Does Myasthenia Gravis Affect the Heart Muscle?
Myasthenia gravis does not typically affect cardiac muscle in the way it affects skeletal muscle, because the autoantibodies target nicotinic acetylcholine receptors at the neuromuscular junction of voluntary skeletal muscles, not the autonomic nervous system or cardiac muscle tissue. 1, 2
Why the Heart Is Generally Spared
Myasthenia gravis is a B-cell mediated autoimmune disorder that specifically attacks components of the neuromuscular junction of skeletal muscles, disrupting transmission of nerve signals to voluntary muscles but not affecting cardiac muscle through the same mechanism. 2
The acetylcholine receptor antibodies in myasthenia gravis target nicotinic receptors at the neuromuscular junction, which are present in skeletal muscles (including extraocular, levator palpebrae, and limb muscles) but not in cardiac muscle, which operates through different receptor systems. 1
Cardiac muscle function depends on different physiologic mechanisms than skeletal muscle, and the autoimmune process in myasthenia gravis does not directly attack the heart in the same way it attacks voluntary muscles. 1
Rare Cardiac Manifestations That Can Occur
While direct cardiac involvement is uncommon, certain cardiac findings have been reported in myasthenia gravis patients:
Cardiac involvement may occasionally manifest as asymptomatic ECG changes, conduction disturbances, myocarditis, or rarely ventricular arrhythmias, though these are not typical features of the disease. 3
The association between myocardial pathology and thymoma (especially malignant thymoma) is well established, suggesting that when cardiac involvement does occur, it may be related to thymoma rather than myasthenia gravis itself. 4
Some studies using tissue Doppler imaging have suggested subtle alterations in left ventricular long-axis function that may be pyridostigmine-responsive, but these findings are not clinically significant in most patients without known cardiac disease. 5
Clinical Implications for Evaluation
Cardiac evaluation with troponin measurement, ECG, and consideration of echocardiography should be performed when respiratory insufficiency, elevated muscle enzymes, or symptoms suggestive of myocarditis are present, as myocarditis can rarely co-occur with myasthenia gravis and significantly raises mortality risk. 1
The presence of thymoma warrants more careful cardiac surveillance, as approximately 30-50% of patients with thymomas have myasthenia gravis, and cardiac involvement is more common in this subset. 1
Important Caveats
Most cardiac findings in myasthenia gravis patients are likely due to other causes such as coronary artery disease in older patients, medication effects (particularly from acetylcholinesterase inhibitors), or intercurrent respiratory problems rather than direct myasthenic involvement of the heart. 4
Certain medications used in myasthenia gravis treatment or that should be avoided (such as β-blockers) can affect cardiac function, making it important to distinguish medication effects from disease-related cardiac involvement. 1, 3
Respiratory compromise from myasthenic crisis can secondarily affect cardiac function through hypoxemia and respiratory failure, but this is not direct cardiac muscle involvement by the disease process. 2