Health Matters

by John P. Vansant, MD, FACC

Speaking from the Heart

Currently, as well as historically, a major goal of clinical cardiology has been to develop a non-invasive test (modality) that provides accurate and predictive information regarding the presence and severity of coronary artery disease (CAD) that would be comparable to the invasive “gold standard” coronary angiography (commonly referred to as a cardiac cath). The list of such tests has grown rapidly over the past decade, predominately due to remarkable technological advances resulting in very sophisticated imaging capabilities.

With that said, some of the most basic and more readily available tests continue to provide important and valuable information.

The value of a test lies not only in its ability to determine the presence of disease, but also in its ability to determine prognosis. Which test a physician may chose depends upon many factors. A critical part of the decision in selecting a test is largely based upon “patient factors” such as age, sex, and body habitus, coupled with an assessment of the likelihood that disease is present. The likelihood of disease presence is determined in large part by the risk factors we discussed in last month’s article. Additionally, a particular study may be selected dependent upon the specific goal. Is the goal to make a diagnosis, or to establish a probability (risk) of the patient who has known CAD of having a future event (heart attack or death)? Many tests actually accomplish both goals at the same time. A specific test result will provide important information for determining a particular treatment plan.

I feel it would be informative to briefly discuss some aspects of the currently used tests for diagnosing and evaluating patients for CAD.

Exercise Electrocardiogram (Treadmill Test)

A time-honored test, readily available, and comparatively inexpensive. However, the patient must be able to vigorously exercise, thereby excluding many individuals who have orthopedic or neurological health conditions or simply have had a long-term sedentary life style. The diagnostic accuracy for detecting CAD is lower than most other available tests, and typically the treadmill test carries an unacceptably high false-positive rate in women. This test may best be used in males who have a moderate (intermediate) risk for CAD. If positive in this population, then further, more definitive tests would be ordered.

Radionuclide Perfusion Scan (Nuclear SPECT Scan)

The most frequently utilized cardiac imaging study in patients with suspected or known CAD, and the study with the most comprehensive clinical data available for defining a prognosis (likelihood) of the patient having future adverse events. The test does require some radiation exposure. The diagnostic principle of the test depends upon the fact that if CAD is present, the blood flow to a particular part of the heart muscle will have detectably lower radioactive tracer activity than the areas of the heart that have normal blood flow. The most accurate results are obtained when the interpretation of the study is performed by an experienced Nuclear Cardiologist. (A pictorial example of how we compare the heart muscle anatomy with the radioactive tracer activity is illustrated).

Echocardiogram (Stress ECHO)

A test favored by many cardiologists. A positive result is highly predictive for the presence of CAD. However, a negative result (normal study) is not as accurate for predicting the absence of disease as the Nuclear SPECT Scan. The diagnostic principle is based upon the observer being able to determine the presence of abnormal heart muscle movement (contraction) resulting from the decrease in blood flow to a specific area of the heart. Therefore, the test is very dependent upon the expertise of the cardiologist performing the study, and in many cases, due to the patient being overweight or other anatomical conditions, it may be difficult to see all areas of the heart. This will decrease the accuracy for detecting the presence of CAD in some cases.

Computed Tomography Angiography (CTA)

A developing modality with clinical ambitions of replacing the need for the patient to have an “invasive” study (coronary angiography). However, due to factors such as cost, degree of radiation exposure, technology availability, limited numbers of experienced physicians, and the need for still more evidence-based clinical data…this is a test that is not yet “prime time.”

Other tests (modalities) currently used but with less frequency: (1) Cardiac PET (positron emission tomography), (2) Cardiac MRI (magnetic resonance imaging), and (3) Coronary Calcium Score. These tests have their specific place in the global arena of evaluating patients with known or suspected CAD. However, their use and availability are not comparable to the former modalities discussed. For the sake of brevity, we will leave these for a later discussion. Clinical cardiology has experienced remarkable advances in the diagnosis and treatment assessment of patients with CAD. We have attempted to provide only a brief overview of a few of the many choices your physician has at hand to provide you with excellence of care if CAD ever becomes a clinical question for your health.