Cardiovascular Disease Prevention

Introduction to Statin Therapy

The American College of Cardiology recommends considering the time horizon when interpreting the Number Needed to Treat (NNT) for statin therapy in preventing ASCVD events, with an NNT of 30 over 10.3 years for patients with coronary artery calcium scores (CACS) > 100 1
The Number Needed to Treat (NNT) is calculated by taking the inverse of the Absolute Risk Reduction (ARR): NNT = 1/ARR, as recommended by the American Heart Association 2, 3, 4

To calculate the NNT, follow these steps: Calculate the Absolute Risk Reduction (ARR) using the formula ARR = Control Event Rate (CER) - Experimental Event Rate (EER), then calculate NNT using the formula NNT = 1 ÷ ARR, always rounding up to the next whole number, as demonstrated in the NASCET trial 2
Example calculation: for symptomatic patients with 70-99% carotid stenosis, the control group event rate (medical therapy) was 26%, the treatment group event rate (CEA) was 9%, resulting in an ARR of 17% and an NNT of 6, indicating that 6 patients need to be treated with carotid endarterectomy instead of medical therapy to prevent one ipsilateral stroke 2

Lower NNT values indicate more effective treatments, with NNT < 10 considered very effective, NNT 10-20 considered effective, and NNT > 20 considered less effective, as suggested by the American College of Cardiology 2, 3, 4
The NNT varies with baseline risk, and higher baseline risk populations generally have lower NNTs, making it essential to report the control group event rate, as emphasized by the American Heart Association 2, 3, 4

Common mistakes include not specifying the time horizon, averaging NNTs from different studies, not considering baseline risk, applying NNT from one population to a different population with different baseline risk, and not reporting confidence intervals, as highlighted by the American College of Cardiology 2, 3, 4
The Likelihood to be Helped or Harmed (LHH) can be calculated by comparing NNT and NNH (Number Needed to Harm), which helps balance benefits and risks, as suggested by the American Heart Association 2, 3, 4

Higher baseline risk populations, such as those with CACS ≥ 100, generally have lower NNTs, with an NNT of 30 to prevent one ASCVD event, compared to an NNT of 154 for those with CACS = 0 1
The NNT for statin therapy varies significantly based on coronary artery calcium scores, with an NNT of 64 for CACS = 0 versus 28 for CACS > 100 over 10.3 years, which can inform comparing treatment options 1
CACS-guided therapy is most cost-effective in intermediate-risk patients when treatment is applied based on calcium scores, which can aid in making cost-effectiveness decisions 1