Understanding ECGs can be challenging at first. It's perfectly normal not to grasp every detail right away just by reading about them. Mastery comes with practice and training, so don't be discouraged … keep at it, and it will become clearer over time

Tachyarrhythmias

Bradyarrhythmias

Pediatric Arrhythmias

Cardiac Implantable Devices

High-yield Overview

ECG basics

Watch 👉 EKG Interpretation

• Video

1. Watch ▶ECG rate and rhythm

2. Watch ▶ECG intervals

3. Watch ▶ECG QRS transition

4. Watch ▶ECG normal sinus rhythm

5. Watch ▶ECG axis

6. Watch ▶ECG cardiac hypertrophy and enlargement

Conduction Pathway

• SA Node → Atria → AV Node → Bundle of His → Right and Left Bundle Branches → Purkinje Fibers → Ventricles
  • Left Bundle Branch divides into left anterior and posterior fascicles

SA Node

• Located in upper part of crista terminalis near SVC opening
• “Pacemaker” with inherent dominance and slow phase of upstroke

AV Node

• Located in interatrial septum near coronary sinus opening
• Blood supply usually from RCA
• 100-msec delay allows time for ventricular filling

Pacemaker Rates

• SA Node > AV Node > Bundle of His / Purkinje Fibers / Ventricles

Speed of Conduction

• His-Purkinje > Atria > Ventricles > AV Node

Electrocardiogram (ECG) Components

1. P Wave
   • Atrial depolarization
2. PR Interval
   • Time from start of atrial depolarization to start of ventricular depolarization (normally 120-200 msec)
3. QRS Complex
   • Ventricular depolarization (normally < 100 msec)
4. QT Interval
   • Ventricular depolarization, mechanical contraction of the ventricles, and ventricular repolarization
5. T Wave
   • Ventricular repolarization (inversion may indicate ischemia or recent MI)
6. J Point
   • Junction between end of QRS complex and start of ST segment
7. ST Segment
   • Isoelectric, ventricles depolarized
8. U Wave
   • Prominent in hypokalemia (hyp“U”kalemia) and bradycardia

<aside> 🧠

Determine ECG Axis

1. Look at the QRS complex in leads I and a VF.
2. If both are mainly positive, then the axis is normal.
3. If mainly positive in lead I and mainly negative in a VF, the axis is deviated lo the left.
4. If mainly negative in lead I and mainly positive in a VF, the axis is deviated to the right.
5. If mainly negative in both I and a VF, then there i.s extreme right axis deviation. </aside>

https://www.youtube.com/watch?v=XNXVGAneSyk

ECG interpretation algorithm 💎 Prior to analysis, confirm patient details, date and time of ECG, and machine calibration (usually 1 mV = 1 cm and paper speed = 25 mm/s). 1. Determine rhythm (best seen in lead II) 2. Determine heart rate (any lead) 3. Determine cardiac axis (e.g., using leads I, II, and aVF) 4. Evaluate morphology and size of P-waves (usually best seen in lead II) 5. Measure PR-interval duration (usually best seen in lead II). 6. Evaluate QRS-complex morphology, size, and duration (look at all leads individually) 7. Evaluate ST-segment morphology (look at all leads individually) 8. Evaluate T-wave morphology (look at all leads individually) 9. Measure QT-interval duration 10. Evaluate U-wave morphology if present (usually best seen in leads V2-V4) 💎The exact sequence in which these components are evaluated may vary → what is important is to evaluate each ECG systematically to avoid missing subtle or unexpected findings.

Most Common ECG Abnormalities - Review