Recent time trends in the incidence and case-fatality of coronary heart disease: the contribution of interrupted-MIs in men and women 35-74 years old

Purpose. In the last decade, new prevention strategies and improvements in treatments have contributed to improve survival from myocardial infarction (MI). Thrombolysis first and PTCA in more recent years not only modified the prognosis but also the evolution of the ischemic damage. Clinicians report the so called non-Q-, aborted- or interrupted-MIs more and more frequently. The aim of this study is to assess the contribution of interrupted-MIs on the estimates rates and time trends of coronary heart disease (CHD). Methods. Between 1997 and 2004, the CAMUNI (CArdiovascular Monitoring Unit in Northern Italy) register was established in a northern Italian population, Brianza, for 35-74 years old residents of both genders. Suspected fatal or non-fatal coronary events were identified and validated according to the standardized WHO-MONICA procedures and criteria. In addition to the standard MONICA definition of MI (validated CHD death and definite MI), a new category is introduced including interrupted MIs, defined as a non-fatal MONICA possible MI that received either thrombolytic therapy or PTCA within 24 hours of symptoms onset. We calculated the age-standardized rates for the first MI, fatal and non-fatal, and case-fatality. The average annual change (AAC) and 95% confidence interval (CI) of rates were estimated using gender-specific log-linear models. Results. Validated CHD death rates decreased in the investigated period by -6.9% and -4.6% per year in men and women, respectively. The average incidence MI rates were 218.8 and 59.4 per 100,000 person-year in men and women, and decreased in both genders (AAC: -8.2%, 95%CI -9.2,-7.3 in men; and -5.1%, -7.2,-3.1 in women). When interrupted-MIs were included, the AAC for MI incidence fell to -3.8% in men and -1.5% in women, remaining statistically significant among men only. The AAC in case fatality was +1.5% and +0.2% in men and women, respectively, for MONICA-validated MIs, while it was -2.8% and -3.3% when interrupted-MIs were added to the standard MONICA MI definition. Similar findings were found when the analysis was restricted to the age 35-64 years old at the onset. Conclusions. Interrupted MIs represent an important proportion of MIs in recent years and need to be considered in MI definitions when time trends are assessed.