CAD vs. CHD
There are semantic subtleties between terms for coronary artery disease and coronary heart disease:
- Coronary artery disease (CAD): is often used synonymously with coronary heart disease (CHD), but CHD includes both the pathologic process (the atherosclerosis in CAD) and the angina, ischemia, myocardial infarction, and mortality that come from CAD.
- Cardiovascular disease (CVD): implies disease in the entire arterial circulation, and as such, includes stroke, claudication, and limb ischemia.
Causes of and Risk Factors for CAD
- Obesity/metabolic syndrome
- Sedentary lifestyle
- Chronic renal disease
Family history is an independent risk factor for CAD, but when combined with any of the above provocations, augments the total, global risk exposure.
When there is atherosclerotic narrowing of the coronary arteries, there is reduced blood flow (oxygenation) to heart tissue. The energy demands of the heart are large, and any decrease in the blood supply can outpace the energy needs, causing ischemia.
Ischemia Can Occur Due to:
- Decreased supply of blood (atherosclerotic coronary narrowing):Atherosclerotic obstruction (the most common cause), coronary artery vasospasm, embolism, and arteritis. Less common causes are anemia, hypotension/shock, and postprandial “steal” angina (redistribution of blood away from diseased coronary arteries to those that are normal).
- Increased demand (exertion): Vigorous exertion/exercise, increased sympathetic tone (stress), tachycardia, hypertension, or ventricular hypertrophy.
Ischemia in any muscle, including the heart, causes pain. Such pain from coronary artery disease is called angina pectoris:
- Stable angina: chest discomfort that is predictable and reproducible with exertion and can be relieved with rest (decrease in energy demand) or nitroglycerin (vasodilator–increase in blood supply).
- Unstable angina: does not follow the typical stable angina patterns. It occurs more frequently and is more severe, can occur at rest, and is not relieved by rest or nitroglycerin.
Angina without chest pain, but with other symptoms, is called “anginal equivalent,” and includes exertional shortness of breath, nausea, diaphoresis, and fatigue. Angina without either chest pain or anginal equivalent symptoms is called “silent angina”. In transitioning from stable angina to unstable angina, a CAD patient has clearly crossed a dividing line into the Acute Coronary Syndrome.
Acute Coronary Syndrome (ACS)
Acute Coronary Syndrome is a spectrum of three types of coronary artery disease:
- Unstable angina (UA)
- Non-ST segment (ECG) elevation myocardial infarction (NSTEMI heart attack)
- ST segment (ECG) elevation myocardial infarction (STEMI heart attack)
The severity of CAD is a continuum in the intolerance of heart muscle to provocations from decreased supply and/or increased demand. At some point, ischemia will become unstable (stable angina to unstable angina) and infarction will occur with or without ST elevations on ECG (indicators of cell death).