Smoking affects life expectancy after acute MI

Current smoking after acute MI was associated with increased mortality at 5 years and at 17 years, researchers reported in Heart.

In previous studies, patients with acute MI who are smokers tended to have a lower mortality rate compared with nonsmokers, but only within the first 5 years after acute MI. Over a longer period, smoking was found to increase mortality.

This “smoker’s paradox” led researchers to more closely analyze the effect of smoking on life expectancy after acute MI. The researchers used data from the Cooperative Cardiovascular Project, a medical records study of 158,349 elderly Medicare patients with acute MI with more than 17 years of follow-up.

The primary outcome was 17-year survival from admission.

Patients included in the study were aged 65 years and older. Diagnosis of acute MI was determined by elevation of lactate dehydrogenase (LDH) level with isoenzyme reversal (LDH₁ > LDH₂) or the presence of at least two of the following: chest pain, twofold elevation in total creatine kinase and/or diagnostic ECG changes.

Overall, 14.8% of patients reported current smoking. Patients in the nonsmoker group had either never smoked or were former smokers. Current smokers tended to be younger than nonsmokers, male, less likely to have diabetes, hypertension or obesity, and have increased risk for chronic obstructive pulmonary disease and peripheral vascular disease.

During the follow-up period, 93.6% of current smokers and 92.9% of nonsmokers died.

Current smokers had lower crude mortality at 30 days (fully adjusted HR = 0.91; 95% CI, 0.87-0.94), comparable mortality at 1 year (fully adjusted HR = 0.97; 95% CI, 0.94-1) and higher mortality at 5 years (fully adjusted HR = 1.07; 95% CI, 1.05-1.1) and 17 years (fully adjusted HR = 1.19; 95% CI, 1.17-1.2) after acute MI.

The difference in life expectancy between smokers and nonsmokers was largely due to the age of the patient at acute MI, according to the researchers. The mean age at admission for current smokers was 72.4 years and for nonsmokers was 77.2 years.

“Overall, crude life-expectancy estimates were lower for current smokers than nonsmokers at all ages, which translated into sizable numbers of life-years lost attributable to smoking,” the researchers wrote. “As age at acute MI increased, the magnitude of life-years lost due to smoking decreased.”

The amount of life-years lost decreased for current smokers who were older at the time of acute MI. Current smoking was associated with 1.96 life-years lost at age 65 years and 0.16 life-years lost at age 85 years.

Due to the marked differences between nonsmokers and current smokers at different ages, the researchers concluded that more research is needed to examine how smoking affects the life expectancy of current smokers who are younger than 65 years at the time of acute MI.

“Our findings lend additional support to smoking-cessation efforts after acute MI. In addition, years of life lost may be particularly helpful for communicating the harms of smoking to patients with [CAD],” the researchers wrote. – by Tracey Romero

Disclosure: One researcher reports receiving grants from Johnson & Johnson and Medtronic through Yale University, working under contract with CMS to develop and maintain performance measures and chairing the Cardiac Scientific Advisory Board for UnitedHealth. The other researchers report no relevant financial disclosures.