Study limitations
One of the limitatations, which may have influenced study results, is that patient number was low and the etiology of low ejection fraction was both ischemic and dialted cardiomyopathy, furthermore were dont have only patients with LBBB but we also have patients with RBBB and LBBB type interventricular conduction delay. All of these may have an influence on the improvement of mitral regurgitaiton after CRT implantation. Another limitation was follow up period restricted to three months, as this period is not adequate to predict improvement either in LVEF or in mitral regurgitation. In three months follow up, no marked change was found in LVEF and volumes but in the long term, improvement in these parameters associated with left ventricle reverse remodelling, may decrease the degree of MR. For its evaluation, long term follow up will be more appropriate.
In addition, although the severity of mitral regurgitation was evaluated with transthoracic echocardiography at the third month follow up , as the patients did not undergo control TEE examination, the parameters of mitral valve, which are evaluated with TEE, improving and influencing the response to treatment of mitral regurgitataion, could not be determined.