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Cardiovascular Epidemiology:DefinitionsHistorical Perspectives and Assessing Risk of CVDRecent trends and population differences in CHD and CHD risk factors Nathan Wong
Definitions • CARDIOVASCULAR DISEASE or CVD includes CORONARY ARTERY DISEASE and other cardiac conditions (congenital, arrhythmias, and congestive heart failure) • CORONARY ARTERY DISEASE (CAD) or CORONARY HEART DISEASE (CHD) (often broadly referred to as ISCHEMIC HEART DISEASE (IHD): primarily myocardial infarction and sudden coronary death, broader definition may include angina pectoris, atherosclerosis, positive angiogram, revascularization, and myocardial infarction
Definitions (cont.) • REVASCULARIZATION includes coronary artery bypass graft (CABG), percutaneous transluminal coronary angioplasty (PTCA), stent, and atherectomy • CEREBROVASCULAR DISEASE includes stroke (ischemic or hemorrhagic) and transient ischemic attack (TIA) • PERIPHERAL VASCULAR DISEASE includes carotid artery disease and intermittent claudication • SURROGATE MEASURES include: carotid intimal medial thickness (IMT), coronary calcium, angiographic stenosis, brachial ultrasound flow mediated dilatation (FMD)
Tools for Diagnosis of CHD • Medical history: risk factors, including family history, assessment of angina pectoris (Rose questionnaire) • Electrocardiogram (12-lead resting) • Exercise stress ECG or thallium ECG • Echocardiogram (m-mode evaluation of wall thickeness, LV hypertrophy, 2D evaluation of wall motion abnormalities, ejection fraction) • Nuclear testing (sestamibi scans) • Coronary angiography
Historical Perspectives of CVD Epidemiology • Concept of “risk factors”, coined by Framingham Heart Study, involved gaining understanding of factors predisposing to occurrence of CVD • Framingham Heart Study was the first large-scale epidemiologic study, begun in 1948 among 5,209 men and women. • First demonstrated epidemiologic relations of cigarette smoking, blood pressure, and cholesterol levels to incidence of CHD.
Misconceptions Corrected • Blood pressure originally thought to be normal to rise with age to ensure adequate perfusion as arteries narrowed, and elevated diastolic blood pressure felt to cause all problems • Skepticism about cholesterol as a risk factor for CHD persisted into the 1980’s until epidemiologic research and clinical trials proved otherwise • Before epidemiologic studies, physical activity was thought to be dangerous to CHD candidates • Left ventricular hypertrophy now shown to be an ominous harbinger to CHD rather than as a compensatory response to hypertension. • CHD is a multifactorial process involving many predisposing factors.
Cardiovascular Risk Profiles • Risk factors easily obtained during an office visit can help assess future risk of CHD • For CHD, these include serum cholesterol, hypertension, diabetes, ECG-LVH, and cigarette smoking, and from more recent profiles, LDL-C (instead of total cholesterol) and HDL-cholesterol. • Tables provide easy determination of 10-year risk of CHD, stroke, peripheral vascular disease, and congestive heart failure. • A simplified version of the CHD table allows use of JNC-VI and NCEP classifications of blood pressure and LDL-cholesterol levels.
Cardiovascular Risk Profiles (continued) • These tables show risk to be additive across categories of two or more risk factors • Risk increases across levels of one risk factor (e.g., cholesterol) may be much greater if other risk factors (e.g., diabetes and hypertension) are present, than if no other risk factors are present • Short-term (e.g., 10 years) risk may, however, not relate to longer, lifetime risk.
Differences and Trends in CHD and CHD Risk Factors across Populations • International comparisons in incidence • Comparisons across regions of the United States and among ethnic groups • Trends in CHD incidence across countries • Trends in CHD risk factors and ethnic differences
International Comparisons in CVD Morbidity and Mortality • CVD accounts for 25-45% of deaths among different countries • CVD death rates (per 100,000) range from 1310 in Russia to 201 in Japan (6.5 fold difference) in men and from 581 in Russia to 84 in France (7-fold difference) • USA ranks 16th for both men (413) and women (201)
CHD Morbidity and Mortality in the USA • In 1995, 960,000 in USA died from CVD, 42% of all deaths, leading cause in men over age 45 and women over age 65. • 58 million or 20% of population have some form of CVD. • Half of CVD deaths due to CHD, 16% due to stroke. • CHD deaths (per 100,000) greatest in New York (180), least in New Mexico (82). California ranks 28th (125). • Stroke deaths (per 100,000) greatest in South Carolina (63), least in New York (31). California ranks 27th (43). • Economic costs of CHD estimated at $274 billion in 1998.
Secular Trends in CHD and Stroke Mortality • From 1985-1992, greatest annual decline (6-7%) in CHD seen in Israel among men and France among women, USA intermediate (4%), increases in Poland and Romania. • Stroke death rates declined most in Australia, Italy, and France (8-9%), USA about 3%.
1980-1996 Trends in Ischemic Heart Disease and Stroke (source: NCHS)
Prevalences of Major CHD Risk Factors: NHANES I (1976-1980) and NHANES III (1988-1994): Males
Prevalences of Major CHD Risk Factors: NHANES I (1976-1980) and NHANES III (1988-1994): Females
Prevalences (%) of Major CHD Risk Factors: California, Behavioral Risk Factor Surveillance System, 1996-1997
Migrant Studies • Ni-Hon-San Study showed Japanese living in Japan to have the lowest cholesterol levels and lowest rates of CHD, those living in Hawaii to have intermediate rates for both, and those living in San Francisco to have the highest cholesterol levels and CHD incidence
CHD Incidence: 1940 vs. 2000 Age-Adjustment Standards • Because age is one of the strongest predictors of CHD, it is an important confounder to consider when making comparisons across groups (gender, ethnic, geographic) • Official US statistics have used the 1940 age distribution as the standard, but with more older age adults, the 2000 standard is being used, resulting in substantial increases in incidence, nearly two-fold higher than when using the 1940 standard • CHD incidence 1995 about 375/100,000 using the 2000 standard, compared to 180/100,000 using the 1940 standard