Overview
This lecture covers the basics of EKG (ECG) interpretation, including heart conduction system anatomy, the PQRST complex, EKG strip analysis, and criteria for normal sinus rhythm.
EKG/ECG & Heart Conduction System
- EKG (ECG) stands for electrocardiogram and records heart electrical activity.
- The heart’s electrical conduction system enables coordinated contraction and blood flow.
- Blood enters the right atrium, moves through the heart, and is pumped to the lungs and body.
- Electrical signals cause depolarization (contraction) and repolarization (relaxation) of heart cells.
Depolarization & Repolarization
- Resting heart cells are negatively charged inside (polarized).
- Depolarization occurs when sodium enters the cell, making it contract.
- Repolarization restores the cell’s negative charge, leading to relaxation.
- Depolarization = contraction; repolarization = relaxation.
Components of the Conduction System
- SA (sinoatrial) node: heart’s pacemaker in right atrium; initiates atrial depolarization (rate: 60-100 bpm).
- Bachmann’s bundle: pathway to left atrium.
- AV (atrioventricular) node: gatekeeper; delays impulse to allow atrial emptying.
- Bundle of His → Bundle branches (right, left) → Purkinje fibers: responsible for ventricular depolarization.
EKG Paper & PQRST Complex
- Each small box on EKG paper = 0.04 sec; each large square (5 boxes) = 0.20 sec.
- P wave: atrial depolarization/contraction; should be present, upright, <0.12 sec.
- PR segment: AV node delay (flat area after P wave).
- PR interval: start of P wave to start of QRS; normal = 0.12–0.20 sec; prolonged interval may indicate heart block.
- QRS complex: ventricular depolarization/contraction; normal = <0.12 sec.
- J point: where QRS meets ST segment.
- ST segment: end of S wave to start of T wave; should be flat (isoelectric); elevation/depression may indicate pathology.
- T wave: ventricular repolarization/relaxation; upright and round.
- QT interval: start of QRS to end of T wave; normal = 0.35–0.44 sec.
EKG Strip Analysis Steps
- Use at least a 6-second EKG strip (30 large squares).
- Examine the "three R’s" for both P waves and QRS complexes: Regularity, Rate, Resemblance.
- Regularity: measure intervals for consistency.
- Rate: count waves or complexes in 6 seconds, multiply by 10.
- Resemblance: check appearance, duration, and sequence (e.g., one P wave before every QRS).
- Assess intervals and segments for their normal measurements.
Key Terms & Definitions
- Depolarization — when heart cells become less negative; causes contraction.
- Repolarization — when heart cells return to negative state; causes relaxation.
- SA node — pacemaker; starts heart’s electrical impulse.
- AV node — delays impulse, allows atrial emptying.
- P wave — atrial contraction.
- QRS complex — ventricular contraction.
- ST segment — early ventricular relaxation, should be flat.
- T wave — ventricular relaxation.
- QT interval — duration of ventricular electrical activity.
Action Items / Next Steps
- Memorize normal values for EKG intervals and segments.
- Practice EKG strip analysis using the “three R’s” method.
- Take the provided quiz for self-assessment.