Purpose of the test

An echocardiogram is performed for a variety of diagnostic reasons, such as to evaluate abnormal heart sounds; to evaluate heart size, chamber size, and valvular function; and to detect tumors, pericardial effusion, septal defects, and wall motion abnormalities. It may be used to determine the cause of syncope by assessing the patient’s ejection fraction and possible structural abnormalities.

Basics the nurse needs to know

An echocardiogram is a noninvasive test that uses ultrasound techniques to detect enlargement of the cardiac chambers or variations in chamber size during the cardiac cycle. Even with the advent of CT angiography, the echocardiogram is the gold standard to evaluate heart valves. When echocardiography has been integrated into stress testing, it is called stress echocardiography or exercise echocardiography (see Stress Testing, Cardiac p. 558). It is frequently used for risk stratification and to assess therapeutic outcomes for patients with coronary artery disease. Stress echocardiography is similar to stress testing, but with an echocardiogram being done at baseline and at each progressive level of exertion. It is especially helpful as a screening tool for women and for persons with a left bundle-branch block. If the patient is unable to use the treadmill or bicycle, stress can be induced with dobutamine or dipyridamole. Sometimes atropine is needed to reach the desired heart rate. Dobutamine stress echocardiography (DSE) is frequently used to assess “stunned” or “hibernating” myocardium.

A major limitation of the standard echocardiography is poor imaging because it is 2-dimensional. Improved visualization can be obtained with real-time 3-D echocardiography (RT3DE). While RT3DE improves image quality at the current time, its use is limited to guiding intracardiac procedures.

How the test is done

An echocardiogram may be carried out at the bedside, in a special laboratory, in a clinic, or in a doctor’s office. A transducer is placed over the third and fourth intercostal spaces to the left of the sternum. The transducer emits ultrasonic beams of high-frequency sound waves that are inaudible to the human ear. The transducer then picks up the echoes created by the deflection of the beams off the various heart structures. This creates a picture on the oscilloscope. The picture is created because the echo varies in intensity based on the differing densities of the structures.

Significance of test results

Interfering factors

Purpose of the test

The purpose of the 12-, 15-, and 18-lead ECG is to diagnose myocardial infarction, injury, and ischemia. An ECG is the most important, rapid, and cost-effective way to assess chest pain. It also assists in identifying hypertrophy, axis deviations, and electrolyte abnormalities, and distinguishes between ventricular and supraventricular tachycardia. Left versus right hypertrophy can be distinguished by comparing the morphologic characteristics of the QRS complex in leads V₁ and V₆, by determining axis deviation, and by interpreting the P-wave.

Basics the nurse needs to know

The electrocardiogram (ECG) is an invaluable tool in the assessment of the heart. It records the heart’s electric activity. Several lead systems are available for the measurement of the electric activity of the heart: 12-, 15-, and 18-lead ECG. The electrochemical physiology characteristics are the same for each of these systems; that is, each uses electrodes on the body surface, amplifies changes in electric potentials, and provides a graphic recording. This is made possible by the body’s fluid system, which acts as a conductor of electric forces. The 12-lead ECG is the system used most commonly; it presents a graphic recording of 12 electric planes of the heart. By manipulating the skin electrodes, 12 various views of the heart’s electric activity are seen.

In a 12-lead ECG, leads I, II, and III are limb leads. In lead I, the negative electrode of the electrocardiograph is connected to the right arm, and the positive electrode is attached to the left arm. In lead II, the negative electrode is placed on the right arm, and the positive electrode is placed on the left leg. In lead III, the negative electrode is placed on the left arm, and the positive electrode is placed on the left leg. Leads I, II, and III form a triangle, which is called Einthoven’s triangle (Figure 42).

Figure 42. Einthoven’s triangle.

The second set of three leads recorded by the electrocardiograph machine is called the augmented limb leads. In these leads, two limbs are attached to negative electrodes, and a third limb is attached to a positive electrode. If the positive electrode is placed on the right arm, the lead is called aVR (augmented voltage right arm). If the positive electrode is on the left arm, it is called aVL (augmented voltage left arm). When the positive electrode is on the left foot, it is called aVF (augmented voltage foot) (Figure 43).

Figure 43. Augmented limb leads.

The limb leads and augmented leads are called the standard leads. If one takes the three sides of Einthoven’s triangle and moves them to the center, they form three intersecting lines of reference (Figure 44, A). If one superimposes the augmented limb leads, the lines of reference and the six limb leads form six intersecting lines (one every 30 degrees). Each limb and augmented lead records a different angle and, therefore, a different view of the same electric activity (Figure 44, B).

Figure 44. Intersecting limb leads and augmented leads.

For the precordial, or chest, leads, the positive electrodes are applied to the person’s chest and the negative electrode is applied to the limbs.

Usually, six chest leads are recorded. This is done by placing the positive electrodes at six different positions across the chest. The chest leads are identified as V₁ through V₆. The chest leads give various views of the horizontal plane of the left ventricle. The precordial leads can be visualized as spokes of a wheel, the center being the atrioventricular (AV) node (Figure 45).

Figure 45. Precordial leads (V₁-V₆).

How the test is done

For a 12-lead ECG, the technician, the physician, or the nurse places the patient in a supine position. Conduction jelly is placed on the electrodes (disposable electrodes already have jelly on the electrode), and the electrodes are applied. The electrocardiograph’s electrode wires are marked and color coded. It is essential that the chest leads be positioned correctly for accurate interpretation.

The chest leads are applied as follows (Figure 46):

Figure 46. Chest lead placement.

Electrocardiographs vary. Older machines record one lead at a time. Newer machines simultaneously record the 12 leads and automatically mark them.

Leads for right ventricular assessment are placed at the right fifth intercostal space at the midclavicular line (V_4r), at the right intercostal space at the anterior axillary line (V_5r), and at the right fifth intercostal space at the midaxillary line (V_6r).

With the 18-lead ECG, a 15-lead ECG is taken, and then three chest electrodes are placed on the line level with the fifth ICS at the posterior axillary line (V₇). The next electrode is placed at the fifth ICS at the posterior midclavicular line (V₈), and the last electrode is placed at the fifth ICS, left of the spinal column (V₉).

Significance of test results

Interfering factors

Purpose of the test

The cardiologist assesses the printout of the signal-averaged electrocardiogram (ECG) for late potentials, which place the patient at risk for sustained ventricular tachycardia (VT). A late potential is seen as a QRS complex that extends 20 to 60 msec into the ST segment.

Basics the nurse needs to know

Signal-averaged electrocardiography (SAECG) is a technique used to detect conduction defects that may precede VT. It is a noninvasive bedside test similar to a 12-lead ECG. With a signal-averaged ECG, the recording is obtained for 15 to 30 minutes, and the electric current from the heart is amplified 1000 times. The machine then integrates all these signals and removes extraneous electric signals.

How the test is done

The procedure is similar to the 12-lead ECG, except that no limb electrodes are necessary and the six chest electrodes and ground lead are positioned differently on the chest.

Significance of test results

Late potentials

Interfering factors

Purpose of the test

The major applications of electroencephalography (EEG) are in the diagnosis of epilepsy and the determination of the type of epilepsy. It may be used to detect brain injury, evaluate sleep disorders, and to monitor function during brain surgery. It is also used to determine brain activity in the patient in deep coma and to help decide if a patient is brain dead.

Basics the nurse needs to know

EEG records the spontaneous brain activity that originates from brain cells on the surface of the brain. The fluctuations of electrical activity from the larger cortical areas of the brain pass through the cranial bones and the scalp. The voltage is detected by the electrodes and is converted to specific wave patterns that are seen on the computer screen.

In the process of electric brain mapping, the brain waves and patterns are demonstrated on the computer screen, allowing for the detection of abnormalities in a specific region of the brain.

The video electroencephalography monitor combines the recording of the EEG waveforms with videotaping to correlate the behavioral events with electroencephalographic seizure activity.

Normal EEG recordings are generally rhythmic and have waveforms of similar height and duration. The interpretation of the EEG considers the frequency of the predominant rhythm, the amplitude, any abnormal waves or wave groups, and the asymmetry between the right and left hemispheres.

How the test is done

Sixteen to twenty-five electrodes are applied to the scalp in a set pattern, using a paste that promotes conduction. The electrode wires are connected to an amplifier and recording machine. The images of the tracings are seen on the computer screen. The EEG procedure usually takes 30 to 90 minutes, but the sleep EEG is recorded all night.

Significance of test results

Interfering factors

Purpose of the test

Urine electrolytes are used to help monitor renal function, fluid and electrolyte balance, and acid-base balance. The urinary calcium level is used to evaluate bone disease, parathyroid disorders, nephrolithiasis, calcium metabolism, and idiopathic hypercalciuria.

Basics the nurse needs to know

Normally, the daily intake of food includes a renewing supply of electrolytes. The glomeruli filter the electrolytes from the blood, and the renal tubules resorb most of them for recirculation and redistribution as needed. Electrolyte excesses are not resorbed and are excreted in urine.

The normal urinary excretion of electrolytes is dependent on the amount of intake, the serum level of the electrolytes, and the state of hydration of the body. The equilibrium of water and electrolytes is controlled by renal and multiple endocrine functions. Any condition that causes a decrease in perfusion to the kidney will cause a decrease in electrolytes excreted in urine.

How the test is done

A 24-hour urine specimen is collected in a large, clean urine collection container. Urine is kept refrigerated or on ice during the collection period. Alternative methods include a 12-hour urine collection or a single random urine sample for electrolyte testing. If a 24-hour urine test for protein or creatinine clearance is also ordered, these tests can be performed simultaneously with the urine electrolyte test, using the same specimen.

Significance of test results

Interfering factors

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