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Heart attack – What causes or prevents it

In Brazil, the risk of a heart attack is five times greater amongst smokers, and falls by almost half with moderate consumption of alcohol

MIGUEL BOYAYANMain risk factor: even smoking a little already doubles the risk of a heart attackMIGUEL BOYAYAN

A recently concluded nationwide study, with 2,558 persons, is determining and classifying the behavior and clinical parameters that increase or diminish the chances of a Brazilian suffering myocardial infarction, a cardiovascular problem that kills some 60,000 persons a year in the country and is one of the main causes of death in the industrialized world. At the top of the list of risk factors is, by far, the habit of smoking.

According to the work, coordinated by the Dante Pazzanese Institute of Cardiology of São Paulo, the daily consumption of more than five cigarettes increases almost fivefold the probability of having a heart attack. Next, featuring on the list of the major risk factors, all in decreasing order of importance, are diabetes mellitus (a high level of sugar in the blood), the excessive building up of fat in the abdomen, a family history of coronary diseases, high levels of LDL cholesterol (the popularly known as bad cholesterol), and high arterial blood pressure (higher than 14 by 9). Each one of these indicators, raises on its own, the risk of having a heart attack two or three times.

At the other extreme, amongst the components that can reduce the incidence of this cardiovascular problem, the study arrived at a surprising result: the consumption of alcohol has proved to be the most effective form of protection against a heart attack. People who drink some kind of alcoholic beverage at least three times a week have 40% less chances of being the victim of a heart attack. Those who consume alcohol up to twice a week show 25% less probability of having a heart attack. The survey, which will be presented for the first time at the end of this month, during the Brazilian Cardiology Congress, in São Paulo, did not investigate the kind of drink consumed by the users of alcohol, nor the quantity.

But the authors of the study warn: this effect, apparently proportional to the quantity of drink consumed, is only valid for moderate consumption of alcohol. It has been proved that excessive doses of wine, whisky, beer or any other kind of drink can, besides causing addiction and all sorts of accidents, increase blood pressure and the levels of triglyceride (a kind of fat), two conditions that favor the appearance of a heart attack.

Besides alcohol, only one other factor – or rather, the simultaneous occurrence of two factors, has achieved a similar protective effect: a high level of schooling in people with monthly earnings of more than R$ 1,200. Within this salary range, individuals with a university education show 32 lower risk of having a heart attack. Oddly enough, working out or doing sports activities did not appear as a factor of protection against a heart attack, although preliminary analyses indicated this benefit.

“This does not mean that physical exercise is not important, but its weight was lower in our study”, explains cardiologist Leopoldo Soares Piegas, the clinical director of the Dante Pazzanese Institute and the coordinator of the study, baptized Assessment of Risk Factors for Acute Myocardial Infarction (Afirmar in the Portuguese acronym). “For smokers, quitting smoking is more important that taking up exercise, in terms of preventing a heart attack”.

Risks multiplied
People with more than one habit or clinical parameter that increases the probabilities of a heart attack occurring should multiply – and not simply add – the odds ratio attributed to this indicator by the survey. The odds ratio is a numerical value that shows how many times a factor increases the chance of having a heart attack in a given population. For example: amongst Brazilians, according to the survey, smoking at least five cigarettes a day is equivalent to a relative risk of 4.9. A person who lights up this quantity of cigarettes has almost 4.9 times more risk of having a heart attack than a non-smoker has.

Accordingly, a person who shows the three main indicators that favor the occurrence of a heart attack – tobacco addiction, diabetes (odds ratio of 2.8), and an excess of abdominal fat (an odds ratio of 2.4) – has 32.8 times more chances (4.9 x 2.8 x 2.4) of being a target for this health problem than an individual without any risk factor for a heart attack. “In terms of public health, smoking, diabetes and obesity can be controlled and mitigated with simple measures, an early diagnosis and information”, says Piegas. The study shows that it is not enough to reduce the number of cigarettes consumed: the ideal is to abandon the habit, because smoking a little – less than five cigarettes a day – is already enough to double the risk of a heart attack.

In Brazil, it is estimated that some 300,000 myocardial infarctions take place every year, one fifth of these cases resulting in death. This cardiovascular problem results from a build up of platelets of fat in the coronary artery that supplies the heart with blood. Unless it is controlled, the phenomenon leads to the formation of clots that obstruct the supply of blood to the cardiac muscle. When this happens, the patient has a heart attack: he feels, in the region of the chest, a sudden, intense pain, which can spread through the neck and the arms. “If we attack the three main risk factors for infarction, we will reduce considerably deaths as a result of this problem”, is Piegas’s opinion. The cardiologist mentions the example of Finland, which just by controlling smoking and the levels of cholesterol, has reduced by 55% deaths from infarction and strokes over the last decade.

The conclusions are founded on the analysis of 33 clinical and laboratory variables from 1,279 heart attack victims and 1,279 people without this kind of problem (the control group), who were attended to between October 1997 and November 2000, in 104 public and private hospitals from 51 cities in 19 states, covering all regions. A comparison was made of a series of variables in patients who had had their first heart attack and were attended to in a clinical center, with healthy persons of the same sex and age range who made up the control group. For each heart attack patient, an attempt was made to find his ideal peer, a control individual, with at the most five years more or less in age and who had preferably been treated in the same hospital or city. This was the way to avoid comparing a heart attack victim from Rio Grande do Sul with a healthy person from Bahia.

The intention was not to understand the mechanism how the risk factors and protection against a heart attack works, but to quantify the weight of their influence on a heart attack. By definition, a person is classified as diabetic when he shows at least 126 milligrams of glucose per deciliter of blood. The quantity of localized fat in the abdomen of an individual is high when the waist- hip ratio – dividing the measurement of the former by the latter – is greater than 0.93 for men and 0.83 for women. And in the case of LDL-cholesterol, the levels are regarded as high when they are more than 100 milligrams per deciliter of blood.

In the majority of studies carried out abroad, smoking is the main habit or clinical fact that favors the occurrence of a heart attack. A similar work carried out in India in 1996 reached this same conclusion, and estimated that the consumption of at least ten cigarettes increases by 3.6 times the risk of a person having a heart attack in the population of that country. In the United States, recent research also put smoking as the main villain for heart attacks, increasing by two or three the probability of a heart attack occurring, far lower levels than those found in Brazil.

“In each country or region, the list of risk and protection factors may be different, as well as the weight of each one of these factors”, says cardiologist Álvaro Avezum, also from the Dante Pazzanese Institute and another of Afirmar’s coordinators. “Hence the importance of our having national and regional data about the risk factors for heart attacks, instead of just importing information”. If the Scandinavian countries had limited themselves to working with the results of research carried out in the United States, they would never have discovered that, in their territory, diabetes – and not tobacco – is the clinical condition that most favors the occurrence of heart attacks.

Peculiarities in São Paulo
After providing a general picture of risk factors for heart attacks in the country, the study, in a second stage, will verify if the weight for each risk and protection factor differs, according to a series of parameters shown by the participants in the research, such as age, sex and geographical origin. In the first study that was derived from Afirmar, Avezum examined the risk and protection factors for heart attacks in a sample of 553 inhabitants of the metropolitan region of São Paulo (271 heart attack victims and 282 from the control group). The results are a bit different from those returned in the nationwide sample, which was, in a way, to be expected. “The weight of each factor can vary, even from region to region, since we are analyzing populations with different characteristics”, he says.

“In the south and southeast, more developed, heart attacks are the sole main cause of death, while in the north and northeast this place is occupied by a cerebral vascular accident (stroke)”. In Greater São Paulo, smoking also appears as the behavior that most increases the probability of a heart attack – though its weight, as a risk factor, was greater than in the nationwide survey. Among the inhabitants of the metropolitan region, the consumption of more than five cigarettes a day increases almost sixfold the chances of a heart attack. In the sample of the whole Brazilian population, this figure was almost five times. Something else in the work that calls attention to the people of São Paulo is the discovery that the second most important risk factor, well ahead of the others, is the accumulation of abdominal fat, which multiples 4.2 times the chances of a heart attack.

“The inhabitants of Greater São Paulo, compared with the other regions, have greater spendingpower and sometimes end up eating more than they should and leading a very sedentary life”, explains Avezum. After smoking and obesity, risk factors featuring for the people of São Paulo are hypertension, high levels of LDL-cholesterol, diabetes, and a family history of heart disease. In the column of protection factors, only one of the clinical variables has proved to be capable of reducing the chances of a heart attack happening amongst the people of São Paulo: the existence of high levels of HDL-cholesterol, the good cholesterol.

People with over 40 milligrams of this kind of lipid per deciliter of blood have a risk 47% lower of suffering from this cardiovascular problem. In the São Paulo sample, the consumption of alcohol and its association with higher education and an income of over R$ 1,200, which were revealed as favorable conditions for reducing the probability of a heart attack occurring in the nationwide survey, did not have the same protective effect.

The Project
Afirmar – Assessment of Risk Factors for Acute Myocardial Infarction
Regular research project benefit line
Leopoldo Soares Piegas – Dante Pazzanese Institute of Cardiology
R$ 9,150.30