NQMI typically occurs when a partial or incomplete blockage of a coronary artery causes ischemia (lack of blood flow) to the heart muscle. This leads to damage to the heart muscle, but not complete necrosis. As a result, there is no Q wave on the ECG.

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A non-Q wave heart attack, also known as a non-ST elevation myocardial infarction (NSTEMI), is a type of heart attack characterized by ST depression or T-wave changes on an electrocardiogram (ECG) but without the development of pathological Q waves. This type of heart attack is often caused by a partial blockage in a coronary artery and can be a serious condition requiring immediate diagnosis and treatment, though it is sometimes considered less damaging to the heart than a STEMI (ST-elevation myocardial infarction). The key diagnostic findings on an ECG are ST segment depression or T-wave inversion, rather than the development of new Q waves that indicate a full-thickness (transmural) heart attack.
Coronary artery blockage: This type of event is often a result of a partial, rather than a complete, blockage of a coronary artery.
Acute coronary syndrome: It falls under the umbrella of acute coronary syndrome, which also includes unstable angina. The distinction between a non-Q wave MI and unstable angina is the rise in cardiac enzymes (like troponin) in the blood that indicates heart muscle damage.
Prognosis
Short-term risk: Non-Q wave heart attacks typically have a lower in-hospital death rate than Q-wave infarctions.
Long-term risk: However, they carry a higher risk of subsequent coronary events and reinfarction in the long term. This is because even though the initial damage may be smaller, the underlying cause of the partial blockage still exists, making it a dangerous condition that requires ongoing risk management.