Diagnostic Value of Combined Light and Electron Microscopic Examination in Endomyocardial Biopsy in Patients with Cardiac Amyloidosis.

Background: Despite advances in imaging techniques, endomyocardial biopsy remains the gold standard for confirming cardiac amyloidosis (CA) and defining the amyloid type. Electron microscopy may detect amyloid deposits with greater sensitivity than light microscopy; however, its capabilities have not been thoroughly investigated.

Methods: Patients with pathologically diagnosed CA were prospectively enrolled. Myocardial specimens were collected from the right ventricular septum, and light and electron microscopy were performed on the samples to compare their efficacy in detecting amyloid deposits.

Results: Sixty-five patients were pathologically diagnosed with CA, including 13 with light-chain amyloidosis, 51 with transthyretin amyloidosis, and one with unclassified amyloidosis. Amyloid deposits were detected through both examinations in 60 (92.3%) of the 65 patients. However, they were detected through only light microscopy in two cases (3.1%) and only electron microscopy in three cases (4.6%). Patients with amyloid deposits detected through a single method had reduced thickness of the intraventricular septal wall (9.5 vs. 15.1 mm, p=0.001), lower left ventricular (LV) mass index (94 vs. 147 g/m², p= 0.013), greater LV diastolic dimension (45 vs. 41 mm, p=0.044), lower LVEF (49% vs. 57%, p=0.004), lower mean pulmonary capillary wedge pressure (9 vs. 19 mmHg, p=0.021), and lower right atrial pressure (4 vs. 8 mmHg, p=0.043) than did those in whom they were detected using both methods.

Conclusions: Concomitant use of electron microscopy may improve the detection rate of amyloid deposits and prevent CA misdiagnosis, especially in patients with atypical features such as mild hypertrophy or eccentric hypertrophy with LV systolic dysfunction.