Does a thickened mitral valve raise risk of sudden cardiac arrest/death?

Yes: A thickened mitral valve can lead to decreased and inadequate blood flow from the atrium to the ventricle which can lead to ventricular tachycardia or ventricular fibrillation. It is directly proportional to how stiff the valve becomes. These two conditions put one at higher risk of sudden death/cardiac arrest

No.: Thickening of the mitral valve alone may be related to age, prior inflammation as in rheumatic disease etc. Unless there is a significant abnormality of the function of the valve or of the heart muscle, valve thickening itself should not be of concern significant concern particularly with regard to cardiac or sudden death.