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.