C67 ATRIOVENTRICULAR BLOCK DUE TO CARDIAC CONDUCTION TISSUE INFILTRATION: A CLINICAL PRESENTATION OF TRANSTHYRETIN CARDIAC AMYLOIDOSIS

Abstract

Abstract Background In cardiac amyloidosis, the deposition of insoluble amyloid fibrils can affect the cardiac conduction tissue, causing bradyarrhythmic clinical manifestations, often in the advanced stages of the disease. In this clinical case, atrioventricular block represented the clinical onset of transthyretin cardiac amyloidosis. Clinical case A 68–year–old man was admitted to our ward for recurrent syncopal episodes. He had in his medical history bilateral carpal tunnel syndrome. The electrocardiogram documented sinus rhythm with preserved QRS voltages, right bundle branch block, left anterior hemiblock, and first and second degree atrioventricular block with mean ventricular rate of 38 beats/min. A color–Doppler echocardiogram revealed increased left and right ventricular thickness (maximum thickness 16 and 10 mm, respectively), diastolic dysfunction, and preserved ejection fraction (60%). The patient underwent a coronary angiography, which was normal, and an endomyocardial biopsy of the left ventricle, which revealed the presence of hypotrophic and degenerated cardiomyocytes surrounded by large areas of amorphous substance that exhibited apple–green birefringence in polarized light after staining with Congo red, suggesting the diagnosis of cardiac amyloidosis. Sections of conduction tissue were included in the specimens, which appeared on histology as small myocytes positive by immunohistochemistry for HCN4, suggestive of conduction tissue cardiomyocytes. The conducting tissue was almost completely replaced by amyloid deposits positive by immunohistochemistry for transthyretin. The affected patient underwent a genetic test which revealed the mutation of the TTR gene (p.Thr79Lys). The patient subsequently underwent pacemaker implantation and started treatment with Tafamidis due to the absence of neurological involvement. Conclusion In patients presenting clinically with syncope and conduction abnormalities, the diagnosis of cardiac amyloidosis should always be considered, because they may represent the clinical onset of the disease.