OCs: Low heart attack risk for young, healthy women

Smoking, hypertension, age boost risks

For your patients under 35 who have no risk factors for cardiovascular disease, oral contraceptives (OCs) can be used safely with a very low, if any, risk of heart attack, a new international study confirms.1 But if you have a patient who is over 35 and smokes or has high blood pressure, know that her risk of heart attack increases substantially, according to the study’s results.

These findings from the World Health Organization (WHO) Study of Cardiovascular Diseases and Steroid Hormone Contraception show that the risk of heart attack is extremely rare in young nonsmoking women who use OCs and can be lowered by careful screening for high blood pressure and other predisposing risk factors, says Neil Poulter, MD, lecturer in clinical epidemiology and public health at University College London Medical School and lead author of the study.

The hospital-based case-control study examined the association between a first heart attack and current OC use. Women in 17 countries in Africa, Asia, Europe, and Latin America were enrolled, with 21 research centers involved in the effort. A total of 368 women, ages 20 to 44, who had heart attacks were compared with 941 women who were admitted to hospitals for other unrelated reasons.

Researchers compared the proportion who were current OC users with those who had other risk factors such as smoking, high blood pressure, diabetes, and a family history of stroke or heart attack to calculate whether OC use causes any increase of heart attacks over those attributable to the other risk factors.

The study is one in a series of reports released by the Special Programme of Research, Devel-opment, and Research Training in Human Reproduction (HRP), a joint effort of WHO in Geneva, Switzerland, the United Nations Development Programme in New York, the United Nations Population Fund in New York, and the World Bank in Washington, DC.

Take a look at the results

According to the study, the overall relative risk of heart attack for all pill users of all ages increased if they smoked or had high blood pressure. In those pill users who smoked 10 or more cigarettes a day, the relative risk of heart attack was more than 20 times higher than in women who did not smoke or use the pill. For pill users with a history of high blood pressure, including during pregnancy, the overall relative risk of heart attack was 10 times higher than in those who did not have high blood pressure or use the pill.

Heart attack is rare in women under 35, but its incidence increases steadily after that age, the researchers note. In young women who neither smoke nor use the pill, the scientists calculate less than one heart attack would occur each year in one million women (0.8 cases per million woman-years). If the same one million women were using the pill, about 3.5 cases would occur in one year.

Smoking and pill use do not combine well, the study reveals. For women under 35 who smoke and use the pill, the incidence of heart attack increases to some 40 cases per million women per year. And for those women over 35 who are both smokers and pill users, the incidence rate can reach 500 cases per million women per year, or one in 2,000 women per year, the study estimates.

Preventing heart problems

The length of pill use does not affect the risk of heart attack, the findings indicate. Women who have stopped using the pill are not at an increased risk for the condition, the report notes.

Poulter stresses the need for checking blood pressures before and during the use of oral contraceptives as an important safeguard in reducing the risk for heart attack. "I think one of the key findings of this study is to contrast these results with similar contemporary studies, which were carried out mainly in America, where I think we’re dealing with a different type of woman.2-4

"I think these other studies were carried out in settings where women usually have their blood pressures checked routinely before use and during. Many of our subjects that we studied did not. And the WHO study consistently showed that having blood pressure checked before pill use was associated with lower risk with oral contraceptives."

Be sure to check your patient’s medications if she is an established hypertensive and is requesting birth control pills, says Joyce Carlone, MN, RN, CFNP, a nurse practitioner at the Atlanta-based Emory University Hypertension Research Center. You may be surprised at the results.

Carlone sees young women in their 20s with no other health complications who are on five to six medications for treatment of their hypertension. She recommends carefully evaluating patients to determine if a combined OC is the best form of contraception.

A potential pill candidate may be a young woman with well-controlled hypertension (blood pressure under 140/90), who is taking a single anti-hypertensive, perhaps with one diuretic, and is managing her medications well, she notes. A trial of a low-dose OC can be administered, along with a careful monitoring of the blood pressure level. Evaluation is key, she stresses. Many hypertensives who cannot tolerate a low-dose combined OC may do best with a progestin-only pill or another form of birth control.

The Scientific Group Meeting on Cardiovas-cular Disease and Steroid Hormone Contracep-tion, a division of WHO, will review the relationships between hormonal contraception and risk of cardiovascular disease to make recommendations to member states and delineate outstanding research issues, says Olav Meirik, MD, PhD, head of the research component on surveillance and evaluation at the HRP. The group is convening a private session Nov. 3-7 to advise WHO’s director general on its findings.

What’s next in research?

Researchers are analyzing the impact of the third-generation progesterone-containing pills as they relate to stroke, Poulter reports, adding that the currently published study on heart attack contained an insufficient number of women to determine the risks involved with the new pills. This third-generation pill study will be followed by an analysis of progesterone-only products, either pills or injectables, he notes.

References

1. WHO Collaborative Study of Cardiovascular Disease and Steroid Hormone Contraception. Acute myocardial infarction and combined oral contraceptives: results of an international multicentre case-control study. Lancet 1997; 349:1,202-1,209.

2. Rosenberg L, Palmer JR, Lesko SM, et al. Oral contraceptive use and the risk of myocardial infarction. Am J Epidemiol 1990; 131:1,009-1,016.

3. Sidney S, Petitti DB, Quesenberry CP, et al. Myocardial infarction in users of low-dose oral contraceptives. Obstet Gynecol 1996; 88:939-944.

4. Thorogood M, Mann J, Murphy M, et al. Is oral contraceptive use still associated with an increased risk of fatal myocardial infarction? Report of a case-control study. Br J Obstet Gynaecol 1991; 98:1,245-1,253.