Diagnostic Tests

Diagnostic testing can determine the type and extent of heart disease and guide treatment strategies. Since complications can occur with most diagnostic tests, the least invasive test is used first when possible. The most invasive tests generally give the most information about cardiac disease. Patients need to understand the reasons for diagnostic tests and what to expect during the test.

Objectives

In this chapter, you will learn:

1. Some of the noninvasive tests used to evaluate a patient for coronary artery disease

2. Noninvasive tests used to evaluate valve function

3. What information is gathered during a cardiac catheterization

NONINVASIVE TESTING TO DETECT CORONARY ARTERY DISEASE

Noninvasive testing strategies carry the least risk for patients, but there is the possibility for false positives and false negatives. Noninvasive tests involve two parts: stressing the heart and imaging the heart. The stress portion may involve either exercise or medications to increase heart rate and oxygen demand. The imaging portion may involve electrocardiography (ECG), echocardiography (echo), or nuclear imaging.

FAST FACTS in a NUTSHELL

A positive noninvasive test is an indication for a more invasive test, usually cardiac catheterization.

Exercise Treadmill Test and Exercise Stress Echo

An exercise treadmill test involves having a patient follow a specified, graded protocol on a treadmill to stress the heart; a continuous 12-lead ECG is used to evaluate the heart for ischemic changes. Ischemic changes occur in the distribution of the affected coronary artery.

An exercise stress echo includes exercise on a treadmill and a continuous 12-lead ECG, and adds evaluation of wall motion. An echo is obtained before and again during exercise to determine changes in response to elevated heart rate. If an artery is occluded enough to limit blood flow, stress on the heart from exercise will cause wall motion irregularities in the area fed by that artery. If the patient is unable to exercise, dobutamine may be used to stress the heart in place of exercise (dobutamine stress echo).

NURSING IMPLICATIONS: Patients who will receive a noninvasive test involving exercise should be able and prepared to exercise. Patients who have poor balance or who do not walk well are not good candidates for these tests. Patients should be sent for their test wearing pants and supportive shoes, if possible.

Myocardial Perfusion Imaging

Patients who undergo nuclear perfusion imaging are injected with radioactive tracers, which can be detected as they are “taken up” by the heart muscle. The most common tracers include thallium-201, technetium-99m sestamibi (Cardiolite), and technetium-99m tetrofosmin (Myoview). The tracer is injected during peak exercise and imaging is performed. The agents are taken up into viable myocardium and these areas light up on the imaging scan. Infarcted or dead myocardium remains dark. Myocardium that is ischemic may have a delay in the uptake of tracer, so images are taken a short time later to evaluate redistribution of the tracer. Patients who cannot exercise are given a medication such as adenosine or dipyridamole (Persantine) to mimic the effect of exercise on blood flow in the heart.

NURSING IMPLICATIONS: Patients need to understand that they will need to lie still while images are being taken. Patients should be reassured that they will receive only a very small amount of radiation during the test.

Computed Tomography and Magnetic Resonance Imaging

CT is used primarily for evaluating diseases of the aorta. New advances in CT scanning hold promise for evaluation of coronary artery disease. Electron beam CT can give information about coronary calcification, which is associated with the presence of coronary artery plaques. This is typically done to screen asymptomatic patients. Use of a multislice CT with contrast (CT angiography [CTA]) can give information about specific coronary arteries and can identify coronary artery narrowing. Until recently, there has been little evidence in the literature about the clinical outcomes associated with noninvasive testing in patients with symptoms suggesting CAD. A recent randomized study showed no difference in clinical outcomes between CTA and three common functional tests (exercise treadmill test, exercise stress echo, and myocardial perfusion imaging; Douglas et al., 2015).

Like CT scanning, MRI technology is improving and becoming more versatile. MRI is primarily used to evaluate diseases of the aorta and pericardium. This test is also useful to detect masses and other irregularities. When contrast dye is used (magnetic resonance angiography), occlusions in the proximal coronary arteries may be detected.

DIAGNOSTIC TESTING TO DETECT VALVE DISEASE

Echocardiogram (Echo)

An echocardiogram is an ultrasound of the heart that provides two- and three-dimensional moving pictures and gives much valuable information about the structures of the heart, wall motion and ventricular function, and blood flow. This test may be done via the transthoracic (ultrasound probe is on the external chest wall) or transesophageal (ultrasound probe is placed inside the esophagus at the level of the heart) method. A transesophageal echocardiogram (TEE) provides the most detailed information about valve function because, in the esophagus, the probe is very close to the heart. An echo and TEE are frequently performed before, during, and after heart surgery to evaluate valve and ventricular function.

NURSING IMPLICATIONS: Patients who undergo an echo should understand that it is a noninvasive ultrasound of the heart. A TEE should be explained fully so patients understand that it will be uncomfortable and that sedation will be used.