Lipoprotein(a) and the risk of recurrent coronary heart disease: the Dubbo Study

Abstract

Objective Elevated Lipoprotein(a) [Lp(a)] has not been firmly established as a risk factor for recurrent coronary heart disease (CHD). The present analysis explored this relationship in senior citizens. Methods This was a longitudinal study in 607 subjects, all with prevalent CHD, mean age 71 years, followed for 16 years. Baseline examinations of lipids and other CHD risk factors were conducted in 1988–89 in Dubbo, Australia. The independent contribution of Lp(a) to a further CHD event was examined in proportional hazards regression models. Results There were 399 incident CHD cases. Median Lp(a) in CHD cases was 130 mg/L (Interquartile range 60–315) and in non-cases 105 mg/L (45–250) (p < .07, U-Test). 26% of CHD cases and 19% of non-cases had Lp(a) 300 + mg/L; 18% of CHD cases and 8% of non-cases had Lp(a) 500 + mg/L. Lp(a) in Quintile 5 of its distribution (355 + mg/L), using Lp(a) Quintile 1 (<50mg/L) as reference, significantly predicted recurrent CHD with Hazard Ratio 1.53 (95% CI 1.11–2.11, p = .01). Prediction was independent of other risk factors. Lp(a) 500 + mg/L versus lower, significantly predicted recurrent CHD with Hazard Ratio 1.59 (1.16–2.17, p < .01). Prediction was similarly significant for Lp(a) 300 + mg/L versus lower, with Hazard Ratio 1.37 (1.09–1.73, p < .01). Conclusion Elevated Lp(a) is an independent and significant predictor of recurrent CHD in senior citizens. Upper reference Lp(a) levels of 500 mg/L (≈125nmol/L) or 300 mg/L (≈75nmol/L) both appear to be appropriate. The clinical benefit of therapy to reduce elevated Lp(a) remains to be confirmed.