What goes on during chest pain that may be a heart attack?
Coronary artery disease leads to heart attacks, which remain a major cause of death in the United States. While treatment options do exist, statistics have not improved significantly due to persistence of risk factors. To understand how serious a heart attack is, one must understand not just the risk factors but also the disease process itself.
Stable Angina
Coronary arteries perfusing the heart itself can be narrowed by atherosclerosis. Suppose one artery is narrow enough for blood flow to be deficient (ischemia) if the heart pumps more aggressively, as with exercise. Chest pain, which may radiate to the left arm, neck, or jaw, results and persists until blood flow becomes adequate again, as when the heart slows with rest. Chest pain triggered by activity and relieved with rest is called stable angina. This can be further evaluated with stress testing. Using exercise or medication to stimulate the heart in conjunction with electrocardiogram, echocardiogram, or perfusion scan, the test can show how much activity the heart can tolerate. If significantly poor, further testing can be done as with the acute coronary syndromes, described later.
The treatment includes a nitrate medication, such as nitroglycerin, as needed to widen the arteries and veins and maximize cardiac perfusion. A physician may also consider giving aspirin to take daily. If diabetes or other risk factors are present, they are addressed as well.
At this point, two things are worth noting. Atherosclerosis is only one cause for angina, though it is a common cause. Examples of other causes include anemia and spasm of the coronary arteries (Prinzmetal angina). In addition, stable angina is a harbinger for three other cardiac conditions of greater severity that are more emergent and therefore part of the spectrum of acute coronary syndromes.
Unstable Angina and Non-ST Elevation Myocardial Infarction
Now suppose chest pain from cardiac ischemia is no longer relieved with rest, or it occurs even with little or no activity. Often, the atherosclerotic plaque ruptures and is sealed up by clumping platelets, further occluding cardiac blood flow. This kind of chest pain is no longer stable angina.
At this point, further tests are done. An electrocardiogram (EKG) can show the heart's electrical pattern, normally a sequence of P wave, QRS complex, and T wave. Cardiac ischemia can manifest with T waves that are turned upside down, flattened, or even more peaked than usual. The EKG may also show the segment between S and T raised or lowered from baseline. These findings must be seen in portions of the EKG corresponding to specific regions of the heart. Sometimes, none of these signs are present.
In addition, the heart muscle contains enzymes: creatine kinase (CK), including a subtype more specific for the heart (CK-MB), and a protein called troponin I very specific for cardiac muscle. If the heart is deprived of blood long enough, the muscle dies. This is called myocardial infarction, what the layperson calls a heart attack. It is suggested when levels of these cardiac enzymes are significantly elevated in the blood as a result of heart muscle cells dying and bursting open.
Unstable angina occurs without elevated cardiac enzymes or ST-segment elevation on EKG. If there are elevated cardiac enzymes but no ST-segment elevation, it is called non-ST elevation myocardial infarction. In either case, the next question is how bad cardiac perfusion is. A myocardial perfusion scan can demonstrate if blood flow to part of the heart is inadequate at rest and with stress from either exercise or heart-stimulating medication. If the test is abnormal, then a coronary angiogram can visualize the arteries with dye. From there, any detected narrow arteries are widened with balloon angioplasty and held open with stents. Another option is coronary artery bypass graft (CABG), surgically placing vessel grafts around the obstructions of the affected arteries.
Medical treatment for both UA and NSTEMI generally involves aspirin as an antiplatelet agent, a statin to lower cholesterol, a beta-blocker medication to slow the heart and minimize stress, and an ACE inhibitor for additional survival benefit. If a patient is hospitalized with NSTEMI, he or she would also have additional medications like heparin and maybe Integrilin to break up any clot in the arteries until a coronary angiogram is done. Plavix may be given if a coronary artery stent is placed. For chest pain relief, nitroglycerin and morphine are available.
ST Elevation Myocardial Infarction
Chest pain with elevated cardiac enzymes and ST-segment elevation on EKG is ST elevation myocardial infarction. This is the most serious type because there is a high risk of death without treatment. This warrants immediate coronary angiogram followed by balloon angioplasty or CABG. The medications for these are similar to that for UA and NSTEMI.
Final Words
The preceding conditions involve varying degrees of cardiac ischemia with UA, NSTEMI, and STEMI belonging to the spectrum of acute coronary syndromes. All of them, however, should be evaluated by a physician without delay.
