Diagnostic Testing: Cardiovascular PDF

Diagnostic Testing: Cardiovascular Diagnostic Tests Advances in diagnostic testing allow for earlier and easier diagnosis and treatment of cardiovascular disorders. For example, in some patients, echocardiography—a noninvasive and risk-free test—can provide as much diagnostic information on valvu...

Diagnostic Testing: Cardiovascular Diagnostic Tests Advances in diagnostic testing allow for earlier and easier diagnosis and treatment of cardiovascular disorders. For example, in some patients, echocardiography—a noninvasive and risk-free test—can provide as much diagnostic information on valvular heart disease as can cardiac catheterization—an invasive and high-risk test. 12-lead Electrocardiogram The 12-lead electrocardiogram (ECG) measures the heart’s electrical activity and records it as waveforms. It’s one of the most valuable and commonly used diagnostic tools. A test with 12 views The standard 12-lead ECG uses a series of electrodes placed on the patient’s extremities and chest wall to assess the heart from 12 different views (leads). The 12 leads include three bipolar limb leads (I, II, and III), three unipolar augmented limb leads (aVR, aVL, and aVF), and six unipolar precordial limb leads (V1 to V6). The limb leads and augmented leads show the heart from the frontal plane. The precordial leads show the heart from the horizontal plane. ECG can be used to identify myocardial ischemia and infarction, rhythm and conduction disturbances, chamber enlargement, electrolyte imbalances, and drug toxicity. In addition to the 12-lead ECG, two other ECGs may be used for diagnostic purposes, the right chest-lead ECG and posterior lead ECG. 12 lead ECG Placement  Nursing considerations Use a systematic approach to interpret the ECG recording. (See Normal ECG waveforms) Compare the patient’s previous ECG with the current one, if available. This will help you identify changes. Cardiac marker studies Analysis of cardiac markers (proteins) aids diagnosis of acute MI. Release the enzymes! After infarction, damaged cardiac tissue releases significant amounts of enzymes into the blood. Serial measurement of enzyme levels reveals the extent of damage and helps to monitor the progress of healing. Heart-zymes The cardiac enzymes include creatine kinase (CK) and its isoenzyme MB (found specifically in heart muscle). Tests for troponin T and I and myoglobin are more specific to cardiac muscle and can be used to detect damage more quickly, allowing faster and more effective treatment. Ischemia Modified Albumin (IMA) measures changes in serum albumin when it comes in contact with ischemic tissue. IMA rises faster than any other cardiac enzyme. Meaning in markers Here’s what the results of cardiac marker studies mean: P waves should be upright; however, they may be inverted in lead aVR or biphasic or inverted in leads III, aVL, and V1. A P wave should be present before each QRS complex. PR intervals should always be constant, just like QRS-complex durations. Depolarization of the heart is the orderly Repolarization is the process by which the cells passage of electrical current sequentially return to their negatively charged state. This through the heart muscle, changing it, cell occurs when the cell membrane becomes more by cell, from the resting polarized state to permeable to potassium ions, which exit the the depolarized state until the entire heart cell. The loss of positive ions from the cell causes is depolarized. the cells to become negatively charged again, leading to relaxation. Meaning in markers cont…. QRS-complex deflections vary in different leads. Observe for pathologic Q waves. ST segments should be isoelectric or have minimal deviation. ST-segment elevation greater than 1 mm above the baseline and ST-segment depression greater than 0.5 mm below the baseline are considered abnormal. Leads facing an injured area have ST -segment elevations, and leads facing away show ST-segment depressions. The T wave normally deflects upward in leads I, II, and V3 through V6. It’s inverted in lead aVR and variable in the other leads. T-wave changes have many causes and aren’t always a reason for alarm. Excessively tall, flat, or inverted T waves occurring with symptoms, such as chest pain, may indicate ischemia. A normal Q wave generally has a duration less than 0.04 second. An abnormal Q wave has either a duration of 0.04 second or more, a depth greater than 4 mm, or a height one-fourth of the R wave. Abnormal Q waves indicate myocardial necrosis, developing when depolarization can’t follow its normal path because of damaged tissue in the area. Remember that aVR normally has a large Q wave, so disregard this lead when searching for abnormal Q waves. Echocardiography Echocardiography is used to examine the size, shape, and motion of cardiac structures. It’s done using a transducer placed at an acoustic window (an area where bone and lung tissue are absent) on the patient’s chest. The transducer directs sound waves toward cardiac structures, which reflect these waves. Echo The transducer picks up the echoes, converts them to electrical impulses, and relays them to an echocardiography machine for display on a screen and for recording on a strip chart or videotape. The most commonly used echocardiographic techniques are M-mode and two-dimensional. Motion mode In M-mode (motion mode) echocardiography, a single, pencil-like ultrasound beam strikes the heart, producing an “ice pick,” or vertical, view of cardiac structures. This mode is especially useful for precisely viewing cardiac structures. Echo in 2-D In two-dimensional echocardiography, the ultrasound beam rapidly sweeps through an arc, producing a cross- sectional, or fan-shaped, view of cardiac structures; this technique is useful for recording lateral motion and providing the correct spatial relationship between cardiac structures. In many cases, both techniques are performed to complement each other. TEE combination In transesophageal echocardiography (TEE), ultrasonography is combined with endoscopy to provide a better view of the heart’s structures. (See A closer look at TEE.) Echo abnormalities The echocardiogram may detect mitral stenosis, mitral valve prolapse, aortic insufficiency, wall motion abnormalities, and pericardial effusion (excess pericardial fluid). Nursing considerations Explain the procedure to the patient and advise him to remain still during the test because movement can distort results. Tell him that conductive gel is applied to the chest and quarter-sized transducer is placed directly over it. Because pressure is exerted to keep the transducer in contact with the skin, warn the patient that he may feel minor discomfort. ▪ After the procedure, remove the conductive gel from the skin. Cardiac catheterization Cardiac catheterization involves passing a catheter into the right, left, or both sides of the heart. A multipurpose procedure Cardiac catheterization permits measurement of blood pressure and blood flow in the chambers of the heart. It also allows the doctor to visualize the coronary arteries and determine the presence of any narrowing or occlusions. It’s used to determine valve competence and cardiac wall contractility and to detect intracardiac shunts. The procedure also enables collection of blood samples and taking of diagnostic films of the ventricles (contrast ventriculography) and arteries (coronary arteriography or angiography). Balloon catheter treatments, such as angioplasty or placement of a coronary artery stent, may be done in conjunction with cardiac catheterization. Cardiac calculations Use of thermodilution catheters allows calculation of cardiac output. Such calculations are used to evaluate valvular insufficiency or stenosis, septal defects, congenital anomalies, myocardial function and blood supply, and heart wall motion. Confirming common problems Common abnormalities and defects that can be confirmed by cardiac catheterization include CAD, myocardial incompetence,valvular heart disease, and septal defects.  Make sure that the patient or a responsible family member has signed a consent form. Check for and tell the practitioner about hypersensitivity to shellfish, iodine, or contrast media used in other diagnostic tests. Discontinue anticoagulant therapy, as ordered, to reduce the risk for complications from bleeding. Check the patient’s renal function tests (BUN and creatinine), and notify the practitioner of abnormalities. Make sure the patient has a patent I.V. access site. Review activity restrictions that may be required of the patient after the procedure, such as lying flat with the limb extended for 4 to 6 hours and use of sandbags, if a femoral sheath is used. Document the presence of peripheral pulses, noting their intensity. Mark the pulses so they may be easily located after the procedure. Determine if a hemostatic device, such as a collagen plug or suture closure system, was used to close the vessel puncture site. If either method was used, inspect the site for bleeding or oozing, redness, swelling, or hematoma formation. Maintain the patient on bed rest for 1 to 2 hours. Enforce bed rest for 8 hours if no hemostatic device was used. If the femoral route was used for catheter insertion, keep the patient’s leg extended for 6 to 8 hours; if the antecubital fossa route was used, keep the arm extended for at least 3 hours.  Monitor vital signs every 15 minutes for 2 hours, then every 30 minutes for the next 2 hours, and then every hour for 4 hours. If no hematoma or other problems arise, check every 4 hours. If signs are unstable, check every 5 minutes and notify the practitioner. Continually assess the insertion site for a hematoma or blood loss and reinforce the pressure dressing as needed. Check the patient’s color, skin temperature, and peripheral pulse below the puncture site. Administer I.V. fluids as ordered (usually 100 mL per hour) to promote excretion of the contrast medium. Monitor for signs of fluid overload. Watch for signs of chest pain, shortness of breath, abnormal heart rate, dizziness, confusion, diaphoresis, nausea or vomiting, or extreme fatigue. Notify the practitioner immediately if these complications occur. Electrophysiology studies Electrophysiology studies (EPS) are used to diagnose and treat abnormal heart rhythms. The procedure involves passing two to four temporary electrode catheters into multiple heart chambers. The electrodes are usually positioned in the right atrium, the AV node, the bundle of His region, and the apex of the right ventricle. The electrodes stimulate (pace) the heart and record the heart's electrical conduction. Normal conduction intervals in adults are as follows: HV interval (measured from the earliest onset of the bundle of His deflection to the earliest registered surface or intracardiac ventricular activation), 35 to 55 msec; AH interval (represents the interval from the earliest rapid deflection of the atrial recording to the earliest onset of the bundle of His deflection), 45 to 150 msec; and PA interval (measured from the onset of the earliest registered surface P wave to the onset of the atrial deflection on the bundle of His catheter recording), 20 to 60 msec. Nursing considerations Explain to the patient that EPS evaluate the heart's conduction system. Instruct him to restrict food and fluids for at least 6 hours before the test. Inform him that the studies take 1 to 3 hours. Have the patient void before the test. Monitor the patient's vital signs, as ordered. If they're unstable, check them every 15 minutes and alert the doctor. Observe for shortness of breath, chest pain, pallor, or changes in pulse rate, cardiac rhythm, or blood pressure. Enforce bed rest for 4 to 6 hours. Check the catheter insertion site for bleeding; apply a pressure bandage and sandbag to the site until bleeding stops. Hemodynamic monitoring Hemodynamic monitoring is used to assess cardiac function and determine the effectiveness of therapy by measuring: cardiac output mixed venous blood oxygen saturation intracardiac pressures blood pressure. The methods behind the monitoring Follow your facility’s procedure for setting up, zero referencing, calibrating, maintaining, and troubleshooting equipment. Common uses of hemodynamic monitoring include arterial blood pressure monitoring, central venous pressure (CVP) monitoring, and pulmonary artery pressure (PAP) monitoring. Minimally and noninvasive hemodynamic monitoring techniques are also proving to be reliable, safe options that are easier to use and can be applied in many clinical settings. Arterial blood pressure monitoring In arterial blood pressure monitoring, the practitioner inserts a catheter into the radial or femoral artery to measure blood pressure or obtain samples of arterial blood for diagnostic tests such as arterial blood gas (ABG) studies. A transducer transforms the flow of blood during systole and diastole into a waveform, which appears on an oscilloscope. The waveform has five distinct components. (See Normal arterial waveform.) Arterial blood pressure monitoring In arterial blood pressure monitoring, the practitioner inserts a catheter into the radial or femoral artery to measure blood pressure or obtain samples of arterial blood for diagnostic tests such as arterial blood gas (ABG) studies. A transducer transforms the flow of blood during systole and diastole into a waveform, which appears on an oscilloscope. The waveform has five distinct components. (See Normal arterial waveform.) Nursing considerations Explain the procedure to the patient and his family, including the purpose of arterial pressure monitoring. After catheter insertion, observe the pressure waveform to assess arterial pressure. (See Recognizing abnormal arterial waveforms.) Assess the insertion site for signs of infection, such as redness and swelling. Notify the practitioner immediately if you note such signs. Maintain 300 mm Hg pressure in the pressure bag to allow a flush flow of 3 to 6 mL per hour. Document the date and time of catheter insertion, catheter insertion site, type of flush solution used, type of dressing applied, and patient’s tolerance of the procedure. Central venous pressure In CVP monitoring, the doctor inserts a catheter through a vein and advances it until its tip lies in or near the right atrium. Because no major valves lie at the junction of the vena cava and right atrium, pressure at end diastole reflects back to the catheter. When connected to the transducer or manometer, the catheter measures CVP, an index of right ventricular function. Nursing considerations Explain the procedure, including the purpose of CVP monitoring, to the patient and his family. After catheter insertion, observe the waveform to assess CVP. (See Recognizing abnormal CVP waveforms.) Monitor the patient for complications, such as infection, pneumothorax, air embolism, and thrombosis. Notify the practitioner immediately if you notice such complications. Adhere to your facility’s policy for dressing, tubing, catheter, and flush changes. Document the date and time of catheter insertion, catheter insertion site, type of flush solution used, type of dressing applied, and patient’s tolerance of the procedure. Document the CVP per your facility’s policy or as ordered. Pulmonary artery pressure monitoring Continuous PAP and intermittent pulmonary artery wedge pressure (PAWP) measurements provide important information about left ventricular function and preload. (See Understanding pulmonary artery pressures.) Use this information for monitoring and for aiding diagnosis, refining assessment, guiding interventions, and projecting patient outcomes. PAP purposes PAP monitoring is indicated for patients who: are hemodynamically unstable need fluid management or continuous cardiopulmonary assessment are receiving multiple or frequently administered cardioactive drugs. PAP monitoring is also crucial for patients experiencing shock, trauma, pulmonary or cardiac disease, or multiple organ dysfunction syndrome. PAP’s parts A pulmonary artery (PA) catheter has up to six lumens that gather hemodynamic information. In addition to distal and proximal lumens used to measure pressures, a PA catheter has a balloon inflation lumen that inflates the balloon for PAWP measurement and a thermistor connector lumen that allows cardiac output measurement. Some catheters also have a pacemaker wire lumen that provides a port for pacemaker electrodes and measures continuous mixed venous oxygen saturation. PAP and PAWP procedures The doctor inserts the balloon-tipped, multilumen catheter into the patient’s internal jugular or subclavian vein. When the catheter reaches the right atrium, the balloon is inflated to float the catheter through the right ventricle into the pulmonary artery. This permits PAWP measurement through an opening at the catheter’s tip. The deflated catheter rests in the pulmonary artery, allowing diastolic and systolic PAP readings. The balloon should be totally deflated except when taking a PAWP reading because prolonged wedging can cause pulmonary infarction. (See Normal PA waveforms.) Nursing considerations Inform the patient he’ll be conscious during catheterization and he may feel temporary local discomfort from the administration of the local anesthetic. Catheter insertion takes about 15 to 30 minutes. After catheter insertion, you may inflate the balloon with a syringe to take PAWP readings. Be careful not to inflate the balloon with more than 1.5 cc of air. Overinflation could distend the pulmonary artery causing vessel rupture. Don’t leave the balloon wedged for a prolonged period because this could lead to a pulmonary infarction. After each PAWP reading, flush the line; if you encounter difficulty, notify the practitioner. Maintain 300 mm Hg pressure in the pressure bag to allow a flush flow of 3 to 6 mL per hour. If fever develops when the catheter is in place, inform the practitioner; he may remove the catheter and send its tip to the laboratory for culture. Make sure stopcocks are properly positioned and connections are secure. Loose connections may introduce air into the system or cause blood backup, leakage of deoxygenated blood, or inaccurate pressure readings. Also make sure the lumen hubs are properly identified to serve the appropriate catheter ports. Nursing considerations cont. Because the catheter can slip back into the right ventricle and irritate it, check the monitor for a right ventricular waveform to detect this problem promptly. Be aware that running a continuous infusion through the distal lumen will interfere with your ability to monitor this waveform for changes. To minimize valvular trauma, make sure the balloon is deflated whenever the catheter is withdrawn from the pulmonary artery to the right ventricle or from the right ventricle to the right atrium. Adhere to your facility’s policy for dressing, tubing, catheter, and flush changes. Document the date and time of catheter insertion, the doctor who performed the procedure, the catheter insertion site, pressure waveforms and values for the various heart chambers, balloon inflation volume required to obtain a wedge tracing, arrhythmias that occurred during or after the procedure, type of flush solution used and its heparin concentration (if any), type of dressing applied, and the patient’s tolerance of the procedure. Cardiac output monitoring Cardiac output—the amount of blood ejected by the heart in one minute—is monitored to evaluate cardiac function. The normal range for cardiac output is 4 to 8 L per minute. The most widely used method for monitoring cardiac output is the intermittent bolus thermodilution technique. (See A closer look at the intermittent bolus thermodilution method.) The ability to continuously monitor CO is also available. (See A closer look at the continuous cardiac output method.) Nursing considerations Make sure your patient doesn’t move during the procedure because movement can cause an error in measurement. Perform cardiac output measurements and monitoring at least every 2 to 4 hours, especially if the patient is receiving vasoactive or inotropic agents or if fluids are being added or restricted. Discontinue cardiac output measurements when the patient is hemodynamically stable and weaned from his vasoactive and inotropic medications. Monitor the patient for signs and symptoms of inadequate perfusion, including restlessness, fatigue, changes in level of consciousness (LOC), decreased capillary refill time, diminished peripheral pulses, oliguria, and pale, cool skin. Add the fluid volume injected for cardiac output determinations to the patient’s total intake. Record the patient’s cardiac output, cardiac index, and other hemodynamic values and vital signs at the time of measurement. Note the patient’s position during measurement.