Explain 10 most common heart disease with Ecg changes and Ecg diagrams. Explain in Simplest words
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ECG changes 10 common heart diseases explained simply diagrams 2024
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Here is your complete, simple guide to the 10 most common heart diseases and their ECG changes, with diagrams.
ECG Overview Diagram
First, Understand a Normal ECG
A normal ECG has these waves in order:
- P wave = Atria contracting (upper chambers pumping)
- QRS complex = Ventricles contracting (lower chambers pumping)
- T wave = Ventricles recovering (recharging)
- PR interval = Travel time from atria to ventricles (should be 0.12-0.20 sec)
- QRS width = Should be narrow (<0.12 sec)
🫀 The 10 Heart Diseases + ECG Changes
1. STEMI (ST-Elevation Myocardial Infarction) - Heart Attack (Full Blockage)
What it is: A major heart attack where a coronary artery is completely blocked. Heart muscle is dying right now.
What happens: The dead muscle cells can no longer properly recover between beats. They push current outward, elevating the ST segment.
ECG changes:
- ST segment elevation ≥ 1mm in 2 or more leads (looks like a tombstone or "tented" shape)
- Hyperacute T waves - very tall, peaked T waves (earliest sign, within minutes)
- Later: Q waves develop (deep negative deflection = dead tissue scar)
- Mirror-image ST depression in opposite leads
Simple memory trick: The ST goes UP like the heart is screaming for help.
Location clues:
- Inferior MI (blockage in right coronary): ST elevation in leads II, III, aVF
- Anterior MI (blockage in LAD): ST elevation in V1-V4
- Lateral MI: ST elevation in I, aVL, V5-V6
2. NSTEMI (Non-ST-Elevation Myocardial Infarction) - Partial Heart Attack
What it is: A heart attack where the artery is partially blocked. The inner layer of the heart wall is damaged, but not the full thickness.
ECG changes:
- ST segment depression (goes DOWN instead of up) - most common finding
- T wave inversion - T wave flips upside down
- No ST elevation (that's the key difference from STEMI)
- No Q waves (usually - though they can appear)
Special pattern: Deep T-wave inversions in V1-V4 = "Wellens' sign" - means dangerous blockage in the left anterior descending artery (LAD).
Simple memory trick: ST goes DOWN (depressed) = inner layer hurting.
3. Stable Angina (Coronary Artery Disease - Ischemia)
What it is: Narrowed but not blocked arteries. The heart gets enough blood at rest but not during exercise. Chest pain/tightness comes with exertion, goes away with rest.
ECG changes (at rest): Often NORMAL
ECG changes (during chest pain or exercise stress test):
- Horizontal or downsloping ST depression ≥ 1mm
- T wave flattening or inversion
- These changes RESOLVE when pain stops
Simple memory trick: ECG is only abnormal when the heart is stressed.
4. Atrial Fibrillation (AF) - Chaotic Upper Chambers
What it is: The upper chambers of the heart (atria) fire chaotically - thousands of disorganized electrical signals instead of one clean wave. The result: completely irregular heartbeat.
ECG changes:
- No P waves - completely absent (replaced by chaotic "fibrillatory" waves - a fuzzy/wavy baseline)
- Irregularly irregular QRS - beats come at completely random intervals (no pattern)
- QRS complexes are narrow and look normal (the lower chambers still work fine)
Simple memory trick: AF = Absolutely no P waves + Absolutely irregular rhythm.
Danger: Blood clots can form in the non-contracting atrium and travel to the brain, causing stroke.
5. Complete Heart Block (3rd Degree AV Block)
What it is: The electrical signal from the upper chambers cannot reach the lower chambers at all. The atria and ventricles beat independently, completely out of sync.
ECG changes:
- P waves and QRS complexes are totally dissociated - they march at their own separate rates
- P waves appear at regular intervals (~60-100/min)
- QRS complexes appear at slower regular intervals (~30-50/min)
- Wide, bizarre QRS if escape rhythm comes from ventricles (ventricular escape)
- Narrow QRS if escape rhythm comes from just below AV node (junctional escape)
Simple memory trick: P waves and QRS waves are "divorced" - they don't talk to each other.
Danger: Very slow heart rate (bradycardia) - patient may faint or go into cardiac arrest. Needs a pacemaker.
6. Left Bundle Branch Block (LBBB)
What it is: The left electrical wire (bundle branch) that carries the signal to the left ventricle is blocked. The left ventricle gets activated late, the "wrong way."
ECG changes:
- Wide QRS ≥ 0.12 seconds (broad, slurred complexes)
- No Q wave in V5-V6 (an important clue)
- "W" pattern in V1 (rS complex)
- "M" pattern in V5-V6 (broad, notched R wave)
- T wave points OPPOSITE to the main QRS direction (discordant T waves)
Simple memory trick: LBBB = "WiLLiaM" - W in V1, M in V5
Important: New LBBB in a patient with chest pain = treated like STEMI until proven otherwise.
7. Right Bundle Branch Block (RBBB)
What it is: The right electrical wire is blocked. The right ventricle gets activated late.
ECG changes:
- Wide QRS ≥ 0.12 seconds
- "rSR' pattern" in V1 (looks like rabbit ears or the letter "M" in V1) - this is the hallmark
- Wide S wave in V5-V6 and lead I (slurred, broad S wave)
- T wave inverted in V1-V2
Simple memory trick: RBBB = "MaRRoW" - M in V1, W in V5; or think: R = Right = rSR' in V1
Isolated RBBB is often benign (can be seen in normal hearts), but LBBB almost always means heart disease.
8. Ventricular Tachycardia (VT)
What it is: A dangerous rhythm where the lower chambers (ventricles) fire very rapidly (>100-150 beats/min) from an abnormal focus. The heart pumps poorly at this speed.
ECG changes:
- Wide, bizarre QRS complexes (>0.12 sec) - because signal spreads abnormally
- Very fast rate - typically 100-250 beats/min
- AV dissociation - P waves may be visible but unrelated to QRS
- "Fusion beats" - occasional normal-looking QRS when sinus beat and VT beat merge
- "Capture beats" - occasional narrow QRS (diagnostic of VT)
- All QRS complexes point in same direction
Simple memory trick: Wide + Fast = Ventricular Tachycardia until proven otherwise.
Danger: Can degenerate into ventricular fibrillation and cardiac arrest. Medical emergency.
9. Hypertrophic Cardiomyopathy / Left Ventricular Hypertrophy (HCM/LVH)
What it is: The heart muscle is abnormally thickened - either from long-term high blood pressure (LVH) or from a genetic condition (HCM). More muscle = more electrical activity = bigger voltages on ECG.
ECG changes:
- Very tall R waves in V5-V6 (left-sided leads) and/or deep S waves in V1-V2
- Voltage criteria for LVH: S in V1 + R in V5 or V6 > 35mm (Sokolow-Lyon)
- "Strain pattern" - ST depression and T wave inversion in V5-V6 (left ventricle is overloaded)
- Left axis deviation (QRS axis shifted left)
- In HCM specifically: may also see deep Q waves in lateral leads (from septal hypertrophy)
Simple memory trick: LVH = Tall towers on the left side of the ECG.
10. Pulmonary Embolism (PE) - Blood Clot in Lung
What it is: A blood clot travels to the lungs, blocking blood flow. The right side of the heart suddenly has to work much harder (acute right heart strain).
ECG changes:
- Sinus tachycardia - the most common finding (fast heart rate, >100/min)
- Classic S1Q3T3 pattern:
- Deep S wave in Lead I
- Q wave in Lead III
- T wave inversion in Lead III
- (This happens because the right ventricle suddenly enlarges and rotates the heart)
- T wave inversions in V1-V4 (right ventricular strain)
- Right bundle branch block (new RBBB from right heart strain)
- Right axis deviation
Simple memory trick: "S1Q3T3" = the classic PE pattern (though sinus tachycardia is actually most common)
Important: A normal ECG does NOT rule out PE - PE can have a completely normal ECG in up to 20% of cases.
Quick Summary Table
| # | Condition | Most Important ECG Finding |
|---|---|---|
| 1 | STEMI | ST elevation + tombstone T waves + Q waves |
| 2 | NSTEMI | ST depression + T wave inversion (no elevation) |
| 3 | Stable Angina | Normal at rest; ST depression on exertion |
| 4 | Atrial Fibrillation | No P waves + totally irregular rhythm |
| 5 | Complete Heart Block | P waves + QRS completely independent |
| 6 | LBBB | Wide QRS + W in V1 + M in V5-V6 |
| 7 | RBBB | Wide QRS + rSR' (rabbit ears) in V1 |
| 8 | Ventricular Tachycardia | Wide + fast + bizarre QRS |
| 9 | LVH/HCM | Tall voltages + strain pattern |
| 10 | Pulmonary Embolism | Sinus tachycardia + S1Q3T3 + T inversions V1-V4 |
ECG Waves Explained Simply (Reference)
R
|
P | T
/ \ | / \
---/ \-|-----/ \--- = Normal beat
\| /
Q S
- P = atria contract
- QRS = ventricles contract
- T = ventricles recharge
- When the ST segment goes up = the heart muscle is injured (STEMI)
- When the ST goes down = the heart muscle is short of blood (ischemia)
- When there's no P wave = the atria are misfiring (AF)
- When QRS is wide = signal travelling slowly or wrong way (bundle branch block, VT)
Sources: Ganong's Review of Medical Physiology; Harrison's Principles of Internal Medicine 22E (2025); Guyton and Hall Textbook of Medical Physiology; Tintinalli's Emergency Medicine
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