'Coronary heart disease ' (CHD), also called CAD,
ischaemic heart disease,
atherosclerotic heart disease, is the end result of the accumulation of
atheromatous plaques within the walls of the
arteries that supply the
myocardium (the muscle of the
heart) with oxygen and nutrients. While the symptoms and signs of coronary heart disease are noted in the advanced state of disease, most individuals with coronary heart disease show no evidence of disease for decades as the disease progresses before the first onset of symptoms, often a "sudden"
heart attack, finally arise. After decades of progression, some of these
atheromatous plaques may rupture and (along with the activation of the
blood clotting system) start limiting
blood flow to the
heart muscle. The disease is the most common cause of
sudden death[1], and is also the most common reason for death of men and women over 20 years of age.
According to present trends in the United States, half of healthy 40-year-old males will develop CHD in the future, and one in three healthy 40-year-old women.
[2] According to the
Guinness Book of Records,
Northern Ireland is the country with the most occurrences of CHD.
Overview
Atherosclerotic heart disease can be thought of as a wide
spectrum of disease of the heart. At one end of the spectrum is the
asymptomatic individual with atheromatous streaks within the walls of the coronary arteries (the arteries of the heart). These streaks represent the early stage of atherosclerotic heart disease and do not obstruct the flow of blood. A
coronary angiogram performed during this stage of disease may not show any evidence of coronary artery disease, because the lumen of the coronary artery has not decreased in calibre.
Over a period of many years, these streaks increase in thickness. While the atheromatous plaques initially expand into the walls of the arteries, eventually they will expand into the lumen of the vessel, affecting the flow of blood through the arteries. While it was originally believed that the growth of atheromatous plaques was a slow, gradual process, recent evidence suggests that the gradual buildup may be complemented by small plaque ruptures which cause the sudden increase in the plaque burden due to accumulation of thrombus material.
Atheromatous plaques that cause obstruction of less than 70 percent of the diameter of the vessel rarely cause symptoms of obstructive coronary artery disease. As the plaques grow in thickness and obstruct more than 70 percent of the diameter of the vessel, the individual develops symptoms of obstructive coronary artery disease. At this stage of the disease process, the patient can be said to have
ischemic heart disease. The symptoms of ischemic heart disease are often first noted during times of increased workload of the heart. For instance, the first symptoms include exertional
angina or decreased exercise tolerance.
As the degree of coronary artery disease progresses, there may be near-complete obstruction of the
lumen of the coronary artery, severely restricting the flow of oxygen-carrying blood to the myocardium. Individuals with this degree of coronary heart disease typically have suffered from one or more
myocardial infarctions (heart attacks), and may have signs and symptoms of chronic coronary ischemia, including symptoms of
angina at rest and flash
pulmonary edema.
A distinction should be made between myocardial ischemia and myocardial infarction. Ischemia means that the amount of oxygen supplied to the tissue is inadequate to supply the needs of the tissue. When the myocardium becomes ischemic, it does not function optimally. When large areas of the myocardium becomes ischemic, there can be impairment in the relaxation and contraction of the myocardium. If the blood flow to the tissue is improved, myocardial ischemia can be reversed. Infarction means that the tissue has undergone irreversible death due to lack of sufficient oxygen-rich blood.
An individual may develop a rupture of an atheromatous plaque at ''any'' stage of the spectrum of coronary heart disease. The acute rupture of a plaque may lead to an acute
myocardial infarction (heart attack).
Pathophysiology
Limitation of blood flow to the heart causes
ischemia (cell starvation secondary to a lack of oxygen) of the myocardial cells. When myocardial cells die from lack of
oxygen, this is called a
myocardial infarction (commonly called a heart attack). It leads to
heart muscle damage,
heart muscle death and later scarring without
heart muscle regrowth.
Myocardial infarction usually results from the sudden occlusion of a coronary artery when a plaque ruptures, activating the clotting system and
atheroma-clot interaction fills the lumen of the artery to the point of sudden closure. The typical
narrowing of the lumen of the
heart artery before sudden closure is typically 20%, according to clinical research completed in the late 1990s and using
IVUS examinations within 6 months prior to a
heart attack. High grade
stenoses as such exceeding 75% blockage, such as detected by
stress testing, were found to be responsible for only 14% of acute
heart attacks the rest being due to plaque rupture/ spasm. The events leading up to plaque rupture are only partially understood.
Myocardial infarction is also caused, far less commonly, by spasm of the artery wall occluding the lumen, a condition also associated with
atheromatous plaque and CHD.
CHD is associated with
smoking,
obesity,
hypertension and a chronic sub-clinical lack of vitamin C. A family history of CHD is one of the strongest predictors of CHD. Screening for CHD includes evaluating
homocysteine levels,
high-density and
low-density lipoprotein (
cholesterol) levels and
triglyceride levels.
Angina
Angina that occurs regularly with activity, upon awakening, or at other predictable times is termed stable angina and is associated with high grade
narrowings of the
heart arteries. The symptoms of angina are often treated with nitrate preparations such as
nitroglycerin, which come in short-acting and long-acting forms, and may be administered transdermally, sublingually or orally. Many other more effective treatments, especially of the underlying
atheromatous disease, have been developed.
Angina that changes in intensity, character or frequency is termed unstable. Unstable angina may precede myocardial infarction, and requires urgent medical attention. It is treated with morphine, oxygen, intravenous nitroglycerin, and aspirin. Interventional procedures such as
angioplasty may be done.
Risk factors
'The following are confirmed
independent risk factors for the development of CAD, in order of decreasing importance:'
#
Hypercholesterolemia (specifically, serum
LDL concentrations)
#
Smoking
#
Hypertension (high systolic pressure seems to be most significant in this regard)
#
Hyperglycemia (due to diabetes mellitus or otherwise)
#
Type A Behavioural Patterns, TABP. Added in 1981 as an independant risk factor after a majority of research into the field discovered that TABP's were twice as likely to cause CHD than any other personality type.
# Hereditary differences in such diverse aspects as lipoprotein structure and that of their associated receptors, homocysteine processing/metabolism, etc.
'Significant, but indirect risk factors include:'
★ Lack of
exercise
★ Stress
★ Diet rich in
saturated fats
★ Diet low in
antioxidants
★
Obesity
★ Men over 60; Women over 65
[1]
Prevention
Coronary heart disease is the most common form of heart disease in the Western world. Prevention centers on the modifiable risk factors, which include decreasing
cholesterol levels, addressing
obesity and
hypertension, avoiding a
sedentary lifestyle, making healthy dietary choices, and
stopping smoking. There is some evidence that lowering
uric acid and
homocysteine levels may contribute. In
diabetes mellitus, there is little evidence that
blood sugar control actually improves cardiac risk. Some recommend a diet rich in omega-3 fatty acids and
vitamin C. The World Health Organization (WHO) recommends "low to moderate alcohol intake" to reduce risk of coronary heart disease.
[3]
An increasingly growing number of other
physiological markers and
homeostatic mechanisms are currently under scientific investigation. Among these markers are
low density lipoprotein and
asymmetric dimethylarginine. Patients with CHD and those trying to prevent CHD are advised to avoid fats that are readily oxidized (e.g., saturated fats and
trans-fats), limit carbohydrates and processed sugars to reduce production of
Low density lipoproteins while increasing
High density lipoproteins, keeping
blood pressure normal, exercise and stop smoking. These measures limit the progression of the disease. Recent studies have shown that dramatic reduction in LDL levels can cause mild regression of coronary heart disease.
Exercise
Separate to the question of the benefits of exercise; it is unclear whether doctors should spend time counseling patients to exercise. The
U.S. Preventive Services Task Force (USPSTF), based on a
systematic review of
randomized controlled trials, found 'insufficient evidence' to recommend that doctors counsel patients on exercise.
[4] However, the
American Heart Association, based on a non-systematic review, recommends that doctors counsel patients on exercise
[5]
Preventive diets
Main articles: Diet and Heart Disease
It has been suggested that coronary heart disease is partially reversible using an intense dietary regimen coupled with regular cardio exercise.
[6]
★ Vegetarian diet:
Vegetarians have been shown to have a 24% reduced risk of dying of heart disease.
[7]
★ Cretan
Mediterranean diet: The Seven Country Study found that
Cretan men had exceptionally low death rates from heart disease, despite moderate to high intake of fat. The Cretan diet is similar to other traditional Mediterranean diets: consisting mostly of
olive oil, bread, abundant fruit and vegetables, a moderate amount of wine and fat-rich animal products such as lamb, sausage and
goat cheese.
[8][9][10] However, the Cretan diet consisted of less fish and wine consumption than some other Mediterranean-style diets, such as the diet in
Corfu, another region of Greece, which had higher death rates.
The consumption of
trans fat (commonly found in
hydrogenated products such as
margarine) has been shown to cause the development of
endothelial dysfunction, a precursor to
atherosclerosis.
[11]
Aspirin
Aspirin, in doses of less than 75 to 81 mg/d
[12], can reduce the incidence of cardiovascular events.
[13] The
U.S. Preventive Services Task Force 'strongly recommends that clinicians discuss aspirin chemoprevention with adults who are at increased risk for coronary heart disease'.
[14] The Task Force defines increased risk as 'Men older than 40 years of age, postmenopausal women, and younger persons with risk factors for coronary heart disease (for example, hypertension, diabetes, or smoking) are at increased risk for heart disease and may wish to consider aspirin therapy'. More specifically, high-risk persons are 'those with a 5-year risk ≥ 3%'. A risk calculator is available.
[15]
Regarding healthy women, the more recent
Women's Health Study randomized controlled trial found
insignficant benefit from aspirin in the reduction of cardiac events; however there was a
signficant reduction in
stroke.
[16] Subgroup analysis showed that all benefit was confined to women over 65 years old.
16 In spite of the
insignficant benefit for women < 65 years old, recent
practice guidelines by the
American Heart Association recommend to 'consider' aspirin in 'healthy women' <65 years of age 'when benefit for ischemic stroke prevention is likely to outweigh adverse effects of therapy'.
[17]
Omega-3 fatty acids
The benefit of fish oil is controversial with conflicting conclusions reached by a negative
meta-analysis[18] of
randomized controlled trials by the international
Cochrane Collaboration and a partially positive
systematic review[19] by the
Agency for Healthcare Research and Quality. Since these two reviews, a
randomized controlled trial reported a reduction on coronary events in Japanese hypercholesterolemic patients.
[20]
Omega-3 fatty acids are also found in some plant sources including flax seed oil, hemp seed oil, and Walnuts. Plant sources may be safer as fish products have been shown to contain heavy metals and other fat soluble pollutants.
Secondary prevention
Secondary prevention is preventing further sequelae of already established disease. Regarding coronary heart disease, this can mean risk factor management that is carried out during cardiac rehabilitation, a 4-phase process beginning in hospital after MI, angioplasty or heart surgery and continuing for a minimum of three months. Exercise is a main component of cardiac rehabilitation along with diet, smoking cessation, and blood pressure and cholesterol management.
Anti-platelet therapy
A
meta-analysis of
randomized controlled trials by the international
Cochrane Collaboration found "that the use of clopidogrel plus aspirin is associated with a reduction in the risk of cardiovascular events compared with aspirin alone in patients with acute non-ST coronary syndrome. In patients at high risk of cardiovascular disease but not presenting acutely, there is only weak evidence of benefit and hazards of treatment almost match any benefit obtained.".
[21]
Recent research
A 2006 study by the
Cleveland Clinic found a region on Chromosome 17 was confined to families with multiple cases of myocardial infarction.
[22]
A more controversial link is that between ''
Chlamydophila pneumoniae'' infection and atherosclerosis.
[23] While this intracellular organism has been demonstrated in atherosclerotic plaques, evidence is inconclusive as to whether it can be considered a causative factor. Treatment with antibiotics in patients with proven atherosclerosis has not demonstrated a decreased risk of heart attacks or other coronary vascular diseases.
[24]
References
1. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1835183
2. http://circ.ahajournals.org/cgi/content/full/115/5/e69/TBL3179728
3. http://www.who.int/nutrition/topics/5_population_nutrient/en/index12.html
4. Behavioral counseling in primary care to promote physical activity: recommendation and rationale, , , , Ann. Intern. Med., 2002
5. Exercise and physical activity in the prevention and treatment of atherosclerotic cardiovascular disease: a statement from the Council on Clinical Cardiology (Subcommittee on Exercise, Rehabilitation, and Prevention) and the Council on Nutrition, Physical Activity, and Metabolism (Subcommittee on Physical Activity), Thompson PD, Buchner D, Pina IL, ''et al'', , , Circulation, 2003 http://www.ngc.gov/summary/summary.aspx?ss=15&doc_id=5360&string=#s23
6. Can lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial., Ornish D, Brown SE, Scherwitz LW, Billings JH, Armstrong WT, Ports TA, McLanahan SM, Kirkeeide RL, Brand RJ, Gould KL., , , Lancet, 1990
7. Mortality in vegetarians and non-vegetarians: a collaborative analysis of 8300 deaths among 76,000 men and women in five prospective studies., Key TJ, Fraser GE, Thorogood M, Appleby PN, Beral V, Reeves G, Burr ML, Chang-Claude J, Frentzel-Beyme R, Kuzma JW, Mann J, McPherson K, , , Public Health Nutr, 1998
8. Mediterranean diet pyramid: a cultural model for healthy eating., Willett WC, Sacks F, Trichopoulou A, Drescher G, Ferro-Luzzi A, Helsing E, Trichopoulos D., , , Am J Clin Nutr, 1995
9. Perez-Llamas, F., et.al., ''J Hum Nutr Diet'', Dec 1996, 9:6:463-471
10. Dietary studies on two rural Italian population groups of the Seven Countries Study. 1. Food and nutrient intake at the thirty-first year follow-up in 1991., Alberti-Fidanza A, Paolacci CA, Chiuchiu MP, Coli R, Fruttini D, Verducci G, Fidanza F., , , Eur J Clin Nutr, 1994
11. Consumption of trans fatty acids is related to plasma biomarkers of inflammation and endothelial dysfunction., Lopez-Garcia E, Schulze MB, Meigs JB, Manson JE, Rifai N, Stampfer MJ, Willett WC, Hu FB., , , J Nutr, 2005
12. Aspirin dose for the prevention of cardiovascular disease: a systematic review, Campbell CL, Smyth S, Montalescot G, Steinhubl SR, , , JAMA, 2007
13. Aspirin for the primary prevention of cardiovascular events in women and men: a sex-specific meta-analysis of randomized controlled trials, Berger J, Roncaglioni M, Avanzini F, Pangrazzi I, Tognoni G, Brown D, , , JAMA, 2006
14. Aspirin for the primary prevention of cardiovascular events: recommendation and rationale, , , , Ann Intern Med, 2002
15. http://www.med-decisions.com/
16. A randomized trial of low-dose aspirin in the primary prevention of cardiovascular disease in women, Ridker P, Cook N, Lee I, Gordon D, Gaziano J, Manson J, Hennekens C, Buring J, , , N Engl J Med, 2005
17. http://circ.ahajournals.org/cgi/content/abstract/CIRCULATIONAHA.107.181546v1
18. Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review, Hooper L, Thompson RL, Harrison RA, Summerbell CD, Ness AR, Moore HJ, Worthington HV, Durrington PN, Higgins JP, Capps NE, Riemersma RA, Ebrahim SB, Davey Smith G, , , BMJ, 2006
19. n-3 Fatty acids from fish or fish-oil supplements, but not alpha-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review, Wang C, Harris WS, Chung M, Lichtenstein AH, Balk EM, Kupelnick B, Jordan HS, Lau J, , , Am. J. Clin. Nutr., 2006 http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hstat1a.chapter.38290
20. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis, Yokoyama M, Origasa H, Matsuzaki M, ''et al'', , , Lancet, 2007
21. Clopidogrel plus aspirin versus aspirin alone for preventing cardiovascular disease, Keller T, Squizzato A, Middeldorp S, , , Cochrane database of systematic reviews (Online), 2007
22. Genome-Wide Mapping of Susceptibility to Coronary Artery Disease Identifies a Novel Replicated Locus on Chromosome 17, Farrall M, Green FR, Peden JF, Olsson PG, Clarke R, Hellenius ML, Rust S, Lagercrantz J, Franzosi MG, Schulte H, Carey A, Olsson G, Assmann G, Tognoni G, Collins R, Hamsten A, Watkins H, on behalf of the PROCARDIS Consortium, , , PLoS Genetics, 2006
23. Chronic Chlamydia pneumoniae infection as a risk factor for coronary heart disease in the Helsinki Heart Study., Saikku P, Leinonen M, Tenkanen L, Linnanmaki E, Ekman MR, Manninen V, Manttari M, Frick MH, Huttunen JK., , , Ann Intern Med, 1992
24. Effects of antibiotic therapy on outcomes of patients with coronary artery disease: a meta-analysis of randomized controlled trials., Andraws R, Berger JS, Brown DL., , , JAMA, 2005
See also
★
Diet and Heart Disease
★
ApoA-1 Milano
External links
★
Risk Assessment of having a heart attack or dying of coronary heart disease, from the American Heart Association.
★
The InVision Guide to a Healthy Heart An interactive website on the development and function of the cardiovascular system and cardiovascular diseases and consequences. The website also features treatment options and preventative measures for maintaining a healthy heart.
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