Electrocardiogram (ECG) Findings and Myocardial Infarction Criteria

Flashcards covering ECG stages of infarction, diagnostic criteria for myocardial injury and infarction, and cardiac biomarker timelines.

Hyperacute T wave

The earliest ECG finding of myocardial ischemia, occurring within seconds of infarction, where T wave size exceeds normal criteria ($< 5\,mm$ in limb leads and $< 10\,mm$ in chest leads).

ST elevation

An ECG finding referred to as the 'current of injury' that indicates myocardial injury and typically appears within minutes of infarction.

AHA ST elevation criteria (Male)

New onset ST elevation at the J point of $> 2\,mm$ in leads $V_2-V_3$.

AHA ST elevation criteria (Female)

New onset ST elevation at the J point of $> 1.5\,mm$ in leads $V_2-V_3$, or $> 1\,mm$ in other contiguous chest leads.

Pathological Q waves

ECG findings that develop after $> 1\,hr$ of infarction, indicating cell death or a previous MI, and typically persist for the patient's entire life.

Myocardial injury

Defined by evidence of elevated cardiac troponin ($cTn$) levels with at least one value above the $99^{th}$ percentile upper reference limit ($URL$).

Troponin I ($cTnI$)

A cardiac biomarker that rises in $3 \text{ to } 4 \text{ hrs}$ after infarction; serial measurements are considered the most specific test for diagnosing MI.

CPKMB

A cardiac biomarker that takes approximately $4 \text{ to } 6 \text{ hrs}$ to rise following a myocardial infarction.

Levine's sign

A clinical symptom of myocardial ischemia where a patient holds a clenched fist over their chest to describe ischemic chest pain lasting $> 20\,mins$.

Stunned myocardium

A sudden decrease in heart contractility (regional hypokinesia) visible on imaging, caused by reduced oxygen supply primarily due to a thrombus in a coronary artery.