Predicting Heart Attacks in Individuals Considered Low Risk

Investigators used ultrasound imaging to view the carotid intima media thickness (C-IMT), or thickness of the artery walls.

The findings were presented in November 2008 at the American Heart Association's Scientific Sessions in New Orleans, LA, USA. Researchers from the Baylor College of Medicine (BCM; Houston, TX, USA) used ultrasound imaging to view the C-IMT. "The ultrasound added another dimension to the risk factor score and showed us that those with thick arteries in the higher end of low risk group actually are at intermediate risk for coronary heart disease," said Dr. Vijay Nambi, assistant professor of medicine of atherosclerosis and vascular medicine at BCM and lead author of the study.

Risk prediction is customarily divided into three groups: low, intermediate, and high risk. Low risk is defined as having a less than a 10% chance of having coronary heart disease in the next 10 years. Intermediate is a 10-20% chance of a coronary event, and high risk is anything greater than 20%. This percentage is calculated by doctors using a score based on traditional risk factors that include age, gender, high-density lipoprotein (HDL) cholesterol (good cholesterol), total cholesterol, hypertension, and smoking.

Dr. Nambi and his colleagues monitored more than 13,000 people already taking part in the Atherosclerosis Risk in Communities study, a large-scale study designed to investigate the etiology and natural history of atherosclerosis. Participants in the current study were followed for almost 14 years. After adding imaging to the traditional risk factors, those in the higher end of the low risk group (estimated 10-year risk of 5-10%) were found to have a greater chance of having a heart attack, particularly if imaging revealed them to have a thicker C-IMT. According to Dr. Nambi, approximately 4% of those who fell in the zero percent to 5% estimated risk had a heart attack, while more than 13% of those in the 5-10% suffered from coronary heart events. Furthermore, he pointed out that in the 5-10% risk group, those with the thickest arteries had approximately a 17% risk for coronary heart events when followed for 14 years.

"There is a big difference between 4% and 13%,” said Dr. Nambi. "These results show us that we need to take a closer look at some of those individuals in the low risk category and even reconsider the definition of ‘low risk.'”

"Our goal is to target those in the most need,” said Dr. Christie Ballantyne, chief of atherosclerosis and vascular medicine and professor of medicine at BCM. "Being able to pinpoint those more likely to have a heart attack will allow us to take early, more effective preventive action to stop a heart attack before it happens.”

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Baylor College of Medicine