An understanding of the many factors involved in the

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1 Atrioventricular Valve Dysfunction: Evaluation by Doppler and Cross-Sectional Ultrasound Norman H. Silverman, MD, and Doff B. McElhinney, MD Division of Pediatric Cardiology, Department of Pediatrics, University of California, San Francisco, California Background. An important factor in the management and outcome of patients with complex univentricular or partial biventricular repair is atrioventricular valve function. Cross-sectional and Doppler echocardiography are versatile tools for the evaluation of atrioventricular valve function. However, it is important to understand the physics and applications of this technology to appreciate the strengths and limitations of echocardiography in this application. Methods and Results. In this review, we discuss the preoperative and intraoperative echocardiographic evaluation of atrioventricular valve function in congenital heart disease. The focus is on atrioventricular valve regurgitation, which is the most common type of dysfunction in patients with univentricular or partial biventricular heart disease. We emphasize an understanding of basic jet physics, as well as technical considerations in the evaluation of atrioventricular valve function, with illustrations from our own experience. Conclusions. Cross-sectional and Doppler cardiac ultrasound is the optimal tool for evaluation of atrioventricular valve function in the current era. Although the issue of quantifying regurgitant jets is not yet fully resolved, echocardiography allows for complete qualitative assessment of the anatomic and functional features that influence the function of the atrioventricular valves. (Ann Thorac Surg 1998;66:653 8) 1998 by The Society of Thoracic Surgeons An understanding of the many factors involved in the assessment of atrioventricular valvar function requires substantial understanding of the physics of Doppler ultrasound in relationship to assessing the severity of regurgitation. Atrioventricular Valve Regurgitation The traditional method for assessing regurgitation of an atrioventricular valve relies on measuring the jet length and the diameter of the vena contracta (the narrowest area of the jet). The premise is that the greater the jet length and the wider the orifice diameter, the more severe the degree of regurgitation [1 3]. However, it is important to understand the finer points of ultrasound technique to apply these methods appropriately. For example, it is well known that the apparent size of a jet can be altered by manipulating the system gain or the Nyquist limit, which is the color scale for defining velocity. The Nyquist limit (in cm/s) indicates the point at which the velocity aliases. First, it is necessary to define the nature of the rheologic physics. Jets that eject into large, unrestricted chambers without flow are termed free jets. Clearly, free jets do not exist in the human circulation, but this model is fundamental to the understanding of more complex jet physics. Free jets increase their mass by entrainment of Presented at the Workshop on One and One-Half Ventricle Repairs, Gubbio, Italy, Dec 6 7, Address reprint requests to Dr Silverman, University of California, San Francisco, Box 0214, M342A, San Francisco, CA ( norman_silverman@pedcardgateway.ucsf.edu). particles. Free jets have a defined width based on an experimentally derived constant k 6.3, such that the maximal width will be 6.3 times the orifice size. The larger the orifice, the broader the jet. Velocities along the central line of the jet are called the centerline velocities. The centerline velocities of the jet have been found to decay in proportion to orifice size. In a free jet system, the orifice size can be calculated from an equation relating the ratio of velocities at the orifice and at a distant point of the centerline, divided by a correction factor. The use of centerline velocities may have practical value. In a recent article, Grimes and associates [4] reviewed the experience and assessed the value of this technique using an in vitro model that appears to be valuable for quantitating jet flow. Turbulent jet mass expands laterally as it flows because surrounding fluid becomes entrained. The entrained mass slows jet velocity, which decays along its centerline axis with the relationship: V m /V o 6.3D/X, (1) where V o is the velocity at the orifice of the jet, D is the orifice diameter, V m is the centerline velocity at a given position X, and 6.3 is the constant relating maximal jet width to jet length (Fig 1A). Orificial flow, assuming a circular orifice, is the product of flow velocity at the orifice and its area, from the formula: Qo V o AorV o D 2 /4 (2) Substituting from equation (1), all free jets of any velocity can be solved for D: D V m X/V o 6.3 (3) 1998 by The Society of Thoracic Surgeons /98/$19.00 Published by Elsevier Science Inc PII S (98)

2 VENTRICLE REPAIR SILVERMAN AND McELHINNEY Ann Thorac Surg AV VALVE DYSFUNCTION 1998;66:653 8 Fig 1. (A) This diagram demonstrates the features of jet physics, which are important in the assessment of atrioventricular valve regurgitation. The jet in the lower part of the diagram can be seen to have multiple velocities in aliasing. Its length over its width is a constant of 6.3. The jet has a central core and has entrainment of mass as it decelerates (arrows). Proximal to the jet, the flow velocity accelerates along an isovelocity line related to the first alias. The area of the hemisphere formed by the isovelocity line of the first alias (2 r 2 ), multiplied by the velocity of the Nyquist limit in cm/s (in this example, 38 cm/s), multiplied by 60 and divided by 1,000 to bring the equation to L/min, yields the volume flow of the regurgitant jet. Centerline velocities are the velocities along the jet length, which diminish with continuing entrainment of the jet. (B) An example of centerline velocities. It is known that a turbulent jet expands laterally as it flows because of surrounding fluid entrainment, which slows the jet velocity along its centerline relationship. V o velocity at the orifice of the jet; D diameter of the orifice; V m centerline velocity at a given point X; and 6.3 the constant relating the maximal jet width to length. The flow of the jet can then be related to the velocity measured in the centerline at a given position from the jet s orifice divided by a constant, multiplied by the velocity at the orifice of the jet. (Top right) We can see the potential core decay for velocities beginning at 1 mm (A) and2mm(b and C), their decay levels at velocities starting off initially at 2 (A and B) and 4 m/s (C), respectively. (Bottom left) The relationship of the distal velocity to the orifice velocity at a given position related to the orifice diameter is equivalent for all curves (a, b, and c). (Bottom right) The reciprocal of this relationship, the relationship of the velocity at the orifice over the velocity distally, can be seen to exhibit a linear pattern for all different kinds of curves (a, b, and c). Thus, if one knows the distal velocity at any given relationship distance, one can calculate the flow through the orifice. Fig 2. Apical four-chamber view in a patient with pulmonary hypertension. (Left) The right atrium (RA) and right ventricle (RV) are enlarged. (Middle) Doppler color-flow map with the flow disturbance in the atrium caused by the regurgitation. The velocity signal obtained axial to the jet velocity through the central core is 5.13 m/s, equivalent to a pressure difference between the right atrium and ventricle of 105 mm Hg. (LA left atrium; LV left ventricle.)

3 Ann Thorac Surg VENTRICLE REPAIR SILVERMAN AND McELHINNEY 1998;66:653 8 AV VALVE DYSFUNCTION 655 Fig 3. These series of figures demonstrate the variability of mapping jet size based on changes in various Doppler settings in the same patient as in Figure 2. (A) This figure shows different velocity maps of tricuspid regurgitation. In all of these examples, the Nyquist limit is set at 61, but different maps define different aspects. (Top left) A standard velocity map. (Top right) A velocity plus variance map. (Bottom left) A simple redblue velocity map. (Bottom right) A different velocity variance map. Note particularly the isovelocity change proximal to the tricuspid regurgitation, which is not substantially altered with the respective maps. What appears to be altered is the distal processing of the jet in the atrium. (B) In this same patient, the standard velocity variance map is used, but the Nyquist limit is changed from 61 (top left) to 39(top right) to23(bottom left) to17(bottom right). Note that not only does the jet broaden in the right atrium, but also the size of the alias boundary increases progressively. A B and substituting for equation (2) produces the equation for calculation of jet flow: Qcal V o /4 V m X/6.3V o 2 (4) Thus flow rate can be calculated without a measure of orifice size. This appears to offer promise insofar as it holds up experimentally where there is counterflow (that is, not a strict free jet system), as occurs in the atria. Another method that may be helpful for quantitating regurgitant jets is the proximal isovelocity surface area concept [15]. This technique uses the continuity equation, by assuming that all the flow that is entering the jet area is also leaving it. The proximal isovelocity surface area concept holds that flow in the proximal side of a jet accelerates along concentric isovelocity lines that converge on the orifice. When Doppler color-flow mapping is used, flow accelerates into the orifice and is aliased at given distances from the orifice, depending on the Nyquist limit at which the system is set. The first alias (which forms a hemisphere) reflects the boundary at which the velocity of the converging flow is equal to the Nyquist limit, and the proximal isovelocity surface area can be calculated (in cm 2 ) as the hemispherical area

4 VENTRICLE REPAIR SILVERMAN AND McELHINNEY Ann Thorac Surg AV VALVE DYSFUNCTION 1998;66:653 8 Fig 4. (A) Diagramatic representation of an apical four-chamber image in a patient with transposition of the great arteries and substantial tricuspid regurgitation before pulmonary artery banding. (Left) The dilated right ventricle with tricuspid regurgitation related to chordal position change. (Right) After the band is applied, the left and right ventricular areas change and the ventricular septal configuration is altered, shifting the location and orientation of the subvalvar apparatus of the tricuspid valve and also altering the zone of apposition of the tricuspid valvar leaflets. As a result, tricuspid valve regurgitation diminishes. (B) A series of four-chamber transesophageal views showing gradual tightening of the pulmonary artery band (from left to right and top to bottom) in a patient with right ventricular dysfunction and severe tricuspid regurgitation late after atrial repair of transposition of the great arteries. Note the shift in the position of the ventricular septum. (C) Doppler color-flow images in the same patient demonstrate a marked change in the tricuspid regurgitant velocity during the tightening of the band, as well as a significant decrease in tricuspid regurgitation. Left ventricular pressure was monitored to test the adequacy of the band from 40% to 90% of left ventricular pressure. (LV left ventricle; PA pulmonary artery; PVA pulmonary venous atrium; RV right ventricle; SVA systemic venous atrium.)

5 Ann Thorac Surg VENTRICLE REPAIR SILVERMAN AND McELHINNEY 1998;66:653 8 AV VALVE DYSFUNCTION r 2, where r is the radius of the first alias (from the jet orifice). Flow (Q) can be calculated by multiplying proximal isovelocity surface area by the Nyquist limit (ie, the velocity at r, the first alias): Q cm 3 /s 2 r 2 cm 2 Nyquist limit cm/s with multiplication by 60/1000 for unit conversion, yielding flow in L/min. It should be noted that the application of this method has been associated with a variety of problems relating to orifice shape and size, and to timing (Figs 1B, 2). The pressure on the driving side of the jet also affects its size. In addition, it has been found that the larger an atrium or the higher its ambient pressure, the smaller the jet [6]. It has also been determined that jets adhering to the surface of a valve, for example, change their shape and momentum [7]. The surface tension absorbs energy and lowers the pressure on that side of the jet, creating a pressure difference between the two sides, with deviation of the jet. This phenomenon is known as the Coanda effect. This also leads to distortion of the conical shape of the jet as it adheres and spreads over the valvar surface. This makes the jet larger in one dimension than in another and also limits the length of the jet because of absorption of energy by surface forces. It is also possible to alter jet size by altering the Doppler gain settings, altering the Nyquist limits, and using different maps (Fig 3). In the adult population, where quantitation of regurgitation is augmented by the calculation of volume by cross-sectional echocardiography, the regurgitant fraction is calculated by subtracting volume (derived from cross-sectional echocardiography) from the forward output (calculated by the Doppler method) using the outflow tract velocity time integral and the outflow crosssectional area from the formula: forward stroke volume VTI D 2 /4 and total stroke volume is calculated from the stroke volume, which is derived from biplane (or in some cases from single plane) measurements [8, 9]. The difference between the two reflects the regurgitant volume: or regurgitant volume stroke volume two-dimensional echocardiography) stroke volume Doppler regurgitant fraction 100 regurgitant volume/stroke volume two-dimensional Values greater than 40% are considered highly significant, whereas values less than 20% are considered to be mild. In the age range we are considering, however, there are frequently atrial shunts and additional valvar or outflow anomalies, which make it unlikely that these calculations can be applied because of the inability to make accurate calculations of both forward and regurgitant stroke volume in such circumstances. Intraoperative Assessment It is against this background that the approach for evaluating regurgitation is determined in the operating room. We insist on preoperative examination, particularly to evaluate all anatomic and physiologic factors in a less stressful environment than the operating room, allowing time for extensive and complete examination. This provides both a framework for evaluating all the associated lesions and an opportunity to define regurgitation with the methods outlined above. When studies are conducted in the operating room rather than in the preoperative setting, blood pressure and cardiac output are often diminished by the combined effects of a reduced basal metabolic rate, premedication and anesthetic agents, and the addition of artificial respiration. Frequently, regurgitation appears less severe in the operating room than it did preoperatively. Additionally, the evaluation of regurgitation after valvar repair and cessation of cardiopulmonary bypass is altered by the residual hypothermia, depressed cardiac function, and volume changes characteristic of the acute postoperative state. It is common to find small degrees of regurgitation even in patients without preoperative regurgitation, because of the myocardial factors mentioned above. These generally tend to diminish as the effects of the bypass run are alleviated. The advantage for assessing the change in regurgitation is that one can locate the transducer in the same position and with precisely the same gain settings. With these constraints in mind, the use of simple color to assess jet length and vena contracta the minimum size of a Doppler jet has been valuable for assessing the severity of tricuspid regurgitation with intraoperative transesophageal echocardiography (Fig 4). Atrioventricular Valve Stenosis Evaluating atrioventricular valve stenosis is more straightforward than evaluating atrioventricular valve regurgitation. In the heart in which a one and a half ventricle repair is being considered, the question of annulus size is important. The tricuspid Z score can be determined by cross-sectional echocardiography [10, 11]. In addition, the peak velocities and mean velocity of the diastolic signal assist in defining the severity of stenosis [12]. In the operating room, the evaluation can be performed from the transesophageal approach, using the same methods as preoperatively. Estimation of atrial size provides additional information for evaluating the consequences of elevated pressure, when atrial enlargement is present. These findings can be complemented with the measurement of left atrial pressure, providing the opportunity to evaluate the degree of atrioventricular valve stenosis. Abnormalities of the atrioventricular valves such as Ebstein s malformation have been discussed in another section of this symposium.

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