Cardiovascular Emergencies
Learning Objectives
- Recognize the clinical presentation and ECG findings of STEMI, NSTEMI, and unstable angina.
- Apply the initial management sequence (MONA-B, reperfusion decisions) for acute coronary syndrome.
- Walk through the ACLS cardiac arrest algorithm for shockable and non-shockable rhythms.
- Identify the classic presentation and diagnostic workup of aortic dissection and distinguish it from ACS.
- Avoid common pitfalls in recognizing and managing cardiovascular emergencies.
Quick Answer
Cardiovascular emergencies are time-critical conditions — acute coronary syndrome (ACS), cardiac arrest, and aortic dissection being the "big three" — where minutes determine whether the patient survives or how much myocardium/tissue is salvaged. The unifying skill is pattern recognition: read the ECG, decide "shockable or not," and know which chest pain needs a cath lab versus a CT scan versus a scalpel. Getting this wrong (e.g., giving anticoagulation to a dissection, or thrombolytics to a dissection mistaken for STEMI) can kill a patient in minutes. This topic is high-yield because exams test the exact decision points where management diverges.
Overview
Every cardiovascular emergency shares one theme: a sudden interruption of blood flow to the heart, brain, or great vessels, where treatment delay directly costs tissue and lives ("time is muscle," "time is brain"). Three conditions dominate both real-world emergency departments and exam papers — acute coronary syndrome, cardiac arrest, and aortic dissection — because they present with overlapping symptoms (chest pain, hemodynamic collapse) but demand completely different, sometimes opposite, treatments. Learning to tell them apart quickly, using history, exam, and a 12-lead ECG, is the core clinical skill this chapter builds.
Acute Coronary Syndrome (ACS)
Definition: ACS is a spectrum of conditions caused by sudden reduction in coronary blood flow, ranging from unstable angina (no myocardial necrosis) to NSTEMI (partial-thickness necrosis, no ST elevation) to STEMI (full-thickness necrosis with ST elevation, usually from complete coronary occlusion).
Explanation: Most ACS results from rupture or erosion of an atherosclerotic plaque, triggering platelet aggregation and thrombus formation. A completely occlusive thrombus produces transmural infarction and ST elevation (STEMI); a partially occlusive thrombus produces subendocardial ischemia (NSTEMI/unstable angina). Troponin distinguishes NSTEMI (elevated) from unstable angina (normal).
Recognition:
- Chest pain/pressure, often retrosternal, radiating to the left arm, neck, jaw, or back
- Dyspnea, diaphoresis, nausea, or "impending doom"
- Silent or atypical presentation is common in diabetics, women, and the elderly
- ECG: ST elevation (STEMI), ST depression/T-wave inversion (NSTEMI/UA), or normal ECG (doesn't exclude ACS)
- Troponin rises 3-6 hours after onset and stays elevated for days
Management (remember MONA-B, given in the order that helps, not alphabetically):
- Aspirin 162-325 mg chewed, immediately
- Oxygen only if SpO2 < 90%
- Nitroglycerin sublingual for pain (avoid if hypotensive, right ventricular infarct, or recent PDE-5 inhibitor use)
- Morphine for pain refractory to nitrates (use cautiously — associated with worse outcomes in some studies)
- Beta-blocker within 24 hours if no contraindication (avoid in acute decompensated heart failure or cardiogenic shock)
- STEMI: primary PCI within 90 minutes of first medical contact (or fibrinolysis if PCI unavailable within 120 minutes)
- NSTEMI/UA: dual antiplatelet therapy, anticoagulation (heparin), and risk-stratified early invasive angiography
Why it matters: STEMI is the single diagnosis where "time to reperfusion" is a directly measured quality metric in hospitals worldwide — every 30-minute delay to PCI measurably increases mortality.
Common misunderstanding: Students assume a normal ECG rules out a heart attack. It does not — serial ECGs and troponins over several hours are needed, and posterior or right-ventricular STEMIs are easy to miss on a standard 12-lead.
Cardiac Arrest and the ACLS Algorithm
Definition: Cardiac arrest is the abrupt loss of effective cardiac mechanical function, confirmed by absence of a palpable pulse, unresponsiveness, and absent or agonal breathing.
Explanation: Outcome depends on rhythm. Ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT) are "shockable" — defibrillation is the single most effective intervention. Asystole and pulseless electrical activity (PEA) are "non-shockable" — survival depends on finding and reversing the underlying cause (the Hs and Ts: Hypovolemia, Hypoxia, Hydrogen ion/acidosis, Hypo/hyperkalemia, Hypothermia; Tension pneumothorax, Tamponade, Toxins, Thrombosis-coronary, Thrombosis-pulmonary).
Management sequence: high-quality CPR (rate 100-120/min, depth 5-6 cm, full recoil, minimal interruptions) → rhythm check every 2 minutes → shock if VF/pVT → epinephrine 1 mg IV every 3-5 minutes regardless of rhythm → amiodarone or lidocaine for refractory VF/pVT → identify and treat reversible causes → advanced airway once compressions are optimized.
Why it matters: Survival to discharge for out-of-hospital VF arrest falls by roughly 7-10% for every minute defibrillation is delayed — bystander CPR and early AED use are the strongest modifiable predictors of survival.
Common misunderstanding: Students think epinephrine or intubation is the priority. In reality, chest compression quality and early defibrillation matter far more than any drug; interrupting compressions to secure an airway or start a line early actually worsens outcomes.
Aortic Dissection
Definition: Aortic dissection is a tear in the aortic intima allowing blood to dissect through the media, creating a false lumen that can occlude branch vessels or rupture.
Explanation: Classified by the Stanford system — Type A involves the ascending aorta (surgical emergency) and Type B is confined to the descending aorta (usually managed medically unless complicated). Risk factors include hypertension, bicuspid aortic valve, Marfan or Ehlers-Danlos syndrome, and cocaine use.
Recognition:
- Sudden, severe, "tearing" or "ripping" pain, often maximal at onset (unlike ACS pain, which typically crescendos)
- Pain migrating from chest to back or abdomen as the dissection propagates
- Blood pressure or pulse differential between the two arms
- New aortic regurgitation murmur, or signs of tamponade/hypotension if Type A ruptures into the pericardium
- CT angiography is the diagnostic test of choice in a stable patient; transesophageal echo if unstable
Management: Immediate blood pressure and heart rate control with IV beta-blockers (esmolol or labetalol) to a target heart rate under 60 bpm before adding vasodilators (never a vasodilator alone first, or reflex tachycardia worsens shear stress). Type A dissection requires emergent surgery; Type B is managed medically unless there is malperfusion, rupture, or refractory pain, in which case endovascular repair is used.
Why it matters: Type A dissection mortality increases roughly 1-2% per hour without surgery in the first 48 hours — it is one of the few "surgery within hours, not days" diagnoses in medicine.
Common misunderstanding: Dissection is frequently mistaken for STEMI because both cause severe chest pain and can produce ECG changes (dissection can occlude a coronary ostium). Giving thrombolytics to a dissection misdiagnosed as STEMI causes catastrophic hemorrhage — always consider dissection in atypical chest pain with unequal pulses or a widened mediastinum on chest X-ray before thrombolysing.
Key Terms
| Term | Definition |
|---|---|
| STEMI | ST-Elevation Myocardial Infarction — full-thickness infarction from complete coronary occlusion, seen as ST elevation on ECG |
| NSTEMI | Non-ST-Elevation Myocardial Infarction — partial-thickness infarction with elevated troponin but no ST elevation |
| Unstable angina | Ischemic chest pain at rest or worsening pattern without troponin elevation |
| ROSC | Return of Spontaneous Circulation — palpable pulse regained after cardiac arrest |
| PEA | Pulseless Electrical Activity — organized rhythm on monitor without a palpable pulse |
| Stanford Type A/B | Classification of aortic dissection by whether the ascending aorta is involved (A) or not (B) |
| PCI | Percutaneous Coronary Intervention — catheter-based opening of a blocked coronary artery, usually with stenting |
| Hs and Ts | Mnemonic for reversible causes of PEA/asystole (hypovolemia, hypoxia, hydrogen ion, hypo/hyperkalemia, hypothermia, tension pneumothorax, tamponade, toxins, thrombosis) |
Common Mistakes
| Misconception | Why It's Wrong | Correct Understanding |
|---|---|---|
| A normal ECG rules out a heart attack | Early ischemia can be ECG-silent, and posterior/right-ventricular infarcts are easy to miss on a standard 12-lead | Use serial ECGs and troponins over several hours; a single normal ECG never excludes ACS |
| Epinephrine and intubation are the most important arrest interventions | Trials show outcomes depend far more on compression quality and early defibrillation than on any drug or airway device | Prioritize continuous, high-quality compressions and defibrillate shockable rhythms as fast as possible; treat drugs and airway as secondary |
| Tearing chest pain radiating to the back should be treated like ACS with aspirin and anticoagulation | Anticoagulating or thrombolysing a dissection converts a survivable tear into fatal hemorrhage | Check for pulse/BP differentials and widened mediastinum first; get a CT angiogram before anticoagulating atypical chest pain |
Comparison and Connections
| Feature | STEMI | Aortic Dissection | Cardiac Arrest (VF/pVT) |
|---|---|---|---|
| Pain onset | Crescendo over minutes | Sudden, maximal at onset | Not applicable (unresponsive) |
| Pain character | Pressure/heaviness | Tearing/ripping, migrates | N/A |
| Key diagnostic test | ECG + troponin | CT angiography | Rhythm on monitor |
| First-line treatment | Antiplatelets + reperfusion (PCI/lytics) | Heart rate/BP control, then surgery (Type A) | CPR + defibrillation |
| Fatal management error | Delaying reperfusion | Giving thrombolytics/anticoagulants | Delaying defibrillation for other tasks |
Practice Questions
Recall
- What ECG finding differentiates STEMI from NSTEMI?
- Which two rhythms are "shockable" in cardiac arrest?
Answer guidance: (1) ST-segment elevation is present in STEMI and absent in NSTEMI, even though both can have elevated troponin. (2) Ventricular fibrillation and pulseless ventricular tachycardia.
Understanding 3. Explain why beta-blockers are given before vasodilators in suspected aortic dissection. 4. Explain why chest compression quality matters more than drug administration in cardiac arrest.
Answer guidance: (3) Vasodilators alone drop blood pressure but trigger reflex tachycardia, and the resulting increase in the rate of pressure rise (dP/dt) increases aortic wall shear stress, propagating the dissection — heart rate must be controlled first. (4) Coronary and cerebral perfusion during arrest depend entirely on the pressure generated by compressions; interruptions or shallow compressions drop perfusion to near zero, and no drug can substitute for adequate blood flow.
Application 5. A 60-year-old diabetic presents with vague nausea and diaphoresis but no chest pain, and a normal initial ECG. What should you do next? 6. A patient with tearing chest pain has a blood pressure of 180/110 in the right arm and 140/85 in the left arm. What is your next diagnostic step and what should you avoid giving?
Answer guidance: (5) Do not discard ACS — diabetics often have atypical/silent presentations. Obtain serial troponins and repeat ECGs, and keep ACS on the differential despite a reassuring first ECG. (6) The blood pressure differential strongly suggests aortic dissection; order an urgent CT angiogram (or TEE if unstable) and avoid aspirin, anticoagulants, or thrombolytics until dissection is excluded.
Analysis 7. Compare the harm caused by treating a dissection as ACS versus treating ACS as a dissection. Which error is more dangerous and why? 8. A patient in PEA arrest has flat neck veins, unilateral absent breath sounds, and tracheal deviation. Which reversible cause should you treat immediately, and how?
Answer guidance: (7) Treating dissection as ACS (giving thrombolytics/anticoagulation) risks fatal hemorrhage and is generally considered the more catastrophic error because it actively causes harm; treating ACS as a dissection mainly causes a delay in reperfusion, which is harmful but usually not immediately fatal. Both argue for using clinical clues (pulse differential, pain character) before committing to therapy. (8) Tension pneumothorax — perform immediate needle decompression followed by chest tube placement; this is one of the "Ts" in the PEA differential and is rapidly reversible if treated promptly.
FAQ
1. Is chest pain always present in ACS? No. Atypical presentations — dyspnea, fatigue, nausea, or epigastric pain without chest pain — are common in women, diabetics, and the elderly, and are a major cause of missed diagnoses.
2. Why is aspirin given before confirming the diagnosis in suspected ACS? Aspirin's antiplatelet effect reduces mortality and has a very low risk of harm even if the final diagnosis turns out not to be ACS, so it is given empirically as soon as ACS is suspected (unless dissection or active bleeding is suspected).
3. What's the difference between defibrillation and cardioversion? Defibrillation is an unsynchronized shock used for chaotic, pulseless rhythms (VF/pVT); cardioversion is a synchronized shock timed to the QRS complex, used for organized tachyarrhythmias with a pulse (e.g., unstable SVT or atrial fibrillation).
4. Can a patient have a dissection and a STEMI at the same time? Yes — a proximal dissection can shear off a coronary ostium (usually the right coronary artery) and cause an inferior STEMI. This is exactly why unexplained STEMI with unequal pulses or a widened mediastinum should raise suspicion for dissection before thrombolysis.
5. Why does hypothermia complicate cardiac arrest management? Severe hypothermia makes the heart resistant to defibrillation and drugs; guidelines recommend withholding or spacing out epinephrine doses and limiting shocks until the core temperature rises above roughly 30°C, while continuing CPR and active rewarming.
Quick Revision
- ACS spectrum: unstable angina (normal troponin) → NSTEMI (elevated troponin, no ST elevation) → STEMI (ST elevation, transmural infarct).
- STEMI treatment goal: PCI within 90 minutes of first medical contact, or fibrinolysis within 120 minutes if PCI isn't available.
- MONA-B order of priority: Aspirin first, oxygen only if hypoxic, nitrates for pain (avoid in hypotension/RV infarct), morphine if refractory, beta-blocker within 24 hours.
- A normal ECG never excludes ACS — repeat ECG and troponin serially.
- Shockable rhythms: VF and pulseless VT — treat with immediate defibrillation.
- Non-shockable rhythms: asystole and PEA — treat by finding and reversing the Hs and Ts.
- High-quality, minimally interrupted CPR and early defibrillation matter more than any drug in arrest.
- Epinephrine 1 mg IV every 3-5 minutes in all arrest rhythms; amiodarone/lidocaine for refractory VF/pVT.
- Aortic dissection pain is sudden and tearing, unlike the crescendo pressure of ACS.
- Dissection management: control heart rate with beta-blockers first, then blood pressure with vasodilators; Type A needs emergent surgery, Type B is usually medical.
- Never give thrombolytics or anticoagulants to a suspected dissection.
- Unequal blood pressures between arms or a widened mediastinum on chest X-ray should prompt CT angiography before treating chest pain as ACS.
Related Topics
Prerequisites: Basic cardiac anatomy and coronary circulation, ECG interpretation fundamentals, principles of Basic Life Support (BLS)
Related Topics: Cardiogenic shock, arrhythmia recognition, pulmonary embolism, hypertensive emergencies
Next Topics: Advanced airway management in resuscitation, post-cardiac-arrest care and targeted temperature management, cardiac catheterization and revascularization techniques