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

PLAIN LANGUAGE SUMMARYLipoprotein(a) [Lp(a)], a type of "bad cholesterol", has been shown to be an important cause of coronary artery disease (CAD). In the long-term Dubbo Study of senior citizens in Australia, Professor Simons' team have previously shown that citizens with Lp(a) readings greater than 276 mg/L had a 46% greater chance of a first CAD problem (e.g. a heart attack) compared with those having much lower readings. This new study asked whether Lp(a) might also increase the chance of a second or repeat episode of CAD in citizens who had already manifested CAD. In 607 senior citizens with previous CAD followed for 16 years, those with Lp(a) readings greater than 355 mg/L had a 53% greater chance of manifesting another CAD problem compared with those having much lower readings. The team concluded that Lp(a) remains an important cause of repeat CAD in senior citizens. The benefit of emerging treatments to lower Lp(a) remains to be confirmed in ongoing research. ObjectiveElevated 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.MethodsThis 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.ResultsThere 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).ConclusionElevated Lp(a) is an independent and significant predictor of recurrent CHD in senior citizens. Upper reference Lp(a) levels of 500 mg/L (approximate to 125nmol/L) or 300 mg/L (approximate to 75nmol/L) both appear to be appropriate. The clinical benefit of therapy to reduce elevated Lp(a) remains to be confirmed.