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Bicuspid noncalcific aortic stenosis: Diagnostic limitations of intraoperative transesophageal echocardiography
CASE REPORTS
Bicuspid Noncalcific Aortic Stenosis: Diagnostic Limitations of Intraoperative Transesophageal Echocardiography Manuel L. Fontes, MD, Joseph Mathew, MD, Kevin Johnson, MD, and Terence Rafferty, MD NTRAOPERATIVE transesophageal echocardiography (TEE) provides both qualitative and quantitative information about valvular anatomy and function that can facilitate clinical and surgical management. It is important, however, to understand the limitations of TEE, and to always perform a comprehensive examination. In this report, the pitfalls of both the direct short-axis and the Doppler methods of assessing severity of aortic stenosis by TEE are presented.
I
CASE REPORT A 33-year-old female presented for cesarean delivery. Past medical history included the presence of a bicuspid aortic valve diagnosed at 2 years of age. A recent transthoracic echocardiogram (TTE) had revealed left ventricular (LV) hypertrophy, normal LV ejection fraction, and a stenotic, noncalcific bicuspid aortic valve with a Doppler-estimated peak flow velocity of 4.1 m/s (Fig 1). The derived peak and mean pressure gradients were 67 mmHg and 47 mmHg, respectively. Moderate aortic insufficiency and a dilated ascending aorta (diameter, 4.5 cm) were also noted. The cesarean section was performed under general anesthesia. Intraoperative TEE was used as an adjunct to routine monitoring by the anesthesia care team. After induction of anesthesia, a multiplane 5.0-MHz TEE probe (Sonos OR System, Hewlett Packard, Andover, MA) was placed without difficulty. A comprehensive TEE examination was performed to include a systematic evaluation of the aortic valve, which had a bicuspid morphology without calcific changes. 1,2 In contrast to the ambulatory TEE findings, aortic valve area obtained by direct short-axis planimetry appeared to be within normal limits (Fig 2). Doppler-estimated flow velocities from a transgastric approach also appeared to be within normal limits. Additional TEE findings included ascending aortic dilatation qdiameter, 4.3 cm) and moderate aortic valvular insufficiency.
calcific aortic stenosis requiring aortic valve replacement) The valves may be unicommissural, acommissural unicuspid, or, most commonly, bicuspid with two distinct leaflets and commissures. 4 Estimation of the severity of stenosis is most often determined by (1) direct short-axis measurement of the aortic valve area and (2) Doppler estimates of transvalvular gradients and valve area. 4 Measurement of the maximum, long-axis aortic cusp separation and qualitative assessment of leaflets motion may also be used to estimate severity of stenosis. This case highlights the pitfalls of both the direct short-axis and the Doppler methods of assessing severity of aortic stenosis by TEE, and the beneficial effects of a comprehensive, routine TEE examination on the diagnostic process. Reported success rates for short-axis planimetry of the true orifice of the aortic valve range from 13% to 85%. 5-8 One suggested reason for a low success rate is the imaging constraint imposed by supero-inferior motion of the aortic valve in and out of the imaging plane during the cardiac cycle. Further, systolic doming of the leaflets would be expected to compound the technical difficulties involved in obtaining valid short-axis measurements by furnishing the potential for the beam of interrogation to transect the leaflets before the actual stenotic valve orifice. Such a situation would provide an image of an apparently normal orifice (Fig 2). However, the true degree of stenosis was readily evident with long-axis imaging (Fig 3), Systolic doming of the leaflets, with overshoot of leaflet tissue
DISCUSSION Congenital aortic stenosis accounts for approximately 6.1% of all congenital heart disease, and is the leading cause of From the Departments of Anesthesiology and Diagnostic Radiology, Yale University School of Medicine, New Haven, CT. Address reprint requests to Manuel L. Fontes, MD, Department of Anesthesiology, Yale University School of Medicine, 333 Cedar St, PO Box 208051, New Haven, CT06520-8051. Copyright © 1998 by W.B. Saunders Company 1053-0770/98/1201-0010503.00/0 Key words: bicuspid aortic stenosis, TEE, valve area assessment, doming effect, planimetry
58
0.0
m/s 4.0 Fig 1. Preoperative transthoracic continuous wave Doppler flow study of the aortic valve. Turbulent blood flow through the stenotic valve produced a peak flow velocity of 4.1 m/s, corresponding to a peak and mean pressure gradient of 67 mmHg and 47 mmHg, respectively.
Journal o f Cardiothoracic and Vascular Anesthesia,
Vo112,No 1 (February),1998:pp 58-60
BICUSPID NONCALCIFIC AORTIC STENOSIS
59
Fig 2. Intraoperative transesophageal short-axis imaging of the aortic valve, The valve area is estimated at 3.2 cm2 by planimetry. Multiple short-axis attempts with a multiplane probe failed to show a stenotic aortic valve. On the right is a line drawing of the short-axis image of the bicuspid aortic valve. Abbreviations: LA, left atrium; RA, right atrium; TV, tricuspid valve; RV, right ventricle; RVOT, right ventricular outflow tract; AV, aortic valve.
well beyond the annulus, combined with the mobility of the aortic root associated with the hyperdynamic state classically associated with pregnancy and delivery, prevented localization of the true orifice. The inability to obtain short-axis :images of the ~ue orifice could have led to an error in diagnosis. Doppler methods for estimating the severity of aortic stenosis have been shown to correlate well with gradients derived from hemodynamic measurements. 9-12The Doppler-derived estimate of valve area is based on the concept that flow velocity through a stenotic valve must increase to maintain the flow volume constant across the valve. To precisely determine aortic valve gradients by the Doppler method, the peak instantaneous velocities within the stenotic jet must be recorded. Accuracy of this method, however, is dependent on signal sensitivity, angle of interrogation, and technical expertise. 7 With 'FEE, the transgastric long-axis view is typically used to measure aortic
180 °
valve flow velocities. Although this view provides an ultrasonic beam orientation that is frequently parallel to flow, the signal/ noise ratio is diminished because the jet lies in the far field of the transducer. Furthermore, TTE maneuvers to improve the signal/noise ratio, such as recording from the closest possible window or using a small dedicated continuous wave transducer, are not possible with TEE. The intraoperative TEE Doppler-derived measurements in this patient were underestimated, not only by the decreased signal/noise ratio, but also by the angle of interrogation relative to the blood flow. Although the transgastric view typically provides the best orientation, in this patient the interrogating beam intersected the jet at an angle -->30° . Unlike the flow velocity profiles obtained by TTE (Fig 1), the intraoperative flow velocity profiles showed a weak signal with a low peak
J
Fig 3. Transesophageal long-axis view of the aortic valve. Top left. In this view, a very small opening at the tip of the aortic valve depicts the severity of stenosis. Also, note the doming effect produced by the noncalcific and redundant leaflets during systole. Top right. A schematic drawing of the two-dimensional image to show overshoot of the leaflet tissues beyond the annulus. Bottom. Drawings a, b, and c represent sequential cross sections through the domed leaflets, showing different valve areas depending on the imaging plane. Rapid supero-inferior motion of the leaflets in and out of the imaging plane complicated identification of the stenotic orifice. Abbreviations: LA, left atrium; MV, mitral valve; LV, left ventricle; LVOT, left ventricular outflow tract; AO, aorta; TV, tricuspid valve; RA, right atrium; RVOT, right ventricular outflow tract; AV, aortic valve.
60
FONTES ET AL
velocity. A signal of greater intensity and velocity could not be obtained by TEE. This case also serves to illustrate the need to perform a complete TEE examination on a routine basis, not only to develop the technical expertise of TEE, but also to recognize the echocardiographic findings that are suggestive of a disease process. Acquiring a transgastric long-axis view and, in particular, recording the clearest Doppler flow velocity profile with the interrogating beam aligned parallel to blood flow requires experience and skill. The correlation between Doppler and catheter mean gradients has been shown to improve as the number of patients studied increases. 4 The anesthesiologist's ability to consistently obtain a clear Doppler signal will improve only if the Doppler measurements are attempted as a routine part of every intraoperative TEE examination. Although it is tempting, on the basis of these intraoperative findings of a normal planimetered orifice and low peak velocity, to suggest that aortic stenosis was not present in this patient, three other echocardiographic findings were characteristic of significant stenosis. The "Prussian helmet-like" systolic dora-
ing seen in the long-axis view (Fig 3) is a classic finding in aortic stenosis. 13Additionally, the diagnosis of ascending aortic dilatation (poststenotic dilation) and left ventricular hypertrophy points to the presence of long-standing aortic stenosis. ~4 Again, a TEE examination limited simply to the evaluation of planimetered area and transvalvular gradients would not have provided the clues that corroborated the presence of severe stenosis. In summary, anesthesiologists are frequently called upon to confirm or to make echocardiographic diagnoses in the operating room. A thorough understanding of the limitations of TEE will make this task easier. The intraoperative diagnosis of aortic stenosis can be made with confidence only when the true orifice is planimetered or when a clear Doppler velocity profile is recorded. When planimetry or Doppler measurements are inconclusive, technical expertise is necessary to recognize the coexistent echocardiographic findings. Such experience and skill in TEE can be obtained only by the routine performance of a comprehensive examination.
REFERENCES
1. Seward JB, Khandheria BK, Freeman WK, et al: Multiplane transesophageal echocardiography: Image orientation, examination technique, anatomy correlation, and clinical application. Mayo Clin Proc 68:523-551, 1993 2. GoldsteinAS, Mintz SG, Lindsay J: Comprehensive evaluation by echocardiography and transesophageal echocardiography. J Am Soc Echocardiogr 6:634-659, 1993 3. Roberts WC: The congenitally bicuspid aortic valve. A study of 85 autopsy cases. Am J Cardio126:72-83, 1970 4. Kirklin JW, Barratt-Boyes GB, Blackstone EH, et al: Acquired valvular heart disease, in Kirklin JW, Barratt-Boyes GB (eds): Cardiac Surgery. New York, NY, Churchill Livingstone, 1993, p 493-494 5. Hoffman R, Flachskampf, Hanrath P: Planimetry of orifice area in aortic stenosis using multiplane transesophageal echocardiography. J Am Coll Cardio122:529-534, 1993 6. Stoddard MF, Arce J, Liddell NE, et al: Two-dimensional transesophageal echocardiographic determination of aortic valve area in adults with aortic stenosis. Am Heart 22:1415-1422, 1991 7. Weyman AE, Griffin BP: Left ventricular outflow tract: The aortic valve, aorta, and subvalvular outflow tract, in Weyman AE (ed): Principles and Practice of Echocardiography. Philadelphia, PA, Lea & Febiger, 1994, pp 511-520 8. Leo LP: Determination of aortic valve area by cross-sectional
echocardiography in assessing the severity of valvular aortic stenosis. Chest 79:657-660, 1981 9. Smith MD, DawsonPL, ElionJL, et al: Correlation of continuous wave Doppler velocities with cardiac catheterization gradients: An experimental model of aortic stenosis. J Am Coll Cardiol 6:1306-1314, 1985 10. Currie PJ, Seward JB, Reeder GS, et al: Continuous-wave Doppler echocardiographic assessment of severity of calcific aortic stenosis: A simultaneous Doppler-catheter correlative study in 100 adult patients. Circulation 71:1162-1169, 1985 11. Seitz WS, McIlroy MB, Kline H, et al: Echocardiography application of the Gorlin formula for assessment of aortic stenosis: Correlation with cardiac catheterization in pediatric patients. Am Heart J 111:1118-1122, 1986 12. Skjaerpe T, Hegrenaes L, Hatle L: Noninvasive estimation of valve area in patients with stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 72:810-818, 1985 13. Zema MJ, Caccavano M: Two-dimensional echocardiographic assessment of aortic valve morphology: Feasibility of bicuspid valve detection. Br Heart J 48:428-433, 1982 14. Kosturakis D, Allen HD, Goldberg SJ, et al: Noninvasive quantification of stenotic semilunar valve areas by Doppler echocardiography. JAm Coll Cardiol 3:1256-1262, 1984
Bicuspid Noncalcific Aortic Stenosis: Diagnostic Limitations of Intraoperative Transesophageal Echocardiography Manuel L. Fontes, MD, Joseph Mathew, MD, Kevin Johnson, MD, and Terence Rafferty, MD NTRAOPERATIVE transesophageal echocardiography (TEE) provides both qualitative and quantitative information about valvular anatomy and function that can facilitate clinical and surgical management. It is important, however, to understand the limitations of TEE, and to always perform a comprehensive examination. In this report, the pitfalls of both the direct short-axis and the Doppler methods of assessing severity of aortic stenosis by TEE are presented.
I
CASE REPORT A 33-year-old female presented for cesarean delivery. Past medical history included the presence of a bicuspid aortic valve diagnosed at 2 years of age. A recent transthoracic echocardiogram (TTE) had revealed left ventricular (LV) hypertrophy, normal LV ejection fraction, and a stenotic, noncalcific bicuspid aortic valve with a Doppler-estimated peak flow velocity of 4.1 m/s (Fig 1). The derived peak and mean pressure gradients were 67 mmHg and 47 mmHg, respectively. Moderate aortic insufficiency and a dilated ascending aorta (diameter, 4.5 cm) were also noted. The cesarean section was performed under general anesthesia. Intraoperative TEE was used as an adjunct to routine monitoring by the anesthesia care team. After induction of anesthesia, a multiplane 5.0-MHz TEE probe (Sonos OR System, Hewlett Packard, Andover, MA) was placed without difficulty. A comprehensive TEE examination was performed to include a systematic evaluation of the aortic valve, which had a bicuspid morphology without calcific changes. 1,2 In contrast to the ambulatory TEE findings, aortic valve area obtained by direct short-axis planimetry appeared to be within normal limits (Fig 2). Doppler-estimated flow velocities from a transgastric approach also appeared to be within normal limits. Additional TEE findings included ascending aortic dilatation qdiameter, 4.3 cm) and moderate aortic valvular insufficiency.
calcific aortic stenosis requiring aortic valve replacement) The valves may be unicommissural, acommissural unicuspid, or, most commonly, bicuspid with two distinct leaflets and commissures. 4 Estimation of the severity of stenosis is most often determined by (1) direct short-axis measurement of the aortic valve area and (2) Doppler estimates of transvalvular gradients and valve area. 4 Measurement of the maximum, long-axis aortic cusp separation and qualitative assessment of leaflets motion may also be used to estimate severity of stenosis. This case highlights the pitfalls of both the direct short-axis and the Doppler methods of assessing severity of aortic stenosis by TEE, and the beneficial effects of a comprehensive, routine TEE examination on the diagnostic process. Reported success rates for short-axis planimetry of the true orifice of the aortic valve range from 13% to 85%. 5-8 One suggested reason for a low success rate is the imaging constraint imposed by supero-inferior motion of the aortic valve in and out of the imaging plane during the cardiac cycle. Further, systolic doming of the leaflets would be expected to compound the technical difficulties involved in obtaining valid short-axis measurements by furnishing the potential for the beam of interrogation to transect the leaflets before the actual stenotic valve orifice. Such a situation would provide an image of an apparently normal orifice (Fig 2). However, the true degree of stenosis was readily evident with long-axis imaging (Fig 3), Systolic doming of the leaflets, with overshoot of leaflet tissue
DISCUSSION Congenital aortic stenosis accounts for approximately 6.1% of all congenital heart disease, and is the leading cause of From the Departments of Anesthesiology and Diagnostic Radiology, Yale University School of Medicine, New Haven, CT. Address reprint requests to Manuel L. Fontes, MD, Department of Anesthesiology, Yale University School of Medicine, 333 Cedar St, PO Box 208051, New Haven, CT06520-8051. Copyright © 1998 by W.B. Saunders Company 1053-0770/98/1201-0010503.00/0 Key words: bicuspid aortic stenosis, TEE, valve area assessment, doming effect, planimetry
58
0.0
m/s 4.0 Fig 1. Preoperative transthoracic continuous wave Doppler flow study of the aortic valve. Turbulent blood flow through the stenotic valve produced a peak flow velocity of 4.1 m/s, corresponding to a peak and mean pressure gradient of 67 mmHg and 47 mmHg, respectively.
Journal o f Cardiothoracic and Vascular Anesthesia,
Vo112,No 1 (February),1998:pp 58-60
BICUSPID NONCALCIFIC AORTIC STENOSIS
59
Fig 2. Intraoperative transesophageal short-axis imaging of the aortic valve, The valve area is estimated at 3.2 cm2 by planimetry. Multiple short-axis attempts with a multiplane probe failed to show a stenotic aortic valve. On the right is a line drawing of the short-axis image of the bicuspid aortic valve. Abbreviations: LA, left atrium; RA, right atrium; TV, tricuspid valve; RV, right ventricle; RVOT, right ventricular outflow tract; AV, aortic valve.
well beyond the annulus, combined with the mobility of the aortic root associated with the hyperdynamic state classically associated with pregnancy and delivery, prevented localization of the true orifice. The inability to obtain short-axis :images of the ~ue orifice could have led to an error in diagnosis. Doppler methods for estimating the severity of aortic stenosis have been shown to correlate well with gradients derived from hemodynamic measurements. 9-12The Doppler-derived estimate of valve area is based on the concept that flow velocity through a stenotic valve must increase to maintain the flow volume constant across the valve. To precisely determine aortic valve gradients by the Doppler method, the peak instantaneous velocities within the stenotic jet must be recorded. Accuracy of this method, however, is dependent on signal sensitivity, angle of interrogation, and technical expertise. 7 With 'FEE, the transgastric long-axis view is typically used to measure aortic
180 °
valve flow velocities. Although this view provides an ultrasonic beam orientation that is frequently parallel to flow, the signal/ noise ratio is diminished because the jet lies in the far field of the transducer. Furthermore, TTE maneuvers to improve the signal/noise ratio, such as recording from the closest possible window or using a small dedicated continuous wave transducer, are not possible with TEE. The intraoperative TEE Doppler-derived measurements in this patient were underestimated, not only by the decreased signal/noise ratio, but also by the angle of interrogation relative to the blood flow. Although the transgastric view typically provides the best orientation, in this patient the interrogating beam intersected the jet at an angle -->30° . Unlike the flow velocity profiles obtained by TTE (Fig 1), the intraoperative flow velocity profiles showed a weak signal with a low peak
J
Fig 3. Transesophageal long-axis view of the aortic valve. Top left. In this view, a very small opening at the tip of the aortic valve depicts the severity of stenosis. Also, note the doming effect produced by the noncalcific and redundant leaflets during systole. Top right. A schematic drawing of the two-dimensional image to show overshoot of the leaflet tissues beyond the annulus. Bottom. Drawings a, b, and c represent sequential cross sections through the domed leaflets, showing different valve areas depending on the imaging plane. Rapid supero-inferior motion of the leaflets in and out of the imaging plane complicated identification of the stenotic orifice. Abbreviations: LA, left atrium; MV, mitral valve; LV, left ventricle; LVOT, left ventricular outflow tract; AO, aorta; TV, tricuspid valve; RA, right atrium; RVOT, right ventricular outflow tract; AV, aortic valve.
60
FONTES ET AL
velocity. A signal of greater intensity and velocity could not be obtained by TEE. This case also serves to illustrate the need to perform a complete TEE examination on a routine basis, not only to develop the technical expertise of TEE, but also to recognize the echocardiographic findings that are suggestive of a disease process. Acquiring a transgastric long-axis view and, in particular, recording the clearest Doppler flow velocity profile with the interrogating beam aligned parallel to blood flow requires experience and skill. The correlation between Doppler and catheter mean gradients has been shown to improve as the number of patients studied increases. 4 The anesthesiologist's ability to consistently obtain a clear Doppler signal will improve only if the Doppler measurements are attempted as a routine part of every intraoperative TEE examination. Although it is tempting, on the basis of these intraoperative findings of a normal planimetered orifice and low peak velocity, to suggest that aortic stenosis was not present in this patient, three other echocardiographic findings were characteristic of significant stenosis. The "Prussian helmet-like" systolic dora-
ing seen in the long-axis view (Fig 3) is a classic finding in aortic stenosis. 13Additionally, the diagnosis of ascending aortic dilatation (poststenotic dilation) and left ventricular hypertrophy points to the presence of long-standing aortic stenosis. ~4 Again, a TEE examination limited simply to the evaluation of planimetered area and transvalvular gradients would not have provided the clues that corroborated the presence of severe stenosis. In summary, anesthesiologists are frequently called upon to confirm or to make echocardiographic diagnoses in the operating room. A thorough understanding of the limitations of TEE will make this task easier. The intraoperative diagnosis of aortic stenosis can be made with confidence only when the true orifice is planimetered or when a clear Doppler velocity profile is recorded. When planimetry or Doppler measurements are inconclusive, technical expertise is necessary to recognize the coexistent echocardiographic findings. Such experience and skill in TEE can be obtained only by the routine performance of a comprehensive examination.
REFERENCES
1. Seward JB, Khandheria BK, Freeman WK, et al: Multiplane transesophageal echocardiography: Image orientation, examination technique, anatomy correlation, and clinical application. Mayo Clin Proc 68:523-551, 1993 2. GoldsteinAS, Mintz SG, Lindsay J: Comprehensive evaluation by echocardiography and transesophageal echocardiography. J Am Soc Echocardiogr 6:634-659, 1993 3. Roberts WC: The congenitally bicuspid aortic valve. A study of 85 autopsy cases. Am J Cardio126:72-83, 1970 4. Kirklin JW, Barratt-Boyes GB, Blackstone EH, et al: Acquired valvular heart disease, in Kirklin JW, Barratt-Boyes GB (eds): Cardiac Surgery. New York, NY, Churchill Livingstone, 1993, p 493-494 5. Hoffman R, Flachskampf, Hanrath P: Planimetry of orifice area in aortic stenosis using multiplane transesophageal echocardiography. J Am Coll Cardio122:529-534, 1993 6. Stoddard MF, Arce J, Liddell NE, et al: Two-dimensional transesophageal echocardiographic determination of aortic valve area in adults with aortic stenosis. Am Heart 22:1415-1422, 1991 7. Weyman AE, Griffin BP: Left ventricular outflow tract: The aortic valve, aorta, and subvalvular outflow tract, in Weyman AE (ed): Principles and Practice of Echocardiography. Philadelphia, PA, Lea & Febiger, 1994, pp 511-520 8. Leo LP: Determination of aortic valve area by cross-sectional
echocardiography in assessing the severity of valvular aortic stenosis. Chest 79:657-660, 1981 9. Smith MD, DawsonPL, ElionJL, et al: Correlation of continuous wave Doppler velocities with cardiac catheterization gradients: An experimental model of aortic stenosis. J Am Coll Cardiol 6:1306-1314, 1985 10. Currie PJ, Seward JB, Reeder GS, et al: Continuous-wave Doppler echocardiographic assessment of severity of calcific aortic stenosis: A simultaneous Doppler-catheter correlative study in 100 adult patients. Circulation 71:1162-1169, 1985 11. Seitz WS, McIlroy MB, Kline H, et al: Echocardiography application of the Gorlin formula for assessment of aortic stenosis: Correlation with cardiac catheterization in pediatric patients. Am Heart J 111:1118-1122, 1986 12. Skjaerpe T, Hegrenaes L, Hatle L: Noninvasive estimation of valve area in patients with stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 72:810-818, 1985 13. Zema MJ, Caccavano M: Two-dimensional echocardiographic assessment of aortic valve morphology: Feasibility of bicuspid valve detection. Br Heart J 48:428-433, 1982 14. Kosturakis D, Allen HD, Goldberg SJ, et al: Noninvasive quantification of stenotic semilunar valve areas by Doppler echocardiography. JAm Coll Cardiol 3:1256-1262, 1984