RCA (about 80%) or circumflex; reciprocal depression in I and aVL
Septal: V1–V2
LAD (septal branches)
Anterior: V3–V4
LAD
Lateral: I, aVL, V5–V6
Circumflex or diagonal
Posterior
ST depression V1–V3 with tall R waves; confirm with V7–V9 (circumflex or RCA)
Right ventricle
ST elevation in V4R with an inferior MI: proximal RCA (preload-dependent)
aVR elevation with diffuse depression
Left main or severe multivessel ischemia
Inferior STEMI with ST elevation in III greater than II, and depression in I, points to the RCA; II greater than III with lateral changes points to the circumflex.
STEMI criteria and equivalents
Fourth universal definition, plus the patterns that count as occlusion
ST elevation in two contiguous leads
V2–V3
Men 40 or older 2 mm or more; men under 40 2.5 mm; women 1.5 mm
Other leads
1 mm or more
New LBBB
No longer STEMI by itself; apply Sgarbossa criteria
Equivalents (treat as occlusion)
Sgarbossa (LBBB or paced)
Concordant ST elevation 1 mm or more; concordant depression in V1–V3; discordant elevation 25% or more of the S wave (Smith-modified)
Posterior MI
ST depression V1–V3 with upright T waves; V7–V9 elevation 0.5 mm or more
de Winter
Upsloping ST depression with tall symmetric precordial T waves: proximal LAD
Hyperacute T waves
Broad, tall T waves before ST elevation develops
High-risk, not occlusion yet
Wellens
Biphasic or deep T waves in V2–V3 while pain-free: critical proximal LAD stenosis; no stress testing
STEMI mimics
ST elevation that is not acute occlusion
Pericarditis
Diffuse concave ST elevation, PR depression, no reciprocal changes (except aVR and V1)
Early repolarization
Young patients; J-point notching, concave ST, stable over time
LVH
Large voltages with discordant ST-T changes in V1–V3
LBBB or paced rhythm
Discordant ST changes are expected; use Sgarbossa
LV aneurysm
Persistent ST elevation with Q waves weeks after an MI
Takotsubo
Anterior ST elevation, often after stress; normal coronaries
Brugada
Coved ST elevation in V1–V2 with T-wave inversion
Hyperkalemia
Peaked T waves and pseudo-ST elevation; check potassium
Vasospasm (Prinzmetal)
Transient ST elevation that resolves
Axis, rate and intervals
The numbers on every 12-lead
Axis (leads I and aVF)
Normal
−30° to +90°: I and aVF positive (or I and II positive)
Left axis deviation
I positive, aVF and II negative: left anterior fascicular block, inferior MI, LVH, paced rhythm
Right axis deviation
I negative, aVF positive: RVH, acute PE, lateral MI, left posterior fascicular block
Extreme axis
I and aVF negative: ventricular rhythm, lead reversal
Rate and intervals
Rate
300 ÷ large boxes between R waves; or R waves in 6 seconds × 10
PR
120–200 ms
QRS
Under 120 ms (110–119 incomplete block)
QTc
Under 450 ms men, 460–470 women; over 500 high torsades risk
Bundle branch and fascicular blocks
Recognize them in V1 and V6
RBBB
QRS 120 ms or more; rSR′ in V1; wide S in I and V6
LBBB
QRS 120 ms or more; broad notched R in I, aVL, V5–V6; deep S in V1; no septal q waves
Left anterior fascicular block
Left axis −45° or more; qR in aVL, rS in II, III, aVF
Left posterior fascicular block
Right axis; rS in I, qR in III (exclude RVH and lateral MI)
Bifascicular block
RBBB plus a fascicular block; watch for progression to complete heart block
New LBBB with symptoms needs Sgarbossa assessment; new bifascicular block after MI or TAVR raises the risk of complete heart block.
Electrolytes, drugs and temperature
Patterns that change management
Hyperkalemia
Peaked T waves → long PR, flat P → wide QRS → sine wave → VF or asystole
Hypokalemia
Flat T waves, U waves, ST depression, long QU
Hypocalcemia
Long QT from a long ST segment
Hypercalcemia
Short QT
Hypomagnesemia
Long QT; torsades risk
Digoxin effect
Scooped ST depression; toxicity: almost any arrhythmia, classically atrial tachycardia with block, bidirectional VT
TCA or sodium-channel blocker
QRS over 100 ms, terminal R in aVR over 3 mm, right axis of the terminal QRS
Hypothermia
Osborn (J) waves, bradycardia, long intervals, shivering artifact
Acute PE
Sinus tachycardia most common; S1Q3T3, right strain T inversions V1–V4, new RBBB
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow your local protocols and medical direction.