Standard cardiovascular risk prediction scores underestimate risk in immune-mediated thrombotic thrombocytopenic purpura survivors.

BACKGROUND

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare hematologic disorder with improved survival due to advancements in treatment. However, long-term cardiovascular morbidity and mortality remain significant. Established cardiovascular risk calculators, such as the 2008 Framingham Heart Study (FHS) global cardiovascular disease (CVD) and the American College of Cardiology/American Heart Association (ACC/AHA) atherosclerotic CVD (ASCVD) risk estimators, may not adequately account for the elevated and unique cardiovascular risks in iTTP survivors.

OBJECTIVES

To evaluate the discrimination and calibration of the ACC/AHA ASCVD and FHS global CVD models in predicting major adverse cardiovascular events (MACEs) among iTTP survivors.

METHODS

This retrospective study analyzed 135 iTTP survivors from Johns Hopkins University (1994-2024). Presence of MACEs, including myocardial infarction, stroke, and cardiac revascularization, was the primary outcome and was assessed during clinical remission. Discriminatory ability of the model was assessed using c-statistics, while calibration was evaluated with Hosmer-Lemeshow tests and calibration plots. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were also calculated.

RESULTS

MACEs occurred in 37.8% of the cohort over a median follow-up of 3.8 years. The ASCVD and FHS models demonstrated poor discrimination (c-statistics, 0.54 and 0.52, respectively) and poor calibration, with observed MACE rates exceeding predicted probabilities (Hosmer-Lemeshow < .05). The ASCVD model showed sensitivity of 56.5%, specificity of 49.4%, PPV of 36.6%, and NPV of 64.9%, while the FHS model showed sensitivity of 69.6%, specificity of 39.3%, PPV of 37.2%, and NPV of 67.9%.

CONCLUSION

Standard cardiovascular risk models inadequately predict MACE risk in iTTP survivors, underscoring the need for tailored tools that incorporate iTTP-specific factors to improve cardiovascular risk stratification and management.