Myocardial Infarction in a Seven-Year-Old Girl With Left Atrial Myxoma

Introduction

Primary cardiac neoplasms are rare in the pediatric population with a reported incidence of 0.03% to 0.08% in autopsies. ¹ These neoplasms are classified into benign (90%) and malignant (10%). ¹ Myxomas are uncommon representing 18% of benign cardiac lesions and left atrial (LA) myxoma related coronary embolic events have only been reported in 0.62% of cases.^1,2 Our case highlights an elevated troponin initially suspected to be myocarditis that was subsequently found to be due to an infarction resulting from embolic phenomenon secondary to a LA myxoma.

Case Presentation

A seven-year-old female presented to an outside hospital emergency room with a one-day history of chest pain, shortness of breath, and presyncopal event while playing at a playground. Emergency room bloodwork revealed a high-sensitivity troponin I of 49 ng/L (normal < 51 ng/L), and an initial electrocardiogram (ECG) revealed no abnormalities (Supplemental Figure 1A). She was admitted for observation and presumed myocarditis. Troponins however rose out of proportion to the provisional diagnosis of myocarditis. A transthoracic echocardiogram revealed a large left atrial pedunculated mass ∼20 mm × 10 mm attached to the interatrial septum with to-and-fro motion across the mitral valve, concerning for atrial myxoma. It also demonstrated hypokinesis of the inferior and inferolateral segments of the left ventricle. The patient was transferred to our intensive care unit (ICU) for monitoring and management. Troponin (TN) peaked at 19,725 ng/L (normal <31 ng/L). A follow-up ECG revealed inverted T-waves in inferior leads and ST depression in lateral leads (Supplemental Figure 1B). Cardiac catheterization was performed for coronary evaluation, revealing an occluded midportion posterior lateral branch (PLB) from the right coronary artery (RCA) with evidence of compensatory collateralization from the left coronary system (Figure 1). She was subsequently started on a heparin drip. Cardiac magnetic resonance imaging (MRI) demonstrated the pedunculated mass consistent with an atrial myxoma and subendocardial fibrosis suggestive of an acute on chronic coronary event. Of note, there was no epicardial enhancement as typically observed in acute myocarditis. A brain MRI was done to rule out embolic phenomena and revealed two punctate foci of restrictive diffusion within gray-white junctions consistent with embolic changes. She had no neurologic symptoms, and the patient was promptly sent for surgical excision.

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Figure 1.

(A) Right coronary artery (RCA) angiogram demonstrating distal occlusion of the RCA at the posterior lateral branch (PLB) (B) Normal left anterior descending (LAD) coronary artery and circumflex coronary (Circ) artery with visible collaterals. PDA: posterior descending coronary artery.

Operative Technique/Clinical Course

The patient received a median sternotomy, aortic arterial cannulation, and bicaval venous cannulation for cardiopulmonary bypass (CPB). The heart was arrested and tumor exposure was via the LA dome. We utilized a no touch technique to prevent fragmentation of the myxoma. A suture was placed in the stalk of the myxoma (Video 1), which extended onto the interatrial septum and the myxoma was excised from the septum (Figure 2). The defect in the atrial septum was closed primarily. The aortic cross-clamp was removed and we separated from CPB uneventfully. Intraoperative transesophageal echocardiogram (TEE) demonstrated good function, no visible mass, no residual atrial septal defect (ASD), and trace to mild mitral regurgitation. The patient was extubated prior to transfer to the ICU and discharged home on postoperative day 3.

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Figure 2.

Surgical specimen: resected left atrial myxoma. Gelatinous structure with visible hemorrhage. The single attachment through a stalk is visible as part of the atrial septum with the myxoma. A portion of the atrial septum was taken to prevent recurrence.

The patient was readmitted 20 days later for four additional days due to a pericardial effusion requiring pericardiocentesis. She is now over five months post myxoma resection and thriving as an outpatient. Histopathology of the excised lesion identified a hypocellular lesion characterized by abundant myxoid stroma admixed with myxoma cells consistent with an atrial myxoma (Supplemental Figures 2 and 3). Genetic evaluation is pending.

Discussion

This case represents an unusual presentation for a myxoma and highlights the need to maintain a broad differential diagnosis. Myocarditis and even COVID-19/MISC-C are common causes of troponin elevation, but a complete workup is necessary. Although serial ECGs and troponins remain the cornerstone in early patient screening for cardiac related symptoms, even subtle findings should prompt further investigation in the pediatric population. Echocardiography is a high sensitivity/specificity test which represents little risk to patients in these situations. Observed regional wall motion abnormalities are possible but uncommon in myocarditis and this finding should prompt clinicians to consider evaluation of coronary anatomy. Once a diagnosis is determined, a management pathway can be established. Although surgical management of myxomas has been described, the ideal timing is not always clear. Genetic pathology such as Carneys Complex should be considered and appropriate testing initiated. In the setting of myxomas where embolization has been described, ³ definitive surgical management should be pursued without delay. A complicating factor is the circumstance where a cerebral embolism has occurred and the risk of hemorrhagic conversion needs to be characterized and considered. The presence of cerebral hemorrhage may preclude immediate surgical intervention as it renders the use of CPB as high risk for propagation of bleeding in the short term. In our case, the cerebral MRI findings of punctate foci represented a small, but acceptable risk for the use of CPB.

The management of infarction secondary to embolism in this setting is analogous to embolism in other settings such as endocarditis. The infarction can be treated conservatively with medical therapy. Thrombolytic use has been described in managing pediatric infarction where acute thrombus is the flow limiting lesion but was not necessary in our case. ⁴ The presence of collaterals in the affected location (PLB) is suggestive that this process may have started earlier than in the days prior to the clinical presentation and we may have seen a propagation of an old thrombus or repeat embolic events. The PLB was small, and the infarction was stable precluding aggressive intervention. Our team discussed the value in performing a surgical embolectomy or catheter-based embolectomy but the risks significantly outweighed the benefit of restoring antegrade flow to this area of perfusion. There have also been reports of spontaneous recanalization in the setting of tumor-related emboli and proposed mechanisms for this which would support a conservative approach. ⁵ It is interesting to note that there have been several reports of embolization to the RCA region in adult case reports. ⁵ In our patient, given the presence of collaterals, this may have represented repeated embolization to the same location. This raises the interesting question of whether the location of embolization in our case is random or favored for an anatomical reason.

Our operative approach to this myxoma was focused on minimizing contact with the lesion and thus lessening the risk of an iatrogenic embolism. The LA dome access point allowed us to visualize the mass clearly without disturbing it. Other recognized approaches to exposure would be through Sondergaard's groove or the interatrial septum. In this case, access through the interatrial septum would require approaching the mass through the septal area where the myxoma may be attached. The decision of which approach to utilize should be based on optimizing exposure, minimizing contact with the mass, and operator experience.

Conclusions

Left atrial myxomas in the pediatric cardiac population are rare and can present atypically. Troponin elevation is often suggestive of myocarditis, but a full workup is necessary to rule out more sinister processes such as embolism. Once a diagnosis is made, surgical excision of a myxoma can be done immediately with good results.

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