Myocardial Infarction - Causes - Risk Factors

Risk Factors

Myocardial infarction results from atherosclerosis. Smoking appears to be the cause of about 36% of coronary artery disease and obesity 20%. Lack of exercise has been linked to 7-12% of cases. Job stress appear to play a minor role accounting for about 3% of cases.

Risk factors for myocardial infarction include:

  • Age
  • Gender: At any given age men are more at risk than women, particularly before menopause, but because in general women live longer than men ischemic heart disease causes slightly more total deaths in women.
  • Diabetes mellitus (type 1 or 2)
  • High blood pressure
  • Dyslipidemia/hypercholesterolemia (abnormal levels of lipoproteins in the blood), particularly high low-density lipoprotein, low high-density lipoprotein and high triglycerides
  • Tobacco smoking, including secondhand smoke
  • Short term exposure to air pollution including: carbon monoxide, nitrogen dioxide, and sulfur dioxide but not ozone.
  • Family history of ischaemic heart disease or myocardial infarction particularly if one has a first-degree relative (father, brother, mother, sister) who suffered a 'premature' myocardial infarction (defined as occurring at or younger than age 55 years (men) or 65 (women).
  • Obesity (defined by a body mass index of more than 30 kg/m², or alternatively by waist circumference or waist-hip ratio).
  • Lack of physical activity.
  • Psychosocial factors including, low socio-economic status, social isolation, negative emotions and stress increase the risk of myocardial infarction and are associated with worse outcomes after myocardial infarction. Socioeconomic factors such as a shorter education and lower income (particularly in women), and unmarried cohabitation are also correlated with a higher risk of MI.
  • Alcohol — Studies show that prolonged exposure to high quantities of alcohol can increase the risk of heart attack.
  • Oral contraceptive pill – women who use combined oral contraceptive pills have a modestly increased risk of myocardial infarction, especially in the presence of other risk factors, such as smoking.
  • Hyperhomocysteinemia (high homocysteine) in homocysteinuria is associated with premature atherosclerosis, whether elevated homocysteine in the normal range is causal is contentious.

Inflammation is known to be an important step in the process of atherosclerotic plaque formation. C-reactive protein (CRP) is a sensitive but non-specific marker for inflammation. Elevated CRP blood levels, especially measured with high-sensitivity assays, can predict the risk of MI, as well as stroke and development of diabetes. Moreover, some drugs for MI might also reduce CRP levels. The use of high-sensitivity CRP assays as a means of screening the general population is advised against, but it may be used optionally at the physician's discretion in patients who already present with other risk factors or known coronary artery disease. Whether CRP plays a direct role in atherosclerosis remains uncertain. Inflammation in periodontal disease may be linked to coronary heart disease, and, since periodontitis is very common, this could have great consequences for public health. Serological studies measuring antibody levels against typical periodontitis-causing bacteria found that such antibodies were more present in subjects with coronary heart disease. Periodontitis tends to increase blood levels of CRP, fibrinogen and cytokines; thus, periodontitis may mediate its effect on MI risk via other risk factors. Preclinical research suggests that periodontal bacteria can promote aggregation of platelets and promote the formation of foam cells. A role for specific periodontal bacteria has been suggested but remains to be established. There is some evidence that influenza may trigger an acute myocardial infarction.

Baldness, hair greying, a diagonal earlobe crease (Frank's sign) and possibly other skin features have been suggested as independent risk factors for MI. Their role remains controversial; a common denominator of these signs and the risk of MI is supposed, possibly genetic.

Calcium deposition is another part of atherosclerotic plaque formation. Calcium deposits in the coronary arteries can be detected with CT scans. Several studies have shown that coronary calcium can provide predictive information beyond that of classical risk factors.

Many of these risk factors are modifiable, so many heart attacks can be prevented by maintaining a healthier lifestyle. Physical activity, for example, is associated with a lower risk profile. Non-modifiable risk factors include age, sex, and family history of an early heart attack, which is thought of as reflecting a genetic predisposition. To understand epidemiological study results, it is important to note that many factors associated with MI mediate their risk via other factors. For example, the effect of education is partially based on its effect on income and marital status.

Read more about this topic:  Myocardial Infarction, Causes

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