Cardiac involvements in myasthenia gravis associated with anti-Kv1.4 antibodies

Background and purpose: There is no general consensus as to whether autoimmune myasthenia gravis (MG) is associated with heart diseases, despite the fact that myocarditis, a serious cardiac involvement treatable by immunotherapy, is a complication of MG. It has been observed previously that MG patients with clinically suspected myocarditis had anti-Kv1.4 antibodies. The purpose of this study was to disclose the association between anti-Kv1.4 antibodies and cardiac involvements in MG patients. Methods: Anti-Kv1.4 antibody was detected by an immunoprecipitation assay using ³⁵S-labeled rhabdomyosarcome cellular extract as the antigen source. Cardiac findings including electrocardiography (ECG) and clinical features of clinically suspected myocarditis in MG patients with anti-Kv1.4 antibodies were investigated. Ultrasound echocardiography (UCG) of ex vivo chick embryos was performed to determine the suppressive effects of sera with or without anti-Kv1.4 antibodies on heart muscle functions. Results: Seventy (10.8%) of 650 MG patients had anti-Kv1.4 antibodies and 60% of them had abnormal ECG findings with high frequencies of T-wave abnormality and QT prolongation. Clinically suspected myocarditis was found in eight MG patients with anti-Kv1.4 antibodies but in none of the MG patients without anti-Kv1.4 antibodies. Most patients showed rapid deterioration with lethal arrhythmias such as ventricular tachycardia, sick sinus syndrome, or complete atrial ventricular block and severe heart failure. It was concluded using UCG of ex vivo chick embryos that MG serum with anti-Kv1.4 antibodies suppressed heart muscle functions. Conclusion: It has been demonstrated that anti-Kv1.4 antibodies are possible markers for cardiac involvements in MG patients.