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Dyspnea Declare Yourself! Decoding Doppler

Published:March 18, 2022DOI:https://doi.org/10.1053/j.jvca.2022.03.014
      AN APPRECIATION of the utility of echocardiographic Doppler spectral profile analysis in diagnosing cardiac pathology and guiding surgical intervention more than justifies an investment in obtaining proficiency in these skills. Given the relatively low incidence of significant complications associated with transesophageal echocardiographic examination, the facile use of both spectral and color Doppler principles to diagnose unusual pathology is essential. Doppler modalities are used to characterize blood flow, pressure gradients, chamber dimensions, and other anatomic and physiological parameters. The authors present a case in which several Doppler principles were used to evaluate and diagnose the etiology of dyspnea and a high aortic valve gradient.

      Key Words

      The clinical application of Doppler ultrasound in cardiac patients dates back to the 1950s when Shigeo Satomura recorded Doppler signals simultaneously with electrocardiography and phonocardiography to investigate myocardial and valvular motion.
      • Satomura S.
      Ultrasonic Doppler method for inspection of cardiac functions.
      Over the subsequent 2 decades, Doppler device output improved from audio to spectral and then pulsed Doppler.
      • Franklin DL
      • Baker DW
      • Ellis RM
      • et al.
      A pulsed ultrasonic flowmeter.
      ,
      • Peronneau PA
      • Leger F.
      Doppler ultrasonic pulsed blood flow meter.
      The latter 2 provided graphical real-time data for the evaluation of flow and have since become remarkably sophisticated.
      • Lai WW
      • Mertens LL
      • Cohen MS
      • et al.
      Echocardiography in pediatric and congenital heart disease.
      ,
      • Otto CM.
      Textbook of clinical echocardiography.
      Curry and White were credited with early use of color in Doppler assessment of the carotid artery in 1978.
      • Curry GR
      • White DN.
      Color coded ultrasonic differential velocity scanner (EchoFLOW) ultrasound.
      Later on, color maps were developed by multiple teams on different continents. Although the convention for color representation varies, the international community agrees on the essential value of color Doppler and other Doppler modalities in cardiac evaluation.
      • Stevenson JG.
      The development of color Doppler echocardiography: Innovation and collaboration.
      • Ludomirsky A
      • Tani L
      • Murphy DJ
      • et al.
      Usefulness of color-flow Doppler in diagnosing and in differentiating supracristal ventricular septal defect from right ventricular outflow tract obstruction.
      • Nishimura RA
      • Tajik AJ.
      Quantitative hemodynamics by Doppler echocardiography: A noninvasive alternative to cardiac catheterization.
      • Anavekar NS
      • Oh JK.
      Doppler echocardiography: A contemporary review.
      There is a myriad of potential complications related to cardiac valvular surgery. Physicians proficient in the echocardiographic evaluation of structural and physiological aberrations use Doppler analysis to obtain data on pressure gradients, the direction and magnitude of shunts, and valve dimensions, among other findings.

      Clinical Case

      A 56-year-old (weight 77 kg; height 177 cm) previously healthy man presented initially in acute congestive heart failure with fever. He was diagnosed with Group B Streptococcus bacteremia and aortic valve endocarditis complicated by severe aortic valve regurgitation and aortic root abscess, for which he underwent open mechanical aortic valve replacement. Postoperatively the patient had normal ventricular function with an end-diastolic diameter of 6.3 cm. The peak velocity and mean gradient were 2.7 m/s and 18 mmHg. The other valves were normal with no significant regurgitation. Despite timely recovery and discharge home on antibiotics, he presented 1 month postoperatively with acute heart failure. Transthoracic echocardiogram demonstrated an increased end-diastolic diameter consistent with a borderline dilated left ventricle (LV). The ejection fraction was 70% to 75%, and there were no regional wall motion abnormalities. There was a new ‘wall-hugging’ jet in the left atrium (LA) on color Doppler (Fig 1; Video 1). The aortic valve peak velocity and mean gradients had both increased to 4.3 m/s and 56 mmHg (Fig 2). No abnormal aortic regurgitation suggestive of a paravalvular leak could be seen. Additional echocardiographic parameters were obtained in a comprehensive fashion to identify and characterize the hemodynamic impact of the pathology (Table 1).
      Fig 1
      Fig 1Transthoracic echocardiogram showing ‘Wall-Hugging’ Jet on color Doppler. (A) Apical 4-chamber view and (B) parasternal long-axis view.
      Fig 2
      Fig 2Spectral Doppler profiles of transvalvular aortic flow (A) after index surgery and (B) at re-presentation for heart failure.
      Table 1Relevant Echocardiographic Doppler Measurements
      ParameterValue
      RightTricuspid valve peak regurgitant velocity, m/s3.48
      Tricuspid valve peak gradient, mmHg40.2
      Hepatic vein flowsHolosystolic reversal of flow
      LeftAortic valve mean pressure gradient, mmHg56
      Left ventricular outflow tract peak velocity, m/s2.1
      Aortic valve peak velocity, m/s4.3
      Acceleration time, ms75
      Dimensionless index0.49
      Left ventricle end diastolic internal diameter, cm6.3
      Pulmonary vein flowsReversal of S wave
      E prime velocity, cm/s8
      Isovolumetric relaxation time, ms40

      E-Challenge

      Given the echocardiographic findings presented in Figures 1 and 2, Video 1, and Table 1, what additional pathology could explain the elevated gradient across the aortic valve prosthesis?

      Clinical Course

      The size 21 bileaflet tilting disc mechanical aortic valve appeared well-seated with normal disc function. Given the dimensionless index (DI) of 0.49 and acceleration time <100 ms, the elevated peak velocity and mean gradient across the aortic valve was likely flow-related rather than due to intrinsic valve dysfunction. There was also systolic pulmonary vein flow reversal and a shortened isovolumic relaxation time (Table 1) consistent with elevated LA pressure that in the context of a posteriorly directed jet might be interpreted as coexistent severe mitral regurgitation (MR). Consistent with these metrics suggesting elevated left atrial pressure, the pulmonary artery systolic pressure was severely elevated as measured using the tricuspid regurgitation jet. However, severe MR typically results in a reduction rather than an increase in the LV outflow tract (LVOT) stroke volume and transvalvular aortic peak velocities and gradients as were present in this patient.
      To solve this seemingly incongruent echocardiographic puzzle, a transesophageal echocardiogram was performed as the next step in the evaluation of the patient. On inspection of color Doppler and leaflet coaptation, the functional MR was reassessed as only mild to moderate in severity. However, an unusual color flow into the LA was observed to originate from either the LVOT or aortic root. Jet flow was confirmed throughout the cardiac cycle with color Doppler and continuous wave Doppler (CWD) (Fig 3). Comprehensive assessment ultimately revealed a perforation in the aorto-mitral curtain at the level of the aortic valve annulus (Fig 3). A final diagnosis of aortic root to LA fistula causing congestive heart failure was made, and the patient proceeded to the operating room for surgical intervention.
      Fig 3
      Fig 3(A) Pancyclic flow through fistula on continuous wave Doppler. (B) Discontinuity in aorto-mitral curtain (yellow arrow). (C) Flow from aortic root to left atrium on color Doppler.
      At surgery, the mechanical aortic valve was removed, and the aortic root to LA fistula was found at the expected location and resected, along with the necrotic annular portion of the anterior mitral valve leaflet. The anterior mitral valve leaflet and aorto-mitral curtain were reconstructed with bovine pericardium (Fig 4). The aortic valve was replaced with a new mechanical prosthesis. The patient recovered uneventfully and was discharged home 2 weeks later.
      Fig 4
      Fig 4Intraoperative images of surgical field before and after repair of defect.

      Discussion

      The key to this E-Challenge is that while the velocity and mean gradient across the aortic prosthesis were significantly elevated, the DI of 0.49 and acceleration time <100 ms suggested the presence of a high flow rate rather than prosthetic valve dysfunction.
      • Whitener GB
      • Shanahan PC
      • Wolf BJ
      • et al.
      Grading aortic valve stenosis with dimensionless index during pre-cardiopulmonary bypass transesophageal echocardiography: A comparison with transthoracic echocardiography.
      ,
      • Nanditha S
      • Malik V
      • Hasija S
      • et al.
      Comparison of grading of aortic stenosis between transthoracic and transesophageal echocardiography in adult patients undergoing elective aortic valve replacement surgeries: A prospective observational study.
      The data presented in the initial assessment was consistent with high-output congestive heart failure.
      Attention should be turned to explaining the reason for a dilated LV with hyperdynamic function and supranormal aortic transvalvular flow. Transesophageal echocardiogram allowed for better visualization of the chambers involved. Given the systolic reversal of flow in the pulmonary veins, one would expect severe regurgitation. However, this was not supported upon close inspection of the mitral leaflets, their coaptation, and color Doppler interrogation. There was a newly appreciated slight anterior leaflet override of the posterior leaflet consistent with mildly increased tethering resulting from ventricular dilation related to the new volume overload. Compounding this, the flow through this fistula resulting in increased LA pressure may have diminished systolic closure, further contributing to decreased coaptation. While acoustic shadowing on 2-dimensional assessment obscured color flow assessment, CWD interrogation differentiated the aortic root origin from the possibility of LVOT origin, eliminating the latter. Flow into the LA throughout the cardiac cycle is only possible from a structure that has a pressure higher than the LA in both systole and diastole. Aortic root pressure always exceeds LA pressure. Conversely, during ventricular diastole, the flow should not occur from the LVOT into the LA, as the pressure between these 2 chambers in diastole does not favor significant flow in that direction.
      Aortic root fistula also may develop between the root and other surrounding chambers or spaces. Had such a high-output communication occurred from the aortic root into the pericardial space, acute tamponade physiology likely would have been rapidly fatal. An aortic root to LV fistula may present clinically similar to aortic regurgitation, again with elevated LVOT and aortic valve systolic gradients, but with a normal DI. An aortic root communication with the right ventricle (RV) may cause RV systolic failure due to volume overload, with resultant dilation and possibly functional tricuspid regurgitation. In this instance, however, left heart echocardiographic features of LV overload, high cardiac output, severe MR, and abnormal pulmonary vein flow would be replaced with those of an underfilled LV. A fistula between the aortic root and RV outflow tract may produce elevated gradients across the pulmonic valve, despite a normal valve area. An aortic root fistula to the proximal pulmonary artery would produce similar findings. Spectral Doppler and tissue Doppler would indicate pulmonary hypertension and RV pressure overload, respectively. In the setting of RV dysfunction, RV free wall peak longitudinal strain as measured by tissue Doppler imaging would be reduced (normal –28.5% ± 4.8%).
      • Simon MA
      • Rajagopalan N
      • Mathier MA
      • et al.
      Tissue Doppler imaging of right ventricular decompensation in pulmonary hypertension.
      ,
      • Morris DA
      • Krisper M
      • Nakatani S
      • et al.
      Normal range and usefulness of right ventricular systolic strain to detect subtle right ventricular systolic abnormalities in patients with heart failure: A multicentre study.
      Features of left-sided volume overload and MR are less likely, with the caveat that progressive ‘downstream’ changes increase with the chronicity of pathology.
      A Gerbode defect is a fistulous communication between the LVOT and right atrium (RA) that may either course directly into the RA through the membranous interventricular septum or follow a more indirect course through the RV, tricuspid valve septal leaflet, and into the RA. On echocardiography, most patients with a Gerbode defect exhibit RA and RV dilation, tricuspid regurgitation, and pulmonary hypertension.
      • Yuan SM.
      Left ventricular to right atrial shunt (Gerbode defect): Congenital versus acquired.
      Valvular surgery is a major risk factor for this defect, which is often misdiagnosed as severe TR.15 In the setting of turbulent color flow surrounding the tricuspid valve, careful inspection from multiple angles and the thoughtful use of Doppler modalities should be performed. In differentiating the origin of this fistula from the aortic root, color Doppler and 3-dimensional reconstruction are useful, considering that both would produce flow throughout the cardiac cycle on CWD into the low-pressure right-sided system.
      Coronary cameral fistulae are another fistulous abnormality of the aortic root. These rare anomalous shunts (incidence 0.1%-0.2%) between a main coronary artery or its subdivision and a cardiac chamber may be congenital or acquired from an inflammatory process or after aortic valve or root surgery.
      • Bucherri D
      • Chirco PR
      • Geraci S
      • et al.
      Coronary artery fistulae: Anatomy, diagnosis and management strategies.
      They are usually clinically silent and involve the right coronary artery and right-sided cardiac chambers. However, in 45% of patients, the left coronary system is involved. If a large amount of blood flow is shunted into the LV, the clinical picture may mimic severe aortic regurgitation and result in congestive heart failure. Similarly, if left coronary blood flow drains directly into the LA, physiology resembling severe MR may develop, leading to congestive heart failure.
      When investigating a shunt, it is helpful to recall that pressure gradients (and by extension shunt conditions) are dependent on loading conditions, which are influenced by general anesthesia. There is no prescribed gold standard for the assessment of unusual intracardiac shunts or communications. The echocardiographer must examine with a keen eye and reasonable index of suspicion for certain pathologies in each clinical context.

      Conclusion

      This case demonstrates 2 important teaching points. First, when a mysterious jet is visualized on echocardiography, but identification of its nature and origin are challenging, the combined use of multiple Doppler imaging modalities is invaluable in the assessment of the pathology. Reliance on a sole measurement or technique may lead to missed or erroneous diagnoses. Second, complications of aortic valve surgery include the development of fistulas between the aortic root and surrounding chambers, with varied pathophysiologic consequences. Echocardiographers should be knowledgeable about these differential diagnoses and consider their presence in the postoperative cardiac surgery patient who presents with congestive heart failure.

      Appendix. Supplementary materials

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      Linked Article

      • Learning from Sherlock Holmes: Deductive Reasoning in Echocardiographic Enigma
        Journal of Cardiothoracic and Vascular AnesthesiaVol. 36Issue 8
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          CLINICAL DIAGNOSIS IS IN many ways similar to the work of a detective. Every day, medical personnel are presented with clues or evidence to solve a problem or, at times, a mystery. Echocardiography ultimately is just a tool with various capabilities of interpreting the truth; its utility, therefore, will depend on the comprehensiveness, experience, and insight of the echocardiographer. Like a detective who may come to the wrong conclusion based on selective attention only to certain clues, medical personnel can at times fail to make the connection among several seemingly incongruent findings.
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