EKG Basics and Heart Rhythms

Overview

This lecture covers the basic principles of reading EKGs (electrocardiograms), focusing on normal sinus rhythms, the meaning of EKG components, and how to determine heart rate from EKG strips, especially for NCLEX exam preparation.

EKG Basics and Electrical Impulse

• An EKG records the heart's electrical activity caused by movement of electrolytes (sodium and potassium) across cardiac cell membranes.
• The electrical impulse in a healthy heart originates at the SA (sinoatrial) node, known as the heart's pacemaker.
• The SA node sets the heart rate at 60–100 bpm; no other heart cells can exceed this pace.

EKG Waveforms and What They Represent

• The P wave represents atrial depolarization (when the atria contract).
• The QRS complex represents ventricular depolarization (when the ventricles contract).
• The T wave represents ventricular repolarization (when ventricles reset).

Depolarization and Repolarization

• Depolarization: sodium enters the cell, potassium exits, generating an electrical impulse.
• Repolarization: sodium and potassium return to original positions so the next impulse can occur.

Identifying Sinus Rhythm

• An upright P wave followed by a narrow QRS complex indicates a sinus rhythm (SA node is pacing the heart).
• No P wave = not a sinus rhythm.
• The QRS should be narrow (≤ 0.10 seconds, or 2.5 small boxes on EKG paper).

Analyzing the QRS Complex

• Narrow QRS means a strong, fast ventricular contraction.
• Wide QRS means weak, slow ventricular contraction and may indicate abnormal rhythm.

Determining Heart Rate on an EKG

• Each small box = 0.04 sec; each large box (5 small boxes) = 0.20 sec.
• A 6-second strip = 30 large boxes; count the number of QRS complexes and multiply by 10 to get bpm.
• Rate classifications:
  • Normal sinus rhythm: 60–100 bpm
  • Sinus bradycardia: <60 bpm
  • Sinus tachycardia: 101–140 bpm

Rhythm Terminology

• The first word in an EKG rhythm name indicates where the impulse starts (e.g., sinus, atrial, ventricular).
• Atrial rhythms (e.g., atrial fibrillation) start in the atria but not the SA node; often have abnormal P waves.
• Ventricular rhythms (e.g., ventricular tachycardia) start in the ventricles; often show wide QRS without P waves.

Key Terms & Definitions

• Electrolytes — minerals that generate electrical impulses in the heart (e.g., sodium, potassium).
• Depolarization — movement of ions generating an electrical impulse (cell contracts).
• Repolarization — return of ions to original positions (cell resets).
• SA node (Sinoatrial node) — heart’s natural pacemaker.
• Sinus rhythm — heart rhythm where the SA node is pacing the heart.
• QRS complex — EKG wave representing ventricular contraction.
• P wave — EKG wave representing atrial contraction.
• T wave — EKG wave representing ventricular repolarization.
• Bradycardia — slow heart rate (<60 bpm).
• Tachycardia — fast heart rate (>100 bpm).

Action Items / Next Steps

• Practice identifying upright P waves and narrow QRS complexes on sample EKG strips.
• Memorize the definitions for depolarization, repolarization, and normal EKG waveforms.
• Review calculating heart rate using a 6-second EKG strip.
• Watch upcoming lectures on atrial and ventricular rhythms for further NCLEX prep.