ST elevation myocardial infarction risk factors

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

In these chapters on ST elevation, the word risk factors refers to those epidemiologic and genetic variables that expose someone to a higher risk of developing atherosclerotic plaque. The word triggers refer to those factors in the patients immediate history or environment that may have lead to rupture of the atherosclerotic plaque.

Nomenclature

Muller et al have developed the following nomenclature to categorize and analyze data pertaining to triggers of MI :

(1) Trigger: An activity that produces short-term physiological changes that may lead directly to onset of acute CVD.

(2) Acute risk factor: A short-term physiological change, such as a surge in arterial pressure or heart rate, an increase in coagulability, or vasoconstriction, that follows a trigger and may result in disease onset.

(3) Hazard period: The time interval after trigger initiation associated with an increased risk of disease onset because of the trigger. The onset and offset times of the hazard period, which could also be designated a “vulnerable period,” may be sharply defined, as in heavy exertion, or less well defined, as with respiratory infection. The duration of the hazard period may also vary, eg from < 1 hour during heavy physical exertion to weeks or months with bereavement.

(4) Triggered acute risk prevention (TARP): Cardiovascular risk reduction that focuses on the short-term increase in risk associated with a trigger.

Risk Factors

Traditional Risk Factors for Atherosclerosis

Risk factors for atherosclerosis are generally risk factors for myocardial infarction:

• Advancing age
• Male gender
• Cigarette smoking
• Hypercholesterolemia (more accurately hyperlipoproteinemia, especially high low density lipoprotein and low high density lipoprotein)
• Diabetes (with or without insulin resistance)
• High blood pressure
• Obesity (defined by a body mass index of more than 30 kg/m², or alternatively by waist circumference or waist-hip ratio).
• Elevated homocysteine

Genetic Disorders

• Mendelian inherited conditions

Familial mixed hyperlipidaemia

LDL receptor deficiency

• Autosomal dominant conditions

Pseudoxanthoma elasticum dominant type 1

• Autosomal recessive conditions

Cystathionine beta-synthase deficiency

Sitosterolemia

Family History and Heart Disease

According to present trends in the United States, half of healthy 40-year-old males and 1 in 3 healthy 40-year-old women will develop coronary artery disease (CAD) in the future. This chance is greater when a family history of heart disease is involved.

Studies have reported that the risk of CAD increases two- to sevenfold when there is a genetic link. The studies by Nora and Nora (1978a) evaluated a large number of patients with congenital heart disease. Results show that about 8% of the defects were primarily genetics-related, 2% were environmental (caused by drugs, viruses, maternal nutrition, maternal metabolism, or fetal hemodynamics) and 90% were multifactorial (due to a combination of environmental and genetic factors). The study also noted that there is a two- to threefold increase in the recurrence risk for congenital heart disease when two of the family members are affected. This is particularly the case when the parent is severely affected or when the affected members are child and parent. The risk for a myocardial infarction is two to three times greater in a first-degree relative than in a person with no family history of heart disease. This fact speaks in particular to the early presentation of CAD in patients with no other risk factors. Second cousins have a 1 in 23 chance of sharing a particular gene and third cousins have a 1 in 128 likelihood.

Genetic hypertension and hyperlipidemia are strong predictors of familial heart disease. Hypertensive people are twice as likely to have a family history of the condition than are normotensives. Genetic hypertension is an example of a polygenic mode of inheritance that reflects cellular sodium transport defects and an abnormal response to psychogenic stress. There is indication that Pheochromocytoma, a rare cause of hypertension, may be familial as well.

Endocrine Conditions

• Diabetes mellitus type 2 (NIDDM)
• Primary hyperparathyroidism

Rheumatologic and Autoimmune Conditions

• Systemic lupus erythematosus (SLE)

Socioeconomic Factors

Socioeconomic factors such as a shorter education and lower income (particularly in women), and living with a partner may also contribute to the risk of MI. To understand epidemiological study results, it's 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.

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.

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 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.

Controversial Risk Factors

Baldness, hair greying, a diagonal earlobe crease and possibly other skin features are independent risk factors for MI. Their role remains controversial; a common denominator of these signs and the risk of MI is supposed, possibly genetic.

Risk Factor Modification

While family history, along with age and sex, is uncontrollable, many of the risk factors for heart disease can be eliminated by maintaining a healthy lifestyle. In fact, a person's daily habits significantly affect the risk of heart disease due to genetic predisposition. Studies have shown that deaths can be avoided by attending to the controllable risk factors. Such risk factors include: obesity, blood pressure, cigarette smoking and plasma cholesterol.

A study published in Circulation shines some light on the importance of eliminating these controllable risk factors in people with a family history of heart disease. Data demonstrated that in men with a genetic link to heart disease, an estimated 68% of the excess deaths were due to the addition of smoking, a modifiable risk factor; concluding that the risk of heart disease in men with a family history of the condition is significantly related to the additional risk factors he accumulates.

References

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