I often see a patient who requests that I…“check out his/her heart…. because I don’t want to have a heart attack”. Well I am here to tell you a little secret about medicine and cardiology. We have no way to ever prevent anyone from having a heart attack. It is a sad yet unfortunate reality. What we do have is the ability to identify patients who are at risk for a heart attack (myocardial infarction or MI) and perform testing in those patients exhibiting symptoms prior to an actual event. I would like review the symptoms of coronary artery disease (CAD) which can lead to heart attack (MI) and the diagnostic testing that is available when a patient has symptoms of CAD and is at risk for a potential MI in the near future.
The first step in treatment of coronary artery disease is the recognition of symptoms. If the patient is not having any symptoms to suggest a narrowed or blocked artery, performing stress testing or treating with stents or bypass surgery has no effect on reducing the incidence of heart attack or death for CAD (diabetics are the exception to this case). The symptoms of CAD are related to obstruction of blood flow through the arteries due to cholesterol plaque formation. The resulting decrease in oxygen delivered to the tissue leads to symptoms. Surprisingly, when an artery is narrowed 50% or less there will be no symptoms related to decreased blood flow. Symptoms do not usually occur until the narrowing is at least 75% and then only with exertion or increases in tissue demand for blood and oxygen. When a narrowing approaches greater than 90%, there can be symptoms with little to no activity or at rest. When the blood supply to the heart is reduced through a significantly narrowed artery, the person typically feels a chest tightness, squeezing, pressure, heaviness (elephant on my chest) that is not localized to one spot. Symptoms can radiate to the arm, neck or jaw and very commonly the person gets sweaty and often nauseated. Often the symptoms are just shortness of breath or a decrease in exercise capacity. It can feel like a band across the chest, a toothache or heaviness in the arms. Symptoms more often occur with physical activity and resolve with rest. The chest discomfort can start with the activity and then subside as the activity continues, which can be misleading for doctors and patients alike. Over time the symptoms come on with progressively less and less activity until it occurs with no activity at all. At this point the obstruction is almost certainly > 90%. In some situations plaque may produce less than 50% obstruction, but rupture. This leads to the acute formation of a thrombus or clot, which causes a complete obstruction of the artery. In this case, symptoms come on relatively quickly and severely and do not resolve. This is an acute MI and requires immediate attention and treatment with a stent in the artery, which is often lifesaving. The onset of symptoms and their severity determines subsequent testing and treatment.
The nature of the patients’ symptoms is what dictates the type of testing and treatment. Patients who present acutely with abrupt symptoms and an abnormal electrocardiogram (ECG) suggesting an acute MI are treated emergently with a coronary angiogram (the arteries are imaged with “dye” and degree of obstruction (if any) is determined. These patients usually get a coronary stent or sometimes bypass surgery. Patients’ with symptoms at little to no activity and risk factors (diabetes, smoking, family history or prior atherosclerotic cardiovascular disease (ASCVD) or have laboratory evidence for an sub-acute MI, go directly to coronary angiography. Treatment is then based on the imaging of the arteries. Patients with classic symptoms of exertional chest pain or atypical symptoms and cardiac risk factors will undergo some form of stress testing:
Standard ECG Treadmill Stress Test:
Patient will exercise on a treadmill with ECG and blood pressure being monitored. The test goes through 3 minute stages in which the speed and incline increase progressively. The patient is monitored for symptoms and the test is stopped at patient discretion or if there is limiting chest discomfort and abnormal ECG or abnormal drop in the blood pressure. There is no abnormal test- only test results that indicate a low, intermediate or high probability for obstruction of one or more arteries. About 35% of patients with ASCVD will have a low risk result (false negative or FN) and 20% with an intermediate or high risk result (false positive or FP).
Standard ECG Treadmill Stress Test with Imaging:
Stress Echocardiogram is similar to the stress test described above with one difference. The heart muscle contractions are imaged with an ultrasound (echocardiogram) at rest and at the peak level of exercise. The images are compared and if there is a decrease in the contractions with exercise it is strongly indicative of narrowed arteries. The FN rate improves to about 15-20% and FP rate to 10-15%. The exercise portion can also be performed with a recumbent bicycle.
Nuclear stress testing also incorporates exercise as above. The imaging is performed with radioactive drugs that are distributed into the heart muscle based on flow through the arteries. An injection of the drug is done at rest and at peak exercise. The images are compared and again a decrease in flow seen during exercise that is not present at rest is indicative of narrowed arteries. FN rates are about 10-15% and FP rates about 10%.
Pharmacologic Stress Testing with Imaging:
Pharmacologic stress testing with imaging is utilized when the individual cannot exercise due to physical or otherwise limitations. Medications are used to either increase the heart rate and blood pressure (dobutamine) or cause a change in blood flow through dilation of the arteries (dypiridamole, adenosine or Lexiscan). In this form of stress testing, images are taken at rest before the pharmacologic stress is performed and then again after the stress agent has been injected. Images are compared and if there is an abnormality in flow or function with the stress agent then narrowed arteries is the main concern. The FN and FP rates are similar with exercise testing and imaging as described already.
CAD and heart attack or myocardial infarction is not a disease that can be identified or prevented by an examination or test. There are certainly risk factors that can be controlled and treated, but the presence of coronary artery disease with narrowed, obstructed arteries can only be diagnosed and treated if the symptoms are recognized early. If someone develops abrupt onset of chest pain that does not resolve in less than 15-30 minutes then a call to 911 and a trip to a chest pain receiving medical center may well prevent a fatal heart attack and limit long-term damage. For people with exertional chest discomfort or other symptoms that are suggestive of CAD, then there are multiple different stress testing modalities that can accurately diagnosis its presence. Once the degree of obstruction is determined, then the best treatment approach can be determined, which will limit symptoms and long term problems like heart failure. So if you want to “prevent” a heart attack, do not ignore any of the aforementioned symptoms I have described and seek immediate care at an E.R. or urgent care.The information provided is for general interest only and should not be misconstrued as a diagnosis, prognosis or treatment recommendation. This information does not in any way constitute the practice of medicine, or any other health care profession. Readers are directed to consult their health care provider regarding their specific health situation. Marque Medical is not liable for any action taken by a reader based upon this information.