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Sinus Rhythm

  • Definition: Normal heart rhythm with electrical impulses originating from the Sinoatrial (SA) node, the heart's natural pacemaker.
  • Function: Ensures coordinated heartbeats for efficient blood circulation.

Key Characteristics

  • Heart Rate: 60-100 beats per minute (bpm) in adults.
  • Regularity: Consistent timing between heartbeats.
  • P Wave: Indicates atrial contraction, preceding the QRS complex.
  • PR Interval: Delay between atrial and ventricular contraction; normal range is 0.12-0.20 seconds.
  • QRS Complex: Narrow and normal shape indicating proper ventricular contraction.

Mechanism

  1. SA Node generates electrical impulses.
  2. Impulses spread through the atria, causing contraction (P wave).
  3. Signal reaches the AV Node, slowing impulses to allow ventricular filling.
  4. Impulse travels down the Bundle of His to Purkinje Fibers, leading ventricles to contract (QRS complex).
  5. Ventricles relax followed by T wave; cycle repeats.

Variants of Sinus Rhythm

  • Sinus Bradycardia: Heart rate slower than 60 bpm (normal in athletes or during sleep).
  • Sinus Tachycardia: Heart rate faster than 100 bpm (normal during exercise or stress).
  • Sinus Arrhythmias: Slight variations in rhythm, often due to breathing.

Supraventricular Tachycardia (SVT)

  • Definition: Abnormally fast heart rhythm originating above the ventricles (atria or AV node).
  • Heart Rate: Over 100 bpm, typically 150-250 bpm.

Mechanism

  • Normally, the SA Node generates impulses; in SVT, abnormal reentry circuit or an extra electrical pathway overrides the SA node.
  • Causes rapid firing of impulses, leading to fast heartbeats.

Effects

  • Rapid contractions can lead to inefficient heart function:
    • Reduced ventricular filling time.
    • Symptoms: Dizziness, shortness of breath, palpitations.

Body Compensation

  • Vagus Nerve: Can help slow down rapid heart rates.
  • Vagal Maneuvers: Techniques like coughing, breath-holding, or cold water immersion can slow heart rate.

Atrial Fibrillation (Afib)

  • Definition: Irregular and rapid heart rhythm originating in the atria.

Mechanism

  • Involves disorganized electrical signals causing atria to quiver instead of contracting.
  • Results in inefficient heartbeat and increased stroke risk.

Characteristics

  • Multiple electrical impulses firing simultaneously from different areas of atria.
  • Reduced atrial function leads to blood pooling, increasing clot risk.
  • Ventricular rate: Typically between 100-175 bpm.

Types

  • Paroxysmal Afib: Episodes come and go, lasting minutes to days.
  • Persistent Afib: Lasts over 7 days, usually requires treatment.
  • Long-standing Persistent Afib: Lasts over a year; harder to correct.
  • Permanent Afib: Heart remains in afib permanently, focusing on rate control.

Body Compensation

  • AV Node: Filters chaotic signals to regulate ventricular rate.
  • May increase stroke volume to compensate for irregular rhythm.

Atrial Flutter

  • Definition: Fast but regular heart rhythm originating in the atria.
  • Heart Rate: Typically 250-350 bpm.

Mechanism

  • Abnormal loop of electrical signals causes fast atrial beats, usually in the right atrium.

Characteristics

  • Organized Pattern: Unlike afib, atrial flutter has a more repetitive electrical pattern.
  • The AV Node blocks some atrial impulses, leading to a ventricular rate of about 150 bpm.

Body Compensation

  • The AV node prevents excessively fast ventricular rates by blocking some impulses.
  • Vagal responses may be triggered to regulate heart rate during deep breaths or coughing.

Ventricular Tachycardia (VT)

  • Definition: Fast and abnormal heart rhythm originating from the ventricles.
  • Heart Rate: Over 100 bpm, often 150-250 bpm.

Mechanism

  • An abnormal electrical site in the ventricles rapidly fires impulses, overriding SA node control.

Risks

  • Dangerous due to potential progression to ventricular fibrillation (Vfib) and cardiac arrest if untreated.

Types

  • Sustained VT: Lasts more than 30 seconds; can cause severe symptoms.
  • Non-Sustained VT: Lasts less than 30 seconds; may be asymptomatic.
  • Monomorphic VT: All QRS complexes look the same (single abnormal focus).
  • Polymorphic VT: QRS complexes vary in shape; associated with electrolyte imbalances (e.g., Torsades de Pointes).