audience was transported 30 years into the future as an older Dr Chin diagnosed himself initially with non-severe aortic stenosis, which then over time progressed to severe.  The future role of FDG-PET and calcium score to predict the progression of aortic stenosis from mild/moderate to severe, as well as a marker to measure response to future anti-calcification treatment was discussed. Once Dr Chin’s hypothetical aortic stenosis reached the severe stage, he could at least be comforted that T1 mapping and fibrosis volume would accurately prognosticate the optimum time for surgery.  (Picture) I strongly agree with Dr Chins closing remark, “With a lot of developments in imaging the aortic valve, and drug treatment likely it will be very interesting to see what happens in 30 years.”

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.