CARDIAC INVESTIGATION. Diagnostic investigation in cardiology

Common Cardiac investigation in cardiology

1. CARDIAC INVESTIGATION Presenter by: Sundari M M.Sc (N), I st Year Student CON, MMC

2. REVIEW OF SYSTEM

3. Function of the Heart Cardiac Electrophysiology The cardiac conduction system generates and transmits electrical impulses that stimulate contraction of the myocardium. Under normal circumstances, the conduction system first stimulates contraction of the atria and then the ventricles. The synchronization of the atrial and ventricular events allows the ventricles to fill completely before ventricular ejection, thereby maximizing cardiac output is maintained. The specialized electrical cells, the nodal cells and the Purkinje cells, provide this synchronization:

4. Automaticity: ability to initiate an electrical impulse Excitability: ability to respond to an electrical impulse Conductivity: ability to transmit an electrical impulse from one cell to another Sinoatrial (SA) node and the atrioventricular (AV) node are composed of nodal cells. The SA node, the primary pacemaker of the heart, SA node is located at the junction of the superior vena cava and the right atrium. The SA node in a normal resting adult heart has an inherent firing rate of 60 to 100 impulses per minute, but the rate changes in response to the metabolic demands of the body.

5. The Cardiac investigation includes Family History Assessment Patient Assessment Health History Physical Assessment Physical Assessment General Appearance Inspection of the Skin Pulse Pressure Blood Pressure

6. Postural Blood Pressure Changes Jugular Venous Pulsations Heart Inspection and Palpation T he examination, the patient lies supine, with the head of the bed slightly elevated. A right-handed examiner stands at the right side of the patient, a lefthanded examiner at the left side. Each area of the precordium is inspected and then palpated. The heart is examined by inspection, palpation, and auscultation of the chest wall. A systematic approach is used to examine the chest wall in the following six areas

7. Progression of dental caries Aortic area Second intercostal space to the right of the sternum. To determine the correct intercostal space, the nurse first finds the angle of Louis by locating the bony ridge near the top of the sternum, at the junction of the body and the manubrium. From this angle, the second intercostal space is located by sliding one finger to the left or right of the sternum. Subsequent intercostal spaces are located from this reference point by palpating down the rib cage. 2. Pulmonic area Second intercostal space to the left of the sternum

8. 3. Erb’s point - third intercostal space to the left of the sternum 4. Tricuspid area - lower half of the sternum along the left parasternal area 5. Mitral (apical) area - left fifth intercostal space at the midclavicular line 6. Epigastric area - below the xiphoid process

9. Heart Auscultation Normally, S1 and S2 are the only sounds heard during the cardiac cycle. S1—First Heart Sound. Tricuspid and mitral valve closure creates the first heart sound (S1). The word “ lub ” is used to replicate its sound. S2—Second Heart Sound. Closure of the pulmonic and aortic valves produces the second heart sound (S2), commonly referred to as the “dub” sound.

10. Diagnostic Evaluation Laboratory Tests Cardiac Biomarker Analysis The diagnosis of MI is made by evaluating the history and physical examination, the 12-lead ECG, and results of laboratory tests that measure serum cardiac biomarkers. Myocardial cells that become necrotic from prolonged ischemia or trauma release specific enzymes (creatine kinase [CK]), CK isoenzymes (CK-MB), and proteins ( myoglobinroponin T, and troponin I). These substances leak into the interstitial spaces of the myocardium and are carried by the lymphatic system into general circulation. As a result, abnormally high levels of these substances can be detected inserum blood samples.  

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12. Lipid Profile Cholesterol, triglycerides, and lipoproteins are measured to evaluate a person’s risk of developing atherosclerotic disease, especially if there is a family history of premature heart disease, or to diagnose a specific lipoprotein abnormality. Cholesterol and triglycerides are transported in the blood by combining with plasma proteins to form lipoproteins. The lipoproteins are referred to as low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). The risk of CAD increases as the ratio of LDL to HDL or the ratio of total cholesterol (LDL _ HDL) to HDL increases.

13. Although cholesterol levels remain relatively constant over 24hours, the blood specimen for the lipid profile should be obtained after a 12-hour fast.

14. Blood Chemistry, Hematology, and Coagulation Studies Table 26-4 provides information about some common serum laboratory tests and the implications for patients with CVD. Discussion of lipid, brain (B-type) natriuretic peptide, C-reactive protein, and homocysteine measurements follows.

15. Brain (B-Type) Natriuretic Peptide Brain (B-type) natriuretic peptide (BNP) is a neurohormone that helps regulate BP and fluid volume. BNP levels are useful for prompt diagnosis of HF in settings such as the emergency department. Elevations in BNP can occur from a number of other conditions such as pulmonary embolus, MI, and ventricular hypertrophy A BNP level greater than 100 pg /mL is suggestive of HF. C-Reactive Protein protein ( hs -CRP) is a venous blood test that measures levels of CRP, a protein produced by the liver in response to systemic inflammation.

16. Chest X-Ray and Fluoroscopy A chest x-ray is obtained to determine the size, contour, and position of the heart. It reveals cardiac and pericardial calcifications and demonstrates physiologic alterations in the pulmonary circulation. Although it does not help diagnose acute MI, it can help diagnose some complication. Correct placement of pacemakers and pulmonary artery catheters is also confirmed by chest x-ray. Fluoroscopy is an x-ray imaging technique that allows visualization of the heart on a screen. It shows cardiac and vascular pulsations and unusual cardiac contours.

17. Electrocardiography The ECG is a graphic representation of the electrical currents of the heart. The ECG is obtained by placing disposable electrodes in standard positions on the skin of the chest wall and extremities . Recordings of the electrical current flowing between two electrodes is made on graph paper or displayed on a monitor. Several different recordings can be obtained by using a variety of electrode combinations, called leads. 1. History The ECG has been in use for over a century. A British physiologist, Augustus Waller, performed the first ECG recording in 1887, and he gave demonstrations of his technique, using his dog, Jimmy, as the “patient”. Einthoven, from Holland, was present at such a demonstration.

18. Willem Einthoven constructed his well-known triangle and the hexaxial system to help us gain further insight into the electrical activity of the heart. 2. Information obtainable from an ECG ECGs can give us much information about the heart and also give us clues about other aspects of an individual’s state of health, such as: Rhythm – sinus/non-sinus Conduction – normal/abnormal Size of heart chambers Presence of ischaemic heart disease

19. Pulmonary embolism Inflammation of the pericardium/effusion Emphysema Drugs the patient may be on e.g. Digoxin, Calcium channel blockers Electrolyte status of the patient – potassium, calcium levels Temperature – pyrexia or hypothermia Endocrine status – AF in thyrotoxicosis; bradycardia in hypothyroidism Raised intracranial pressure.

20. The standard ECG is composed of 12 leads or 12 different views, although it is possible to record 15 or 18 leads. The 12-lead ECG is used to diagnose dysrhythmias, conduction abnormalities, chamber enlargement, and myocardial ischemia, injury, or infarction. It can also suggest cardiac effects of electrolyte disturbances (high or low calcium and potassium levels) and the effects of antiarrhythmic medications.

21. Lead V1 Right ventricle Right and left atria Interventricular septum (superior aspect) Endocardial aspect of the posterior left ventricle (Thus V1 has a view of all four cardiac chambers) Lead V2 Interventricular septum (superior aspect) Endocardial aspect of posterior left ventricle. Lead V3 Interventricular septum (inferior aspect) Lead V4 Interventricular septum (inferior aspect)Apex Areas of the myocardium viewed by specific leads Std II, Std III, aVF Inferior (diaphragmatic) surface of LV

22. Leads V5, V6 Lateral aspect of left ventricle (inferior aspect) Std I, aVL Lateral aspect of left ventricle (superior aspect A 15-lead ECG adds three additional chest aVR Endocardial aspect of left ventricle 5. ECG paper The ECG is recorded such that the 6 limb leads (standard & augmented) are recorded on the left (pink) the 6 chest (V) leads on the right (yellow) the rhythm strip at the bottom (blue), either Std Lead II or Lead V1.  

23. The ECG paper consists of small squares 1mm x 1mm, and big squares 5mm x 5mm In the horizontal plane The value of a big square (5mm) is 0.2 seconds; a small square (1mm) is 0.04seconds. In the vertical plane The value of two big squares (10mm) is 1millivolt (mV), so each small square in the vertical plane is equivalent to 0.1mV  

24. 1. Calibration The ECG is calibrated such that the 1mV standardisation mark is 10 mm tall and the horizontal line of the mark is 5mm wide (0.2 seconds) This means that the ECG is being recorded at 25mm/second.

25. Interpreting the Electrocardiogram The ECG waveform reflects the function of the heart’s conduction system, which normally initiates and conducts the electrical activity, in relation to the lead. The ECG offers important information about the electrical activity of the heart. ECG waveforms are printed on graph paper that is divided by light and dark vertical and horizontal lines at standard intervals. Waves, Complexes, and Intervals The ECG is composed of waveforms (including the P wave, the QRS complex, the T wave, and possibly a U wave) and of segments and intervals (including the PR interval, the ST segment, and the QT interval.

26. The P wave represents the electrical impulse starting in the sinus node and spreading through the atria. Therefore, the P wave represents atrial depolarization. It is normally 2.5 mm or less in height and 0.11 seconds or less in duration.

27. The QRS complex represents ventricular depolarization. Not all QRS complexes have all three waveforms. The Q wave is the first negative deflection after the P wave. The Q wave is normally less than 0.04 seconds in duration and less than 25% of the R-wave amplitude. The R wave is the first positive deflection after the P wave, and the S wave is the first negative deflection after the R wave. When a wave is less than 5 mm in height, small letters (q, r, s) are used; when a wave is taller than 5 mm, capital letters (Q, R, S) are used to label the waves. The QRS complex is normally less than 0.12 seconds in duration.

28. The T wave represents ventricular repolarization (when the cells regain a negative charge; also called the resting state). It follows the QRS complex and is usually the same direction as the QRS complex. Atrial repolarization also occurs but is not visible on the ECG because it occurs at the same time as the QRS.

29. The U wave is thought to represent repolarization of the Purkinje fibers, but it sometimes is seen in patients with hypokalemia (low potassium levels), hypertension, or heart disease. If present, the U wave follows the T wave and is usually smaller than the P wave. If tall, it may be mistaken for an extra P wave.

30. The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex and represents the time needed for sinus node stimulation, atrial depolarization, and conduction through the AV node before ventricular depolarization. In adults, the PR interval normally ranges from 0.12 to 0.20 seconds in duration.

31. The ST segment, which represents early ventricular repolarization, lasts from the end of the QRS complex to the beginning of the T wave. The beginning of the ST segment is usually identified by a change in the thickness or angle of the terminal portion of the QRS complex. The end of the ST segment may be more difficult to identify because it merges into the T wave. The ST segment is normally isoelectric (see discussion of TP interval). It is analyzed to identify whether it is above or below the isoelectric line, which may be, among other signs and symptoms, a sign of cardiac ischemia.

32. The QT interval, which represents the total time for ventricular depolarization and repolarization, is measured from the beginning of the QRS complex to the end of the T wave. The QT interval varies with heart rate, gender, and age, and the measured interval needs to be corrected for these variables through specific calculations. Several ECG interpretation books contain charts for these calculations. The QT interval is usually 0.32 to 0.40 seconds in duration if the heart rate is 65 to 95 bpm (beats per minute). If the QT interval becomes prolonged, the patient may be at risk for a lethal ventricular dysrhythmia called torsades de pointes.

33. The TP interval is measured from the end of the T wave to the beginning of the next P wave, an isoelectric period . When no electrical activity is detected, the line on the graph remains flat; this is called the isoelectric line. The ST segment is compared with the TP interval to detect changes from the line on the graph during the isoelectric period.

34. The PP interval is measured from the beginning of one P wave to the beginning of the next. The PP interval is used to determine atrial rhythm and atrial rate. The RR interval is measured from one QRS complex to the next QRS complex. The RR interval is used to determine ventricular rate and rhythm

35. Regular rhythm : Estimate the rate by counting the number of big squares between successive R waves, and dividing this number into 300. R – R interval of: 1 square corresponds to a heartrate of 300/min 2 squares 150/min 3 squares 100/min 4 squares 75/min 5 squares 60/min 6 squares 50/min  

36. Irregular rhythm: Count the number of QRS complexes in 50 big squares and multiply your answer by 6 (5 big squares = 1 second, 50 big squares = 10 seconds)  

41. Continuous Electrocardiographic Monitoring Continuous ECG monitoring is the standard of care for patients who are at high risk for dysrhythmias. This form of cardiac monitoring detects abnormalities in heart rate and rhythm. Many systems have the capacity to monitor for changes in ST segments, which are used to identify the presence of myocardial ischemia or injury. There are two types of continuous ECG monitoring techniques used in health care settings: hardwire cardiac monitoring, found in emergency departments, critical care units, and progressive care units; and telemetry, found in general nursing care units or outpatient cardiac rehabilitation programs. Hardwire cardiac monitoring and telemetry systems vary in sophistication.  

42. • Monitor more than one lead simultaneously • Monitor ST segments (ST-segment depression is a marker of myocardial ischemia; ST-segment elevation provides evidence of an evolving MI) • Provide graded visual and audible alarms (based on priority, asystole merits the highest grade of alarm) • Interpret and store alarms  

43. Cardiac Stress Testing Normally, the coronary arteries dilate to four times their usual diameter in response to increased metabolic demands for oxygen and nutrients. However, coronary arteries affected by atherosclerosis dilate less, compromising blood flow to the myocardium and causing ischemia. Therefore, abnormalities in cardiovascular function are more likely to be detected during times of increased demand, or “stress.” The cardiac stress test procedures—the exercise stress test, the pharmacologic stress test, and the mental or emotional stress test—are noninvasive ways to evaluate the response of the cardiovascular system to stress.

44. The stress test helps determine the following: presence of CAD, (2) cause of chest pain, (3) functional capacity of the heart after an MI or heart surgery, (4) effectiveness of antianginal or antiarrhythmic medications, (5) dysrhythmias that occur during physical exercise, and (6) specific goals for a physical fitness program. Contraindications to stress testing include severe aortic stenosis, acute myocarditis or pericarditis, severe hypertension, suspected left main CAD, HF, and unstable angina. Because complications of stress testing can be life-threatening (MI, cardiac arrest, HF, and severe dysrhythmias), testing facilities must have staff and equipment ready to provide treatment, including advanced cardiac life support.

45. Stress testing is often combined with echocardiography or radionuclide imaging. These techniques are performed during the resting state and immediately after stress testing. Exercise Stress Testing Procedure During an exercise stress test, the patient walks on a treadmill (most common), pedals a stationary bicycle, or uses an arm crank. Exercise intensity progresses according to established protocols. The goal is to increase the heart rate to the “target heart rate,” which is 80% to 90% of the maximum predicted heart rate based on the patient’s age and gender.

46. Echocardiography Traditional Echocardiography Echocardiography is a noninvasive ultrasound test that is used to measure the ejection fraction and examine the size, shape, and motion of cardiac structures. It is particularly useful for diagnosing pericardial effusions; determining chamber size and the etiology of heart murmurs; evaluating the function of heart valves, including prosthetic heart valves; and evaluating ventricular wall motion.

47. Procedure Echocardiography involves transmission of high-frequency sound waves into the heart through the chest wall and recording of the return signals. The ultrasound is generated by a handheld transducer applied to the front of the chest. The transducer picks up the echoes, converts them to electrical impulses, and transmits them for display on an oscilloscope and recording on a videotape. An ECG is recorded simultaneously to assist with interpreting the echocardiogram. Two-dimensional or cross-sectional echocardiography creates a sophisticated, spatially correct image of the heart. Other techniques, such as Doppler and color flow imaging echocardiography, show the direction and velocity of the blood flow through the heart.

48. Echocardiography may be performed with an exercise or pharmacologic stress test. Images are obtained at rest and then immediately after the target heart rate is reached. Myocardial ischemia from decreased perfusion during stress causes abnormalities in ventricular wall motion and is easily detected by echocardiography. A stress test using echocardiography is considered positive if abnormalities in ventricular wall motion are detected during stress but not during rest. These findings are highly suggestive of CAD and require further evaluation, such as a cardiac catheterization.

49. Nursing Interventions Before echocardiography, the nurse informs the patient about the test, explaining that it is painless. Echocardiographic monitoring is performed while a transducer that emits sound waves is moved over the surface of the chest wall. Gel applied to the skin helps transmit the sound waves. Periodically, the patient is asked to turn onto the left side or hold a breath. The test takes about 30 to 45 minutes. If the patient is to undergo an exercise or pharmacologic stress test with echocardiography, information on stress testing is also reviewed with the patient.

50. Radionuclide Imaging Computed Tomography Procedure Computed tomography (CT), also called computerized axial tomographic (CAT) scanning or electron-beam computed tomography (EBCT), uses x-rays to provide crosssectional images of the chest, including the heart and great vessels. These techniques are used to evaluate cardiac masses and diseases of the aorta and pericardium . It is used to evaluate bypass graft patency, congenital heart lesions, left and right ventricular muscle mass, chamber volumes, cardiac output, and ejection fraction. For people without previous MI, PCI, or coronary artery bypass surgery, EBCT is used to determine the amount of calcium deposits in the coronary arteries and underlying atherosclerosis.

51. Nursing Interventions Patient preparation for these tests is the nursing role. The nurse explains to the patient that he or she will be positioned on a table during the scan while the scanner rotates around him or her. The procedure is noninvasive and painless. However, to obtain adequate images, the patient must lie perfectly still during the scanning process. An IV access line is necessary if contrast enhancement is to be used.

52. Positron Emission Tomography Positron emission tomography (PET) is a noninvasive scanning method that has been used primarily to study neurologic dysfunction. More recently, and with increasing frequency, PET has been used to diagnose cardiac dysfunction. PET provides more specific information about myocardial perfusion and viability than does TEE or thallium scanning. For cardiac patients, including those without symptoms, PET helps in planning treatment ( eg , coronary artery bypass surgery, PCIs). PET also helps evaluate the patency of native and previously grafted vessels and the collateral circulation.

53. Procedure During a PET scan, radioisotopes are administered by injection; one compound is used to determine blood flow in the myocardium, and another determines the metabolic function. The PET camera provides detailed three-dimensional images of the distributed compounds. The viability of the myocardium is determined by comparing the extent of glucose metabolism in the myocardium to the degree of blood flow. For example, ischemic but viable tissue will show decreased blood flow and elevated metabolism. For a patient with this finding, revascularization through surgery or angioplasty will probably be indicated to improve heart function. Restrictions of food intake before the test vary among institutions, but because PET evaluates glucose metabolism, the patient’s blood glucose level should be within the normal range before testing.

54. Nursing Interventions The nurse should instruct the patient to refrain from using tobacco and ingesting caffeine for 4 hours before the PET procedure. The patient should also be reassured that radiation exposure is at safe and acceptable levels, similar to those of other diagnostic x-ray studies.

55. Magnetic Resonance Angiography Procedure Magnetic resonance angiography (MRA) is a noninvasive, painless technique that is used to examine both the physiologic and anatomic properties of the heart. MRA uses a powerful magnetic field and computer-generated pictures to image the heart and great vessels. It is valuable in diagnosing diseases of the aorta, heart muscle, and pericardium, as well as congenital heart lesions. The application of this technique to the evaluation of coronary artery anatomy is limited, however, because the quality of the images obtained during MRA is distorted by respirations, the beating heart, and certain implanted devices (stents and surgical clips).

56. In addition, this technique cannot adequately visualize the small distal coronary arteries as well as conventional angiography that is performed during a cardiac catheterization. Therefore, the latter technique remains the “gold standard” for the diagnosis of CAD. Nursing Interventions Because of the magnetic field used during MRA, diagnostic centers where these procedures are performed carefully screen patients for contraindications, including the presence remain motionless during the scan.

57. Cardiac Catheterization Cardiac catheterization is an invasive diagnostic procedure in which radiopaque arterial and venous catheters are introduced into selected blood vessels of the right and left sides of the heart. Catheter advancement is guided by fluoroscopy. Most commonly, the catheters are inserted percutaneously through the blood vessels, or via a cutdown procedure if the patient has poor vascular access. Pressures and oxygen saturation levels in the four heart chambers are measured. Cardiac catheterization is most frequently used to diagnose . CAD, assess coronary artery patency, and determine the extent of atherosclerosis and determine whether revascularization procedures, including PCI or coronary artery bypass surgery, may be of benefit to the patient.

58. Cardiac catheterization is also used to diagnose pulmonary arterial hypertension or to treat stenotic heart valves via percutaneous balloon valvuloplasty. During cardiac catheterization, the patient has one or more IV lines in place for the administration of sedatives, fluids, heparin, and other medications. BP and ECG monitoring is necessary to observe for hemodynamic instability or dysrhythmias. The myocardium can become ischemic and trigger dysrhythmias as catheters are positioned in the coronary arteries or during injection of contrast agents. Resuscitation equipment must be readily available, and staff must be prepared to provide advanced cardiac life support measures as necessary.

59. Radiopaque contrast agents are used to visualize the coronary arteries. Some contrast agents contain iodine, and the patient is assessed before the procedure for previous reactions to contrast agents or allergies to iodine-containing substances ( eg , seafood). If the patient has a suspected or known allergy to the substance, antihistamines or methylprednisolone (Solu-Medrol) may be administered before the procedure. In addition, the following blood tests are performed to identify abnormalities that may complicate recovery: blood urea nitrogen (BUN) and creatinine levels, international normalized ratio (INR) and prothrombin time (PT), activated thromboplastin time ( aPTT ), hematocrit and hemoglobin values, platelet count, and electrolyte levels.

60. Patients undergoing cardiac catheterization who have comorbid conditions—including diabetes, HF, preexisting renal disease, hypotension, or dehydration, or who are elderly—are at risk for contrast agent–induced nephropathy (defined as an increase in the baseline serum creatinine by 25% or more within 2 days of the procedure). Although this form of acute renal failure is usually reversible, temporary dialysis may be necessary. Preventive strategies for high-risk patients include preprocedure and postprocedure hydration with IV infusions of saline or sodium bicarbonate and the antioxidant acetylcysteine ( Mucomyst ) ( Briguori , Airoldi , D’Andrea , et al., 2007).

61. Diagnostic cardiac catheterization is commonly performed on an outpatient basis and requires 2 to 6 hours of bed rest after the procedure before the patient is allowed to ambulate. Variations in time to ambulation are related to the size of the catheter used during the procedure, the site of catheter insertion (femoral or radial artery), the patient’s anticoagulation status, and other variables ( eg , advanced age, obesity, bleeding disorder). The use of smaller (4 or 6 Fr) catheters is associated with shorter recovery times. Several options to achieve arterial hemostasis after catheter removal, including manual pressure, mechanical compression devices such as the FemoStop (placed over puncture site for 30 minutes), and percutaneously deployed devices, are used.

62. The latter devices are positioned at the femoral arterial puncture site after completion of the procedure. They deploy a saline-soaked gelatin sponge ( QuickSeal ), collagen ( VasoSeal ), sutures ( Perclose , Techstar ), or a combination of both collagen and sutures (Angio-Seal). Other newer products that expedite arterial hemostasis include external patches ( Syvek Patch, Clo-Sur PAD). These products are placed over the puncture site as the catheter is removed and manual pressure is applied for 4 to 10 minutes. Once hemostasis is achieved, the patch is covered with a dressing that remains in place for 24 hours. A number of factors, such as the patient’s condition, cost, institutional availability of these devices, and the physician’s preference, determine which closure devices are used.

63. Major benefits of the percutaneously deployed vascular closure devices include reliable, immediate hemostasis and a shorter time on bed rest without a significant increase in bleeding or other complications. However, these devices are not without risk. Bleeding around the closure device, infection, and arterial obstruction due to embolization or local injury to the vessel during placement have all been reported, although they are rare complications ( Kalapatapu , Ali, Masroor , et al., 2006).

64. Patients hospitalized for angina or acute MI who require cardiac catheterization usually return to their hospital rooms for recovery. In some cardiac catheterization laboratories, a PCI (discussed in Chapter 28) may be performed immediately during the catheterization if indicated.

65. Angiography Cardiac catheterization is usually performed with angiography, a technique in which a contrast agent is injected into the vascular system to outline the heart and blood vessels. When a specific heart chamber or blood vessel is singled out for study, the procedure is known as selective angiography.