ECG/EKG Interpretation

by | Sep 11, 2024 | Nurse Article | 0 comments

ECG/EKG Interpretation – Basic ECG interpretation, recognizing common arrhythmias, and understanding how to react to abnormal findings.

ECG/EKG Interpretation: Basics and Common Arrhythmias

Electrocardiography (ECG or EKG) is a non-invasive diagnostic tool that records the electrical activity of the heart. Understanding how to interpret an ECG is crucial for identifying normal heart rhythms, arrhythmias, and other cardiac abnormalities.

1. Basics of ECG/EKG

An ECG tracing is divided into different waves and intervals, each representing different electrical activities of the heart:

  • P wave: Atrial depolarization (contraction of the atria).
  • PR interval: Time from the start of atrial depolarization to the start of ventricular depolarization.
  • QRS complex: Ventricular depolarization (contraction of the ventricles).
  • ST segment: Time between ventricular depolarization and repolarization.
  • T wave: Ventricular repolarization (relaxation of the ventricles).
  • QT interval: Total time for ventricular depolarization and repolarization.

2. ECG Leads

  • Limb Leads: I, II, III, aVR, aVL, aVF.
  • Precordial (Chest) Leads: V1, V2, V3, V4, V5, V6.

These leads view the heart from different angles, allowing for the identification of issues in specific areas of the heart (e.g., inferior, lateral, anterior, septal walls).

3. Normal ECG

A normal sinus rhythm (NSR) should have the following characteristics:

  • Heart rate: 60-100 bpm.
  • Regular rhythm: The intervals between R waves are consistent.
  • P wave: Present before every QRS complex.
  • PR interval: 0.12-0.20 seconds.
  • QRS complex: Narrow (≤0.12 seconds).
  • T wave: Upright in most leads (especially in leads I, II, V3-V6).

4. Common Arrhythmias and Their Interpretation

a. Sinus Bradycardia

  • Heart rate: <60 bpm.
  • ECG findings: P waves and QRS complexes are normal but slower.
  • Causes: May occur in athletes, during sleep, or due to medications (e.g., beta-blockers). It can also be caused by hypoxia or hypothyroidism.
  • Management: If symptomatic (e.g., dizziness, hypotension), atropine may be given or pacing may be required.

b. Sinus Tachycardia

  • Heart rate: >100 bpm.
  • ECG findings: P waves and QRS complexes are normal but faster.
  • Causes: Fever, pain, dehydration, anxiety, anemia, or medications (e.g., stimulants).
  • Management: Treat the underlying cause (e.g., fluids for dehydration, antipyretics for fever).

c. Atrial Fibrillation (AFib)

  • Heart rate: Variable (may be fast or normal).
  • ECG findings:
    • Irregularly irregular rhythm.
    • No discernible P waves.
    • Fibrillatory baseline.
  • Causes: Hypertension, heart failure, valvular disease, hyperthyroidism.
  • Management: Rate control (e.g., beta-blockers, calcium channel blockers), rhythm control (antiarrhythmics), anticoagulation (to prevent stroke).

d. Atrial Flutter

  • Heart rate: Atrial rate of 250-350 bpm, ventricular rate may vary.
  • ECG findings:
    • “Sawtooth” flutter waves in place of P waves.
    • Regular or variable ventricular response.
  • Causes: Similar to AFib (heart disease, lung disease).
  • Management: Rate control, anticoagulation, possible cardioversion.

e. Supraventricular Tachycardia (SVT)

  • Heart rate: 150-250 bpm.
  • ECG findings:
    • Narrow QRS complexes.
    • P waves often hidden in the preceding T wave.
  • Causes: Often triggered by stress, caffeine, or certain medications.
  • Management: Vagal maneuvers (e.g., carotid massage), adenosine, or synchronized cardioversion if unstable.

f. Ventricular Tachycardia (VTach)

  • Heart rate: 100-250 bpm.
  • ECG findings:
    • Wide QRS complexes (>0.12 seconds).
    • No P waves.
  • Causes: Myocardial infarction, electrolyte imbalances (e.g., hypokalemia), heart failure.
  • Management:
    • If stable: Antiarrhythmics (e.g., amiodarone).
    • If unstable: Immediate defibrillation (if pulseless) or synchronized cardioversion.

g. Ventricular Fibrillation (VFib)

  • Heart rate: Rapid and chaotic.
  • ECG findings:
    • No identifiable P waves, QRS complexes, or T waves.
    • Appears as a chaotic, disorganized electrical activity.
  • Causes: Myocardial infarction, severe electrolyte disturbances, electrocution.
  • Management: Immediate defibrillation and CPR.

h. Asystole

  • Heart rate: Absent (flatline).
  • ECG findings:
    • No electrical activity (straight line).
  • Causes: Severe hypoxia, cardiac arrest.
  • Management: CPR, epinephrine, and treat underlying causes (e.g., hypoxia, electrolyte imbalances). Do not defibrillate asystole.

i. First-Degree AV Block

  • ECG findings:
    • Prolonged PR interval (>0.20 seconds), but every P wave is followed by a QRS complex.
  • Causes: May occur with increased vagal tone or certain medications (e.g., beta-blockers, digoxin).
  • Management: Often no treatment is needed unless symptomatic.

j. Second-Degree AV Block (Type I – Wenckebach)

  • ECG findings:
    • Progressive prolongation of the PR interval until a QRS complex is dropped.
  • Causes: Often benign, may be due to medications or increased vagal tone.
  • Management: Usually does not require treatment unless symptomatic.

k. Second-Degree AV Block (Type II)

  • ECG findings:
    • Some P waves are not followed by QRS complexes (dropped beats) without PR interval prolongation.
  • Causes: More concerning, may progress to third-degree block.
  • Management: Requires monitoring and possible pacing.

l. Third-Degree AV Block (Complete Heart Block)

  • ECG findings:
    • P waves and QRS complexes are present, but there is no association between them.
    • Atrial and ventricular rates are independent.
  • Causes: Can occur with myocardial infarction or degeneration of the conduction system.
  • Management: Requires pacing (temporary or permanent pacemaker).

5. Interpretation Steps

  1. Rate: Calculate the heart rate by counting the number of QRS complexes in a 6-second strip and multiplying by 10.
  2. Rhythm: Is it regular or irregular? Check the distance between R waves.
  3. P waves: Are they present and do they precede each QRS complex?
  4. PR Interval: Is it within 0.12-0.20 seconds?
  5. QRS Complex: Is it narrow (normal) or wide (abnormal)?
  6. ST Segment and T Waves: Look for elevation or depression in the ST segment (indicative of ischemia or infarction).

6. Responding to Abnormal ECG Findings

  • For bradycardia: Assess for symptoms (e.g., dizziness, fatigue). If symptomatic, give atropine or prepare for pacing.
  • For tachycardia: Determine if the patient is stable or unstable. Treat underlying causes such as pain, fever, or dehydration.
  • For arrhythmias like AFib or VTach: Focus on rate/rhythm control and consider anticoagulation if necessary.
  • For life-threatening arrhythmias (e.g., VFib, pulseless VTach): Initiate CPR and defibrillation immediately.

Summary

  • A systematic approach to ECG interpretation is essential for recognizing normal sinus rhythm and identifying arrhythmias.
  • Common arrhythmias include AFib, SVT, VTach, and VFib, each requiring specific interventions.
  • In emergencies (e.g., VFib, pulseless VTach), prompt defibrillation is life-saving.