Systematic review

The review sought studies with patients diagnosed with previous heart attack, or stable or unstable angina and who were smoking at baseline with smoking status well defined. Prospective cohort studies had to include current smokers at baseline, with smoking status measured to find who had quit smoking, in which the follow up was at least two years and with all cause mortality as an outcome measure.

The search strategy was extensive, examining nine electronic databases, and studies were not restricted by language.

Results

There were 20 included studies with 12,600 patients, mostly using data collected in the 1960s and 1970s. Most cases were men (80%), and average cessation rate was 45%. Follow up ranged from two to 26 years, though most studies reported follow up of three to seven years, with a mean of five years.

Most studies involved follow up hospital case series, and reporting of smoking status was usually at some follow up appointment, though it was not validated, for example by biochemical measurement, in most studies. Most studies had a clear definition of the cardiac event. Loss to follow up was usually small. Size varied from under 100 to over 4,000 patients.

There were fewer deaths in quitters (18%) than in people who continued to smoke (27%), and the degree of reduction was consistent across all death rates reported (Figure 1). Results were broadly similar in all studies, and in six higher quality studies with about two-thirds of all patients (Table 1). Higher quality here was defined by a sample size of 500 smokers at baseline, with fewer than 15% dropouts, and with adequate or good control of confounding.