6 Updated ECGs

Basic Electrocardiogram Interpretation

History of the ECG

• Development of the electrocardiogram (ECG) over time.

• Understanding its clinical relevance in diagnosing heart conditions.

Cardiac Cycle

• Phases of the heart's contraction and relaxation process.

• Importance of timing in the heart's electrical and mechanical activities.

Basics of the ECG

• Overview of ECG as a tool for measuring electrical activity of the heart.

• Interpretation of different waveforms and intervals in the ECG tracing.

Cardiac Arrhythmias

• Types of arrhythmias and their significance.

• Understanding how irregular heartbeats manifest on an ECG.

Lead Placement

• Limb Leads (Bipolar):

  • I: Right Arm (RA) to Left Arm (LA)

  • II: RA to Left Leg (LL)

  • III: LA to LL

• Augmented Leads (Unipolar):

  • aVR: Right Arm positive

  • aVL: Left Arm positive

  • aVF: Left Leg positive

• Precordial Leads:

  • Positioning for chest leads, e.g., V1-V6, central to heart's electrical activities.

Cardiac Myocytes

Types of Myocytes

• Myocardiocytes

  • Form muscular walls of atria (A) and ventricles (V).

  • Responsible for contractility (shortening) and extensibility (stretching).

• Cardiac Pacemaker Cells

  • Regulate heart rhythm via automaticity (spontaneous impulse generation).

Electrical Activities

• Depolarization:

  • Cell's membrane potential shifts positively, generating an impulse.

  • Influx of Ca2+ and Na+ ions.

• Repolarization:

  • Return to a resting negative membrane potential, leading to muscle relaxation.

• Electrical activities graphically represented on an EKG.

Cardiac Conduction System

Path of Electrical Conduction

• Sinoatrial Node (SAN):

  • Primary pacemaker of the heart.

• Atrioventricular Node (AVN):

  • Receives impulses from SAN, delaying them for ventricular filling.

• Bundle of His:

  • Divides into right and left bundle branches critical for ventricular depolarization.

• Purkinje Fibers:

  • Spread the impulse throughout ventricular walls for coordinated contraction.

Phases of the Cardiac Cycle

Atrial Systole

• Atria contract, AV valves open, pulmonary and aortic valves closed.

• Electrical depolarization shown as P-wave on ECG.

• Atrial contraction increases pressure allowing blood flow to ventricles.

Ventricular Systole

1. Early Phase:

   • Ventricles begin to contract, all valves closed, QRS complex on ECG seen.

2. Rapid Ejection Phase:

   • Aortic and pulmonic valves open, blood ejected due to increased intraventricular pressure.

3. Reduced Ejection Phase:

   • Ventricular repolarization occurs (T-wave), atrial pressures rise due to venous return.

Isovolumetric Relaxation

• All valves closed, pressure in arteries exceeds ventricular pressure causing closure of A & P valves.

• Ventricular volume remains constant until next phase begins.

Interpreting ECG Rhythm Strips

Systematic Approach

1. Heart Rate: Calculate BPM.

2. Heart Rhythm: Regular or irregular intervals.

3. P Wave: Presence and morphology.

4. PR Interval: Length and consistency.

5. QRS Complex: Width and regularity.

Identifying Arrhythmias

• Normal Sinus Rhythm (NSR): 60-100 BPM with consistent P waves.

• Bradycardia: Heart rate < 60 BPM.

• Tachycardia: Heart rate > 100 BPM.

• Arrhythmias: P waves and QRS complex characteristics to identify specific types.

Common Arrhythmias

Premature Complexes

• Early beats from various origins in the heart.

Atrial Fibrillation

• Chaotic rhythm with risk of stroke, characterized by absent P waves.

Heart Blocks

• First Degree: Prolonged PR interval with no dropped beats.

• Second Degree: Dropped beats present with varying PR intervals.

• Third Degree: Complete dissociation between atrial and ventricular rhythms.

Ventricular Tachycardia/Fibrillation

• Rapid rates with wide QRS complexes, requiring immediate intervention.

Asystole

• Complete absence of electrical activity.

Conclusion

• Understanding ECG interpretation is essential for diagnosing various cardiac conditions.

• Mastery of lead placement and rhythm analysis enhances clinical skills in cardiac assessment.