FOR SOME, LDL CHECK DOES NOT PREDICT HEART’S FUTURE

By Paula Rasich Reviewed by Elizabeth Klodas, MD, FACC  January 21, 2009--New evidence shows that some people can be at increased risk for heart trouble even when their “bad” LDL cholesterol is at what’s considered a healthy level.

In an analysis from the INTERHEART study----a large-scale, case-control study looking at the relationship between blood fats and first heart attack in Asians---an international team of researchers found that even though LDL levels were on average 10 points lower in Asians than non Asians, heart attack risk was similar.

This scientific research, involving more than 12,000 people, is the first to compare data on ethnic groups across Asia---including South Asians, Southeast Asians, Chinese, and Japanese---as well as non Asians.  Researchers found that a greater proportion of Asians have LDL levels below 100 compared to non Asians, yet still have a high rate of heart attack. 

In recent years doctors have realized that some versions of “bad” cholesterol and other fats are worse than others. And they reason that two protein checks, apolipoprotein A (Apo A-1) and apolipoprotein B (Apo B), may be just as---if not more---important as your cholesterol reading in predicting heart risk.

Apo A-1 is a protein that ushers artery-clogging fats out of the bloodstream, while Apo B delivers those potentially damaging substances to vessel walls and leaves them behind. HDL cholesterol (the “good” kind) carries Apo A-1 protein.  LDL cholesterol and several other “bad” fats carry the Apo B protein type.  So having a high concentration of Apo B containing particles predisposes to artery wall damage and plaque build up.

In this study, abnormal protein levels---a low apolipoprotein A (apo A-1) and a high apoliprotein B (Apo B)---emerged as the strongest warning signaling risk of first heart attack.

The implication of this study is that LDL and HDL may not be the best targets in regard to therapy for reducing cardiovascular events, says study co-author Salim Yusuf, DPhil, professor of medicine at McMaster University in Ontario, Canada. “Apo A-I and Apo B are better markers. We were looking at the wrong component of lipids in assessing risk.”

Editors Comment:  Apo A-1 and Apo B levels are tests which are not routinely performed in clinical practice today.  However, data continues to mount with respect to the utility of these measurements, and it is very possible that apolipoprotein monitoring will replace traditional cholesterol evaluations in the future.  Some laboratories do offer this analysis and patients should check with their physicians to see if they are good candidates for this type of testing.  Because the absolute cholesterol values which placed Asian patients at higher risk for heart attack were relatively low in this large study, goal cholesterol levels and thresholds for initiating cholesterol lowering therapy may need to be adjusted for this population.

This study was published in the January 27, 2009 issue of the Journal of the American College of Cardiology. 

SOURCES:

Karthikeyan G. et al. Lipif Profile, Plasma Apoliproteins, and Risk of a First Myocardial Infarction Among Asians: An Analysis from the INTERHEART Study. The Journal of the American College of Cardiology, 2008.

 Salim Yusuf, DPhil, Professor of Medicine, McMaster University, Hamilton, Ontario, Canada.