Final answer:
The diagnosis suggested by substernal chest pain that worsens when lying down and improves when leaning forward is pericarditis, an inflammation of the pericardium. This symptom is distinct from myocardial infarction, which usually includes additional symptoms and the pain does not vary with position.
Step-by-step explanation:
The symptoms described—substernal chest pain that worsens when lying down and improves upon leaning forward—can be indicative of pericarditis. This condition is characterized by inflammation of the pericardium, the fibrous sac surrounding the heart. The pain associated with pericarditis may mimic that of myocardial infarction (heart attack), but the positional nature of the pain is more typical of pericarditis. While acute myocardial infarction (MI), commonly known as a heart attack, also presents with substernal chest pain, it is usually accompanied by other symptoms such as difficulty breathing, irregular heartbeat, nausea, and sweating. It's essential for the patient to seek medical evaluation immediately for a proper diagnosis, as both conditions require prompt medical attention.
Pain that improves by leaning forward is a classic sign of pericarditis, which differentiates it from the pain due to a myocardial infarction. In the case of a heart attack, pain is often retrosternal, radiating down the left arm in males (but not always in females) and does not vary with position. Patients experiencing these symptoms should undergo assessment for potential coronary artery disease (CAD), which can manifest as stable or unstable angina, with the latter being more serious and requiring urgent care.