The Role of Epicardial Echocardiography in the Measurement of Transvalvular Flow Velocities During Aortic Valve Replacement

The Role of Epicardial Echocardiography in the Measurement of Transvalvular Flow Velocities During Aortic Valve Replacement Ravi Taneja, FRCA,* Bert Quaghebeur, MD,* Larry W. Stitt, MSc,† Mackenzie A. Quantz, FRCSC,‡ Lin R. Guo, MD,‡ Bob Kiaii, FRCSC,‡ and Daniel T. Bainbridge, FRCPC* Objective: The purpose of this study was to compare transvalvular flow velocities obtained by transesophageal echocardiography and epicardial echocardiography (EE) during aortic valve replacement (AVR). Design: Prospective observational study. Setting: University hospital. Participants: Patients undergoing AVR for aortic stenosis. Interventions: After institutional review board approval, 17 patients undergoing AVR consented. Deep transgastric (deep TG LAX) and transgastric long-axis (TG LAX) views and epicardial aortic valve long-axis views (S8 probe) were obtained on a SONOS 5500 (Phillips Medical Systems, Bothell, WA) before and after AVR. Transvalvular flow velocity and velocity time integral (VTI) were recorded via each technique. Measurements were made offline by 2 independent reviewers. Agreement between measurements made by different views was evaluated by using Bland-Altman analysis. Measurements and Main Results: The epicardial probe was well tolerated. Quality images were obtained in all

patients with TEE and 30 of 34 studies via epicardial scanning. The mean bias for peak velocities derived through EE and deep TG LAX was 96.3 cm/s (95% confidence interval [CI], 51.1-141.4) before AVR and 58 cm/s (95% CI, 32.4-83.7) after AVR. The mean bias for peak velocities between EE and TG LAX was 70 cm/s (95% CI, 31.1-108.9) before and 84.7 cm/s (95% CI, 55.6-113.7) after AVR. Similar results were obtained for VTI. Conclusions: Peak transaortic valve velocities and VTI measured with epicardial echocardiography are higher in comparison to measurements via TEE in patients undergoing AVR. The precise role of epicardial echocardiography in the comprehensive echocardiographic examination of patients undergoing aortic valve replacement needs further evaluation. © 2009 Elsevier Inc. All rights reserved.

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provide measurement of more accurate flow velocities in comparison to TEE. Hence, the authors sought to compare transvalvular flow velocity measurements between TEE and EE in patients undergoing aortic valve replacement.

CHOCARDIOGRAPHIC ASSESSMENT of the aortic valve is important during aortic valve replacement (AVR),1-3 and intraoperative transesophageal echocardiography (TEE) is performed routinely to provide information about valvular anatomy and pathology. However, a TEE probe occasionally may be difficult or impossible to advance into the esophagus. TEE also may rarely be associated with complications or be contraindicated in a small proportion of patients.4,5 Image acquisition by TEE also may be difficult because a comprehensive TEE examination may be inadequate in about 20% of patients.6 According to recent guidelines by the Society of Cardiovascular Anesthesiologists and American Society of Echocardiography, competence in imaging modalities such as epicardial echocardiography (EE) may be an advantageous adjunct or substitute to TEE to facilitate a comprehensive echocardiographic examination during cardiac surgery.7,8 Limited literature exists with regards to the utility and accuracy of epicardial echocardiography.9,10 The authors hypothesized that the Doppler beam from the epicardial probe can have improved alignment with the blood flow through the aortic valve and, thus,

From the Departments of *Anesthesia and Perioperative Medicine, †Epidemiology and Biostatistics, and ‡Division of Cardiovascular and Thoracic Surgery, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada. Presented at the American Society of Anesthesiologists Meeting, San Francisco, CA, October 14, 2007. Address reprint requests to Ravi Taneja, MBBS, MD, FFARCSI, FRCA, Department of Anesthesia and Perioperative Medicine, London Health Sciences Centre, 339 Windermere Road, London, ON N6A 5A5, Canada. E-mail: [email protected] © 2009 Elsevier Inc. All rights reserved. 1053-0770/09/2303-0004$36.00/0 doi:10.1053/j.jvca.2009.01.007 292

KEY WORDS: transesophageal, epicardial, echocardiography, transvalvular velocities, aortic valve

METHODS After obtaining institutional review board approval, 17 patients with aortic stenosis scheduled for AVR were prospectively studied. Patients were excluded from the study if TEE was contraindicated, they were less than 18 years old, they could not give written consent, and they did not have a normal sinus rhythm either preoperatively or at the time of image acquisition. After induction of anesthesia, an Omniplane II TEE phased-array probe with a 4- to 7-MHz transducer (Phillips Medical Systems, Bothell, WA) was inserted into the esophagus. All images needed for clinical management were acquired on a SONOS 5500 (Phillips Medical Systems, Bothell, WA) as per standard guidelines.11 TEE and epicardial images for the study were acquired in close temporal proximity (within 5 minutes) to minimize the hemodynamic differences between image acquisitions. TEE images were acquired by study investigators with testamur status (a candidate who had passed the examination of special competence in perioperative TEE held by the National Board of Echocardiography) and more than 4 years of clinical experience as an attending anesthesiologist. The deep transgastric long-axis view (deep TG LAX) and the transgastric long-axis view (TG LAX) were acquired as per standard guidelines.11 The left ventricular outflow tract (LVOT), aortic valve, and ascending aorta were identified and the multiplane angle altered to optimize the image for further interrogation. Color Doppler was first used to identify flow through the aortic valve orifice and, after that, continuous-wave Doppler (CWD) was used to obtain transvalvular flow velocities through the aortic valve and LVOT (double-envelope technique)12,13 (Fig 1). Angle correction for improving alignment with blood flow was not used in any study. For EE, all images were acquired by 1 study investigator under the direct supervision of cardiac surgeons who have extensive experience in epiaortic scanning at the authors’ center. A second anesthesiologist holding testamur status was present during each EE

Journal of Cardiothoracic and Vascular Anesthesia, Vol 23, No 3 (June), 2009: pp 292-297

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Fig 1. TEE views for obtaining transvalvular flow velocities through the aortic valve. The deep TG LAX was obtained at a depth of 45 to 50 cm from the incisor with anteflexion of the TEE probe. The TG LAX was acquired at an angle at a depth of 40 to 45 cm. Doppler velocities for aortic valve and LVOT were then obtained. (Reprinted with permission.11)

study to operate the controls on the echo machine. An S8 probe (Phillips Medical Systems) was placed in a sterile sheath (Surgi Transducer cover; CIVCO, Kalona, IA) filled with normal saline and placed on the aortic root to obtain the aortic root view14 (the

epicardial aortic valve long-axis view7) (Fig 2). The ascending aorta, aortic valve, and LVOT were identified, and the ultrasound beam was directed toward the LVOT. CWD interrogation was performed as mentioned previously.

Fig 2. The epicardial aortic valve long-axis view is obtained by placing the probe on the aortic root with the ultrasound beam directed toward the LVOT. CWD from this view typically revealed a dense signal of blood flowing through the aortic valve with absence of LVOT flow velocities.

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Table 1. Correlation Coefficients, Bias and Limits of Agreement Between Peak Velocities Measured by EE (Aortic Valve Long-Axis View) and TEE (Deep TG LAX and TG LAX Views) Method 1 (Mean ⫾ Standard Deviation) (cm/s)

Method 2 (Mean ⫾ Standard Deviation) (cm/s)

Pre-AVR

EE (459.7 ⫾ 129.5)

Pre-AVR Pre-AVR

EE (455.3 ⫾ 127.3) Deep TG LAX (363.4 ⫾ 98.9) EE (337.6 ⫾ 81.1)

Deep TG LAX (363.4 ⫾ 98.9) TG LAX (385.4 ⫾ 111) TG LAX (382.8 ⫾ 113.6) Deep TG LAX (279.6 ⫾ 64.3) TG LAX (269 ⫾ 86.3) TG LAX (243.4 ⫾ 67.6)

Time

Post-AVR Post-AVR Post-AVR

EE (353.7 ⫾ 99.8) Deep TG LAX (270.6 ⫾ 71)

Bias (95% CI) (cm/s)

Lower Limit of Agreement (95% CI) (cm/s)

Upper limit of Agreement (95% CI) (cm/s)

0.72

96.3 (51.1-141.4)

⫺85.3 (⫺157.9 to ⫺12.6)

277.8 (205.1-350.4)

0.78 0.66

70.0 (31.1-108.9) ⫺19.3 (⫺63.3 to 24.6)

⫺91.4 (⫺154.3 to ⫺28.6) ⫺196.1 (⫺266.8 to ⫺125.4)

231.4 (168.5-294.3) 157.5 (86.7-288.2)

Correlation

0.84

58.0 (32.4-83.7)

⫺30.7 (⫺71.0 to 9.5)

146.8 (106.5-187.1)

0.85 0.88

84.7 (55.6-113.7) 27.2 (8.4-46.1)

⫺20.3 (⫺66.3 to 25.7) ⫺40.8 (⫺70.6 to ⫺11.0)

189.7 (143.7-235.7) 95.2 (65.4-125.0)

All images were saved on an optical disc. Images were analyzed offline on the SONOS 5500 independently by 2 reviewers (anesthesiologists, testamur status) with more than 4 years experience in TEE. Each reviewer was blinded to the results of the other. Transvalvular flow velocities, peak velocity, and velocity time integral (VTI) were obtained individually and averaged between the 2 observers for final analysis. Reviewers could not be blinded to the method of image acquisition (EE or TEE) when measuring Doppler velocities. Quantitative data are presented as mean ⫾ standard deviation. First, the linear relationship between the 2 observers was evaluated by using Pearson correlation coefficients, and the agreement between the 2 observers was evaluated by using the Bland-Altman analysis.15 Second, correlation coefficients were calculated between measurements made by EE and TEE. To further examine the agreement between the 2

techniques, Bland-Altman analysis was performed. Specifically, the 2 views obtained via TEE (deep TG LAX and TG LAX) were compared with the aortic valve long-axis view obtained via EE. Bias was calculated from paired averages of 2 techniques as the mean difference with 95% confidence intervals and limits of agreement defined as mean bias ⫾ 2 standard deviations. The authors considered the bias to be clinically significant if the transaortic velocities measured by TEE were different from EE by 5%. All statistical analyses were conducted by using SAS version 9.1 (SAS Institute Inc, Cary, NC). RESULTS

A total of 17 (10 male and 7 female) patients were evaluated pre- and post-AVR. The mean age was 69 ⫾ 8.6 years. AVR

Fig 3. Bland-Altman analysis to compare peak velocity measurements obtained by epicardial echocardiography and (A and B) deep TG LAX and (C and D) TG LAX views. The plots show mean bias and the limits of agreement.

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was performed in all patients as planned. Six of 17 patients received mechanical prosthetic valves. The sizes of replaced aortic valves ranged from 23 to 27 mm (24.3 ⫾ 1.4 mm). Four of 17 patients had coronary artery bypass graft surgery in addition to their valvular surgery. EE was well tolerated by all patients. It was not associated with any acute (hemodynamic) complications associated with probe manipulation. There were no mediastinal or deep tissue infections in any of the study patients that could have been attributed to EE probe placement. Complete TEE-derived measurements were possible in most (32/34) studies, whereas LVOT VTI envelopes could be obtained in only 4 of 34 studies through the epicardial route. There was a strong association between the analysis of images by the 2 reviewers, with correlation coefficients ranging from 0.85 to 0.97 for VTI and 0.97 to 0.99 for peak velocity (p ⬍ 0.001). Analysis of images also showed good agreement between the reviewers by the BlandAltman analysis, with mean bias ranging from ⫺4.6 cm (limits of agreement ⫺23.0 and 13.7 cm) to 4.5 cm (limits of agreement ⫺20.2 and 29.2 cm) for VTI. The mean bias between reviewers for peak velocity ranged from ⫺2.0 cm/s (limits of agreement ⫺28.0 and 24 cm/s) to18.4 cm/s (limits of agreement ⫺34.1 and 70.8 cm/s). Peak transvalvular velocities measured by EE and TEE are shown in Table 1. Correlation coefficients for measurements made via EE and TEE ranged from 0.72 to 0.85. Mean bias and limits of agreement along with the 95% confidence intervals subsequently were calculated between EE and the two views obtained via TEE. The bias between EE and deep

295

TG LAX for peak velocities across the aortic valve was 96.3 cm/s (95% confidence interval [CI], 51.1-141.4; limits of agreement ⫺85.3 and 277.8 cm/s) before AVR (Fig 3A). Similarly, after AVR, the bias was 58 cm/s (95% CI, 32.483.7; limits of agreement ⫺30.7 and 146.8 cm/s) (Fig 3B). The mean bias between EE and TG LAX peak velocities was 70 cm/s (95% CI, 31.1-108.9; limits of agreement ⫺91.4 and 231.4 cm/s) before and 84.7 cm/s (95% CI, 55.6-113.7; limits of agreement ⫺20.3 and 189.7 cm/s) after AVR (Fig 3C and D). Similar results were obtained for VTI both before and after AVR (Fig 4 and Table 2). The differences between TG LAX and deep TG LAX peak velocities and VTI were small both pre- and post-AVR, with CIs suggesting that the 2 techniques were similar. DISCUSSION

Facilities for EE are often available in the cardiac operating room but remain underused. Intraoperative epicardial scanning has been used in the past to assess the surgical repair of congenital heart defects16,17 and validate the degree of aortic incompetence as measured by TEE.18 In fact, it has been proposed that intraoperative transesophageal and epicardial echocardiography are complementary rather than alternative techniques.19 Recently, the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists have established guidelines for performing epicardial echocardiography during cardiac surgery.7 However,

Fig 4. Bland-Altman analysis to compare VTI obtained by epicardial echocardiography and (A and B) deep TG LAX and (C and D) TG LAX views. The plots show mean bias and the limits of agreement.

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Table 2. Correlation Coefficients, Bias and Limits of Agreement Between VTI Measured by EE (Aortic Valve Long-Axis View) and TEE (Deep TG LAX and TG LAX Views) Method 1 (Mean ⫾ Standard Deviation) (cm)

Method 2 (Mean ⫾ Standard Deviation) (cm)

Pre-AVR

EE (114.7 ⫾ 34.3)

Pre-AVR Pre-AVR

EE (114.7 ⫾ 34.3) Deep TG LAX (83.7 ⫾ 21.8) EE (59.6 ⫾ 13.9)

Deep TG LAX (83.7 ⫾ 21.8) TG LAX (90.6 ⫾ 29) TG LAX (90.6 ⫾ 29)

Time

Post-AVR Post-AVR Post-AVR

EE (59.6 ⫾ 13.9) Deep TG LAX (41.9 ⫾ 10)

Correlation (p Value)

Deep TG LAX (41.9 ⫾ 10) TG LAX (40 ⫾ 14) TG LAX (40 ⫾ 14)

the information obtained from EE has not been compared systematically with TEE, and it is unknown which of these modalities can provide a more accurate assessment of cardiac structure and function. The present results show that there was a lack of agreement between the transaortic flow velocities measured by EE and TEE. Velocities were found to be higher when evaluated by EE as compared with TEE. Because Doppler-derived measurements cannot be overestimated, the authors conclude that EE provides a more accurate measurement of transvalvular flow velocities across the aortic valve during cardiac surgery. Based on this study, the clinician should bear in mind that TEE, compared with EE, underestimates transaortic flow velocities during aortic valve surgery. These results are similar to those of Frenk et al9 who proposed that EE was a good alternative to TEE when they could not insert an esophageal probe in their patient. Similarly, Edrich et al10 also reported a case in which they used epiaortic echocardiography successfully to resolve a discrepancy between peak pressure gradients obtained through transthoracic and transesophageal echocardiography.10 The authors believe that despite limited operator experience, placement of the epicardial probe generally facilitates a more parallel alignment of a Doppler ultrasound beam with the blood flow, thus providing higher transvalvular flow velocities. However, it is also possible that the CWD signal from a distant aortic valve during TEE is attenuated, leading to the underestimation of aortic valve flow velocities. LVOT VTI envelopes only could be acquired in 4 of 34 studies through EE. Although epicardial studies were performed by experienced anesthesiologists taking part in the study, operator inexperience might have contributed to the poor visualization of LVOT. Another potential cause of the inability to image a double envelope was the very strong CWD signal received with EE imaging of the aortic valve. The strength of the signal at the level of the aortic valve may have obscured velocities from the LVOT, thus making measurement impossible. Finally, in epicardial imaging, the LVOT lies on the opposite side of the aortic valve in relation to the probe and the echocardiography signal was likely further attenuated. LVOT VTI could have been recorded through pulse-wave Doppler in

Bias (95% CI) (cm)

Lower Limit of Agreement (95% CI) (cm)

Upper Limit of Agreement (95% CI) (cm)

0.80

30.9 (19.9-41.9)

⫺13.3 (⫺30.9 to 4.4)

75.1 (57.4-92.8)

0.87 0.81

24.2 (16.1-32.3) ⫺6.1 (⫺14.9 to 2.6)

⫺9.6 (⫺22.7 to 3.6) ⫺41.3 (⫺55.3 to ⫺27.2)

58.0 (44.8-71.1) 29.0 (14.9-43.0)

0.78

14.9 (9.5-20.4)

⫺4.3 (⫺13.0 to 4.4)

34.0 (25.3-42.7)

0.86 0.73

19.9 (14.9-24.8) 4.7 (0.4-8.9)

1.9 (⫺5.9 to 9.8) ⫺10.6 (⫺17.3 to ⫺3.9)

37.8 (29.9-45.7) 19.9 (13.2-26.6)

these patients, and, therefore, it is possible that pulse-wave Doppler may be necessary at the LVOT level to calculate the aortic valve area through epicardial echocardiography. Nevertheless, the inability to obtain LVOT VTI envelopes through EE may limit its clinical utility. The present study has limitations. The authors could not blind the observers completely to the method of image acquisition. Probe placement for epicardial and transesophageal routes provided blood flows and Doppler ultrasound beams in opposite directions that were easily apparent. Furthermore, the measurement of transvalvular velocities through EE was difficult in patients who had undergone combined aortic valve and coronary artery bypass graft procedures because the EE probe had to be placed in close proximity to the location of the proximal anastomoses. On the other hand, the main strength of the present study was the offline analysis by 2 independent observers and good agreement between their measurements. Some of the peak velocities obtained after AVR in this study remained considerably elevated. In the authors’ experience, velocities of this magnitude are not unusual and are likely related to 2 factors. First, all valve prostheses result in residual stenosis, albeit usually mild. Second, the use of inotropes to wean from CPB usually results in normal-to-high cardiac indices (which is likely also related to the relative anemia after CPB), thus generating the high transvalvular flow velocities. It also is not known if such high velocities necessarily relate to high peak gradients in this setting. Levy et al20 have reported that intraoperative flow velocities immediately after AVR do not correlate with those on follow-up transthoracic echocardiography.20 The authors conclude that flow velocity measurements across the aortic valve can be acquired via epicardial echocardiography. Peak velocity and VTI obtained through this technique are higher and thus more accurate in comparison to those measured by TEE. However, the inability to acquire LVOT VTI envelopes through CWD may limit the clinical utility of EE. The precise role of EE in the comprehensive echocardiographic examination of patients undergoing cardiac surgery needs further evaluation.

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REFERENCES 1. Rosenhek R, Binder T, Maurer G: Intraoperative transesophageal echocardiography in valve replacement surgery. Echocardiography 19: 701-707, 2002 2. Nowrangi SK, Connolly HM, Freeman WK, et al: Impact of intraoperative transesophageal echocardiography among patients undergoing aortic valve replacement for aortic stenosis. J Am Soc Echocardiogr 14:863-866, 2001 3. Currie PJ, Stewart WJ: Intraoperative echocardiography for surgical repair of the aortic valve and left ventricular outflow tract. Echocardiography 7:273-288, 1990 4. Kallmeyer IJ, Collard CD, Fox JA, et al: The safety of intraoperative transesophageal echocardiography: A case series of 7200 cardiac surgical patients. Anesth Analg 92:1126-1130, 2001 5. Lennon MJ, Gibbs NM, Weightman WM, et al: Transesophageal echocardiography-related gastrointestinal complications in cardiac surgical patients. J Cardiothorac Vasc Anesth 19:141-145, 2005 6. Miller JP, Lambert AS, Shapiro WA, et al: The adequacy of basic intraoperative transesophageal echocardiography performed by experienced anesthesiologists. Anesth Analg 92:1103-1110, 2001 7. Reeves ST, Glas KE, Eltzschig H, et al: Guidelines for performing a comprehensive epicardial echocardiography examination: recommendations of the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. Anesth Analg 105:22-28, 2007 8. Glas KE, Swaminathan M, Reeves ST, et al: Guidelines for the performance of a comprehensive intraoperative epiaortic ultrasonographic examination: recommendations of the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists: Endorsed by the Society of Thoracic Surgeons. J Am Soc Echocardiogr 20:1227-1235, 2007 9. Frenk VE, Shernan SK, Eltzschig HK: Epicardial echocardiography: Diagnostic utility for evaluating aortic valve disease during coronary surgery. J Clin Anesth 15:271-274, 2003 10. Edrich T, Shernan SK, Smith B, et al: Usefulness of intraoperative epiaortic echocardiography to resolve discrepancy between transthoracic and transesophageal measurements of aortic valve gradient—A case report. Can J Anaesth 50:293-296, 2003 11. Shanewise JS, Cheung AT, Aronson S, et al: ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal

echocardiography examination: Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesth Analg 89:870-884, 1999 12. Maslow AD, Haering JM, Heindel S, et al: An evaluation of prosthetic aortic valves using transesophageal echocardiography: The double-envelope technique. Anesth Analg 91:509-516, 2000 13. Maslow AD, Mashikian J, Haering JM, et al: Transesophageal echocardiographic evaluation of native aortic valve area: Utility of the double-envelope technique. J Cardiothorac Vasc Anesth 15:293-299, 2001 14. Eltzschig HK, Kallmeyer IJ, Mihaljevic T, et al: A practical approach to a comprehensive epicardial and epiaortic echocardiographic examination. J Cardiothorac Vasc Anesth 17:422-429, 2003 15. Bland JM, Altman DG: Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1:307-310, 1986 16. Muhiudeen IA, Roberson DA, Silverman NH, et al: Intraoperative echocardiography in infants and children with congenital cardiac shunt lesions: transesophageal versus epicardial echocardiography. J Am Coll Cardiol 16:1687-1695, 1990 17. Sreeram N, Kaulitz R, Stumper OF, et al: Comparative roles of intraoperative epicardial and early postoperative transthoracic echocardiography in the assessment of surgical repair of congenital heart defects. J Am Coll Cardiol 16:913-920, 1990 18. Willett DL, Hall SA, Jessen ME, et al: Assessment of aortic regurgitation by transesophageal color Doppler imaging of the vena contracta: Validation against an intraoperative aortic flow probe. J Am Coll Cardiol 37:1450-1455, 2001 19. Stumper O, Kaulitz R, Sreeram N, et al: Intraoperative transesophageal versus epicardial ultrasound in surgery for congenital heart disease. J Am Soc Echocardiogr 3:392-401, 1990 20. Levy L, Martin JL, Deeb GM, et al: Intraoperative transesophageal echocardiography after aortic valve replacement does not predict subsequent transvalvular gradients. J Heart Valve Dis 13:881-886, 2004