Although lipoprotein(a) is causally related to coronary artery disease and aortic valve stenosis – two known risk factors for atrial fibrillation (AFib) – evidence linking Lp(a) to a causal role in the development of AFib has been lukewarm at best.
A recent Mendelian randomization study showed only a nominally significant effect of Lp(a) on AFib, whereas an ARIC substudy showed high levels of Lp(a) to be associated with elevated ischemic stroke risk but not incident AFib.
A new study that adds the heft of Mendelian randomization to large observational and genetic analyses, however, implicates Lp(a) as a potential causal mediator of AFib, independent of its known effects on atherosclerotic cardiovascular disease (ASCVD).
“Why this is exciting is because it shows that Lp(a) has effects beyond the arteries and beyond the aortic valve, and that provides two things,” senior author Guillaume Paré, MD, MSc, Population Health Research Institute, Hamilton, Ontario, told this news organization.
“First, it provides a potential means to decrease the risk, because there are all these Lp(a) inhibitors in development,” he said. “But I think the other thing is that it just points to a new pathway that leads to atrial fibrillation development that could potentially be targeted with other drugs when it’s better understood. We don’t pretend that we understand the biology there, but it opens this possibility.”
The results were published in the Journal of the American College of Cardiology.
Using data from 435,579 participants in the UK Biobank, the researchers identified 20,432 cases of incident AFib over a median of 11 years of follow-up. They also constructed a genetic risk score for Lp(a) using genetic variants within 500 kb of the LPA gene.
After common AFib risk factors were controlled for, results showed a 3% increased risk for incident AFib per 50 nmol/L increase in Lp(a) at enrollment (hazard ratio, 1.03; 95% confidence interval, 1.02-1.05).
A Mendelian randomization analysis showed a similar association between genetically predicted Lp(a) and AFib (odds ratio, 1.03; 95% CI, 1.02-1.05).
To replicate the results, the investigators performed separate Mendelian randomization analyses using publicly available genome-wide association study (GWAS) statistics from the largest GWAS of AFib involving more than 1 million participants and from the FinnGen cohort involving more than 114,000 Finnish residents.
The analyses showed a 3% increase in risk for AFib in the genome-wide study (OR, 1.03; 95% CI, 1.02-1.05) and an 8% increase in risk in the Finnish study (OR, 1.08; 95% CI, 1.04-1.12) per 50 nmol/L increase in Lp(a).
There was no evidence that the effect of observed or genetically predicted Lp(a) was modified by prevalent ischemic heart disease or aortic stenosis.
Further, MR analyses revealed no risk effect of low-density-lipoprotein cholesterol or triglycerides on AFib.
Notably, only 39% of Lp(a) was mediated through ASCVD, suggesting that Lp(a) partly influences AFib independent of its known effect on ASCVD.
“To me, the eureka moment is when we repeated the same analysis for LDL cholesterol and it had absolutely no association with AFib,” Dr. Paré said. “Because up to that point, there was always this lingering doubt that, well, it’s because of coronary artery disease, and that’s logical. But the signal is completely flat with LDL, and we see this strong signal with Lp(a).”