Pathophysiology of Left Atrial Myxoma
Left atrial myxoma causes clinical manifestations through three distinct pathophysiologic mechanisms: mechanical obstruction of mitral valve blood flow during diastole, systemic embolization of tumor fragments or surface thrombus, and constitutional symptoms from cytokine release. 1
Anatomic Origin and Tumor Characteristics
Left atrial myxomas arise predominantly from the interatrial septum at the fossa ovalis region, which explains their typical attachment site and influences surgical approach. 1
The tumor consists of myxoma cells (lepidic cells) that are polygonal to stellate-shaped with eosinophilic cytoplasm, embedded in abundant myxoid matrix rich in mucopolysaccharides. 1
Vascular channels of varying caliber are scattered throughout the tumor, with endothelial cells lining these channels; hemorrhage and hemosiderin deposits are common, especially in larger tumors. 1
Surface architecture varies from smooth (65% of cases) to friable or villous (35% of cases), with the villous morphology conferring markedly higher embolic potential. 1, 2
Mechanism 1: Mechanical Obstruction
Myxomas cause dynamic obstruction of the mitral valve orifice during diastolic filling, reducing left ventricular filling and cardiac output. 1
Prolapsing tumors (Type I) move from the left atrium into the left ventricle in early diastole and back into the atrium in early systole, creating prominent c and v waves with rapid y descent on left atrial pressure tracings. 3
Nonprolapsing tumors (Type II) remain in the left atrium throughout the cardiac cycle, impeding mitral valve flow continuously and producing a slow y descent indistinguishable from mitral stenosis. 3
This mechanical obstruction leads to syncope from transient reduction in cardiac output and cerebral hypoperfusion, particularly when the tumor intermittently obstructs the valve. 1
Larger tumors correlate with more severe cardiac symptoms, pseudo-mitral auscultation findings (present in 53.5% of patients), and electrocardiographic or radiologic signs of left atrial hypertrophy. 2
Mechanism 2: Embolic Complications
The overall embolism rate with cardiac myxomas is 25%, with embolic stroke being the presenting symptom in up to 50% of cases. 1, 4
Embolic events result from two sources: thrombus formation on the tumor surface or direct embolization of tumor fragments. 1, 4
Villous or papillary surface architecture dramatically increases embolic risk because the friable surface generates thrombus and sheds tumor fragments more readily than smooth-surfaced tumors. 1, 2
Males have statistically greater risk than females of developing embolic complications, though the mechanism for this sex difference is not fully elucidated. 2
Embolic phenomena can cause stroke, peripheral arterial occlusion, coronary artery occlusion leading to myocardial infarction, and formation of myxomatous intracranial aneurysms (present in up to 50% of myxoma-related embolic strokes). 5, 6
Paradoxical embolism can occur in patients with right-sided tumors and patent foramen ovale, allowing venous thrombus or tumor fragments to reach the systemic circulation. 4, 5
Mechanism 3: Constitutional Symptoms
Constitutional symptoms occur in 34% of patients and include fever, weight loss, and symptoms resembling connective tissue disease. 2
These systemic manifestations are mediated by cytokine release, particularly interleukin-6, from the tumor. 2
Female patients have more systemic symptoms, while younger and male patients have more neurologic symptoms. 2
Hemodynamic and Hematologic Consequences
Hemolysis from the tumor can engage systemic heme oxygenase-1, leading to increased carboxyhemoglobin concentrations and plasmatic hypercoagulability through carboxyhemefibrinogen formation. 7
This hypercoagulable state manifests as abnormally large velocity of plasma thrombus growth and strength with reduced vulnerability to lysis on thromboelastography. 7
Severe pulmonary hypertension can develop when large tumors obliterate the left atrium and obstruct mitral valve flow, causing backward transmission of elevated left atrial pressure. 8
Clinical Implications of Pathophysiology
The pathophysiologic mechanisms collectively determine risk profile and urgency of intervention: mechanical obstruction can cause sudden death, embolic complications cause stroke and organ infarction, and constitutional symptoms indicate active tumor biology. 1
Anticoagulation or antiplatelet therapy alone is inadequate because it does not prevent tumor embolization or relieve mechanical obstruction; only surgical excision addresses all three pathophysiologic mechanisms. 1, 5
Complete tumor removal with adequate margin of atrial septum is essential because incomplete excision leads to recurrence in 1-5% of sporadic cases (higher in familial Carney complex). 1, 9