Understanding Various ECG Rhythms

Introduction

Electrocardiography (ECG) is a vital tool in assessing the electrical activity of the heart. Various ECG rhythms reflect different cardiac conditions, ranging from normal physiological states to life-threatening arrhythmias.

Normal Sinus Rhythm (NSR)

• Definition: The normal and expected rhythm of the heart.
• Characteristics:
  • Heart rate: 60-100 beats per minute (bpm)
  • Regular rhythm
  • P wave before every QRS complex
  • PR interval within a normal range (120-200 ms)

Sinus Bradycardia

• Definition: A sinus rhythm with a heart rate below 60 bpm.
• Causes: Can be physiological (e.g., in athletes) or pathological (e.g., hypothyroidism, sick sinus syndrome).

Sinus Tachycardia

• Definition: A sinus rhythm with a heart rate above 100 bpm.
• Common Causes: Fever, dehydration, anemia, hyperthyroidism, or physiological stress.

Atrial Fibrillation (AF)

• Definition: A chaotic and irregular atrial activity without discrete P waves.
• ECG Features:
  • Irregularly irregular rhythm
  • Absence of distinct P waves
  • Variable ventricular response
• Clinical Relevance: Increases the risk of stroke due to blood stasis in the atria.

Atrial Flutter

• Definition: A rapid atrial rhythm with a characteristic sawtooth appearance.
• ECG Features:
  • Regular or irregular rhythm
  • Multiple P waves (flutter waves) between each QRS complex
  • Atrial rate usually around 250-350 bpm
• Clinical Relevance: Can lead to high ventricular rates and hemodynamic instability.

Supraventricular Tachycardia (SVT)

• Definition: A term describing rapid rhythms originating above the ventricles.
• Types:
  • AV nodal reentrant tachycardia (AVNRT)
  • AV reentrant tachycardia (AVRT, as seen in Wolff-Parkinson-White syndrome)
  • Atrial tachycardia

Ventricular Tachycardia (VT)

• Definition: A potentially life-threatening rhythm originating from the ventricles.
• ECG Features:
  • Wide QRS complexes (>120 ms)
  • Regular rhythm
  • Rapid ventricular rate (>100 bpm)
• Clinical Relevance: Can deteriorate into ventricular fibrillation, requiring urgent intervention.

Ventricular Fibrillation (VF)

• Definition: A life-threatening rhythm where the ventricles quiver instead of contracting.
• ECG Features:
  • Completely disorganized electrical activity
  • No discernible P waves, QRS complexes, or T waves
• Clinical Relevance: Causes cardiac arrest; immediate defibrillation is required.

First-Degree AV Block

• Definition: Prolongation of PR interval (>200 ms) with preserved conduction.

Second-Degree AV Block

• Types:
  • Mobitz Type I (Wenckebach): Progressive PR interval prolongation followed by dropped QRS.
  • Mobitz Type II: Intermittent dropped QRS complexes without PR prolongation.

Third-Degree (Complete) AV Block

• Definition: No communication between atria and ventricles, requiring pacemaker therapy.

Conclusion

Recognizing and interpreting different ECG rhythms is crucial in diagnosing and managing various cardiac conditions. Some rhythms require immediate intervention, while others are benign or manageable with medication.

Source recommendations

1. European Society of Cardiology (ESC) Guidelines on the Management of Cardiac Arrhythmias

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
2. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
4. https://www.ahajournals.org/doi/10.1161/01.cir.0000091380.04100.84
5. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Atrial-Fibrillation

2. American College of Cardiology (ACC)/American Heart Association (AHA)/Heart Rhythm Society (HRS) Guidelines for the Evaluation and Management of Arrhythmias

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
2. https://pubmed.ncbi.nlm.nih.gov/30586772/
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193
4. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/03/07/23/36/2017-acc-aha-hrs-guideline-for-syncope
5. https://www.jacc.org/doi/10.1016/j.jacc.2017.03.003