Decreasing mortality from acute myocardial infarctions: effect of attack rates and case severity.

Mortality from myocardial infarction (MI) has declined in many countries and the reasons for the decline have not been fully quantified. We used the database of the Halifax County MONICA Project to test the hypothesis that the decline of in-hospital mortality from MI can be explained by a trend toward less severe disease as opposed to improved treatment. During the study period 1984-1993, 14,130 people aged 25-74 had been admitted to hospital with suspected MI. Of these, 3774 were diagnosed as definite MI by standardized criteria (480 fatal). For each patient, clinical history, serial cardiac enzymes, and ECG treatment regimen during hospital stay were extracted from patient charts. Survival status 28 days after onset of symptoms was determined. A severity index predicting 28-day case fatality was derived from health status at admission time. During the study period the rate of definite MI in the MONICA target population showed a general downward trend from 221 to 179 per 100,000/year (p = 0.0002). The severity index increased during the observation time (p < 0.0001), predicting 25% higher mortality. Case fatality fluctuated, but showed a marginally significant decline. We conclude that part of the decreased in-hospital mortality from MI is due to lower attack rates. The remainder occurred despite increased case severity and is possibly due to improved in-hospital treatment.

Effects of recruitment strategy on response rates and risk factor profile in two cardiovascular surveys.

BACKGROUND: The study was set up to assess the effect of recruitment methods on participation rate, response bias and cardiovascular risk factor estimates. METHODS: Two random samples of men and women in Halifax County aged 25-74 were drawn from the same sampling frame. Their respective sizes were 1007 (NSHHS) and 3036 (MONICA) people. Recruitment by Nova Scotia Heart Health Survey (NSHHS) was through face-to-face contact, whereas the MONICA survey relied on invitation by mail. Outcome measures were response rates at various stages of the recruitment process and the differences in cardiovascular risk factor estimates. RESULTS: Face-to-face recruitment located 51% and mail recruitment located 47% of their respective samples; face-to-face recruitment resulted in fewer individuals who refused to participate in the survey, but also produced fewer who were prepared to provide blood samples in addition to answering questionnaires. By-mail recruits were more likely to have post-secondary education, but did not differ in the proportion of smokers, mean diastolic blood pressure or body mass index, if controlled for education level, gender and age. However, the mean systolic blood pressure was 5.7 mmHg higher and the mean cholesterol level 0.44 mmol/l lower in face-to-face recruits. CONCLUSIONS: Controlling for age, gender and education level eliminates the effect of recruitment bias on most cardiovascular risk factors estimates. The exceptions in our study were systolic blood pressure and cholesterol, where methodological factors may have played a role.

Trends in the in-hospital treatment of acute myocardial infarction between 1984 and 1993 - The Halifax County MONICA Project.

BACKGROUND: The Halifax County MONItoring of trends and determinants in CArdiovascular disease (MONICA) Project found that between 1984 and 1988, the proportion of myocardial infarctions (MIs) that were fatal within 28 days remained constant, but declined between 1989 and 1993. The objective was to investigate association among case fatality, treatment and case severity of MI in hospitalized patients. PATIENTS AND METHODS: The MONICA MI register contains data on demographics, health history, in-hospital investigations, interventions and treatment, and vital status at 28 days after onset of symptoms for all MIs occurring in residents of Halifax County, aged 25 to 74 years. Logistic regression analysis was used to estimate trends in the use of cardioactive drugs and revascularization procedures. A case severity score was developed from patient characteristics at time of admission. Case fatality was calculated as the proportion of MIs that were fatal within 28 days. RESULTS: Between 1984 and 1988, a large increase (OR 1.3) occurred in the use of angiotensin-converting enzyme (ACE) inhibitors, acetylsalicylic acid (ASA), thrombolysis and percutaneous transluminal coronary angioplasty (PTCA); a minor increase occurred in use of calcium channel blockers (OR=1.29, 99% CI 1.19 to 1.40); beta-blocker use decreased; case fatality remained constant and case severity score increased. From 1989 to 1993, ACE inhibitor use increased (OR=1.4, 99% CI 1.27 to 1.55); minor increases occurred in use of ASA and beta-blockers, and in PTCA and coronary artery bypass grafting; case severity did not change and case fatality decreased. CONCLUSIONS: While use of beneficial treatment increased between 1984 and 1988, MI case fatality did not decrease, probably because case severity increased. Between 1989 and 1993, case severity remained constant, and the further increase in the use of beneficial therapy was associated with a decline in case fatality.

Trends in the incidence of acute myocardial infarction between 1984 and 1993 - The Halifax County MONICA Project.

BACKGROUND: According to vital statistics data for Halifax County, between 1984 and 1993 the annual mortality rate decreased for ischemic heart disease and myocardial infarction (MI). OBJECTIVES: To estimate the change in MI mortality, applying standardized diagnostic criteria; to determine whether decreased case fatality or decreased MI event rate, or both, caused decreased mortality; and to determine the contribution of MI incidence rate to altered event rate. PATIENTS AND METHODS: All persons in the study area aged 25 to 74 years and admitted to hospital or dying outside hospital with suspected acute coronary syndromes were registered prospectively. Demographic, health history and clinical data were extracted from medical records or collected from medical examiner reports, next-of-kin interviews or family physicians. Definite or possible MI was diagnosed according to World Health Organization MONItoring of trends and determinants in CArdiovascular disease (MONICA) criteria. Trends in age- and sex-standardized rates were estimated by using log-linear regression analysis. RESULTS: Of 4283 patients admitted to hospital for MI, 23.9% died within 28 days; 1401 patients who had suffered an MI died before admission to hospital. MI mortality decreased annually by 3.9% (95% CI 1.9 to 5.8); two-thirds of the decline was due to MI event rates (2.6%; CI 1.3 to 3.8) and one-third to a decrease in 28-day case fatality (1.3%; CI 0.2 to 2. 3). A decrease in MI incidence rate (3.2%; CI 1.7 to 4.8), rather than a decline in MI recurrence rate (1.4%; CI 0.7 to -3.5), was the major reason for the declining event rate. CONCLUSIONS: A decrease in the incidence of MI, possibly due to primary prevention, had a major impact on the declining MI mortality. Decreased in-hospital MI fatality, possibly due to improved treatment, was responsible for the decline in case fatality.

Ten-year trends of heart disease risk factors in the Halifax County MONICA population. MONItoring of trends and determinants in CArdiovascular disease.

OBJECTIVE: To investigate trends in heart disease risk factors (RFs) in the general population of Halifax County, Nova Scotia during a 10-year period. DESIGN: Two independent random samples of the population of Halifax County were surveyed in 1985 and 1995; age ranges were 25-64 years and 25-74 years. Blood pressure, cholesterol and body weight were measured. Smoking and health history were obtained by questionnaire. MAIN RESULTS: Participation rate was 66.3% in 1985 and 1995. All RFs were negatively correlated with education attainment. RF changes from 1985 to 1995 were related to education level. Among survey participants, mean body mass index increased from 26.7 kg/m2 to 27.6 kg/m2 (P + 0.005) for men, and from 25.5 kg/m2 to 27.3 kg/m2 (P < 0.00001) for women. Average smoking rate increased from 32.0% to 34.6% (not significant) in men and from 27.7% to 29.1% (not significant) in women. Age-specific smoking rate increased by 13% (P = 0.14) in younger women and decreased by 10% in older women. (P = 0.00). Mean levels of blood cholesterol decreased by 0.2 mmol/L (P = 0.002) in men and 0.1 mmol/L (P = 0.20) in women. Systolic blood pressure increased by 6.3 mmHg (P < 0.0001) in men and by 7.9 mmHg (P < 0.0001) in women, being steepest in the lower education group. Mortality predicted from RFs declined between the survey years, but less than the observed mortality. This discrepancy may result from the effect of medical care or the delayed effect of RF changes. CONCLUSIONS: Some risk factors show a disturbing trend, indicating that an increased effort or a change in strategy is needed to combat the risk of ischemic heart disease.

Use of computers in clinical electrocardiography: an evaluation.

The use of computers in clinical electrocardiography is increasing rapidly; however, the role of computers with respect to the electrocardiographer has not been established. At present all electrocardiograms (ECGs) processed by computer are also interpreted by electrocardiographers; hense effort is duplicated. In an investigation of whether conditions can be defined under which the electrocardiographer can use the computer more profitably by eliminating some of the duplication, ECGs recorded in a university teaching hospital were processed by a computer program and subsequently reviewed by 1 of 10 electrocardiographers. For ECGs interpreted as showing normal sinus rhythm the rate of agreement between computer and human reviewer was 99%. For those showing a normal ECG pattern (contour) the rate of direct agreement was only 88%. However, the rate of occurrence of clinically significant differences was only 1.64%; hence the rate of essential agreement for this classification was 98.36%. Other classifications with good agreement were myocardial infarction, sinus bradycardia and sinus tachycardia. Therefore, in circumstances comparable to those of this investigation it is feasible for electrocardiographers to use computers to reduce greatly their workload without compromising the quality of the service provided.

The consequences of reviewing serial changes in the Minnesota code for diagnosis of acute myocardial infarction.

We investigated the effect of reviewing serial electrocardiograms (ECGs) for significance of changes in the Minnesota code, and the influence of this effect on the MONICA diagnosis of myocardial infarction (MI). We used the data from 1340 consecutive admissions to the coronary care units of our MONICA centre and we developed ECG classifications and MONICA diagnoses that were based once on the unreviewed Minnesota code and once on the reviewed code. A comparison of the two ECG classifications showed that codes for evolution of Q-waves and injury currents were much more likely to change as a result of a review (46.8%) than codes for evolution of repolarization changes (12.8%). The review of serial Minnesota codes caused a change of the MONICA diagnosis primarily in the category definite MI (10%). In a blinded clinical assessment, the cases that changed diagnosis were judged to be different from those that remained constant. It is concluded that the use of ECG classification based on unreviewed Minnesota code changes introduces heterogeneity. The significance of this effect depends on the use of the results.

Trends in the prevalence and treatment of hypertension in Halifax County from 1985 to 1995.

BACKGROUND: The objective of this study was to document changes in the prevalence and treatment of hypertension in Halifax County from 1985 to 1995 in an effort to observe, at the population level, the consequences of the availability of new antihypertensive medications. METHODS: The study population comprised a random sample of Halifax County residents, aged 25-64 years, who responded to the 1985 and 1995 surveys of the Halifax County MONICA Project and residents who responded to the Nova Scotia Health Survey conducted in 1995. Data from the two 1995 surveys were pooled. Information on hypertension awareness and use of medication were obtained through questionnaires, and blood pressure was measured according to a standard protocol, using phase I and V of Korotkoff sounds as respective markers for systolic and diastolic pressures. Uncontrolled hypertension was defined as a systolic pressure of 140 mm Hg or greater and a diastolic pressure of 90 mm Hg or greater. Changes in the prevalence of hypertension, prescribing trends and medication costs were examined, and the association between the type of antihypertensive treatment and characteristics of the respondents with self-reported hypertension was investigated by multivariate logistic regression. RESULTS: Of the 917 people interviewed in 1985 and the 1338 in 1995, 274 (29.9%) and 356 (26.6%), respectively, reported a history of hypertension. When age was controlled for, the proportion of respondents reporting hypertension did not differ between survey years or between men and women. The proportion of treated respondents who had uncontrolled hypertension increased between 1985 and 1995, from 32.6% to 57.4% among men and from 38.0% to 42.6% among women. An increase was seen in the use of calcium-channel blockers (from 2.1% to 19.7%) and angiotensin-converting-enzyme inhibitors (from 5.2% to 25.4%); the proportion of patients receiving combination therapy or diuretics decreased (from 39.6% to 15.6% and from 31.3% to 17.2% respectively). These changes were associated with an increase in the average daily cost of medication from $0.48 to $0.85 per patient. INTERPRETATION: The shift to new antihypertensive drugs was not associated with improved blood pressure control, but it was associated with an increase in average medication costs per patient. Uncontrolled hypertension remains a public health problem.

Gender differences in the presentation, treatment, and short-term mortality of acute chest pain.

The Halifax County MONICA database was used to estimate the gender bias in presentation, prehospital and in-hospital treatment, and 28-d mortality of patients suffering an episode of acute chest pain. The study population consisted of all county residents aged 25-74, admitted between 1984 and 1990 to a CCU, or suffering a myocardial infarction anywhere in a hospital. The mean age for men was 58.5 (n = 6561), for women 61.5 (n = 3176). Women of all age groups were more likely to have a history of diabetes or hypertension, and below age 55 had a higher prevalence of peripheral vascular disease. Typical symptoms for infarction were present in 30.8% of women and 38.1% of men (p < 0.0001). More women were taking beta-blockers, Ca-antagonists, digitalis, diuretics, and nitrates (p < 0.001), and more men were on antiarrhythmics. A gender difference was observed for coronary arteriography (24% in men, 18% in women) and for the exercise stress test (23% in men, 18% in women). In hospital, men had more episodes of severe arrhythmias (OR = 1.52). Except for aspirin and antiarrhythmics, the difference in hospital medication and 28-d mortality (9.6% in women vs. 7.8% in men) could be explained by the existing clinical conditions.