Written informed consent was obtained from the patient for publication of this report. A 59-year-old man with hypertrophic cardiomyopathy (HCM) was referred to our institution for myectomy. His symptoms included nonradiating midsternal pain and shortness of breath occurring after mild to moderate physical activity. A preoperative transthoracic echocardiogram revealed systolic anterior motion (SAM) of the anterior mitral leaflet, which increased markedly with exercise resulting in a peak systolic left ventricular outflow tract (LVOT) gradient of 129 mm Hg. A peak systolic left ventricular midcavity gradient of 73 mm Hg was also noted. The basal septum was moderately hypertrophic with a thickness of 1.5 cm. Cardiac magnetic resonance (CMR) imaging was also performed to evaluate papillary muscle (PM) morphology. Apart from a mild hypertrophy of the anterolateral PM, CMR was unremarkable. Since medical management did not improve symptoms, surgical myectomy was advised.
Intraoperative transesophageal echocardiography (TEE) confirmed SAM, systolic flow acceleration in LVOT, and mitral regurgitation of 2+ severity (Figure 1). A hypertrophic anterolateral PM (Figure 2) with abnormal movement toward the interventricular septum during systole was also observed (Supplemental Digital Content 1, Video 1, http://links.lww.com/AA/B498). Further evaluation using 3D TEE revealed a muscle bridge originating from the anterolateral PM and attaching itself to the interventricular septum (Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/B499). This abnormal subvalvular anatomy resulted in abnormal displacement of anterolateral PM toward the septum during systole, causing LVOT obstruction. The details of the abnormal PM anatomy were communicated with the surgical team, aided by 3D images. Routine echocardiographic measurement of the septum was also obtained to determine the extent of myectomy.
The anatomy seen on 3D echocardiography was confirmed surgically. In addition to standard septal myectomy, the vertically oriented bridging segment of the anterolateral PM was excised. After separation from cardiopulmonary bypass, TEE confirmed absence of SAM (Supplemental Digital Content 3, Video 3, http://links.lww.com/AA/B500), and showed trivial mitral regurgitation and absent LVOT gradients (Figure 3), on provocation with isoproterenol at 20 μg/min). Rest of the surgery and postoperative stay was unremarkable.
HCM, with a prevalence of 1 in 500 adult individuals, is the most commonly inherited cardiovascular disease. Presence of LVOT obstruction is the most important predictor of adverse outcome among these patients.1 The classically described mechanism is LVOT narrowing and SAM due to asymmetric hypertrophy of the basal interventricular septum. However, advent of newer imaging modalities, such as 3D echocardiography and CMR, has improved our understanding about the role of mitral subvalvular apparatus in the pathophysiology of LVOT obstruction. Various phenotypic variations and abnormalities of the mitral subvalvular apparatus are reported in HCM, some being associated with dynamic LVOT obstruction, even in the absence of significant septal hypertrophy. For instance, an anteroapically displaced PM would drag the mitral valve leaflet toward the LVOT, resulting in SAM and LVOT obstruction. Location of PM on the apical one-third of the left ventricle, as measured by CMR, increased the risk of LVOT obstruction. Similarly, a double bifid PM and direct insertion of PM into anterior mitral leaflet has been associated with LVOT obstruction.2,3 HCM-related PM abnormalities described in literature are enumerated in the Table.
PM characterization is lacking in contemporary 2D or 3D echocardiography. Some investigators recommend transgastric midpapillary short-axis and 2-chamber views, and midesophageal commissural view to interrogate PM morphology.4 Literature is silent on standard 3D TEE evaluation of PM morphology, but the concept may be extrapolated from CMR imaging. Multiplanar reconstruction of 3D data set allows the operator to reliably align the 2D planes along the desired structures. For instance, aligning the 2 longitudinal axes in the 3D volume to traverse the left ventricular apex can ensure that the reconstructed 2D midesophageal views are not foreshortened, but has the left ventricular apex truly represented. This could assist in quantifying apical displacement of PM. Furthermore, the functionality of adaptive cropping, provided by certain vendors, enhances understanding of spatial anatomical relationship between structures in question. In our case, this allowed us to interrogate the anatomy of the PM in relation to interventricular septum. In comparison with 2D imaging, 3D neither improves image quality nor resolution, but provides a better insight into morphological relationship between structures. In addition, 3D data sets with adequate frame rates can give important dynamic temporal information adding value to the intraoperative diagnostic imaging. Real-time orthogonal imaging, which most 3D probes are capable of, also provides good-quality images without need for postprocessing.
Left ventricular midcavity obstruction is seen in 8%–13% of patients with HCM. It tends to occur in a markedly hypertrophic ventricle with a small cavity and is sometimes associated with a hypertrophied PM. PM hypertrophy is defined as presence of at least one PM with a transverse diameter >1.1 cm, in midpapillary short-axis view.5 Presence of flow acceleration with color flow Doppler and aliasing with pulse wave Doppler is used to diagnose and localize midcavity obstruction. Continuous wave Doppler across the site of dynamic obstruction (in midesophageal 5-chamber or long-axis view) yields a dagger-shaped envelope, providing a gradient to quantify severity. Peak systolic gradients ≥30 mm Hg is suggested to be associated with congestive heart failure and sudden death.6
Identification of all coexisting mechanisms of LVOT and/or midcavity gradients has important therapeutic implications. A standard septal myectomy without intervening on other contributing mechanisms could result in a suboptimal outcome.2 In our patient, a muscle bridge attaching the PM to interventricular septum resulted in abnormal displacement of PM toward the septum during systole, causing the outlet obstruction (Figure 4). This needs to be differentiated from false tendons, which are embryologically similar to chordae tendinae, and extends between left ventricular free wall, septum, or PM. While false tendons typically exhibit systolic laxity, a muscle bridge contracts during systole.
Myectomy is typically performed through an aortotomy and thus substantially relies on echocardiographic findings. American Society of Echocardiography recommends 3D echocardiography as a useful adjunct in assessment of mitral valve apparatus and PM morphology in patients with HCM.7 Although CMR may provide images with higher resolution, 3D echocardiography obtains real-time images in the operating room under various loading conditions. Even though the presence of LVOT obstruction may be known preoperatively, TEE plays an important role in determining unidentified mechanisms of LVOT obstruction. Technology has enabled us to acquire full-volume 3D images of the left ventricle with sufficient volume rates providing information on the orientation, morphology, and mobility of the PMs in the left ventricle. It has immensely helped the intraoperative imaging workflow by being operator friendly and time efficient. With widespread availability of advanced 3D imaging platforms in the operating room and growing experience in acquiring 3D images, it should be more routinely used in the evaluation of complex pathophysiology.
Clinician’s Key Teaching Points
By Kent H. Rehfeldt, MD, and Nikolaos J. Skubas, MD
- Hypertrophic cardiomyopathy (HCM) may be accompanied by left ventricular outflow tract (LVOT) obstruction, which, when present, is an important predictor of adverse outcome. In most cases, LVOT obstruction occurs because of the presence of asymmetric basal ventricular septal hypertrophy and systolic anterior motion (SAM) of the mitral valve.
- In patients with HCM, morphologic abnormalities of the mitral apparatus may include the leaflets, chordae, and papillary muscles (PMs). PM variants include apically displacement, bifid anatomy, or direct insertion into a mitral leaflet without chordal attachments. These variants may contribute to LVOT obstruction.
- In this case, a patient with HCM was referred for septal myectomy. SAM of the mitral valve and LVOT obstruction were detected by intraoperative TEE imaging. In addition, a hypertrophic anterolateral PM was imaged with abnormal systolic motion toward the ventricular septum. Further evaluation with 3D TEE revealed an abnormal muscle bridge between the hypertrophic PM and the ventricular septum. Surgical division of the muscle bridge together with septal myectomy led to resolution of LVOT obstruction.
- The PMs are examined with 2D TEE in the transgastric left ventricular SAX and 2-chamber and midesophageal mitral commissural views. With 3D TEE and multiplanar reconstruction, the PM anatomy and their spatial relationship with other LV structures is detailed further. Failure to detect anomalous PM anatomy may prevent adequate surgical relief of LVOT obstruction.
Name: Abraham Sonny, MD.
Contribution: This author helped design the study, analyze the data, and write the manuscript.
Name: Shiva Sale, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Name: Nicholas G. Smedira, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
This manuscript was handled by: Martin London, MD.
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