10 Common Heart Diseases with ECG Changes

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I now have comprehensive material from authoritative textbooks. Here is a complete, well-organized reference on 10 common heart diseases with their ECG changes:

10 Common Heart Diseases with ECG Changes

1. ST-Elevation Myocardial Infarction (STEMI)

Pathophysiology: Complete occlusion of a coronary artery causes transmural ischemia, injury, and eventually necrosis of the myocardium.

ECG Changes (in sequence):

Phase	Finding
Hyperacute (minutes)	Tall, peaked (hyperacute) T waves in the territory
Acute injury (hours)	ST-segment elevation ≥1 mm in 2+ contiguous leads; reciprocal ST depression in opposite leads
Evolving (hours-days)	Pathological Q waves (>40 ms wide, >25% of R wave amplitude); T-wave inversion
Old/established	Persistent Q waves; T waves may normalize

Territory localization:

Inferior (RCA): ST elevation in II, III, aVF
Anterior (LAD): ST elevation in V1-V4
Lateral (LCx): ST elevation in I, aVL, V5-V6
Posterior (RCA/LCx): Tall R and ST depression in V1-V3 (mirror image)
Right ventricular (RCA): ST elevation in V4R

ECG - Inferior-lateral MI (LCx occlusion):

Inferior-lateral MI ECG showing ST elevation in II, III, aVF and V2 with reciprocal changes in V1-V3

ST-segment elevation in leads II, III, and aVF (inferior) and V2 (lateral). ST depression in V1-V3 represents reciprocal changes. 100% occlusion of left circumflex artery confirmed at catheterization. - Tintinalli's Emergency Medicine

ECG - Left main/proximal LAD occlusion:

ST elevation in aVR with diffuse ST depression suggesting left main occlusion

Elevation in aVR greater than V1 with diffuse ST depression - pattern suggesting left main coronary artery or proximal LAD occlusion. - Tintinalli's Emergency Medicine

2. Non-ST-Elevation ACS (NSTEMI / Unstable Angina)

Pathophysiology: Partial/dynamic coronary occlusion causing subendocardial ischemia without full-thickness necrosis.

ECG Changes:

ST depression (horizontal or downsloping) ≥0.5-1 mm in 2+ contiguous leads - the hallmark
T-wave inversion (deep, symmetric) in affected territory
Transient ST changes that may resolve with symptom relief
ECG may be entirely normal in 1-6% of true NSTEMIs
No pathological Q waves (subendocardial infarction)

"The diagnosis of NSTEMI depends on abnormal elevation of cardiac biomarkers but may include ECG changes not meeting criteria for STEMI." - Tintinalli's Emergency Medicine

Key difference from STEMI: Absence of ST elevation or new LBBB; troponin elevation confirms NSTEMI over unstable angina.

3. Atrial Fibrillation (AF)

Pathophysiology: Chaotic, disorganized electrical activity from multiple re-entrant wavelets in the atria - often triggered by atrial enlargement, valve disease, hypertension, or heart failure.

ECG Changes:

Feature	Finding
P waves	Absent - replaced by fibrillatory baseline (f waves at 350-600 bpm)
Baseline	Irregular, low-voltage oscillations (fine or coarse)
RR intervals	Irregularly irregular - the hallmark
QRS complexes	Normal morphology (unless aberrant conduction or pre-excitation)
Ventricular rate	Variable, typically 100-160 bpm if uncontrolled

ECG of atrial fibrillation (lead II) showing absent P waves and irregularly irregular QRS complexes

Atrial fibrillation (lead II): No P waves visible; QRS and T waves are of normal morphology but occur at irregular intervals. - Guyton and Hall Textbook of Medical Physiology

Diagram of impulse pathways in atrial flutter vs atrial fibrillation

Left: Atrial flutter (single circular re-entry circuit). Right: Atrial fibrillation (multiple chaotic wavelets with functional block zones). - Guyton and Hall

4. Atrial Flutter

Pathophysiology: A single large macro-re-entrant circuit in the right atrium (typically around the tricuspid annulus), producing regular atrial depolarizations at ~300 bpm.

ECG Changes:

Feature	Finding
P waves	Replaced by "sawtooth" flutter waves (F waves) at ~300 bpm, best seen in II, III, aVF, V1
Rhythm	Regular flutter waves; ventricular rate depends on AV conduction ratio
AV conduction	Typically 2:1 (ventricular rate ~150 bpm), 3:1, or 4:1 block
RR interval	Regular if fixed block ratio; irregular if variable
QRS	Normal morphology

A useful bedside trick: a regular narrow-complex tachycardia at exactly 150 bpm should always raise suspicion for atrial flutter with 2:1 block until proven otherwise.

5. Complete Heart Block (Third-Degree AV Block)

Pathophysiology: Complete dissociation between atrial and ventricular conduction - no impulses pass through the AV node. Causes include ischemia (inferior MI most common), Lyme disease, medications (digoxin, beta-blockers), and degenerative conduction system disease.

ECG Changes:

Feature	Finding
P waves	Present at regular rate (sinus rate, typically 60-100 bpm)
QRS complexes	Present at slower, independent "escape" rate
PR interval	Completely variable - no fixed relationship between P and QRS
AV dissociation	P waves and QRS complexes march through each other independently
Escape rhythm	Junctional (narrow QRS, rate 40-60) or ventricular (wide QRS, rate 20-40)

Associated ECG findings:

In inferior MI context: Wenckebach (Mobitz I) or complete block from RCA ischemia to AV node
New LBBB in ischemia context = equivalent of ischemic ECG changes

"Prolonged PR interval, new LBBB, or new RBBB with left anterior hemiblock suggests spread of infection into the conduction system." - Tintinalli's Emergency Medicine (in the context of endocarditis/myocarditis)

6. Left Bundle Branch Block (LBBB)

Pathophysiology: Conduction delay or block in the left bundle branch, causing abnormal, sequential ventricular activation (right then left ventricle).

ECG Changes (the "WiLLiaM" pattern):

Feature	Finding
QRS duration	Broad (≥120 ms)
V1	Deep, broad S wave (W shape: rS or QS pattern)
V5-V6, I, aVL	Tall, notched R wave (no septal Q waves) - "M" shape
ST/T changes	Discordant - ST and T opposite direction to main QRS deflection
Axis	Usually left axis deviation

Clinical significance:

New LBBB in a patient with chest pain = treat as STEMI equivalent
Sgarbossa criteria help identify superimposed MI in LBBB: concordant ST elevation ≥1 mm, concordant ST depression ≥1 mm in V1-V3, or excessive discordant ST elevation >25% of S wave depth

7. Right Bundle Branch Block (RBBB)

Pathophysiology: Conduction delay in the right bundle branch; right ventricle is depolarized late via myocardial cell-to-cell conduction.

ECG Changes (the "MaRRoW" pattern):

Feature	Finding
QRS duration	Broad (≥120 ms)
V1	RSR' ("rabbit ears" / M shape) - rSR' pattern
V5-V6, I	Wide, slurred S wave
T waves	Discordant (opposite direction to terminal QRS deflection)
Axis	Usually normal

"A conduction delay or block in the right bundle branch results in a typical RBBB QRS pattern on the surface ECG (M-shape or rSR' in V1) and may represent a congenital abnormality or underlying organic heart disease." - Morgan and Mikhail's Clinical Anesthesiology

Clinical notes: Isolated RBBB is less ominous than LBBB; new RBBB + left anterior hemiblock (bifascicular block) in chest pain warrants urgent evaluation.

8. Hypertrophic Cardiomyopathy (HCM)

Pathophysiology: Asymmetric septal hypertrophy (usually autosomal dominant sarcomere gene mutation) causing dynamic LVOTO, diastolic dysfunction, and risk of sudden cardiac death - the most common cause of sudden death in young athletes.

ECG Changes:

Feature	Finding
Voltage	Left ventricular hypertrophy (Sokolov-Lyon: S in V1 + R in V5/V6 ≥35 mm)
Septal Q waves	Deep, narrow Q waves in lateral leads (I, aVL, V5-V6) - from septal hypertrophy
T-wave changes	T-wave inversion in lateral leads; if present without Q waves = suggests ischemia
ST changes	ST depression in lateral leads
P waves	Left atrial abnormality (broad, notched P wave) if LA enlarged
Rhythm	May show AF, SVT, or ventricular arrhythmias

ECG in hypertrophic cardiomyopathy showing LVH voltage and narrow septal Q waves in V5-V6

HCM ECG: Deep S-wave voltage (28 mm in V3, large arrow) indicating LVH. Narrow septal Q waves in V5 and V6 (arrowheads). This patient also has atrial flutter with 2:1 block (additional P waves in ST segments, small arrows). - Tintinalli's Emergency Medicine

"An ECG tracing showing Q waves or inferolateral repolarization changes in an athlete favors the diagnosis of hypertrophic cardiomyopathy." - Goldman-Cecil Medicine

9. Wolff-Parkinson-White Syndrome (WPW)

Pathophysiology: An accessory pathway (Bundle of Kent) bypasses the AV node, causing pre-excitation of part of the ventricle before normal conduction arrives. This creates the classic ECG triad and predisposes to re-entrant tachycardias (AVRT) and - if AF develops - rapid ventricular response that can degenerate to VF.

ECG Changes (the classic triad in sinus rhythm):

Feature	Finding
PR interval	Short (<120 ms) - pre-excitation bypasses AV node delay
Delta wave	Slurred upstroke of the QRS complex (initial slow inscription of the QRS)
QRS duration	Prolonged (≥120 ms) due to fusion of pre-excited and normally conducted impulses
ST/T changes	Secondary repolarization abnormalities (discordant to delta/QRS)

During tachycardia:

Orthodromic AVRT: Narrow QRS tachycardia (antegrade via AV node, retrograde via accessory pathway)
Antidromic AVRT: Wide QRS tachycardia (antegrade via accessory pathway - looks like VT)
AF with WPW: Irregularly irregular, very wide, bizarre QRS - life-threatening (avoid AV nodal blocking agents)

"AVNRT caused by an accessory bypass tract (WPW) may be evident on the ECG by the characteristic delta wave (slurred upstroke of QRS complex), short PR interval, and prolonged QRS complex." - Textbook of Family Medicine

10. Long QT Syndrome (LQTS)

Pathophysiology: Delayed ventricular repolarization due to genetic mutations in cardiac ion channel genes (most commonly KCNQ1/LQT1, KCNH2/LQT2, SCN5A/LQT3) or acquired causes (drugs, hypokalemia, hypomagnesemia). Prolonged repolarization creates early afterdepolarizations that trigger torsades de pointes (TdP) and sudden cardiac death.

ECG Changes:

Feature	Finding
QTc interval	Prolonged (≥450 ms males, ≥460 ms females; dangerous if ≥500 ms)
QTc formula	Bazett: QTc = QTm / √RR (in seconds)
T-wave morphology	Broad, notched, or bifid T waves depending on LQTS subtype
LQT1	Broad-based T waves; events triggered by exercise/swimming
LQT2	Low amplitude, notched T waves; events with sudden noise/emotion
LQT3	Long isoelectric ST segment with peaked T waves; events at rest/sleep
Torsades de pointes	"Twisting of the points" - polymorphic VT with QRS axis rotating around baseline

"The long QT syndrome is characterized by prolongation of the corrected QT interval, syncope, and sudden death caused by torsades de pointes and ventricular fibrillation." - Tintinalli's Emergency Medicine

Important acquired causes of prolonged QTc: antipsychotics (haloperidol, ziprasidone), macrolide antibiotics, fluoroquinolones, antifungals (azoles), antiarrhythmics (class IA and III), tricyclic antidepressants, hypokalemia, hypomagnesemia.

Quick Reference Summary Table

Disease	Rate	Rhythm	P Waves	PR	QRS	ST/T Changes	Key Feature
STEMI	Normal/fast	Regular	Normal	Normal	Usually normal	ST elevation territory	Pathological Q waves evolve
NSTEMI/UA	Normal/fast	Regular	Normal	Normal	Normal	ST depression / T inversion	No Q waves
Atrial Fibrillation	100-160	Irregularly irregular	Absent (f waves)	None	Normal	Variable	No P waves
Atrial Flutter	~150 (2:1)	Regular	Sawtooth F waves ~300	Fixed ratio	Normal	None	"Sawtooth" baseline
Complete Heart Block	Atria 60-100; Ventricles 20-60	AV dissociation	Normal, regular	Variable	Wide (ventricular escape)	None	P and QRS completely independent
LBBB	Normal	Regular	Normal	Normal	Broad ≥120 ms, M in V5-V6	Discordant ST/T	W in V1, M in V6
RBBB	Normal	Regular	Normal	Normal	Broad ≥120 ms, RSR' in V1	Discordant T in V1	"Rabbit ears" in V1
HCM	Normal	Regular (may have AF)	±LA abnormality	Normal	Normal-wide	LVH voltage, lateral T inversion	Deep narrow septal Q waves (V5-V6)
WPW	Normal	Regular (sinus)	Normal	Short <120 ms	Broad (fusion)	Secondary changes	Delta wave
Long QT Syndrome	Normal	Regular (sinus)	Normal	Normal	Normal	Broad/notched T waves	QTc ≥450-500 ms, risk of TdP

Sources: Guyton and Hall Textbook of Medical Physiology; Tintinalli's Emergency Medicine: A Comprehensive Study Guide; Goldman-Cecil Medicine; Textbook of Family Medicine; Morgan and Mikhail's Clinical Anesthesiology; Harrison's Principles of Internal Medicine 22E; Braunwald's Heart Disease

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