What is the absolute risk reduction of myocardial infarction with statin (HMG-CoA reductase inhibitor) therapy over time?

Absolute Risk Reduction of Myocardial Infarction with Statin Therapy

Statins reduce the absolute risk of myocardial infarction by approximately 1.3% (95% CI, 0.9%-1.7%) over a median follow-up period of 5 years, with the absolute benefit being proportional to baseline cardiovascular risk. 1

Understanding Statin Benefits in Absolute Terms

The absolute risk reduction provided by statins varies significantly based on baseline cardiovascular risk:

Absolute Risk Reduction by Risk Category

• Low risk patients (<5% 10-year ASCVD risk): Approximately 11 per 1000 over 5 years 2
• Secondary prevention (established CVD): 5-year absolute reduction in risk of 2.2% for fatal/nonfatal stroke 3
• High-risk patients (4S trial): 6-year absolute survival benefit of 3.7% (91.3% vs 87.6%) 4

Risk-Based Absolute Benefits

The 2013 ACC/AHA guideline clearly states that "the absolute benefit in ASCVD risk reduction is proportional to the baseline risk of the patient group or individual and to the intensity of statin therapy." 3

This means:

• Patients at higher baseline absolute risk derive greater absolute benefit from statin therapy over 5-10 years
• The number needed to treat (NNT) improves as baseline risk increases

Myocardial Infarction-Specific Benefits

For myocardial infarction specifically:

• Statins reduce the relative risk of nonfatal myocardial infarction by approximately 27% per 1-mmol/L (38.7-mg/dL) LDL-C reduction 3
• This translates to an absolute risk reduction of approximately 1.3% over a median follow-up of 5 years 1

In the landmark 4S trial, which studied patients with existing coronary heart disease:

• The absolute risk reduction for major coronary events was 9.1% (19% vs 28%) over 5.4 years 5, 4
• The number of patients with one or more major coronary events was reduced from 622 (28%) in the placebo group to 431 (19%) in the simvastatin group 4

Time-Dependent Effects

The absolute risk reduction increases with longer treatment duration:

• Consistent 23%-28% relative reductions in CVD risk per 39-mg/dL reduction in LDL-C were observed from 1 year to beyond 5 years of statin treatment 3
• The absolute benefit accumulates over time, with most trials showing maximum benefit after 4-5 years of therapy

Risk Stratification and Absolute Benefit

The absolute benefit of statin therapy is directly proportional to baseline risk:

• In patients with no CAD: 92 patients needed to treat to prevent one MI or death
• In patients with severe nonobstructive CAD: only 13 patients needed to treat 6

Clinical Application

When considering statin therapy for primary prevention:

1. Calculate the patient's 10-year ASCVD risk using the Pooled Cohort Equations
2. For patients with ≥7.5% 10-year risk, there is clear net absolute benefit with moderate-to-intensive statin therapy 3
3. For patients with 5.0% to <7.5% risk, moderate-intensity statin therapy still provides net absolute benefit, but the tradeoffs require more careful consideration 3

Common Pitfalls to Avoid

1. Focusing only on relative risk reduction: While statins consistently show 20-30% relative risk reductions, the absolute benefit varies widely based on baseline risk
2. Ignoring baseline risk: Treating low-risk patients (10-year ASCVD risk <5%) provides minimal absolute benefit
3. Overlooking the time factor: The absolute benefit of statins increases with longer treatment duration
4. Confusing different outcomes: The absolute risk reduction for all-cause mortality (0.8%) is smaller than for MI (1.3%) 1

Remember that while the absolute risk reduction may seem modest in some populations, the benefit-to-risk ratio remains favorable for most patients at elevated cardiovascular risk, especially considering the low rate of serious adverse effects with statin therapy.