ECG Flashcards
How do you calculate heart rate on an ECG?
300 ÷ (number of large squares between R-R waves).
Example: 2 large squares = 150 bpm.
Alternatively, count R waves in 6 seconds × 10.
What defines sinus rhythm?
Regular rhythm + P wave before every QRS + normal axis (P wave upright in II, inverted in aVR)
What is a normal PR interval?
0.12–0.20 seconds / 120-200ms
3–5 small squares
What does a prolonged PR interval indicate?
First-degree AV block (PR > 0.20s/200ms)
prolonged PR intervals indicate slower conduction between ventricles + atria
What is a normal QRS duration?
< 0.12 seconds/120ms = 3 small squares
Wider (> 120ms) = bundle branch block or ventricular origin.
what does a shortened PR interval indicate?
PR interval <120ms= faster conduction/accessory pathway e.g. Wolf Parkinson White Syndrome
What does ST elevation indicate?
Acute myocardial infarction (STEMI) or pericarditis
What are pathologic Q waves?
Q waves > 1 small square wide/deep (>40ms) in V1, V3 → prior infarction
How do you identify left axis deviation?
QRS positive in I, negative in II/aVF → left ventricular hypertrophy or left bundle branch block.
What are the ECG signs of atrial fibrillation?
Irregularly irregular rhythm.
No P waves.
Fibrillatory (f) waves in baseline.
What does peaked/tall T waves suggest?
Hyperkalemia (high potassium)
What is the “3-2-1 rule” for right bundle branch block (RBBB)?
3 waves: RSR’ pattern in V1 (looks like “rabbit ears”).
2 wide: QRS > 0.12s.
1 slurred: Wide S wave in I/V6.
What ECG changes occur in hypercalcemia?
Short QT interval
What ECG changes occur in hypokalemia?
ST depression, flattened T waves, U waves.
What is the “tombstone” sign?
Massive ST elevation in V1–V6 → anterior STEMI
What parts of the heart do each groups of leads show?
I, aVL, V5,V6= lateral part
II,III, aVF= inferior wall
V1-V4= septum/anterior view
U-wave (pathology) occasionally follow T waves; what are U-waves associated with?
U-waves are associated with electrolyte imbalances or hypothermia
First degree AV heart block
PR interval >200ms (consistent)
Second degree heart block (Mobitz type 1)
Second degree (Mobitz type 1)
PR interval >200 (progressive prolongation)
Dropped QRS complex - Predictable non-conduction
Second degree heart block (Mobitz type 2)
Second degree (Mobitz type 2)
PR interval >200 (consistent)
Dropped QRS complex - Intermittent non-conduction
Third degree (complete heart block)
Atrioventricular dissociation - generation of separate rhythms
Regular P-P and R-R intervals (no relationship)
Left bundle branch block
V1= W wave
V6= M wave
Right bundle branch block
V1= M wave
V6= W wave
Left Axis Deviation causes
Mean electric axis between → -30 to -90 degrees
Anticlockwise from Normal Axis
ECG:
Lead I → Positive QRS Deflection
Lead II / III→ Negative QRS Deflection
causes:
- LV Hypertrophy
- Left Bundle Branch Block
- Left Anterior Fascicular Block
- Inferior MI
- Wolf-Parkinson-White Syndrome → Right-sided Accessory Pathway
Normal Axis
Mean electric axis between → -30 to 90 degrees
ECG:
Lead II → Positive QRS
Lead aVF → Positive QRS
Right Axis Deviation causes
Mean electric axis between → +90 to +180 degrees
Clockwise from Normal Axis
ECG:
Lead I → Negative QRS Deflection
Lead aVF → Positive QRS Deflection
causes:
- Normal Variant
- RV Hypertrophy
- Chronic Lung Disease (Cor Pulmonale) + Pulmonary Embolism
- Left Posterior Fascicular Block
- Hyperkalaemia
- Dextrocardia
- ASD/VSD
- Wolf-Parkinson-White Syndrome → Left-sided Accessory Pathway
Extreme Axis Deviation
Mean electric axis between → -90 to +180 degrees
ECG:
Lead I → Negative QRS
Lead aVF → Negative QRS
causes:
- Severe RV Hypertrophy
- Ventricular rhythms (e.g. Ventricular Tachycardia)
- Hyperkalaemia
which coronary artery corresponds to which leads:
- I, aVL, V5, V6
- II, III, aVF
- V1-V4
I, aVL, V5, V6= lateral wall of LV (left circumflex)
- II, III, aVF= inferior wall (right coronary a.)
- V1-V4= septum/anterior view (left anterior descending)
