Papillary Muscle Insertion Directly into the Anterior Mitral Leaflet in Hypertrophic Cardiomyopathy, Its Identification and Cause of Outflow Obstruction by Cardiac Magnetic Resonance Imaging, and Its Surgical Management




This case presents an uncommon but important mechanism of muscular left ventricular outflow obstruction in hypertrophic cardiomyopathy due to anomalous and direct papillary muscle insertion into the anterior mitral leaflet, a finding reliably identified clinically by cardiac magnetic resonance imaging. The identification of this left ventricular outflow tract morphology is important before invasive ventricular septal reduction therapy because it dictates a specific surgical strategy. These findings further support the role of cardiac magnetic resonance imaging in the early evaluation of hypertrophic cardiomyopathy patients.


Anomalous and direct papillary muscle insertion into anterior mitral leaflet is an uncommon but important mechanism of muscular left ventricular (LV) outflow tract obstruction in hypertrophic cardiomyopathy (HC), leading to progressive heart failure symptoms. Recognition of this unique structural anomaly before invasive ventricular septal reduction therapy is crucial because it dictates a specific surgical approach for septal myectomy with a deep, extended muscular resection well beyond the contact point of the mitral valve and ventricular septum. Alcohol septal ablation is unlikely to be effective in relieving LV outflow obstruction in patients with this anomaly, given that the percutaneous procedure is inflexible with the operator is confined to the fixed anatomic distribution of the first major septal perforator coronary artery. For this vignette, we studied 575 consecutive HC patients with cardiac magnetic resonance imaging (CMR) presenting to 2 major HC centers: 14 patients (2.4%) were identified with anomalous anterolateral papillary muscle insertion directly into anterior mitral leaflet ( Figure 1 ). In 13 of the 14 patients, outflow gradients of 30 to 150 mm Hg were present at rest; 4 of these patients underwent successful surgical myectomy with relief of obstruction and symptoms (including the patient presented here). Preoperative identification of this morphologic abnormality by CMR altered surgical myectomy strategy to include an extended septal resection as well as reduction in papillary muscle thickness.




Figure 1


CMR 3-chamber long-axis images (A) at end-diastole and (B) at mid-systole showing anomalous insertion of anterolateral papillary muscle directly into anterior mitral leaflet in 2 patients with obstructive HC. (A) A 42-year-old man with anterolateral papillary muscle ( arrows; dotted lines represent continuation of papillary muscle, which extends out of the imaging plane) inserting directly into anterior leaflet of the mitral valve (arrowheads) . (B) A 60-year-old man with relatively mild heart failure symptoms due to mid-systolic apposition (large arrowheads) of ventricular septum and anomalous papillary muscle (arrows) inserting into anterior mitral leaflet (small arrowheads) . Ao = Aorta; LA = left atrium; VS = ventricular septum.


Case Report


A 52-year-old man with obstructive HC and progressive heart failure was referred for invasive septal reduction therapy to relieve outflow tract obstruction. He was diagnosed with HC at age 42 (10 years earlier) after a precordial systolic ejection murmur was heard on physical examination. Over the previous 2 years, he experienced progressive exertional dyspnea (New York Heart Association functional class III) refractory to medical therapy with beta blockers and disopyramide. At the time of evaluation, a 2-dimmensional transthoracic echocardiogram demonstrated asymmetric septal hypertrophy with a maximal LV wall thickness of 17 mm (in the basal septum), mild systolic anterior motion (SAM) of the anterior mitral leaflet without septal contact ( Figure 2 ), and peak outflow gradient of 150 mm Hg. The absence of the typical mechanism of subaortic obstruction in HC (i.e., prolonged SAM-septal contact) triggered advanced imaging with CMR to further characterize the morphology of the outflow tract.




Figure 2


Septal myectomy for muscular mid-cavity obstruction. (A) Transthoracic 2-dimensional echocardiogram (apical 5-chamber view in mid-systole) from a 52-year-old man with HC and New York Heart Association functional class III symptoms demonstrates SAM of the mitral valve without septal contact (arrow) but a peak systolic gradient of 150 mm Hg. (B) In the same patient, CMR LV outflow tract view in mid-systole demonstrates anomalous anterolateral papillary muscle (arrows) inserting directly into anterior mitral leaflet (small arrowheads) , forming a single rigid structure contacting the ventricular septum (large arrowheads) and creating a long 12-mm area of muscular outflow obstruction. (C) Surgical septal myectomy was performed and included deep, extended muscular resection (i.e., beyond the contact point of the papillary muscle and ventricular septum, in the area demarcated by dotted line 1); removal of an accessory LV muscle bundle judged as contributing to outflow obstruction because of its proximity to the anomalous papillary muscle during systole (area within dotted line 2); longitudinal partial resection of anterolateral papillary muscle was also performed to reduce its thickness (area within dotted line 3); and additional resection performed at the base of the papillary muscle ( asterisk ) to allow increased mobility of the papillary muscle away from the outflow area during systole. (D) CMR LV outflow tract view in mid-systole obtained 6 months after surgical myectomy demonstrating widening of the LV outflow tract diameter and absence of systolic contact between papillary muscle (arrows) and septum, which resulted in complete elimination of outflow gradients. Ao: aorta; LA: left atrium; VS: ventricular septum.

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Dec 5, 2016 | Posted by in CARDIOLOGY | Comments Off on Papillary Muscle Insertion Directly into the Anterior Mitral Leaflet in Hypertrophic Cardiomyopathy, Its Identification and Cause of Outflow Obstruction by Cardiac Magnetic Resonance Imaging, and Its Surgical Management

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