Myocardial Infarction

Core Concepts

From ischemia to infarction

Think of a neighborhood losing its water supply. When the water stops, the houses are still standing — that is ischemia: cells are alive but starved, and they send out pain signals (angina). If the water stays off too long, the houses begin to burn and collapse — that is infarction: cells die. The boundary between them is not a fixed number of minutes; it depends on whether any collateral circulation exists and how completely the artery is blocked. The key nursing concept: ischemic tissue can be saved, infarcted tissue cannot. The faster blood flow is restored (reperfusion), the smaller the final scar.

The ACS spectrum

Stable angina is predictable: chest pressure with exertion, relieved by rest, caused by a fixed narrowing that limits flow when demand rises. Unstable angina is a warning flare: pain that comes on at rest, is new, or is worse than usual — a sign the plaque is becoming unstable, but no muscle has died yet. NSTEMI (non-ST-elevation MI) is cell death without the classic ST elevation — the artery may be partially or intermittently blocked. STEMI (ST-elevation MI) shows ST-segment elevation on the ECG and usually means a completely occluded artery; it is the ultimate emergency. All four share the same underlying biology — coronary artery disease — but they differ in stability and urgency, and this spectrum explains why "chest pain" gets treated so seriously at triage.

Recognizing the presentation

Classic MI pain is deep, pressure-like chest discomfort — often described as squeezing, heaviness, or an "elephant sitting on my chest" — that may radiate to the left arm, jaw, back, or epigastrium, and is not relieved by rest. But the classic picture is not the only picture. Atypical presentations are common and dangerous to miss: women, older adults, and people with diabetes may have no chest pain at all, presenting instead with shortness of breath, fatigue, nausea, indigestion, diaphoresis, or pain only in the jaw, shoulder, or upper back. People with diabetes may have "silent" ischemia because neuropathy blunts the pain signal. The nursing rule: in anyone with risk factors who "just doesn't feel right," an ECG is cheap and a missed MI is not.

Diagnostic clues

Three tools carry the diagnosis. The ECG can show ST elevation (STEMI), ST depression or T-wave changes (ischemia or NSTEMI), or a new bundle branch block — and a normal ECG does not rule out MI, especially early. Cardiac biomarkers — troponin is the cornerstone — are proteins released into the blood when heart muscle cells die; they rise after damage and stay elevated for days. The lab draws the diagnosis in cases where the ECG is unclear, and serial levels show whether damage is ongoing. The history is just as important: quality, timing, radiation, associated symptoms, and risk factors (smoking, hypertension, diabetes, high cholesterol, family history) all feed the picture. Nursing point: draw the ECG and start monitoring before the troponin results arrive, not after.

Complications to watch

MI is not over when pain stops; the injured muscle is electrically unstable and mechanically weak. Dysrhythmias — especially ventricular tachycardia and fibrillation — are the leading early killer and the reason every MI patient is on a cardiac monitor. Heart failure can develop when the damaged pump cannot handle the workload, signaled by dyspnea, crackles, and low oxygen saturation. Cardiogenic shock — the pump failing so badly that organs are underperfused — is the most severe form and carries a very high mortality. Later complications include pericarditis (inflammation of the sac around the heart, often days after the event) and ventricular wall rupture or aneurysm in extensive infarcts. The nurse's continuous assessment — rhythm, vital signs, lung sounds, urine output, mental status — is the early warning system for all of these.

Nursing priorities: acute and ongoing

In the acute phase, priorities are: recognize and escalate immediately (activate the rapid-response/STEMI pathway per institutional protocol), obtain an ECG within minutes, establish IV access, monitor the rhythm, give oxygen only if the person is hypoxemic, position for comfort, and reassure — fear itself raises the heart's oxygen demand. Reperfusion decisions (catheterization, clot-busting therapy) are made by the provider and are time-critical. Scope note: which medications, oxygen, and reperfusion strategies are used, and in what order, follows the current evidence-based guidelines and institutional protocols — the nurse administers and monitors, and must know the protocol but not improvise it. After the acute phase, the nurse's role shifts to secondary prevention teaching: recognizing recurrent symptoms, medication adherence, cardiac rehabilitation, smoking cessation, and knowing when to call for help.

Common Confusions