A Scoring System to Predict the Risk of Atrial Fibrillation in Chronic Lymphocytic Leukemia and Its Validation in a Cohort of Ibrutinib-Treated Patients

BACKGROUD. The B-cell receptor inhibitor ibrutinib has significantly improved treatment and overall management of chronic lymphocytic leukemia (CLL). Although several data derived from clinical trials suggest that ibrutinib increases the risk of atrial fibrillation (AF), the incidence of AF in a real-life cohort of CLL patients is unknown. Furthermore, it would be clinically relevant to identify patients at high risk of AF during ibrutinib.

The aim of this study is to report the prevalence and risk factors of AF in ibrutinib-naive CLL, in order to define a predictive model for the development of AF and to test it in a cohort of subjects receiving ibrutinib.

METHODS. We retrospectively analyzed data from 860 ibrutinib-naive CLL patients, referred to the Padua University hospital. Comorbidities, clinical and biological prognostic markers were analyzed using the Mann-Whiney, Fisher exact or Chi-square tests, when appropriated. Time to AF (TTAF) and overall survival (OS) were evaluated with Kaplan-Meier method. Univariate and multivariate Cox models were run to identify independent factors associated with AF. Then, risk values were obtained based on the hazard ratios. The score for AF was calculated as the sum of each risk values. Subsequently, the model was evaluated in a cohort of 354 ibrutinib-treated patients referred from 8 Italian hematological centers.

RESULTS. Among the 860 patients from Padua hospital, 60% were male, 49% were older than 65 years, 73% were Binet A stage at diagnosis and 41% underwent at least one line of treatment. A prior history of AF was present in 21 patients (2.4%) at CLL diagnosis, while, among the remaining 839 patients without a previous history of AF, 47 (5.6%) developed it after a median follow-up of 9.4 years, resulting in an estimated incidence of almost 0.8% cases/year. Moreover, the median OS for patients with AF was significantly shorter than that patients without AF (12 vs 22 years, p<0.0001). Based on univariate and multivariate analysis, variables associated with the risk of AF were: age>65 years (p=0.001, 1 point), male gender (p=0.003, 1 point), valvular hearth diseases (p=0.001, 2 points), cardiopathy (p<0.001, 3 points), hyperthyroidism (p=0.001, 1 point), chronic lung diseases (p=0.001, 1 point), diabetes mellitus (p=0.023, 1 point), severe infections (p=0.019, 1 point). As expected, no clinical and biological prognostic markers (i.e. Binet stage, IGHV mutation, TP53 abnormalities) for CLL were associated with an increased risk of AF. A predictive model was designed based on these factors and it stratified patients into 4 different groups. The estimated TTAF after 15 years of follow-up were 0%, 10%, 19% and 61% for patients with score 0, 1-2, 3-4, and ≥5 respectively (p<0.001, Fig. 1A). Furthermore, it underwent internal validation using the bootstrap method.

Subsequently, we applied our AF model to a cohort of 354 ibrutinib-treated patients, 64% were male, the median age was 69 years, 88 were treatment-naive, 70% U-IGHV and 39% harbored TP53 abnormalities. Forty-four subjects developed AF after a median observation of 25 months, with an estimated 2-year TTAF of 12%. Only 9 out of the 44 patients (20%) discontinued ibrutinib. Sixteen patients (4%) were classified as AF score 0, 218 (62%) score 1-2, 73 (21%) score 3-4 and 46 (13%) at least score 5. Our model was also able to identify patients at a higher risk AF during ibrutinib, in fact the 2-year risk of AF was 0%, 5%, 17% and 40% for patients with score 0, 1-2, 3-4, and ≥5 respectively (p<0.001, Fig. 1B). Patients with a score of 5 or higher have a risk 20 times higher to developed AF than the other subjects (HR 19.6, 95% interval 7-52, p<0.0001). So far, the OS of ibrutinib-treated patients with AF was not inferior to that of patients who did not developed AF (2-years OS 89% and 82%, respectively p=0.1252), but the median follow-up is only 2 years.

CONCLUSIONS. In this study, variables associated with an increased risk of developing AF were identified and recapitulated into a scoring system. Our model proved to be a valid tool to identify patients at a higher risk of developing AF, including ibrutinib-treated patients. Taking these data into account, patients with a score ≥5 should be carefully monitored during ibrutinib treatment given the very high-risk of developing AF or should be considered for alternative therapies.