Colchicine in patients with chronic inflammatory cardiomyopathy: rationale and design of the CMP-MYTHiC

Introduction Acute myocarditis can lead to chronic inflammatory cardiomyopathy (Infl-CMP), a condition characterized by increased risk of ventricular arrhythmias (VA), left ventricular (LV) systolic dysfunction (LVSD), and heart failure (HF). Immunosuppressive therapy is generally not recommended for Infl-CMP when diagnosed non-invasively by cardiac magnetic resonance imaging (CMRI) or fluorodeoxyglucose-positron emission tomography (FDG-PET). We are assessing, in the CMP-MYTHiC trial, whether colchicine (0.5 mg in patients <70 kg or 1 mg in patients >= 70 kg), an immunomodulatory drug with a good safety profile, can reduce myocardial inflammation in patients with Infl-CMP. Study design The CMP-MYTHiC, a multicenter investigator-initiated single-blinded randomized controlled trial, screens adult patients diagnosed with Infl-CMP by CMRI or FDG-PET within the prior 3 months at 12 Italian centres. Eligibility is further defined by the presence of VA or LVSD/HF phenotype. VA phenotype is determined by a high burden of premature ventricular complexes (PVCs) on baseline 24-h ECG ambulatory monitoring, non-sustained ventricular tachycardia (NSVT), or sustained ventricular tachycardia (SVT). The LVSD/HF phenotype is characterized by reduced LV ejection fraction (LVEF <50% on echocardiogram or <60% on CMRI) or elevated natriuretic peptide levels. Key exclusion criteria include a history of myocardial infarction, cardiomyopathy attributed to other specific causes, and systemic autoimmune disorders. The efficacy of colchicine compared with placebo will be assessed when CMRI or FDG-PET scans and 24-h ambulatory ECG monitoring are repeated at 6 months after randomization. The primary endpoint of the trial analysed according to the intention-to-treat population is the proportion of patients who are alive and free from any clinical (cardiac death or hospitalization due to HF or VA episodes), arrhythmic (PVC burden increase >= 50%, NSVT increase >= 30%, or any SVT), or imaging (LVEF reduction >10% or new areas of oedema plus increased inflammation) worsening, and who demonstrate improvement in either imaging (reduction in oedema on CMRI or FDG uptake) or arrhythmic (PVC burden reduction >= 70% with no NSVT/SVT) outcomes at 6 months. Assuming 80% power with an overall type I error of 0.025 using one-sided Fisher's Exact test, 40 patients per group are required to demonstrate that the primary endpoint will be reached in 66% of patients in the colchicine group compared with 33% in the placebo. Twenty-nine patients were randomized since December 2023, and the conclusion is expected in 2029. Discussion The results can define the role of colchicine in treating patients with Infl-CMP non-invasively diagnosed by CMRI or FDG-PET.