The Oslo Ischaemia Study: cohort profile

PURPOSE

The Oslo Ischaemia Study was designed to investigate the prevalence and predictors of silent coronary disease in Norwegian middle-aged men, specifically validating exercise electrocardiography (ECG) findings compared with angiography. The study has been important in investigating long-term predictors of cardiovascular morbidity and mortality, as well as investigating a broad spectrum of epidemiological and public health perspectives.

PARTICIPANTS

In 1972-1975, 2014 healthy men, 40-59 years old, were enrolled in the study. Comprehensive clinical examination included an ECG-monitored exercise test at baseline and follow-ups. The cohort has been re-examined four times during 20 years. Linkage to health records and national health registries has ensured complete endpoint registration of morbidity until the end of 2006, and cancer and mortality until the end of 2017.

FINDINGS TO DATE

The early study results provided new evidence, as many participants with a positive exercise ECG, but no chest pain ('silent ischaemia'), did not have significant coronary artery stenosis after all. Still, they were over-represented with coronary disease after years of follow-up. Furthermore, participants with the highest physical fitness had lower risk of cardiovascular disease, and the magnitude of blood pressure responses to moderate exercise was shown to influence the risk of cardiovascular disease and mortality. With time, follow-up data allowed the scope of research to expand into other fields of medicine, with the aim of investigating predictors and the importance of lifestyle and risk factors.

FUTURE PLANS

Recently, the Oslo Ischaemia Study has been found worthy, as the first scientific study, to be preserved by The National Archives of Norway. All the study material will be digitised, free to use and accessible for all. In 2030, the Oslo Ischaemia Study will be linked to the Norwegian Cause of Death Registry to obtain complete follow-up to death. Thus, a broad spectrum of additional opportunities opens.

Physical fitness is a modifiable predictor of early cardiovascular death: A 35-year follow-up study of 2014 healthy middle-aged men

Background

Physical fitness has been shown to predict cardiovascular death during long-term follow-up. In the present study we aimed to investigate how physical fitness and other cardiovascular risk factors at middle-age influenced the risk of cardiovascular death during the early (0–11 years), intermediate (12–23 years) and late (24–35 years) parts of a 35-year observation period.

Methods and results

Age-adjusted physical fitness was calculated in 2014 apparently healthy, middle-aged men after maximal bicycle electrocardiogram-tests in 1972–1975 (Survey 1) and 1979–1982 (Survey 2). The men were assessed through 35 years after Survey 1, and 28 years after Survey 2 by Cox proportional hazards models. Low Survey 1 physical fitness was independently associated with increased risks of early and intermediate, but not late, cardiovascular death. Survey 1 to Survey 2 change in physical fitness, age, smoking status, systolic blood pressure and cholesterol impacted cardiovascular death risks in all periods. Family history of coronary heart disease impacted early and intermediate, but not late, cardiovascular death.

Conclusions

Most classical cardiovascular risk factors were strong predictors of early, intermediate and late cardiovascular death. Physical fitness measured at median age 50 years was independently associated with risk of early cardiovascular death, but the association weakened as time progressed. Change in physical fitness during middle-age impacted cardiovascular death risk in a full lifetime perspective. Thus, our data suggest that physical fitness is a modifiable cardiovascular risk factor with limited duration in contrast to the sustained impact of smoking, blood pressure and cholesterol on cardiovascular mortality.

Temporal Reduction in Chronotropic Index Predicts Risk of Cardiovascular Death Among Healthy Middle-Aged Men: a 28-Year Follow-Up Study

BACKGROUND

Chronotropic index is a standardized measure of heart rate (HR) increment during exercise that reflects the combined effects of age, resting HR, and physical fitness. Low chronotropic index has been reported to predict disease and death. We tested whether temporal change in chronotropic index over 7 years influenced risk of cardiovascular death through up to 28 years.

METHODS AND RESULTS

Chronotropic index was calculated ([achieved maximal HR-resting HR]/[age-predicted maximal HR-resting HR]) after a symptom-limited bicycle ECG exercise test in 1420 healthy men at 2 examinations 7 years apart, in 1972 and 1979. Events of cardiovascular death were registered by manual scrutiny of all participants' hospital charts and the Norwegian Cause of Death Registry. The participants were divided into quartiles of temporal change in chronotropic index, with quartile one having the most negative value. Cox proportional hazard regression models were used to estimate risks and adjusted for classical cardiovascular risk factors. Incidence of cardiovascular death was 310 (22%) during median of 21 years of follow-up. After multivariable adjustment, and comparison with quartile four (mean +0.11), quartiles one (-0.16), two (-0.04), and three (+0.02) were associated with hazard ratios 1.50 (95% CI 1.10-2.05), 1.10 (0.79-1.53), and 1.04 (0.74-1.45) for cardiovascular death. Results remained robust also after exclusion of 31 participants with exercise ECG-induced signs of coronary ischemia.

CONCLUSIONS

Temporal reduction in chronotropic index was associated with increased long-term risk of cardiovascular death and might be a clinically important predictor when assessing risk in healthy individuals over a longer time.

Triglycerides-diabetes association in healthy middle-aged men: modified by physical fitness? A long term follow-up of 1962 Norwegian men in the Oslo Ischemia Study

AIMS

To examine the impact of physical fitness (PF) on the association between fasting serum triglycerides (FTG) and diabetes risk and whether temporal changes in FTG predict diabetes risk in healthy middle-aged men.

METHODS

FTG and PF (bicycle exercise test) were measured in 1962 men aged 40-59 years in 1972-1975 (Survey 1) and repeated in 1387 still healthy men on average 7.3 years later (Survey 2). Diabetes was diagnosed according to WHO 1985-criteria.

RESULTS

During 35 years follow-up 202/1962 (10.3%) men developed diabetes. Compared with the lowest, the upper FTG tertile had a 2.58-fold (95% CI: 1.81-3.74) diabetes risk adjusted for age, fasting blood glucose and maternal diabetes, and a 2.29-fold (95%CI: 1.60-3.33) when also adjusting for PF. Compared with unchanged (±25%) FTG levels (n=664), FTG reduction of more than 25% (n=261) was associated with 56% lower (0.44; 95% CI: 0.24-0.75) diabetes risk, while FTG increase of more than 25% (n=462) was associated with similar risk. These associations were unchanged when adjusted for PF and PF change.

CONCLUSIONS

High FTG-levels predicted long-term diabetes risk in healthy middle-aged men, and the association was only modestly weakened when adjusted for PF. A reduction in FTG was associated with decreased diabetes risk.

Importance of physical fitness on predictive effect of body mass index and weight gain on incident atrial fibrillation in healthy middle-age men

The incidence of both atrial fibrillation (AF) and obesity is increasing in the community, and lifestyle intervention is recommended. We aimed to test whether the predictive effect of body mass index (BMI) and weight change from age 25 years to midlife on incident AF were influenced by physical fitness. In 1972 to 1975, 2,014 healthy middle-age men conducted a bicycle exercise electrocardiographic test as a part of a cardiovascular survey program, defining physical fitness as work performed divided by body weight. During 35 years of follow-up, 270 men developed AF, documented by scrutiny of the health files in all Norwegian hospitals. Risk estimation was analyzed using Cox proportional hazard models and tested for age-adjusted physical fitness above and below the median. The mean BMI of 24.6 kg/m(2) defined a lean baseline cohort. The men with a baseline BMI of ≥28 kg/m(2) (11%) compared to a BMI <28 kg/m(2) had a 1.68-fold risk of AF (95% confidence interval 1.14 to 2.40) and men reporting weight gain of ≥10 kg (24%) compared to weight loss (11%) of 1.66-fold (95% confidence interval 1.00 to 2.89), respectively. The dichotomy into men with age-adjusted physical fitness above and below the median, demonstrated statistically significant risk associations only for men with low fitness. The overall risk of AF was reduced by 23% in the fit men. In conclusion, within our lean baseline cohort of healthy middle-age men, a BMI of ≥28 kg/m(2) and weight gain of ≥10 kg from age 25 to midlife were long-term predictors of incident AF in men with physical fitness below the population median. The fit men had an overall slightly reduced risk of AF.

Low-grade systolic murmurs in healthy middle-aged individuals: innocent or clinically significant? A 35-year follow-up study of 2014 Norwegian men

OBJECTIVE

To determine whether a low-grade systolic murmur, found at heart auscultation, in middle-aged healthy men influences the long-term risk of aortic valve replacement (AVR) and death from cardiovascular disease (CVD). Setting and subjects.  During 1972-1975, 2014 apparently healthy men aged 40-59 years underwent an examination programme including case history, clinical examination, blood tests and a symptom-limited exercise ECG test. Heart auscultation was performed under standardized conditions, and murmurs were graded on a scale from I to VI. No men were found to have grade V/VI murmurs. Participants were followed for up to 35 years.

RESULTS

A total of 1541 men had no systolic murmur; 441 had low-grade murmurs (grade I/II) and 32 had moderate-grade murmurs (grade III/IV). Men with low-grade murmurs had a 4.7-fold [95% confidence interval (CI) 2.1-11.1] increased age-adjusted risk of AVR, but no increase in risk of CVD death. Men with moderate-grade murmurs had an 89.3-fold (95% CI 39.2-211.2) age-adjusted risk of AVR and a 1.5-fold (95% CI 0.8-2.5) age-adjusted increased risk of CVD death.

CONCLUSIONS

Low-grade systolic murmur was detected at heart auscultation in 21.9% of apparently healthy middle-aged men. Men with low-grade murmur had an increased risk of AVR, but no increase in risk of CVD death. Only 1.6% of men had moderate-grade murmur; these men had a very high risk of AVR and a 1.5-fold albeit non-significant increase in risk of CVD death.

Takotsubo cardiomyopathy in acute coronary syndrome; clinical features and contribution of cardiac magnetic resonance during the acute and convalescent phase

OBJECTIVES

Takotsubo cardiomyopathy (TTC) is a diagnostic entity that is increasingly being recognized. Data from cardiac magnetic resonance (CMR) imaging and its impact on differential diagnosis are limited.

METHODS AND RESULTS

After 26 months, coronary angiography revealed normal coronary arteries and left ventriculography and/or echocardiography left ventricular dysfunction with apical ballooning in 20 patients with acute coronary syndrome (ACS). Four patients were excluded from CMR and in three patients an alternative diagnosis was revealed. Thirteen patients (all female; 60 ± 8 years) with TTC underwent a multisequential CMR, in which all showed myocardial oedema with an elevated T2 ratio in the apical region (2.4 ± 0.4; p < 0.001 vs. healthy controls), and five patients an elevated global relative enhancement (gRE; 3.7 ± 1.4; p < 0.05 vs. healthy controls). No late gadolinium enhancement (LGE) was detected on CMR. Follow-up after 132 ± 33 days showed a normalized left ventricular ejection fraction, myocardial mass, T2 ratio, and gRE in all patients.

CONCLUSIONS

TTC is a small but definite group among patients with ACS and normal coronary arteries. CMR allows differentiating TTC from other causes such as myocarditis and cardiomyopathies, as well as to identify the transient increase of myocardial mass and resolution of myocardial oedema as the systolic dysfunction improves. Therefore, CMR might add valuable information for the differential diagnoses and therapeutic decision-making in patients with suspected TTC.

Interaction between inflammation and blood viscosity predicts cardiovascular mortality

OBJECTIVES

Inflammation and increased blood viscosity are associated with increased risk of cardiovascular mortality. Erythrocyte sedimentation rate (ESR) and hematocrit both influence blood viscosity whereas the first also is a marker of inflammation. We aimed to investigate ESR, hematocrit and the interaction between them as predictors of cardiovascular mortality during 26 years follow-up among healthy middle aged men.

DESIGN

Four hundred and eighty eight men aged 40-59 were extensively examined in 1972-1975 and followed over a period of 26 years. Risk estimation was made in Cox proportional hazards and adjusted for age, smoking, systolic blood pressure, total serum cholesterol, and physical fitness.

RESULTS

A 2.44-fold (95% CI 1.37-4.35) adjusted risk of cardiovascular mortality was found in the highest quartile of hematocrit compared to the lowest. Among the 265 men who had an ESR <6 mm/h (median), the adjusted risk of cardiovascular mortality was 3.05-fold (95% CI 1.49-6.23) in the highest quartile of hematocrit compared to the lowest. This association was not observed among the 223 men with ESR <6 mm/h.

CONCLUSION

Elevated hematocrit is independently associated with increased long-term risk of cardiovascular mortality in men with high ESR. Our data suggest that the combination of inflammation and blood viscosity may improve the prediction of cardiovascular risk.