Role of activated protein C resistance in left atrial thrombogenesis in patients with mitral stenosis

Activated protein C resistance (APC-R) is the most common inherited cause o f clinically apparent venous thromboembolism. Previous data indicate that l eft atrial thrombus (LAT) formation is a common complication in mitral sten osis (MS) and a hypercoagulable state exists in these patients. The aim of this study was to invastigate the association between APC-R and LAT formati on in patients with MS. Seventy-seven consecutive patients with rheumatic M S were included in this study. Transesophageal echocardiography was perform ed on all patients to assess the presence of any thrombus or spontaneous ec ho contrast (LASEC) in the left atrial cavity or appendage. Thirty four of the patients had LAT and 43 did not. Prevelance of APC-R was smiliar betwee n the two groups of patients with and without LAT (23% vs 16%, p=0.425). LA T(+) patients had higher incidence of atrial fibrillation (AF, 74% vs 51%, p=0.046) and LASEC (71% vs 19%, p<0.001) compared to LAT(-) patients. On mu ltivariate regression analysis, only the presence of LASEC achieved statist ical significance as an independent risk factor for LAT formation (p=0.0001 , odds ratio=9.589, 95% confidence interval [CI]=3.143-29.251). Because on univariate analysis both LASEC and AF were associated with LAT, we also com pared the prevelance of APC-R in the subgroups of patients who have these r isk factors with and without LAT. There was a correlation between the prese nce of APC-R and LAT in the AF(+) subgroup of MS patients (p=0.033, odds ra tio=8.167, 95% CI=1.001-72.812). However, the presence of APC-R was not ass ociated with the increased risk of LAT in LASEC(+) patients (p=0.217, odds ratio=1.200, 95% CI=1.003-1.435). Although the presence of APC-R itself is not an independent risk factor for LAT formation in MS, it may increase the risk of LAT when present in combination with AF (as an additional risk fac tor) in these patients.