Not Just Clogged Pipes

Coronary Artery Disease as Clogged Pipes


Although the image of coronary arteries as kitchen pipes clogged with fat is simple, familiar, and evocative, it is also wrong.

most cardiac events occur at lesions that appeared mild on previous angiography

These plaques contain a lipid-rich core covered by a thin fibromatous cap. Inflammatory cells (eg, macrophages and mast cells) within the plaque may become activated by microbes, autoantigens, or inflammatory molecules (activated plaque model). The activated cells secrete cytokines and proteases that weaken the fibrous cap, causing it to erode or rupture.

Before rupture, these plaques often do not limit flow and may be invisible to angiography and stress tests.

Anecdote: My dad had ​a stress test and angiography in early 2003. It showed him to have low risk for heart attack. Less than 8 months later Dad had a heart attack, with a subsequent quintuple bypass and a stent.

in the setting of myocardial infarction, the model of an obstructed pipe is accurate, and interventions aimed at eliminating the thrombus, either thrombolytics or angioplasty, can be lifesaving. But for patients with stable disease, local interventions can only relieve symptoms; they cannot prevent future myocardial infarctions.

Although atheromatous plaques contain lipids, they are not composed of fat directly from the diet. Low-density lipoprotein is produced primarily in the liver...

growth within the vessel walls is accommodated by outward enlargement of the vessel. In that case, large plaques may not encroach on the lumen and are therefore hidden from angiography.

High-density lipoprotein removes low-density lipoprotein from peripheral tissues through reverse cholesterol transport to the liver and may have antiinflammatory properties

Although saturated fat increases low-density lipoprotein cholesterol, it also increases high-density lipoprotein, so the net effect on cardiac risk is neutral.

More recent observational studies do not support the use of low-fat diets. ​ low-fat diets had adverse effects on high-density lipoprotein cholesterol. But for patients with elevated low-density lipoprotein, they have tightened restrictions on saturated fats and now recommend that consumption not exceed 7% of total calories.

in many products, fat is simply replaced by sugar. More recently, the AHA recommended that people limit their intake of sugar, which now appears to contribute to obesity, hypertension, and subsequently coronary heart disease.