Everything You Need to Know About Stable angina vs unstable angina for Step 1

Stable vs unstable angina is one of those Step 1/2 topics that sounds straightforward—until the question stem starts throwing in troponins, ECG nuances, and “relieved by rest” bait. The key is to anchor everything to plaque biology (stable cap vs disrupted cap) and demand ischemia vs supply collapse. Once you do that, the presentations, diagnostics, and treatments fall into place.

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Big Picture (Step-Framing)

Angina = myocardial ischemia without infarction (unless it progresses). The myocardium is oxygen-starved, causing chest discomfort and sometimes transient ECG changes. The differentiator is what’s happening in the coronary plaque and whether the ischemia is predictable or new/worsening/resting.

Core Step mantra:

• Stable angina = fixed stenosis → predictable demand ischemia
• Unstable angina = plaque rupture/erosion + non-occlusive thrombus → unpredictable supply reduction

First Aid cross-reference: Cardiovascular — Ischemic heart disease/angina; Acute coronary syndromes; Antianginal drugs.

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Definitions (Know These Cold)

Stable Angina

Predictable chest pain triggered by exertion/emotion and relieved by rest or nitroglycerin.
Due to fixed atherosclerotic narrowing (classically >70%).

Unstable Angina (UA)

An acute coronary syndrome (ACS) characterized by:

• chest pain at rest, new-onset, or increasing frequency/severity (crescendo)
• NO myocardial necrosis markers (troponin negative)

Mechanism: plaque rupture/erosion → platelet aggregation → partially occlusive thrombus ± distal microembolization/vasoconstriction.

Clinical pearl: UA and NSTEMI are often clinically indistinguishable initially—troponins separate them.

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Pathophysiology (Where Questions Live)

Stable Angina: “Fixed Pipe, Higher Demand”

• Stable fibrous cap over an atherosclerotic plaque
• Fixed stenosis limits ability to increase coronary flow during exertion
• Ischemia is usually subendocardial and transient
• ECG during pain: often ST depression and/or T-wave inversion (may be normal at rest)

Why subendocardium? It’s furthest from epicardial vessels and most compressed during systole.

Unstable Angina: “Broken Cap, Platelets, Spasm”

• Thin fibrous cap + large lipid core + inflammation → rupture/erosion
• Platelet plug + thrombus → dynamic obstruction
• Ischemia is still typically subendocardial but more severe/prolonged and can occur at rest

High-yield plaque stability facts (often tested conceptually):

• Vulnerable plaque: thin cap, high macrophages, large lipid core
• Stable plaque: thick cap, more fibrosis/smooth muscle

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Clinical Presentation (Compare Side-by-Side)

Step trap: If biomarkers are positive → it’s NSTEMI, not unstable angina, even if ECG looks the same.

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Diagnosis (Step 1 vs Step 2 Emphasis)

Stable Angina Workup (Classic Step 2 flow)

1. History: exertional chest pressure relieved by rest/nitro
2. Baseline ECG
3. Stress testing if stable and able (exercise ECG; stress imaging if baseline ECG abnormal)
4. Coronary angiography if high-risk features or positive stress test

What stress testing does: provokes demand ischemia, exposing flow limitation from fixed stenosis.

Unstable Angina Workup (Treat like ACS)

Unstable angina is diagnosed in an ACS rule-out framework:

• ECG ASAP (look for ST depression, T inversion, transient ST changes)
• Serial troponins (negative in UA, positive in NSTEMI)
• Risk stratification (TIMI/GRACE in real life; on exams, look for high-risk features)
• Early cardiology evaluation ± angiography depending on risk

High-yield: You don’t “stress test” someone with ongoing or high-risk chest pain suggestive of ACS.

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Treatment (Memorize the “Why,” Not Just the List)

Stable Angina Treatment

Goal: reduce myocardial oxygen demand and improve coronary perfusion; prevent events.

Acute symptom relief

• Sublingual nitroglycerin
  • Venodilation > arterial dilation → ↓ preload → ↓ wall stress → ↓ $MVO_2$

Chronic management (high-yield set)

• Beta-blockers (first-line): ↓ HR, ↓ contractility → ↓ demand
• Calcium channel blockers (esp. if vasospasm or can’t tolerate beta-blockers)
• Long-acting nitrates (tolerance develops; nitrate-free interval)
• Ranolazine: decreases late Na$^+$ current → ↓ wall tension and oxygen demand
  • Side effect: QT prolongation (common testable association)
• Antiplatelet therapy: aspirin (unless contraindicated)
• Statin and aggressive risk factor modification (smoking, HTN, diabetes)

Revascularization

• PCI/CABG for refractory symptoms or high-risk coronary anatomy.

First Aid cross-reference: Antianginal drugs (nitrates, beta-blockers, CCBs, ranolazine); Atherosclerosis/risk factors.

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Unstable Angina Treatment (Treat Like NSTEMI Until Proven Otherwise)

Goal: prevent progression to MI by addressing platelets + thrombus + ischemia.

Immediate/early management (high yield “ACS bundle”)

• Aspirin (inhibits thromboxane A2 via irreversible COX-1 inhibition)
• P2Y12 inhibitor (clopidogrel, ticagrelor, prasugrel) depending on scenario
• Anticoagulation: heparin (UFH/LMWH) to prevent thrombus propagation
• Nitroglycerin for pain (symptom relief)
• Beta-blocker (unless contraindicated like acute decomp HF, severe bradycardia, hypotension)
• High-intensity statin
• Oxygen only if hypoxemic (more Step 2 nuance)

Risk-based invasive strategy

• High-risk features → early angiography ± PCI

Things that are NOT the mainstay in UA

• Fibrinolytics: reserved for STEMI (and some very specific situations)—not UA/NSTEMI.

First Aid cross-reference: Acute coronary syndromes; Antiplatelet agents; Heparin; MI management overview.

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ECG and Biomarkers: The “Most Tested Sorting Algorithm”

Key Sorting Rules

• ST elevation in contiguous leads + ischemic symptoms → think STEMI (not angina)
• ST depression/T inversion can be stable angina, UA, or NSTEMI
• Troponin negative + ACS symptoms → unstable angina
• Troponin positive → NSTEMI (even if no ST elevation)

What’s happening at the tissue level?

• Stable angina/UA: ischemia without necrosis
• NSTEMI: subendocardial necrosis
• STEMI: transmural necrosis due to complete occlusion

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High-Yield Associations & Classic Vignettes

Stable Angina Vignette

• Middle-aged patient with risk factors
• Chest pressure climbing stairs, relieved by rest
• Normal troponin
• Stress test triggers ST depression

Associated pathology: atherosclerosis with stable fibrous cap and fixed narrowing.

Unstable Angina Vignette

• Chest pain at rest or waking from sleep, more frequent over days
• ECG may show ST depression/T inversion or be normal
• Serial troponins negative
• Gets treated like ACS with antiplatelet + anticoagulation

Associated pathology: plaque rupture/erosion, platelet-rich thrombus.

Common Step risk factors (atherosclerosis)

• Smoking, HTN, diabetes, hyperlipidemia, age, family history
• Diabetes is a huge “accelerator” of CAD.

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Rapid-Fire Step Pearls (Easy Points)

• Stable angina: predictable, exertional, relieved by rest/nitro; fixed stenosis.
• Unstable angina: new/worsening/rest pain; plaque disruption + non-occlusive thrombus; troponin negative.
• UA and NSTEMI are both subendocardial ischemia patterns—troponin decides.
• Treat UA like ACS immediately: antiplatelet + anticoagulation + anti-ischemic therapy.
• Fibrinolytics are for STEMI, not UA/NSTEMI.

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Mini Summary Table (Last-Minute Review)