Cardiac Arrythmias (YT)

Heart Rhythms and Origin

  • Rhythm classifications based on their site of origin:

    • Sinus rhythms: Originate from the sinoatrial (SA) node.

    • Atrial rhythms: Originate from the atria.

    • Ventricular rhythms: Originate from the ventricles.

  • Sinus rhythm: Normal heart rhythm controlled by the SA node.

The Sinoatrial Node

  • The SA node fires 60 to 100 times per minute, establishing a normal heart rate of 60 to 100 beats per minute.

  • Common variations include:

    • Sinus bradycardia: Means the SA node fires less than 60 times, resulting in a heart rate of less than 60 bpm; can be normal during sleep.

    • Sinus tachycardia: Means the SA node fires more than 100 times, resulting in a heart rate of over 100 bpm; can be normal during exercise.

  • Both sinus bradycardia and sinus tachycardia could be normal or clinical based on underlying causes.

Cardiac Arrhythmias from the Atria

  • Cardiac arrhythmias from other parts of the atria are always clinical conditions.

  • Common atrial arrhythmias include:

    • Atrial flutter: Caused by a reentrant electrical impulse loop usually in the right atrium.

      • Regular and rapid atrial rate of 250-400 beats per minute.

      • Ventricular rate is slower, typically a three-to-one heart block (one impulse in three reaches the ventricles).

      • On ECG, characterized by absence of normal P waves and presence of flutter waves (F waves) in sawtooth patterns.

    • Atrial fibrillation: Involves multiple chaotic impulses initiated from ectopic sites in the atria.

      • Causes quivering instead of contraction of the atria.

      • Atrial rate can be high, but most impulses don’t pass through the AV node, leading to an irregular ventricular rate (can range from <60 to >100 bpm).

      • On ECG, absence of P waves and irregular narrow QRS complexes, with a baseline that may appear undulating or flat.

    • AV nodal reentrant tachycardia (AVNRT): Small reentrant pathway involving the AV node.

      • Atrial and ventricular rates are identical, fast and regular, ranging from 150 to 250 beats per minute.

Ventricular Rhythms

  • Ventricular rhythms are dangerous, termed lethal rhythms.

  • Ventricular tachycardia (V tach): Results from a single strong firing site within the ventricles.

    • Common in individuals with heart structural issues (e.g., scarring from a heart attack).

    • Produces ventricular premature beats, regular and fast (100-250 bpm);

      • On ECG: wide, bizarre QRS complexes with absent P waves.

    • Can occur in brief episodes (<30 seconds); sustained VTAC (>30 seconds) requires immediate treatment to avoid cardiac arrest.

    • Potential progression to ventricular fibrillation.

  • Ventricular fibrillation (V fib): Caused by multiple weak ectopic sites in the ventricles.

    • Results in chaotic electrical signals causing the ventricles to quiver instead of contract, leading to minimal or no blood pumped.

    • It can rapidly result in cardiac arrest.

    • On ECG: irregular random waveforms without identifiable P wave, QRS complex, or T wave; amplitude decreases over time, evolving from coarse to fine V fib to eventual flatline.