APCU25MPC1 Silent structural abnormality with significant electrical consequences: case report of mitral annular disjunction and high PVC burden

Introduction Mitral annular disjunction (MAD) is an underrecognized structural abnormality defined by the separation of the mitral valve hinge point from the left ventricular myocardium. While historically associated with mitral valve prolapse, recent evidence highlights its role as an arrhythmogenic substrate, even in the absence of significant mitral regurgitation.Case Presentation We describe a 54-year-old Malay woman with a background of undifferentiated connective tissue disease and nodular prurigo who presented with intermittent palpitations. A 12-lead ECG revealed frequent premature ventricular contractions (PVCs) with a right bundle branch block morphology, r-wave transition at V2, and inferior axis, suggesting an origin from the anterior mitral annulus. A 72-hour Holter monitor demonstrated a high PVC burden. Transthoracic echocardiography showed preserved left ventricular systolic function (ejection fraction 60%), grade I diastolic dysfunction, and trivial aortic and tricuspid regurgitation. Coronary computed tomography angiography excluded atherosclerotic coronary disease. Cardiac magnetic resonance imaging (CMR) demonstrated mitral annular disjunction with maximal displacement of 0.6 cm and subtle mid-myocardial fibrosis in the basal septum and inferior wall, without evidence of myocardial infarction or infiltrative disease.Results The constellation of high-burden PVCs, ECG morphology suggesting a mitral annular origin, and CMR findings of MAD with localized fibrosis strongly supports MAD as the arrhythmogenic substrate in this patient, despite preserved ventricular function and the absence of mitral valve prolapse or coronary artery disease.Discussion MAD has a reported prevalence of 8–30%, varying with imaging modality and population studied. Its pathophysiology involves abnormal atrioventricular junction mechanics that impose mechanical stress on the posterior annulus and adjacent myocardium, leading to myocardial stretch, fibrosis, and arrhythmogenesis. Arrhythmias linked with MAD include isolated PVCs, non-sustained and sustained ventricular tachycardia, and, in some cases, sudden cardiac death. In this case, the ECG morphology pointing to a left-sided annular origin aligns with the observed displacement and myocardial fibrosis on CMR, reinforcing the mechanistic association between structural abnormality and electrical manifestation. Beyond arrhythmias, MAD predisposes to progressive mitral regurgitation, myocardial fibrosis, diastolic dysfunction, and eventual heart failure.Conclusion This case illustrates MAD as a clinically significant yet underdiagnosed cause of high-burden PVCs in the absence of mitral valve prolapse or coronary disease. Recognition of ECG features correlating with annular origin, supported by advanced imaging, is crucial for accurate diagnosis, risk stratification, and long-term surveillance in patients with MAD.