Explain most common cardiac emergency conditions with ecg images

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Common Cardiac Emergency Conditions with ECG Findings

Sources: Tintinalli's Emergency Medicine, Rosen's Emergency Medicine, Frameworks for Internal Medicine, Braunwald's Heart Disease

1. ST-Elevation Myocardial Infarction (STEMI)

STEMI results from complete occlusion of a coronary artery causing transmural ischemia. It is the most time-critical cardiac emergency - "door-to-balloon" time must be under 90 minutes.

ECG criteria for STEMI diagnosis:

New ST-segment elevation at the J point in 2 or more contiguous leads
- ≥0.1 mV in all leads except V2-V3
- ≥0.2 mV in V2-V3 in men ≥40 years; ≥0.25 mV in men <40 years; ≥0.15 mV in women
Reciprocal ST depression in mirror leads
Pathological Q waves develop over hours

Evolution of ECG changes over time:

STEMI ECG evolution - hyperacute T-waves, ST elevation, Q wave development, T-wave inversion, then normalization

The earliest sign is hyperacute (tall, broad, symmetric) T-waves, followed by ST elevation, Q-wave development, T-wave inversion, and eventually normalization of ST with persistent Q waves.

Treatment: Immediate reperfusion via primary PCI (preferred) or fibrinolytics. Aspirin, heparin, P2Y12 inhibitors.

2. UA/NSTEMI (Non-ST-Elevation ACS)

Partial coronary occlusion or severe ischemia without full transmural involvement. Distinguished from STEMI by the absence of ST elevation, and from UA by troponin rise.

ECG findings:

New horizontal or downsloping ST depression ≥0.05 mV in 2 contiguous leads
T-wave inversion ≥0.1 mV with prominent R wave
May be entirely normal at presentation

UA/NSTEMI ECG patterns - T-wave inversion or ST depression, resolving to normal weeks later with no Q waves

Unlike STEMI, no Q waves form and the ST/T changes normalize without permanent injury markers.

Treatment: Anticoagulation, dual antiplatelet therapy, risk stratification with TIMI/GRACE score, early invasive strategy if high-risk.

3. Ventricular Fibrillation (VF)

VF is disorganized, chaotic depolarization of ventricular myocardium with no effective cardiac output. It is the most common initial rhythm in sudden cardiac death.

ECG findings:

No discernible P waves, QRS complexes, or T waves
Completely chaotic, irregular baseline
Can appear fine (low amplitude), coarse, or intermediate
Coarse VF can mimic VT (see panel C below)

Ventricular Fibrillation - three examples: A) fine amplitude, B) coarse amplitude, C) coarse mimicking VT

Fine VF (A) is a near-flat chaotic line with no organized deflections. Coarse VF (B, C) has larger oscillations and must be distinguished from pulseless VT - check for a pulse.

Treatment: Immediate defibrillation (200 J biphasic, 360 J monophasic), CPR, epinephrine 1 mg IV, amiodarone or lidocaine. See management algorithm below:

VF/Pulseless VT management algorithm - defibrillation, CPR, epinephrine, amiodarone/lidocaine cycle

4. Ventricular Tachycardia (VT)

VT is 3 or more consecutive ventricular depolarizations at a rate >100 beats/min. It accounts for ~50% of cases in patients with ischemic heart disease. VT cannot be reliably distinguished from SVT by symptoms alone - use the ECG.

ECG findings - Monomorphic VT:

Rate 140-180 bpm (range 120-300)
Wide QRS >100-120 ms with consistent beat-to-beat morphology
No associated P waves (occasional dissociated P wave visible)
Rapid, regular rhythm

ECG findings - Polymorphic VT / Torsades de Pointes:

Wide QRS with constantly changing morphology and direction
Torsades: characteristic "twisting of points" pattern with rotating QRS axis
Associated with prolonged QT interval (congenital or acquired - drugs, electrolyte derangements)

Polymorphic VT (A) and Torsades de Pointes (B) - note the characteristic rotating QRS axis in Torsades

Wide-complex tachycardia differential (ventricular vs. supraventricular sources):

Wide-complex tachycardia spectrum - VT monomorphic (A), VT polymorphic (B), sinus tachy with BBB (C), AF with BBB (D), WPW preexcited AF (E), WPW AVRT (F), and others

Key rule: assume all wide-complex tachycardias are VT until proven otherwise, especially in hemodynamically unstable patients.

Treatment:

Unstable (pulseless): defibrillation + CPR (same as VF protocol)
Unstable (with pulse): immediate synchronized cardioversion + sedation
Stable: IV procainamide, amiodarone, or lidocaine; avoid verapamil/adenosine unless SVT confirmed

5. Atrial Fibrillation (AF)

AF is the most common sustained arrhythmia after sinus tachycardia. Multiple discharging atrial foci cause chaotic atrial activity with no coordinated contraction, reducing cardiac output and increasing thromboembolic risk.

ECG findings:

Absent P waves - replaced by chaotic/fibrillatory baseline (best seen in V1)
Irregularly irregular ventricular rhythm (the hallmark)
Narrow QRS complexes (unless bundle branch block or WPW)
Ventricular rate typically 120-170 bpm if AV node unmedicated

Atrial Fibrillation - three examples showing irregularly irregular QRS complexes with absent P waves

Note the completely irregular R-R intervals and absence of any discernible P waves in all three examples (A, B, C).

Treatment:

Hemodynamically unstable: immediate DC cardioversion (150-200 J)
Stable: rate control (IV diltiazem or metoprolol, target HR <100 bpm) OR rhythm conversion
Anticoagulation: based on CHA₂DS₂-VASc score to prevent stroke

6. Complete (Third-Degree) AV Block

All atrial impulses are blocked from reaching the ventricles. A slow escape pacemaker (junctional or ventricular) takes over, often inadequate to maintain cardiac output.

ECG findings:

P waves and QRS complexes are completely dissociated (no fixed PR relationship)
Atrial rate is faster than ventricular rate
Narrow QRS if junctional escape (40-60 bpm); wide QRS if ventricular escape (<40 bpm)
QRS rate is regular but slow

Third-degree AV block - two examples: arrows mark P waves marching through independently, with a slow escape rhythm below

In both examples, atrial rate = 83 bpm, ventricular escape rate = 50 bpm. P waves are completely dissociated from QRS complexes; some P waves are buried in QRS or T waves.

Clinical context: Occurs in up to 8% of inferior MI patients (nodal block, usually reversible). Infranodal complete block from anterior MI carries high mortality even with pacing.

Treatment: Transcutaneous pacing immediately; atropine may help nodal block but not infranodal. Transvenous pacing is definitive.

7. Second-Degree AV Block - Mobitz Type I (Wenckebach)

Progressive PR prolongation until a P wave is completely blocked (dropped QRS), then the cycle resets.

ECG findings:

Progressive PR lengthening from beat to beat
Dropped QRS after longest PR
Group beating pattern
Usually narrow QRS

Second-degree Mobitz Type I AV block - arrows indicate nonconducted P waves after progressive PR prolongation

Treatment: Usually self-limited. Atropine if hemodynamically compromised. Associated with inferior MI, digoxin toxicity, or myocarditis.

8. First-Degree AV Block

Every atrial impulse conducts but is delayed. Alone it is not an emergency, but in the context of acute MI or drug toxicity it warrants close monitoring as it may progress.

ECG findings:

PR interval consistently >200 ms
Every P wave followed by a QRS
Otherwise normal-appearing rhythm

First-degree AV block - sinus rhythm with PR interval of 300 ms, consistent P-QRS relationship

(Image: Sinus rhythm with PR interval 300 ms - well above the normal upper limit of 200 ms)

Quick Reference Summary

Condition	Key ECG Finding	Rate	Rhythm	Emergency Action
STEMI	ST elevation ≥0.1 mV in 2+ contiguous leads	Variable	Regular	PCI within 90 min
NSTEMI/UA	ST depression, T-wave inversion, or normal	Variable	Regular	Anticoagulate, risk stratify
VF	Chaotic, no QRS	>300	Totally irregular	Defibrillate immediately
Monomorphic VT	Wide QRS, consistent morphology	140-180	Regular	Cardiovert if unstable; antiarrhythmics if stable
Torsades/Polymorphic VT	Wide, twisting QRS axis	140-300	Irregular	Magnesium sulfate; correct QT; defibrillate if pulseless
Atrial Fibrillation	No P waves, irregularly irregular	120-170 (ventricular)	Irregularly irregular	Rate or rhythm control; anticoagulation
Complete Heart Block	P-QRS dissociation, slow escape	<40-60	Regular (slow)	Transcutaneous pacing immediately
Wenckebach	Progressive PR prolongation, dropped QRS	Normal-slow	Regularly irregular	Atropine if symptomatic

Sources: Tintinalli's Emergency Medicine (9e), Rosen's Emergency Medicine, Frameworks for Internal Medicine, Braunwald's Heart Disease (12e)

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