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Echocardiography Lab
C H A P T E R
24 Echocardiography Lab In this chapter, we describe the steps for an echocardiography laboratory experiment. This lab is intended to supplement the heart valve lecture based on Chapter 6. Because ultrasound is not discussed in detail in this textbook, students are advised to read introductory material about ultrasound, such as the ultrasound chapter in Webb (2003). This lab is written for execution using Sonosite equipment, but it can be customized for ultrasound monitors from other manufacturers. Upon completion of this chapter, each student shall be able to: 1. Identify the left ventricular outflow tract (LVOT) in the left parasternal long axis view, and the left ventricle in the apical two chamber view. 2. Understand the anatomy associated with these views. 3. Measure LVOT diameter, velocity time integral, and left ventricular volume; calculate stroke volume and ejection fraction from these measurements.
STRATEGIC PLANNING During this experiment, you will be measuring hemodynamic parameters from one of your fellow students. In preparation for this lab, review the ultrasound chapter given by your instructor. Echocardiography is usually performed by skilled operators called sonographers, who have studied echocardiography for many years. Be patient because it takes time to obtain the views you are seeking. For the parasternal view, find the mitral valve leaflets first, and then make slight adjustments to the transducer to image the other landmarks. For the apical view, try to position the transducer toward the subject’s right shoulder. Note that all your printouts are a required part of your lab report. This lab should take approximately 2.5 hr to conduct.
Medical Device Technologies
471
r 2012 Elsevier Inc. All rights reserved.
472
24. ECHOCARDIOGRAPHY LAB
MATERIALS AND METHODS This experiment requires the following equipment: • • • • • • • • •
1 Sonosite MicroMaxx ultrasound system with P17 transducer 1 Sonosite ECG trunk cable, with leadwires 1 compact flash 1 Sonosite MicroMaxx manual 1 compatible Sony printer 3 ECG electrodes 1 Aquasonic ultrasound transmission gel 1 cot or camping pad Alcohol wipes and paper towels, as needed
Background This experiment uses two echo views to calculate left ventricular (LV) stroke volume (SV) and ejection fraction (EF). LV SV is the volume of blood ejected from the left ventricle with each cardiac beat. LV EF is the percentage of blood ejected from the left ventricle with each cardiac beat. The transducer positions required for parasternal and apical views are shown in Figure 24.1. Your patient lies in the left lateral decubitus position: lying on left side, head propped up by elbow, legs together and bent at the knees. The parasternal long-axis view is usually obtained by placing the transducer in the left parasternal area in the second or third intercostal space (under the second or third rib from the top). This view is illustrated in Figure 24.2. The apical view is usually obtained lateral (left) and inferior (beneath) to the nipple. This view is illustrated in Figure 24.3. While the transducer is positioned along the parasternal long-axis, we can make a pulsed Doppler recording of left ventricular outflow tract velocity, which is shown in Figure 24.4. FIGURE 24.1 The parasternal (A) and apical (B) transducer positions, with the patient in the left lateral decubitus position [Adapted from Oh et al. (1999)].
A
B
II. LAB EXPERIMENTS
473
MATERIALS AND METHODS
Right coronary cusp and ostium Membranous interventricular septum
Ascending aorta Sinuses of Valsalva
Right ventricular outflow tract
Epicardium
*Interannular fibrosa
Right pulmonary artery
Specialized conduction system
* Left atrium
Left ventricle Posterior mitral leaflet (A) Papillary muscle
Chordae tendineae
Anterior mitral leaflet
Right upper and lower pulmonary v.
Coronary sinus and left circumflex artery
RVOT Ao LV LA DA CS
(B)
(C)
FIGURE 24.2 Anatomy (A) observed during left parasternal long axis view. Echo images were recorded at end-diastole (B) and end-systole (C). RVOT 5 right ventricular outflow tract, LV 5 left ventricle, Ao 5 aorta, LA 5 left atrium, CD 5 coronary sinus, DA 5 descending thoracic aorta [The anatomical drawing from Otto (2009a). Figures reproduced by permission from Otto (2009b)].
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24. ECHOCARDIOGRAPHY LAB
LAA LA
LV
LV LV LAA LAA RA
LA
LA
Anatomy observed during apical two chamber view. LA 5 left atrium, LAA 5 left atrial appendage, LV 5 left ventricle, RA 5 right atrium [Reproduced by permission from Otto (2009b)].
FIGURE 24.3
Measurements Stroke volume is estimated from measurements of LVOT diameter and the velocity time integral (VTI). This method was first validated by bioengineer Lee Huntsman in 1983 (Huntsman et al., 1983; Otto, 2009b). The amount of blood flow through a fixed orifice is directly proportional to the product of the orifice cross-sectional area and flow velocity. We
II. LAB EXPERIMENTS
MATERIALS AND METHODS
LV Ao SV
475 FIGURE 24.4 Pulse Doppler recording of left ventricular (LV) outflow tract velocity (LVOTv) just proximal to the aortic (Ao) valve from an apical approach. The Ao valve closing click (arrow) of the outflow tract velocity recording ensures that the sample volume (SV) location is immediately adjacent to the valve, corresponding with the site of outflow tract diameter measurement [Reproduced by permission from Otto (2009b)].
LVOTV
obtain this cross-sectional area by measuring the LVOT diameter and assuming a circular cross-section. We obtain the flow velocity by measuring the area under the velocity curve (VTI) because this is the distance blood flow travels with one stroke (Huntsman et al., 1983): LVOT diamðcmÞ 2 3 UπUVTI ðcmÞ ð24:1Þ SVðcm Þ 5 2 Ejection fraction (EF) is estimated as the percentage difference between the end diastolic volume (EDV) and the end systolic volume (ESV) of the left ventricle. Using Simpson’s rule, each ventricular volume is calculated as the sum of a series of parallel slices from apex to base. This method was first validated by cardiologist Louis Teichholz in 1974 (Teichholz, et al., 1974; Otto, 2009b). EF is then the percentage change in volume: EDV 2 ESV EF ð%Þ 5 U100% ð24:2Þ EDV
Procedure Attach the ECG electrodes in the proper locations (LA 5 black, RA 5 white, LL 5 red), and adjust the ECG amplitude so that the QRS complex is visible. Measure LVOT diameter through the following steps: 1. Apply gel to the MicroMaxx transducer. 2. Select 2D.
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24. ECHOCARDIOGRAPHY LAB
3. Position the transducer on the patient so that the image replicates Figure 24.2. The length of the transducer should be parallel to the length of the intercostal space. Work to find the mitral valve and inferior wall first. Then make small angular adjustments to image the aortic valve also. You may need to adjust the NEAR, FAR, and GAIN knobs. You may have to adjust the DEPTH keys. 4. Leave the transducer in the proper position for 15 s so that the MicroMaxx buffer fills with data. 5. Select FREEZE. Do not hit FREEZE again till you are finished with step 10. 6. Use the FREEZE left and right arrows to position to the first (or next) systolic LVOT diameter. To determine the systolic LVOT diameter, check your ECG and that the diameter is at its widest length. 7. Select CALIPER. Select SELECT, which will enable you to position over one side of the LVOT diameter. 8. Select SELECT, which will enable you to position over the other side of the diameter, to make the measurement. 9. Select SAVE on the blue panel. Manually record the LVOT diameter. 10. Repeat steps 69 to obtain two other estimates of LVOT diameter. 11. Select FREEZE to unfreeze. Measure VTI through the following steps: 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.
Position the transducer on the patient so that the image replicates Figure 24.2. Select DOPPLER. Position sample volume so that it is in the center of LVOT. Select UPDATE. Leave the transducer in the proper position (look for a V-shaped velocity profile just past the QRS complex with high-frequency sound, per Figure 24.4) for 15 s so that the buffer fills with data. Select FREEZE. Do not hit FREEZE again till you are finished with step 25. Use the FREEZE left and right arrows to position to the first (next) systolic Doppler spectrum. Select CALCS. Move cursor to select AV, then LVOT VTI. Select SELECT. This enables you to start tracing the systolic Doppler spectrum. Begin to trace from 0 m/s (the x-axis) as the valve opens, around the V, and back to 0 m/s as the valve closes. When you have finished tracing, select SELECT. Select SET. Select SAVE on the blue panel. Manually record LVOT VTI. Repeat steps 1824 to obtain two other estimates of VTI. Select FREEZE to unfreeze.
You can view your six measurements by: 27. Select REVIEW. 28. Select each saved measurement.
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MATERIALS AND METHODS
477
29. Select DONE. Show these measurements to your instructor. Print your images on the Sony printer interfaced to your MicroMaxx. When the measurements are approved, you can manually calculate the mean LVOT diameter and mean VTI, and calculate SV. Measure EF through the following steps: 30. Apply gel to the MicroMaxx transducer. 31. Select 2D. 32. Position the transducer on the patient so that the image replicates Figure 24.3. Again, the length of the transducer should be parallel to the length of the intercostal space. Work to image four chambers first. When these are in view, turn the transducer 90 to isolate only the left atrium and left ventricle in the image. You may need to adjust the NEAR, FAR, and GAIN knobs. You may have to adjust the DEPTH keys. 33. Leave the transducer in the proper position for 15 s so that the MicroMaxx buffer fills with data. 34. Select FREEZE. Do not hit FREEZE again till you are finished with step 42. 35. Use the FREEZE left and right arrows to position to the first (or next) left ventricular end diastolic volume. To determine diastolic volume, check your ECG and that the volume is at its largest area. 36. Select CALCS. 37. Move cursor to select A2Cd. 38. Select SELECT to start cursor. Trace around volume. 39. Select SELECT to end cursor. 40. Select SAVE on the blue panel. Manually record value. Select CALCS to remove volume display. 41. Repeat steps 3540 to obtain two other estimates of end diastolic volume. 42. Repeat steps 3541 to obtain three estimates of end systolic volume. Make sure you use the same beats as were selected for end diastolic volume. In these iterations, use the label A2Cs, instead of A2Cd. 43. Select FREEZE to unfreeze. You can view your six measurements by: 44. Select REVIEW. 45. Select each saved measurement. 46. Select DONE. You can view your calculated EF by: 47. Select REPORT. 48. View calculated EF. 49. Select DONE. Show these measurements to your instructor. Print your images on the Sony printer interfaced to your MicroMaxx.
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24. ECHOCARDIOGRAPHY LAB
RESULTS AND ANALYSIS Record the answers to the questions in the written procedure in the Results section of your lab report.
DISCUSSION Answer the following questions in the Discussion section of your lab report: • Why is the VTI transducer position tuned by using sound? • How accurate do you believe your four measurements (LVOT diameter, VTI, EDV, ESV) are? Give reasons. • Which do you believe is the least accurate measurement? Give reasons.
References Huntsman, L. L., Stewart, D. K., Barnes, S. R., Franklin, S. B., Colocousis, J. S., & Hessel, E. A. (1983). Noninvasive Doppler determination of cardiac output in man. Clinical validation. Circulation, 67, 593602. Oh, J. K., Seward, J. B., & Tajik, A. J. (1999). The echo manual (2nd ed.). Philadelphia: Lippincott Williams & Wilkins. Otto, C. M. (2009a). Echocardiographic evaluation of valvular heart disease. In: C. M. Otto, & R. Bonow (Eds.), Valvular heart disease: A companion to Braunwald’s heart disease. Philadelphia: Elsevier/Saunders. Otto, C. M. (2009b). Textbook of clinical echocardiography (4th ed.). Philadelphia: Elsevier Saunders. Teichholz, L. E., Cohen, M. V., Sonnenblick, E. H., & Gorlin, R. (1974). Study of left ventricular geometry and function by B-scan ultrasonography in patients with and without asynergy. New England Journal of Medicine, 291, 12201226. Webb, A. (2003). Introduction to biomedical imaging. Hoboken, NJ: John Wiley/IEEE Press.
II. LAB EXPERIMENTS
24 Echocardiography Lab In this chapter, we describe the steps for an echocardiography laboratory experiment. This lab is intended to supplement the heart valve lecture based on Chapter 6. Because ultrasound is not discussed in detail in this textbook, students are advised to read introductory material about ultrasound, such as the ultrasound chapter in Webb (2003). This lab is written for execution using Sonosite equipment, but it can be customized for ultrasound monitors from other manufacturers. Upon completion of this chapter, each student shall be able to: 1. Identify the left ventricular outflow tract (LVOT) in the left parasternal long axis view, and the left ventricle in the apical two chamber view. 2. Understand the anatomy associated with these views. 3. Measure LVOT diameter, velocity time integral, and left ventricular volume; calculate stroke volume and ejection fraction from these measurements.
STRATEGIC PLANNING During this experiment, you will be measuring hemodynamic parameters from one of your fellow students. In preparation for this lab, review the ultrasound chapter given by your instructor. Echocardiography is usually performed by skilled operators called sonographers, who have studied echocardiography for many years. Be patient because it takes time to obtain the views you are seeking. For the parasternal view, find the mitral valve leaflets first, and then make slight adjustments to the transducer to image the other landmarks. For the apical view, try to position the transducer toward the subject’s right shoulder. Note that all your printouts are a required part of your lab report. This lab should take approximately 2.5 hr to conduct.
Medical Device Technologies
471
r 2012 Elsevier Inc. All rights reserved.
472
24. ECHOCARDIOGRAPHY LAB
MATERIALS AND METHODS This experiment requires the following equipment: • • • • • • • • •
1 Sonosite MicroMaxx ultrasound system with P17 transducer 1 Sonosite ECG trunk cable, with leadwires 1 compact flash 1 Sonosite MicroMaxx manual 1 compatible Sony printer 3 ECG electrodes 1 Aquasonic ultrasound transmission gel 1 cot or camping pad Alcohol wipes and paper towels, as needed
Background This experiment uses two echo views to calculate left ventricular (LV) stroke volume (SV) and ejection fraction (EF). LV SV is the volume of blood ejected from the left ventricle with each cardiac beat. LV EF is the percentage of blood ejected from the left ventricle with each cardiac beat. The transducer positions required for parasternal and apical views are shown in Figure 24.1. Your patient lies in the left lateral decubitus position: lying on left side, head propped up by elbow, legs together and bent at the knees. The parasternal long-axis view is usually obtained by placing the transducer in the left parasternal area in the second or third intercostal space (under the second or third rib from the top). This view is illustrated in Figure 24.2. The apical view is usually obtained lateral (left) and inferior (beneath) to the nipple. This view is illustrated in Figure 24.3. While the transducer is positioned along the parasternal long-axis, we can make a pulsed Doppler recording of left ventricular outflow tract velocity, which is shown in Figure 24.4. FIGURE 24.1 The parasternal (A) and apical (B) transducer positions, with the patient in the left lateral decubitus position [Adapted from Oh et al. (1999)].
A
B
II. LAB EXPERIMENTS
473
MATERIALS AND METHODS
Right coronary cusp and ostium Membranous interventricular septum
Ascending aorta Sinuses of Valsalva
Right ventricular outflow tract
Epicardium
*Interannular fibrosa
Right pulmonary artery
Specialized conduction system
* Left atrium
Left ventricle Posterior mitral leaflet (A) Papillary muscle
Chordae tendineae
Anterior mitral leaflet
Right upper and lower pulmonary v.
Coronary sinus and left circumflex artery
RVOT Ao LV LA DA CS
(B)
(C)
FIGURE 24.2 Anatomy (A) observed during left parasternal long axis view. Echo images were recorded at end-diastole (B) and end-systole (C). RVOT 5 right ventricular outflow tract, LV 5 left ventricle, Ao 5 aorta, LA 5 left atrium, CD 5 coronary sinus, DA 5 descending thoracic aorta [The anatomical drawing from Otto (2009a). Figures reproduced by permission from Otto (2009b)].
II. LAB EXPERIMENTS
474
24. ECHOCARDIOGRAPHY LAB
LAA LA
LV
LV LV LAA LAA RA
LA
LA
Anatomy observed during apical two chamber view. LA 5 left atrium, LAA 5 left atrial appendage, LV 5 left ventricle, RA 5 right atrium [Reproduced by permission from Otto (2009b)].
FIGURE 24.3
Measurements Stroke volume is estimated from measurements of LVOT diameter and the velocity time integral (VTI). This method was first validated by bioengineer Lee Huntsman in 1983 (Huntsman et al., 1983; Otto, 2009b). The amount of blood flow through a fixed orifice is directly proportional to the product of the orifice cross-sectional area and flow velocity. We
II. LAB EXPERIMENTS
MATERIALS AND METHODS
LV Ao SV
475 FIGURE 24.4 Pulse Doppler recording of left ventricular (LV) outflow tract velocity (LVOTv) just proximal to the aortic (Ao) valve from an apical approach. The Ao valve closing click (arrow) of the outflow tract velocity recording ensures that the sample volume (SV) location is immediately adjacent to the valve, corresponding with the site of outflow tract diameter measurement [Reproduced by permission from Otto (2009b)].
LVOTV
obtain this cross-sectional area by measuring the LVOT diameter and assuming a circular cross-section. We obtain the flow velocity by measuring the area under the velocity curve (VTI) because this is the distance blood flow travels with one stroke (Huntsman et al., 1983): LVOT diamðcmÞ 2 3 UπUVTI ðcmÞ ð24:1Þ SVðcm Þ 5 2 Ejection fraction (EF) is estimated as the percentage difference between the end diastolic volume (EDV) and the end systolic volume (ESV) of the left ventricle. Using Simpson’s rule, each ventricular volume is calculated as the sum of a series of parallel slices from apex to base. This method was first validated by cardiologist Louis Teichholz in 1974 (Teichholz, et al., 1974; Otto, 2009b). EF is then the percentage change in volume: EDV 2 ESV EF ð%Þ 5 U100% ð24:2Þ EDV
Procedure Attach the ECG electrodes in the proper locations (LA 5 black, RA 5 white, LL 5 red), and adjust the ECG amplitude so that the QRS complex is visible. Measure LVOT diameter through the following steps: 1. Apply gel to the MicroMaxx transducer. 2. Select 2D.
II. LAB EXPERIMENTS
476
24. ECHOCARDIOGRAPHY LAB
3. Position the transducer on the patient so that the image replicates Figure 24.2. The length of the transducer should be parallel to the length of the intercostal space. Work to find the mitral valve and inferior wall first. Then make small angular adjustments to image the aortic valve also. You may need to adjust the NEAR, FAR, and GAIN knobs. You may have to adjust the DEPTH keys. 4. Leave the transducer in the proper position for 15 s so that the MicroMaxx buffer fills with data. 5. Select FREEZE. Do not hit FREEZE again till you are finished with step 10. 6. Use the FREEZE left and right arrows to position to the first (or next) systolic LVOT diameter. To determine the systolic LVOT diameter, check your ECG and that the diameter is at its widest length. 7. Select CALIPER. Select SELECT, which will enable you to position over one side of the LVOT diameter. 8. Select SELECT, which will enable you to position over the other side of the diameter, to make the measurement. 9. Select SAVE on the blue panel. Manually record the LVOT diameter. 10. Repeat steps 69 to obtain two other estimates of LVOT diameter. 11. Select FREEZE to unfreeze. Measure VTI through the following steps: 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.
Position the transducer on the patient so that the image replicates Figure 24.2. Select DOPPLER. Position sample volume so that it is in the center of LVOT. Select UPDATE. Leave the transducer in the proper position (look for a V-shaped velocity profile just past the QRS complex with high-frequency sound, per Figure 24.4) for 15 s so that the buffer fills with data. Select FREEZE. Do not hit FREEZE again till you are finished with step 25. Use the FREEZE left and right arrows to position to the first (next) systolic Doppler spectrum. Select CALCS. Move cursor to select AV, then LVOT VTI. Select SELECT. This enables you to start tracing the systolic Doppler spectrum. Begin to trace from 0 m/s (the x-axis) as the valve opens, around the V, and back to 0 m/s as the valve closes. When you have finished tracing, select SELECT. Select SET. Select SAVE on the blue panel. Manually record LVOT VTI. Repeat steps 1824 to obtain two other estimates of VTI. Select FREEZE to unfreeze.
You can view your six measurements by: 27. Select REVIEW. 28. Select each saved measurement.
II. LAB EXPERIMENTS
MATERIALS AND METHODS
477
29. Select DONE. Show these measurements to your instructor. Print your images on the Sony printer interfaced to your MicroMaxx. When the measurements are approved, you can manually calculate the mean LVOT diameter and mean VTI, and calculate SV. Measure EF through the following steps: 30. Apply gel to the MicroMaxx transducer. 31. Select 2D. 32. Position the transducer on the patient so that the image replicates Figure 24.3. Again, the length of the transducer should be parallel to the length of the intercostal space. Work to image four chambers first. When these are in view, turn the transducer 90 to isolate only the left atrium and left ventricle in the image. You may need to adjust the NEAR, FAR, and GAIN knobs. You may have to adjust the DEPTH keys. 33. Leave the transducer in the proper position for 15 s so that the MicroMaxx buffer fills with data. 34. Select FREEZE. Do not hit FREEZE again till you are finished with step 42. 35. Use the FREEZE left and right arrows to position to the first (or next) left ventricular end diastolic volume. To determine diastolic volume, check your ECG and that the volume is at its largest area. 36. Select CALCS. 37. Move cursor to select A2Cd. 38. Select SELECT to start cursor. Trace around volume. 39. Select SELECT to end cursor. 40. Select SAVE on the blue panel. Manually record value. Select CALCS to remove volume display. 41. Repeat steps 3540 to obtain two other estimates of end diastolic volume. 42. Repeat steps 3541 to obtain three estimates of end systolic volume. Make sure you use the same beats as were selected for end diastolic volume. In these iterations, use the label A2Cs, instead of A2Cd. 43. Select FREEZE to unfreeze. You can view your six measurements by: 44. Select REVIEW. 45. Select each saved measurement. 46. Select DONE. You can view your calculated EF by: 47. Select REPORT. 48. View calculated EF. 49. Select DONE. Show these measurements to your instructor. Print your images on the Sony printer interfaced to your MicroMaxx.
II. LAB EXPERIMENTS
478
24. ECHOCARDIOGRAPHY LAB
RESULTS AND ANALYSIS Record the answers to the questions in the written procedure in the Results section of your lab report.
DISCUSSION Answer the following questions in the Discussion section of your lab report: • Why is the VTI transducer position tuned by using sound? • How accurate do you believe your four measurements (LVOT diameter, VTI, EDV, ESV) are? Give reasons. • Which do you believe is the least accurate measurement? Give reasons.
References Huntsman, L. L., Stewart, D. K., Barnes, S. R., Franklin, S. B., Colocousis, J. S., & Hessel, E. A. (1983). Noninvasive Doppler determination of cardiac output in man. Clinical validation. Circulation, 67, 593602. Oh, J. K., Seward, J. B., & Tajik, A. J. (1999). The echo manual (2nd ed.). Philadelphia: Lippincott Williams & Wilkins. Otto, C. M. (2009a). Echocardiographic evaluation of valvular heart disease. In: C. M. Otto, & R. Bonow (Eds.), Valvular heart disease: A companion to Braunwald’s heart disease. Philadelphia: Elsevier/Saunders. Otto, C. M. (2009b). Textbook of clinical echocardiography (4th ed.). Philadelphia: Elsevier Saunders. Teichholz, L. E., Cohen, M. V., Sonnenblick, E. H., & Gorlin, R. (1974). Study of left ventricular geometry and function by B-scan ultrasonography in patients with and without asynergy. New England Journal of Medicine, 291, 12201226. Webb, A. (2003). Introduction to biomedical imaging. Hoboken, NJ: John Wiley/IEEE Press.
II. LAB EXPERIMENTS