Echocardiography of the Repaired Mitral Valve: Enabling 3-Dimensional Evaluation

See Article, p 300 The mitral valve is a complex asymmetric cardiac structure. Under normal conditions, mitral annulus, leaflets, tendinous chords, and papillary muscles interact throughout the cardiac cycle. In systole, leaflet coaptation separates the left atrium from the left ventricle facilitating filling of the former and forward emptying of the latter. In diastole, a wide mitral orifice directs the blood toward the lateral left ventricular (LV) wall to provide adequate filling. In the developing and developed world, the most frequent native mitral valve pathology is regurgitation. The optimal intervention for a severely diseased degenerative mitral valve is a successful repair.1 The repaired mitral valve must have trivial regurgitation during systole and adequate orifice area during diastole. The orifice of a mitral valve is contained by the 2 leaflets. The leaflets have unequal surface and range of motion—characteristics that become particularly pronounced after mitral valve repair. Due to a combination of leaflet interventions—including posterior leaflet reduction or anterior leaflet realignment away from the septal walls—the repaired mitral valve orifice is a nonplanar structure.2 It has an angulated funnel shape, with a broad proximal orifice on the left atrial side and a narrow distal orifice, defined by the leaflet tips on the LV side. The hemodynamically important orifice is always the distal, narrow one. At times, this diastolic orifice may be difficult to visualize using echocardiography, if the tip of the anterior leaflet lies underneath the posterior leaflet or is shadowed by an annuloplasty ring. Intraoperative echocardiography represents a class I indication for mitral valve repair.3 Immediately after separation from cardiopulmonary bypass, the echocardiographer must evaluate the repaired mitral valve to verify elimination of preoperative pathology and absence of “new” pathology, that is, iatrogenic mitral stenosis. Iatrogenic mitral stenosis requiring surgical reintervention occurs in <2% of mitral valve repairs and is typically associated with increased pressure gradients.4 Therefore, a detailed evaluation of the function of the repaired mitral valve is important for patient care and favorable outcomes. In this issue of Anesthesia & Analgesia, Karamnov et al5 present a new technique to evaluate the repaired mitral valve. Many echocardiographic techniques either estimate the functional or measure the anatomic diastolic mitral valve orifice. Currently, the same criteria and techniques apply for native and repaired mitral valves and for ambulatory and anesthetized patients.6 Using continuous-wave Doppler, the diastolic velocity (transmitral flow [TMF]) is measured at the narrowest mitral valve orifice and a mean pressure gradient <5 mm Hg characterizes a nonstenotic mitral valve. The decay of the velocity is used to measure the pressure half-time (PHT); from it, a mitral valve area (MVAPHT) may be determined according to the calculation . The anatomic orifice of the mitral valve can be directly measured (using planimetry) by tracing the mitral leaflet tips with 2- (MVA2D) or 3-dimensional (MVA3D) echocardiography. Mean pressure gradient, PHT, and planimetry represent level 1 recommendations. In addition, the integral of the transmitral velocity (TMFVTI) can be measured and used to calculate a functional orifice (MVACON), if the LV stroke volume (SV) is known (measured by tracing the LV endocardial border in 2 orthogonal, end-diastolic, and end-systolic frames; SVLVMOD) using the continuity equation . The many available and suggested echocardiographic techniques and measurements offer flexibility and choices. This becomes essential in the busy environment of the operating theater, when the anesthesiologist-echocardiographer is multitasking between managing rapidly changing hemodynamic conditions and echocardiographic imaging. In case of a repaired mitral valve with new stenosis, accurate estimation of the diastolic orifice is important, if return to cardiopulmonary bypass is needed to revise it. However, these techniques are not interchangeable and have important limitations. As a result, they may not all apply to the repaired mitral valve orifice. The flow-dependent techniques depend on parallel alignment of the Doppler beam with the direction of the blood flow, and this is not always the case, if the repaired mitral orifice has the shape of an angulated funnel. The planimetry-based measurements may be inaccurate, if tracing (planimetry) of the nonplanar orifice is done on a single plane. Karamnov et al5 show an intuitively better way to measure the repaired mitral valve “diastolic” orifice. They investigated a convenience cohort of patients with similar pathology (degenerative mitral valve, primarily of the posterior leaflet), who underwent similar repairs (all had annuloplasty ring inserted). Their tested 3-dimensional (3D) technique is an adaptation of the one used to measure the systolic orifice of a regurgitant mitral valve. Here, the authors applied the 3D technique in a “diastolic” frame to measure the diastolic orifice (3DOA). They compared 3DOA to 2- (MVA2D) and 3-dimensional (MVA3D) planimetered orifices, as well as, a functional orifice (MVAPHT). The 3D measurements were performed at the same diastolic frame using standardized 3-dimensional volume data sets. The results demonstrated good reproducibility. As expected, the 3 anatomic and 1 functional orifices differed: the 3D techniques produced smaller orifices, and 3DOA measured consistently smaller than areas obtained by planimetry (MVA3D and MVA2D) as well as, MVAPHT. The authors have to be congratulated for exploring a relevant, and at times overlooked or omitted component of the postoperative transesophageal echocardiography (TEE) examination. The results of a mitral valve repair are often considered in terms of grades of residual mitral regurgitation. The nonplanar mitral valve orifice is qualitatively evaluated by observing the color-flow Doppler velocities traversing it in diastole and measuring the TMF velocities. The diastolic velocities may be underestimated, considering the funnel-shaped orifice, that is not always aligned with the Doppler beam. High-flow state, volume status, LV compliance, and any coexisting aortic valve pathology are additional factors confounding the TMF velocities, pressure gradients, and PHT. The nonplanar orifice cannot be accurately traced on a single plane because is the case with either MVA2D or MVA3D planimetry measurements. The retrospective comparison of various echocardiographic techniques from a convenience sample at a single institution does not permit generalization of the findings. Without a reference measurement, such as magnetic resonance imaging, it becomes impossible to tell which one valve area was the “real one.” The study was not designed to determine superiority or accuracy of one technique. Despite these, we should not disregard the salient observation that 3 of the 20 patients could have been considered as having at least moderate mitral stenosis: they all had 3DOA <1.5 cm2. How should we use this study? As technology advances, inquisitive thinking leads us to new applications of current techniques. The authors are recognized experts in perioperative imaging of the mitral valve, and here, they advance our knowledge with a novel application of existing technology. Their methodology begs to be reproduced, and future results by others should be shared and compared. Even better, adaptation of these readily available techniques by all will enable a better description of the results of mitral valve interventions. In the era of catheter-based, percutaneous mitral valve interventions, when the only window to the repaired mitral valve is echocardiography, the incremental value of the techniques such as 3DOA may become even more relevant. Anesthesiologist-echocardiographers, being in the front line, have the unique opportunity to explore this and similar techniques. DISCLOSURES Name: Andrej Alfirevic, MD, FASE. Contribution: This author helped analyze the data. Name: Nikolaos J. Skubas, MD, DSc, FACC, FASE. Contribution: This author helped analyze the data and prepare the manuscript. This manuscript was handled by: Kent H. Rehfeldt, MD.