Observational Study of Cardiac Arrhythmias During Treatment With BTK Inhibitors or Venetoclax

Study Description: Pharmacologic therapy with BTK inhibitors (BTKi) is associated with an increased risk of cardiac arrhythmias which can lead to sudden death. There is currently no standard for cardiac screening or monitoring patients on BTKi. We hypothesize that thorough and routine comprehensive cardiac evaluations prior to starting therapy with BTKi and repeated during therapy with BTKi will result in earlier identification of cardiac arrhythmias with the goal of minimizing associated morbidity and mortality. In addition, venetoclax, a different standard therapy for chronic lymphocytic leukemia, has not been associated with increased cardiac adverse events and could serve as a control group. Objectives: Primary objective: Identify, monitor, and analyze the arrhythmogenic effects of BTKi as well as sudden death Secondary objective: Assess the utility of different cardiac tests for identifying and monitoring cardiac arrhythmias in patients receiving BTKi or venetoclax Exploratory objective: To examine the relationship between the development of cardiac arrhythmias in patients on BTKi as it relates to other variables Endpoints: Primary endpoint: -A composite endpoint of clinically significant cardiac arrhythmias and sudden death in patients starting a BTKi (Cohort A) and in patients already receiving BTKi (Cohort B). Secondary endpoints: * Detection of arrhythmias on devices (rest/stress EKG, ambulatory EKG monitor, KardiaMobile) * Arrhythmia (treatment emergent or worsening) in patients on BTKi * Sudden death in patients on BTKi * A composite endpoint of clinically significant cardiac arrhythmias and sudden death in patients starting venetoclax * Difference in cardiac arrhythmias and sudden death between different BTKi groups (e.g., ibrutinib vs. non-ibrutinib group) * Difference in cardiac arrhythmias and sudden death between BTKi and venetoclax groups Exploratory endpoints: * Pharmacokinetic levels of BTKi * Duration of BTKi exposure * Cumulative BTKi dose * Genetic variants * Cardiac structural remodeling * Medical comorbidities * Concomitant medications * Substance use * Identify risk factors or biomarkers for arrhythmia