Volatilome and Single-Lead Electrocardiogram Optimize Ischemic Heart Disease Diagnosis Using Machine Learning Models

Inclusion Criteria: 1. Age ≥40 years; 2. Absence of acute exacerbations of psychiatric disorders or cognitive impairments that would preclude study participation; 3. Provision of written informed consent for study participation, blood sample collection, and anonymous publication of research results; 4. Pre-test probability of ischemic heart disease between 1% and 33%. Non-inclusion criteria: 1. Pregnancy and breastfeeding; 2. Diabetes mellitus; 3. Presence of acute myocardial ischemia (acute coronary syndrome or myocardial infarction within the preceding 48 hours) or a history of myocardial infarction; 4. Active infectious or non-infectious inflammatory diseases in the acute/exacerbation phase; 5. Connective tissue diseases (regardless of disease activity); 6. Respiratory disorders (e.g., bronchial asthma, chronic bronchitis, cystic fibrosis, or other conditions associated with significant respiratory dysfunction); 7. Acute pulmonary thromboembolism involving the pulmonary artery or its branches; 8. Aortic dissection; 9. Hemodynamically significant decompensated cardiac valvular defects\*\*; 10. Active malignancy; 11. Decompensated chronic heart failure (NYHA class III-IV) or acute heart failure; 12. Neurological disorders (e.g., Parkinson's disease, multiple sclerosis, acute psychosis, Guillain-Barré syndrome); 13. Cardiac arrhythmias or conduction abnormalities contraindicating stress testing; 14. Musculoskeletal disorders precluding exercise testing (e.g., bicycle ergometry); 15. Allergy to radiocontrast agents and/or adenosine triphosphate (ATP); 16. Chronic kidney disease with an estimated glomerular filtration rate (eGFR) \<30 mL/min/1.73 m² (CKD-EPI formula); 17. Severe hepatic insufficiency and/or Child-Pugh class B or C liver cirrhosis. Exclusion Criteria: 1. Poor recording quality of single-channel electrocardiogram (ECG) and/or plethysmography data; 2. Failure to complete the stress test due to reasons unrelated to cardiac conditions; 3. Voluntary withdrawal of consent to continue participation in the study; 4. Post-enrollment development of conditions or identification of pathologies listed in the exclusion criteria.