Rationale and design of the imaging for detection rate of cardiac transthyretin amyloidosis study (the IMPACT study)

Abstract

Background: The real prevalence of transthyretin cardiac amyloidosis (ATTR-CA) remains unknown because most studies have focused on selected populations. Early diagnosis of ATTR-CA is crucial for these patients to benefit from appropriate treatments.

Aims: The primary aim was to determine the detection rate of ATTR-CA in a minimally selected cardiology population. Secondary aims were to compare this wide screening strategy to the usual strategy based on red flags identification, on the detection of the disease and regarding cost-effectiveness; to evaluate the detection rate of ATTR-CA and the characteristics of patients in subgroups (other left ventricular hypertrophy [LVH] factors, number of red flags); and to propose a new diagnostic score.

Methods: Between October 2021 and June 2023, 400 patients were prospectively included at our institution and underwent technetium-99m hydroxymethylene-diphosphate bone scintigraphy and immune tests. Inclusion criteria were age ≥60 years and LVH ≥12mm on transthoracic echocardiography. Main exclusion criteria were a previous diagnosis of cardiac amyloidosis, history of heart transplant, recent bone scintigraphy, contraindication to scintigraphy and current bisphosphonates treatment. ATTR-CA was confirmed in the presence of significant cardiac uptake on bone scintigraphy (Perugini ≥2) without significant monoclonal gammopathy.

Conclusion: This prospective interventional study is the first to focus on cardiology patients with LVH, irrespective of overlapping causes of LVH or any other red flag. These data will provide new insights about ATTR-CA epidemiology and help refine the selection of patients who could benefit from this early screening strategy, to shorten diagnostic delay and ultimately improve outcomes.

Keywords: Bone scintigraphy; Cardiac amyloidosis; Screening; Transthyretin.