Aspirin Likely Still Benefits Heart Health Despite New Study
For years people with a high risk for heart disease have relied on aspirin as part of their health regimen. Lately, there have been numerous news stories based on the recent POPADAD Trial that trumpet that aspirin is of no benefit in reducing first heart attacks. Let's clear the air and separate the science from the hysteria - and also look at a major flaw in this and other studies like it.
The POPADAD Trial found "no evidence that aspirin or antioxidants are of any benefit in the primary prevention of cardiovascular events in diabetic patients with asymptomatic peripheral arterial disease (PAD)." However, the study's author did comment there was a benefit for those who had established heart disease as evidenced by a previous cardiac event. Remember, this last sentence. It will be the key to pointing out a major flaw in heart disease studies and treatment.
First of all, the study looked only at patients with diabetes and asymptomatic PAD as established by an Ankle-Brachial Index (ABI) of 0.99 or less. This is a very specific population which makes it difficult to extrapolate its results to the general population. It could easily be that diabetics have unusual blood chemistry or routinely take other drugs that may affect the ability of aspirin to show an effect. For example, if diabetics have higher blood levels of thromboxane (studies suggest they do) then diabetics may require a significantly higher dose of an anti-thromboxane agent like aspirin to be beneficial. Study participants received only 100mg of aspirin.
Next, consider the study size of only 1276 participants. That may sound like a fair-sized group but not in relation to what they observed. The annual vascular (heart attack, stroke, above ankle amputation) event rate observed was only 2.9%. When looking for variations in very small numbers you need a very large population to detect a meaningful difference. Medical statisticians typically use a confidence level of 95% to construct what is known as a "confidence interval." The confidence interval statistically determines the range the "true" study result would likely fall into with 95% confidence (i.e. if they ran the same study 20 times they would get a result within the confidence interval 19 out of 20 times). In this case the confidence interval for vascular event-rate for those taking aspirin was 0.76 to 1.26. That means that the probable "true" aspirin effect could have been as much as a 24% DECREASE in vascular events (which is consistent with other studies) or conversely as high as a 26% increase! It is academically and statistically bankrupt to "average" the confidence interval and say the net effect is zero. This is typical of journalists who simply do not understand statistics.
Finally, we get to my pet peeve - using heart attack and stroke as the only positive confirmation of having coronary artery disease (CAD). Here is where I believe the study really goes off the deep end. The (questionable) suggestion being made by the POPADAD study is that aspirin is ineffective as a primary preventive therapy because their participants did not yet have a heart attack or stroke at the start of the study. CAD is a chronic disease where arteries become burdened by plaque. We now know that heart attacks are primarily caused by plaque ruptures in arteries that have (until the rupture) perfectly good blood flow. When the plaque ruptures, its core is exposed to blood, a clot forms, and the once open artery closes off. We also know that plaques are consistently composed of about 20% calcium. Therefore, a positive calcium score via heart scan is almost ALWAYS a positive diagnosis for some degree of CAD. I would have liked to have seen the heart scan scores of the study participants. I am willing to bet a significant number (close to all) of them did have pre-existing CAD with plaques that had simply not yet ruptured.
The POPADAD study author admits aspirin is of benefit to persons with established CAD. Why wait to have a heart attack to diagnose CAD and start secondary prevention measures that most all agree are effective? Seems kind of silly to me when a simple heart scan can help make the diagnosis! Once again, we find the media hyping a study and making hysterical extrapolations about statistically curious results to the general public. I would urge everyone currently taking aspirin to calm down and discuss the matter with your doctor before making any changes to your heart health regimen.
Looking out for your heart health,