STEMI - ST elevation in the territory of the blocked artery, with reciprocal depression. Q waves follow necrosis. Anterior and inferior patterns are shown with their evolving sequences.

NSTEMI/Unstable Angina - ST depression and T-wave inversions without Q waves. The Wellens sign (deep V1-V4 T inversions) signals critical LAD disease.

Atrial Fibrillation - The only rhythm with a completely absent P wave AND an irregularly irregular QRS. Three real ECG examples are shown from Tintinalli's.

Ventricular Fibrillation - No QRS, no P waves, just chaotic waveforms. Fine, coarse, and VT-mimicking patterns are shown.

LVH/RVH - Voltage-based diagnosis. Tall lateral R waves + "strain" ST changes for LVH; dominant R in V1 + right axis for RVH. The comparison diagram from Harrison's is shown.

AV Heart Block - Three degrees, each progressively worse. Mobitz II and complete heart block ECGs are shown from Harrison's - both require urgent attention.

Bundle Branch Block - RBBB = rSR' in V1; LBBB = broad R in V6 + QS in V1. The side-by-side comparison diagram from Harrison's is included.

WPW - Short PR + delta wave + widened QRS during sinus rhythm. Dangerous when combined with AF (rates >200 bpm).

Acute Pericarditis - Diffuse saddle-shaped ST elevation + PR depression. Distinguished from STEMI by the distribution (all leads, not one artery territory) and concave shape.

Pulmonary Embolism - Sinus tachycardia is most common; S1Q3T3 and new RBBB are more specific but less sensitive markers of acute RV strain.