Cardiac Arrhythmias Overview

Overview

This lecture discusses the classification of cardiac arrhythmias by their site of origin and details the features, causes, and ECG characteristics of common arrhythmias.

Cardiac Rhythm Classification

• Arrhythmias are classified based on origin: sinus (SA node), atrial (atria), or ventricular (ventricles).
• Sinus rhythm is the normal heart rhythm, set by the SA node.

Sinus Rhythms

• Normal sinus rhythm: SA node fires 60–100 times per minute; heart rate 60–100 bpm.
• Sinus bradycardia: SA node fires <60 times/min; heart rate <60 bpm; can be normal (e.g., during sleep).
• Sinus tachycardia: SA node fires >100 times/min; heart rate >100 bpm; can be normal (e.g., during exercise).

Atrial Arrhythmias (Supraventricular Tachycardias)

• Atrial arrhythmias are always clinical, not normal variations.
• Common types: atrial flutter, atrial fibrillation, AV nodal reentrant tachycardia (AVNRT).

Atrial Flutter (ALF)

• Caused by a reentry circuit, usually in the right atrium.
• Atrial rate: 250–400 bpm; ventricular rate slower due to AV node block.
• ECG: no normal P waves; sawtooth flutter (F) waves.

Atrial Fibrillation (AF)

• Caused by multiple random ectopic signals, often near pulmonary veins.
• Atria quiver instead of contracting; irregular ventricular response.
• ECG: absent P waves; irregular narrow QRS; baseline may be wavy or flat.

AV Nodal Reentrant Tachycardia (AVNRT)

• Caused by a reentry circuit involving the AV node.
• Atrial and ventricular rates are identical; rate 150–250 bpm and regular.

Ventricular Arrhythmias

• Most dangerous, called lethal rhythms.

Ventricular Tachycardia (VT)

• Triggered by a strong, single site in a ventricle, often after heart damage.
• Produces premature ventricular contractions; regular and rapid (100–250 bpm).
• ECG: wide, abnormal QRS; absent P wave.
• Short episodes can be asymptomatic; prolonged VT (>30s) needs immediate treatment.

Ventricular Fibrillation (VF)

• Caused by multiple, weak ectopic sites in ventricles; ventricles quiver without pumping blood.
• Can rapidly lead to cardiac arrest.
• ECG: irregular, random waves; no recognizable P, QRS, or T waves; amplitude decreases over time.

Key Terms & Definitions

• Sinus rhythm — Normal heart rhythm from the SA node.
• Sinus bradycardia — Slow heart rhythm (<60 bpm) from the SA node.
• Sinus tachycardia — Fast heart rhythm (>100 bpm) from the SA node.
• Atrial flutter (ALF) — Rapid, regular atrial rhythm from a reentry circuit.
• Atrial fibrillation (AF) — Chaotic, irregular atrial rhythm from multiple ectopic sites.
• AVNRT — Fast, regular rhythm from a reentry circuit in the AV node.
• Ventricular tachycardia (VT) — Rapid rhythm from a single ventricular site.
• Ventricular fibrillation (VF) — Chaotic ventricular rhythm from multiple ectopic sites.

Action Items / Next Steps

• Review ECG patterns for each arrhythmia type.
• Prepare to identify arrhythmias based on rate, rhythm, and ECG features.