Atrial Fibrillation and Valvular Heart Disease
Do patients with degenerative aortic stenosis treated with TAVR still count as patients with ’valvular heart disease’? There is evidence to say that this may not be the case.
Firstly, the pathophysiological mechanism of atrial fibrillation in aortic stenosis is different than in other valvular lesions. For example, mitral regurgitation is associated with left atrial volume overload, and the left atrium is often enlarged. In aortic stenosis, there is left ventricular pressure overload, which leads to left atrial pressure overload; consequently, left atrial size is not the important outcome measure in aortic stenosis. Different valvular disorders affect the left atrium differently.38
Secondly, the original papers on the presence of clot in the LAA focused on the different presence of clots based on rheumatic and non-rheumatic valve disease; however, patients with rheumatic valve disease were more likely to have mitral stenosis as opposed to aortic valve disease. Blackshear et al.39 analysed the results of 23 studies, comparing a total of 3,504 patients with rheumatic valve disease and 1,288 patients without rheumatic valve disease. In this paper, there were found to be more LAA clots in the patients with non-rheumatic valve disease than in patients with rheumatic valve disease. Based on these findings, the idea arose that LAA obliteration may be an answer for atrial fibrillation without valvular heart disease. However, the vast majority of these valvular heart disease patients were patients with rheumatic mitral valve disease. It is a significant jump from patients with untreated rheumatic valvular heart disease to patients after TAVR.
Finally, not all prosthetic valves are alike. Compared with mechanical valves, bioprosthetic valves have a lower risk of stroke, as low as 1.3 ± 0.3 %.40 With a different stroke rate, there is even more evidence that the valve replacement type plays a significant role in the overall anticoagulation strategy.
How Will Left Atrial Appendage Closure Decrease the Stroke Risk in Transcatheter Aortic Valve Replacement?
There are four main areas where there is risk of stroke in patients undergoing TAVR. These include:
LAA closure only affects the risk of clot in the LAA. As soon as the valve has been replaced in aortic stenosis, the risk of clot in the LAA should be similar to patients with ‘non-valvular’ atrial fibrillation. The atrium is not excessively dilated, such as in mitral stenosis or mitral regurgitation. This would be the area where LAA occlusion may have an impact.
For the TAVR procedural risk, LAA closure does not have a significant impact. This may account to 50 % of strokes that happen in the first 30 days, as these occur in the first 24 hours. All steps of the procedure add to the risk, especially valve advancement and positioning.8 The key to success here may be smaller sheaths, better delivery systems and easier to position valves. Carotid protection systems may also provide a reduction in risk, but this has not yet been proven. In fact, placement of the carotid protection system can lead to an embolic risk or interference with the TAVI valve delivery system.7
The risk of thrombus on the valve is difficult to estimate. The guidelines therefore point to aspirin (indefinitely) and clopidogrel (1–6 months), as listed in the ACCF/AATS/SCAI/STS guidelines41 and the CCS guidelines.19 Use of LAA closure to replace warfarin is not likely to change this risk, and dual antiplatelet strategy should be continued.
Finally, there can be clots in other areas. These include left atrium (outside of the LAA), left ventricle, aorta and carotids. TAVR may increase left-sided outflow and decrease stasis, which may decrease the risk of stroke from thrombus in the left atrium or left ventricle. Use of smaller delivery systems or a transaortic/transapical strategy may also decrease risk of stroke from an atherosclerotic aorta. Risk of stroke from carotid artery disease would be similar.
LAA closure is therefore only likely to help decrease part of the overall stroke risk for these patients, but may help in patients with atrial fibrillation, where the risk of stroke from the LAA is increased.