High lipoprotein(a) levels linked to repeated heart disease events in older adults

By Dr. Chinta SidharthanReviewed by Benedette Cuffari, M.Sc.Jun 18 2023

In a recent study published in the journal Current Medical Research and Opinion, researchers report that high lipoprotein(a) levels were linked to repeated coronary heart disease events in older adults.

Study: Lipoprotein(a) and the risk of recurrent coronary heart disease: the Dubbo Study. Image Credit: SUWIT NGAOKAEW / Shutterstock.com

Background

The lipoprotein(a) structure consists of a low-density lipoprotein (LDL) structure attached to a glycoprotein apolipoprotein. Recent studies indicate that high levels of lipoprotein(a) contribute to aortic valve disease and atherosclerotic cardiovascular disease.

Lipoprotein(a) is believed to be a similar risk factor as LDL for cardiovascular disease and mortality. Therefore, by reducing lipoprotein(a) levels, patients may be at a reduced risk for future cardiovascular events.

A previous study by the same authors demonstrated the link between lipoprotein(a) levels and the occurrence of coronary heart disease among adults in Australia above the age of 60 years, with a follow-up of 16 years. Within the top quartile of lipoprotein(a) distribution, there was a 45% excess risk in the first presentation of coronary heart disease. However, only recently have studies examined the relationship between increases in lipoprotein(a) levels and the possibility of recurrent cardiovascular disease.           

About the study

In the present study, researchers invited the participants from their first study, known as the Dubbo study, to participate in the second study examining the association between elevated levels of lipoprotein(a) and the risk of repeated coronary heart disease events.

Baseline observations for demographic, cardiovascular, and psychosocial risk assessments were recorded. A range of medical assessments was performed, including blood tests, anthropometry, resting electrocardiogram, and blood pressure. Blood samples were collected after 12 hours of fasting to measure glucose, lipoproteins, and lipids levels.

Prevalent coronary heart disease at the onset of the study was defined as previous angina or myocardial infarction—resting electrocardiogram changes recorded during the baseline measurements.

Incident coronary heart disease events that could have occurred over the 16 years between the first and second study were determined from records for hospitalization or death and postal surveys that were conducted to confirm the vital status of the patient every two years.

A modified enzyme-linked immunosorbent assay (ELISA) called sandwich ELISA was used to measure the levels of lipoprotein(a). LDL cholesterol levels were also determined and corrected for the cholesterol content from lipoprotein(a).

The Cox proportions hazard regression model was used to determine the independent association between elevated lipoprotein(a) levels and recurrent coronary heart disease.

Study findings

A total of 399 cases of coronary heart disease with median lipoprotein(a) levels of 130 mg/liter were included in the current study. Comparatively, the median lipoprotein(a) levels in cases with no recurrent coronary heart disease were 105 mg/liter. The difference between the lipoprotein(a) levels of individuals with and without recurrent coronary heart disease was mildly significant.

Other significant differences between those with and without recurrent coronary heart disease included older age, male gender, low high-density lipoprotein (HDL) cholesterol levels, and high triglyceride levels. Additionally, many recurrent coronary heart disease cases used anti-hypertensive therapies, atrial fibrillation, or diabetes. LDL cholesterol levels were not higher in individuals with recurrent coronary heart disease events.

The distribution of lipoprotein(a) levels was highly skewed, which led to identifying individuals with elevated lipoprotein(a) levels and using multivariate models to identify their relative risk of coronary heart disease.

To this end, for individuals with lipoprotein(a) levels higher than 300 mg/liter, the excessive relative risk was 37% as compared to individuals with lipoprotein(a) levels lower than 300 mg/liter. Similarly, for individuals with lipoprotein(a) levels higher than 500 mg/liter, the relative risk increased to 59% when compared to those with lipoprotein(a) levels lower than 500 mg/liter.

Notably, the concentration of LDL after correcting for the 30% lipoprotein(a) derived cholesterol in the body was not a predictor of coronary heart disease in this study.

Conclusions

High levels of lipoprotein(a) were a risk factor for recurrent events of coronary heart disease among individuals above the age of 60 years. For individuals with lipoprotein(a) levels of 355 mg/liter or greater, the possibility of another coronary artery disease event was 53% higher.

While the impact of treatments that focus on lowering lipoprotein(a) levels to limit the incidence of recurrent coronary heart disease remains unclear, the current study reported that low-density lipoprotein levels did not predict the risk of recurrent cardiovascular events.