This is an exploratory, prospective, non-profit study (SUBDIMA) designed to investigate the prevalence and potential prognostic significance of subclinical depression in patients admitted with a first acute myocardial infarction (AMI). Subclinical depression refers to the presence of mild depressive symptoms (PHQ-9 score 5-9) that do not meet DSM-5 TR criteria for major depressive disorder but may still be clinically relevant. The primary aim is to estimate the prevalence of subclinical depression in this setting. Secondary, exploratory objectives include evaluating associations with inflammatory and metabolic biomarkers, autonomic dysfunction, cardiac function, cognitive performance, quality of life, treatment adherence, and the risk of recurrent cardiovascular events over 12 months. The study is expected to generate new descriptive data that may inform future confirmatory trials and support early, personalized approaches to integrated cardiac and mental health care.

Depression is a recognized risk factor for adverse outcomes in patients with acute coronary syndromes. While most studies have focused on major depressive disorder, subclinical depression (defined as PHQ-9 scores between 5 and 9 in the absence of DSM-5 TR criteria for major depression) remains poorly characterized. Its prevalence in patients with a first acute myocardial infarction (AMI) is largely unknown, as are its potential associations with clinical, biological, and psychosocial outcomes.

The SUBDIMA study is a prospective, exploratory, single-center, non-profit clinical investigation conducted at Fondazione Policlinico Universitario A. Gemelli IRCCS. Consecutively admitted patients with a first AMI will undergo systematic screening with the PHQ-9 and a structured clinical assessment to exclude major depression. Based on these evaluations, patients will be classified into two groups: with or without subclinical depression. All participants will be followed for 12 months, with visits at baseline, 3 months, and 12 months, and intermediate phone contacts at 6 and 9 months.

The primary aim of the study is descriptive: to estimate the prevalence of subclinical depression in this population. Secondary, exploratory aims are to examine potential associations between subclinical depression and:

• inflammatory and metabolic biomarkers,
• measures of autonomic dysfunction (e.g., heart rate variability),
• cardiac function parameters (e.g., echocardiographic strain indices, NT-proBNP),
• cognitive and anxiety assessments,
• health-related quality of life and lifestyle factors,
• adherence to treatment,
• and the incidence of recurrent cardiovascular events during follow-up.

Given its exploratory design, the study is not powered to test confirmatory hypotheses. Instead, it is expected to provide novel descriptive data that will inform the design of future confirmatory trials and contribute to the integration of psychosocial screening in cardiology care pathways.

Inclusion Criteria:

• Age ≥18 years
• Hospital admission for first acute myocardial infarction (STEMI or NSTEMI) within 7 days from the index event
• PHQ-9 administered at screening
• Mini Mental State Examination (MMSE) score ≥26
• Written informed consent obtained

Exclusion Criteria:

• Previous history of acute myocardial infarction
• Diagnosis of major depression according to DSM-5 TR criteria
• Severe cognitive impairment (MMSE <26)
• Severe comorbidities with expected survival <12 months
• Inability to participate in scheduled follow-up assessments
• Refusal or inability to provide informed consent
• Concurrent participation in other interventional clinical studies that could interfere with study outcomes

No masking will be applied. Both investigators and participants will be aware of group classification (open label).