What question did this study set out to answer?

To present a rare case of isolated atrial myocarditis and discuss its diagnostic process and management.

January 10, 2026European Heart Journal - Case Reports0 citationsOpen Access

Isolated Atrial Myocarditis Presenting with Atrial Arrhythmias and Diffuse Thickening of the Atrial Wall Diagnosed via Atrial Biopsy: A Case Report

MEMakoto EdayoshiSaga University KYKensuke YokoiSaga University TYTakanori YamaguchiKyushu University

Key Result

Lymphocytic atrial myocarditis resolved with anticoagulation and spontaneous improvement, as the patient remained symptom-free at 1-year follow-up.

Key Points

To present a rare case of isolated atrial myocarditis and discuss its diagnostic process and management.
Clinical presentation and symptoms assessment
Electrocardiogram for arrhythmia detection
Multimodality imaging including echocardiography and CT
Histological investigation via endomyocardial biopsy
Follow-up imaging to assess resolution
Diagnosis of isolated lymphocytic atrial myocarditis via biopsy confirmed by multimodality imaging.
Patient showed improvement in atrial arrhythmia and wall thickening without immunosuppressive therapy.
Thrombus in left atrial appendage resolved completely with anticoagulation in 3 months.
No recurrence of symptoms like atrial fibrillation at 1-year follow-up.

Structured PICO

Population

A 69-year-old woman presenting with general fatigue, syncope, sick sinus syndrome (HR 40 bpm), left atrial wall thickening, mild pericardial effusion, and left atrial appendage thrombus.

Intervention

Transcatheter endomyocardial atrial biopsy, multimodality imaging (TTE, CT, FDG-PET/CT), and anticoagulation therapy

Outcome

Diagnosis of isolated lymphocytic atrial myocarditis and clinical resolution

A combination of multimodality imaging and transcatheter atrial biopsy is useful for definitively diagnosing isolated atrial myocarditis in patients presenting with atrial arrhythmias and wall thickening.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

Abstract Background Isolated atrial myocarditis is rarely diagnosed in non-open-heart surgical cases. We report a case of isolated lymphocytic atrial myocarditis presenting with atrial arrhythmias, syncope, and atrial wall thickening, confirmed histologically by transcatheter atrial biopsy and multimodality imaging. Case Summary A 69-year-old woman presented to the emergency department with general fatigue and a syncopal episode. Electrocardiogram revealed sick sinus syndrome (SSS) with a heart rate of 40 beats/min. Laboratory tests indicated a mild inflammatory response without cardiac enzyme level elevation. Transthoracic echocardiography demonstrated left atrial wall thickening and mild pericardial effusion. Contrast-enhanced computed tomography revealed a thrombus in the left atrial appendage, 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) showed diffuse uptake in both atria without ventricular involvement. Three weeks later, the patient presented with atrial fibrillation. An endomyocardial atrial biopsy was performed to histologically investigate the cause of atrial wall thickening, which revealed lymphocytic myocarditis, thereby ruling out malignant lymphoma and amyloidosis. No causative virus was identified, and immunosuppressive therapy was not initiated because the patient showed spontaneous improvement in atrial arrhythmia and atria wall thickening. Anticoagulation therapy resulted in complete resolution of the thrombus within 3 months. Follow-up FDG-PET/CT at 5 months confirmed the resolution of atrial uptake, and the patient remained symptom-free without SSS or AF recurrence at the 1-year follow-up. Discussion In cases of isolated atrial myocarditis presenting with atrial arrhythmias and atrial wall thickening, a combination of imaging modalities and histological evaluation by atrial biopsy may be helpful in establishing a definitive diagnosis.

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