Lecture on ECG Waveforms

Learning Objectives

• Understand the significance of each ECG waveform and interval.
• Identify normal values and duration of key ECG waveforms.
• Interpret correlation between ECG waveforms and phases of the cardiac cycle.
• Recognize abnormalities in ECG waveforms and their clinical implications.

Key Terms

• ECG (Electrocardiogram): Records electrical activity of the heart via skin electrodes.

Overview of ECG Waveforms

• P Wave: Represents atrial depolarization; essential for understanding atrial function.

  • Normal Duration: < 0.12 seconds.
  • Abnormalities: Tall or broad can indicate atrial enlargement; variations can indicate arrhythmias.

• QRS Complex: Indicates ventricular depolarization; crucial for assessing ventricular function.

  • Normal Duration: 0.06 to 0.12 seconds.
  • Abnormalities: Prolonged duration can indicate bundle branch blocks or hypertrophy.

• T Wave: Represents ventricular repolarization; indicates recovery phase of ventricles.

  • Normal Appearance: Upright, rounded, and smooth.
  • Abnormalities: Inverted T waves can indicate ischemia; tall T waves can indicate hyperkalemia.

• PR Interval: Time from onset of P wave to start of QRS complex; reflects conduction from atria to ventricles.

  • Normal Duration: 0.12 to 0.2 seconds.
  • Abnormalities: Prolongation may indicate first-degree heart block.

• QT Interval: Duration encompassing ventricular depolarization and repolarization.

  • Normal Duration: < 0.44 seconds in men, < 0.46 seconds in women.
  • Abnormalities: Prolongation can lead to arrhythmias like torsade de pointes.

• ST Segment: Represents the period when ventricles are depolarized.

  • Normal Appearance: Isoelectric line.
  • Abnormalities: Elevation indicates myocardial infarction; depression indicates ischemia.

• U Wave: Associated with repolarization of Purkinje fibers; can indicate electrolyte imbalances.

Clinical Implications

• Arrhythmias: Abnormal rhythms like atrial fibrillation, ventricular tachycardia.
• Ischemia/Infarction: ST segment changes indicate reduced blood flow or heart attack.
• Electrolyte Imbalances: Affect T and U waves; critical for diagnosis.

ECG Lead Placement

• Limb Electrodes: RA, LA, RL, LL for reference and grounding.
• Chest Electrodes: V1-V6 for detailed view of heart's electrical activity.

Importance of Accurate ECG Interpretation

• Measurement: Precise calculation of intervals and waveforms critical for diagnosis.
• Comparison: Use previous ECGs for detecting changes over time.
• Treatment Guidance: ECG findings guide interventions like medication adjustments and procedures.

Conclusion

• ECGs are pivotal in diagnosing and managing cardiac conditions.
• Regular monitoring is essential for patients with known heart conditions.
• Accurate interpretation aids in timely and effective treatment decisions.

For questions, ask in class or send a message. Remember to balance study with practical nursing activities.