Explain me 10 common ecg change with reauly

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I now have comprehensive textbook content and ECG images from Harrison's Principles of Internal Medicine. Here is the full, well-illustrated answer:

10 Common ECG Changes

Reference ECG - Normal 12-lead

Normal 12-lead ECG from a healthy male subject

Normal sinus rhythm: HR 75 bpm, PR 160 ms, QRS 80 ms, QTc ~390 ms. This is your baseline for comparison.

1. ST Elevation (STEMI pattern)

What you see: ST segments raised ≥1 mm in two or more contiguous leads. The classic "tombstone" or convex upward shape indicates transmural ischemia/infarction.

Leads affected by territory:

Anterior STEMI: V1-V4 (LAD)
Inferior STEMI: II, III, aVF (RCA or LCx)
Lateral STEMI: I, aVL, V5-V6

Key rule: Reciprocal ST depression appears in the "mirror" leads (e.g., inferior STEMI causes reciprocal depression in V1-V3).

Anterior STEMI ECG sequence - acute and evolving with ST elevation and Q-wave development

Top row = acute anterior STEMI; Bottom row = evolving inferior STEMI. Note ST elevation and subsequent Q-wave formation.

Other causes of ST elevation: Pericarditis (diffuse, saddle-shaped), Brugada pattern (right precordial, coved/saddle morphology), LVH strain, hypothermia (J/Osborn waves), hyperkalemia (V1-V3).

2. ST Depression

What you see: ST segment falls below the isoelectric line. Morphology matters:

Horizontal or downsloping depression - strongly suggestive of ischemia or posterior STEMI
Upsloping depression - less specific, can be a normal variant at high heart rates

Causes: Subendocardial ischemia/NSTEMI, posterior STEMI (depression in V1-V3 = "reciprocal" of posterior elevation), LVH strain pattern, digoxin effect ("scooped" or "reverse-tick"), hypokalemia, right ventricular hypertrophy.

3. Pathological Q Waves

What you see: Q wave ≥40 ms (1 small square) wide OR ≥25% the height of the following R wave, in two contiguous leads. These represent electrically dead (infarcted) myocardium that produces no depolarization signal.

Where they appear by territory:

V1-V4: anterior infarct (LAD territory)
II, III, aVF: inferior infarct
I, aVL: high lateral infarct

Remember: Small q waves in I, aVL, V5-V6 are normal septal vectors; only qualify as "pathological" when they exceed the above criteria.

4. Right Bundle Branch Block (RBBB)

What you see:

QRS ≥120 ms (wide complex)
rSR' ("rabbit ears") in V1 - the R' is taller than the initial r
Wide, slurred S wave in V6 and lead I
T-wave inversion in V1-V3 (secondary repolarization change - discordant to the last QRS deflection)

RBBB vs LBBB vs normal QRS morphology in V1 and V6

Top: Normal. Middle: RBBB - note rSR' in V1 and qRS in V6. Bottom: LBBB - note QS in V1 and wide R in V6.

Causes: Can be normal (no structural disease), atrial septal defect, pulmonary embolism, right heart strain, ischemic heart disease.

5. Left Bundle Branch Block (LBBB)

What you see:

QRS ≥120 ms
Broad, predominantly negative (QS) complex in V1 - no r wave
Broad, monophasic R wave in V6 (no q, no s wave)
Discordant T-wave inversion in leads with dominant R wave (V5-V6, I, aVL)
Normal septal q waves are absent in lateral leads

Clinical importance: New LBBB in a patient with chest pain is treated as a STEMI equivalent until proven otherwise (Sgarbossa criteria apply). LBBB is frequently a marker of one of four underlying conditions: coronary artery disease, hypertensive heart disease, aortic valve disease, or cardiomyopathy.

6. Left Ventricular Hypertrophy (LVH)

What you see:

Tall R waves in left lateral leads (R in aVL >20 mm in women, >28 mm in men)
Deep S waves in right precordial leads (S in V1 + R in V5 or V6 >35 mm - Sokolov-Lyon criterion)
LVH "strain" pattern: ST depression + T-wave inversion in leads with tall R waves (I, aVL, V5-V6)
Left atrial abnormality is often coexistent (broad, notched P in II; biphasic P in V1)

Causes: Hypertension (most common), aortic stenosis, hypertrophic cardiomyopathy, athletic heart.

7. Right Ventricular Hypertrophy (RVH)

What you see:

Tall R wave in V1 (R ≥ S in V1, or R >7 mm)
Right axis deviation (QRS axis >+90°)
Deep S waves in V5-V6 (prominent S in lateral leads)
ST depression and T-wave inversion in right precordial leads (V1-V3) - "right ventricular strain"
May also show qR pattern in V1 with severe pressure overload

Causes: Pulmonary hypertension, pulmonary stenosis, atrial septal defect (volume overload - associated with RBBB pattern), chronic lung disease.

8. Atrial Abnormalities (P-wave changes)

What you see:

P-wave morphology comparison: Normal vs Right atrial vs Left atrial abnormality in leads II and V1

Left column: Normal P wave. Middle: Right atrial overload - tall, peaked P (≥2.5 mm) = "P-pulmonale." Right: Left atrial abnormality - broad, notched P in II; deep terminal negative deflection in V1 = "P-mitrale."

Finding	Morphology	Cause
Right atrial overload	Tall peaked P ≥2.5 mm in II, III, aVF	Pulmonary hypertension, tricuspid stenosis
Left atrial abnormality	Broad (≥120 ms), notched P in II; biphasic P in V1 with prominent negative terminal	Mitral stenosis/regurgitation, LVH, left heart failure
Absent P waves	No identifiable P waves, irregularly irregular rhythm	Atrial fibrillation

9. Hyperkalemia ECG Changes (Electrolyte Changes)

What you see (in sequence with rising K+):

Mild-moderate (K+ 5.5-6.5 mEq/L): Peaked, "tented" T waves (tall, narrow, symmetric) - earliest sign
Moderate-severe (K+ 6.5-8.0 mEq/L): PR prolongation, P waves flatten and disappear, QRS widens
Very severe (K+ >8.0 mEq/L): Wide QRS merges with T wave producing a sine-wave pattern - risk of VF/asystole

Hyperkalemia ECG spectrum from mild-moderate to very severe showing peaked T waves, widening QRS, and sine-wave pattern

Mild-moderate (left): peaked T waves. Moderate-severe (middle): QRS widening, P waves still visible. Very severe (right): classic sine-wave pattern.

Hypokalemia ECG changes:

ST depression, T-wave flattening/inversion
Prominent U waves (a positive deflection after the T wave, most visible in V2-V3)
Apparent QT prolongation (actually QU prolongation)

Hypokalemia ECG showing prominent U wave in lead II and V3

Hypokalemia: flat T wave with a distinct U wave in V3.

10. Prolonged QT Interval

What you see: The QT interval (from start of QRS to end of T wave) is prolonged when QTc (Bazett's formula: QT ÷ √RR) exceeds:

>450 ms in men
>460 ms in women (some sources use >470 ms)

Clinical significance: Prolonged QTc predisposes to torsades de pointes (TdP) - a polymorphic ventricular tachycardia that can degenerate into VF and cause sudden cardiac death.

Common causes:

Category	Examples
Drugs	Class Ia/III antiarrhythmics (amiodarone, sotalol), antipsychotics (haloperidol, quetiapine), antibiotics (azithromycin, fluoroquinolones), methadone
Electrolytes	Hypokalemia, hypomagnesemia, hypocalcemia
Congenital	Romano-Ward syndrome (autosomal dominant), Jervell-Lange-Nielsen (with deafness)
Cardiac	Bradycardia, AV block, myocarditis
Other	Hypothyroidism, intracranial hypertension, hypothermia

Quick Summary Table

ECG Change	Key Feature	Common Cause
ST elevation	Raised ST in contiguous leads	STEMI, pericarditis, Brugada
ST depression	Depressed ST, horizontal/downsloping	NSTEMI, ischemia, LVH strain
Pathological Q waves	≥40 ms wide or >25% R height	Prior MI
RBBB	rSR' in V1, wide S in V6, QRS ≥120 ms	Normal variant, PE, ASD
LBBB	QS in V1, broad R in V6, QRS ≥120 ms	CAD, HTN, cardiomyopathy
LVH	Tall R lateral + deep S right precordial	Hypertension, AS
RVH	Tall R in V1, right axis, S in V6	Pulmonary HTN, PS
P-wave changes	Peaked (RA) or broad-notched (LA)	Lung disease, mitral disease
Hyperkalemia	Peaked T → wide QRS → sine wave	Renal failure, Addison's
Prolonged QT	QTc >450-460 ms	Drugs, electrolytes, congenital

Sources: Harrison's Principles of Internal Medicine, 22nd Ed. (2025), Harriet Lane Handbook, 23rd Ed.

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