This recent article out of JAMA garnered headlines primarily for the insight into the risk of non-obstructive coronary artery disease – headlines such as: “Risk of Heart Attack Jumps with Non-Obstructive Heart Disease” or “Increased Risk Found For People With Even ‘Minor’ Narrowing of Heart Arteries”.
Somehow, this is profound – that individuals with measurable atherosclerotic plaque are at greater danger of suffering an acute coronary syndrome than those without. And, frankly, despite this “significantly increased risk”, the most interesting insights – from an Emergency Medicine standpoint – are tied to how low the risks of MI were, overall.
This is a Veterans Affairs database of coronary angiography findings observed on “elective” cardiac catheterization – meaning the indication for coronary angiography in all cases was not associated with an acute coronary syndrome. Most cases were referred primarily for chest pain, with a minority for a positive functional study. Catheterization findings were classified as non-obstructive, 20-70% stenoses, or >70%/>50% left main stenoses, subdivided into single, double, or triple vessel disease. Center for Medicare Services data was queried to determine 1-year outcomes, specifically myocardial infarction or death from any cause.
As expected from a VA study, the cohort is mostly male and aged between 50 and 70 years. Nearly all had a history of hypertension and hyperlipidemia, while smoking, diabetes, and obesity were well-represented. In short, exactly the folks you’d expect to refer for catheterization in the setting of chest pain – the sort of individual every Emergency Physician would consider “high risk”.
But the catheterization only revealed obstructive coronary artery disease in about half of these patients. And, among those, only a little more than half received an intervention associated with angiography – either PCI or CABG. The remainder were amenable only to medical intervention. But, even in this cohort with pervasive vascular disease, the 1-year rate of MI was only between 1.18% and 2.47%, depending on the number of vessels involved. Then, if non-obstructive disease was found, the 1-year rate of MI falls to 0.24% to 0.59%. And, those without CAD had a 0.11% incidence of MI within a year.
My takeaway from all this? As a whole, even this highest-risk cohort has a combined ~1% risk of MI within a year – meaning one could theoretically discharge nearly every chest pain patient from the Emergency Department if proper short-term follow-up were in place, and the number of adverse outcomes would be a tiny fraction of a percent. [Add: Stephen Smith takes issue with the generalizability of this elective catheterization cohort to our Emergency Department population, and suspects we have a much higher prevalence of unstable plaques – and potential for a greater number of adverse events.]
What’s unfortunate in the data presented, however, are few obvious differences between those who had severe – even 3-vessel disease – and those who had no disease whatsoever. In aggregate, even though the differences met statistical significance, the absolute differences were small. Indications were similar between groups, comorbid disease was similar between groups, and, perhaps, those with more advanced disease were slightly older. Perhaps some type of matching algorithm could be used to generate more precise, individualized estimates for individual patients, but such is just speculation.
“Nonobstructive Coronary Artery Disease and Risk of Myocardial Infarction”
http://jama.jamanetwork.com/article.aspx?articleid=1920971