The SA Node as the Heart's Natural Pacemaker
Placeholder sentence: normal rhythm begins as one organized impulse.
- 60–100: Normal atrial rate (bpm placeholder)
- 1:1: Conduction (AV node placeholder)
- Present: P wave (ECG placeholder)
- ~99%: Regularity (placeholder metric)
Sinoatrial node pacing
Placeholder: SA node depolarizes and the wave spreads uniformly.
Pulmonary Vein Foci Igniting Extra Beats
Placeholder sentence: an ectopic focus near the pulmonary veins fires.
- Pulm. veins: Common trigger site (placeholder)
- PACs: Extra beats (placeholder)
- Paroxysmal: Onset (placeholder)
- Atrial stretch: Risk factor (placeholder)
Ectopic focus mechanism
Placeholder: rapid firing tissue overrides the SA node briefly.
Multiple Wavelet Reentry Circuits Forming
Placeholder sentence: spiral wavelets circle through atrial tissue.
- Moe 1959: Wavelet theory (placeholder)
- Multiple: Circuits (placeholder)
- Reentrant: Path (placeholder)
- Unstable: Stability (placeholder)
Reentry circuit formation
Placeholder: wavefronts loop back on refractory tissue edges.
Chaotic, Disorganized Atrial Electrical Activity
Placeholder sentence: coordinated contraction is lost entirely.
- 400–600: Atrial rate (bpm placeholder)
- Absent: P waves (fibrillatory placeholder)
- Quivering: Contraction (placeholder)
- Elevated: Clot risk (placeholder)
Fibrillatory conduction
Placeholder: countless mini-wavelets collide continuously.
AV Node Filtering Produces an Irregular Pulse
Placeholder sentence: ventricles beat irregularly despite atrial chaos.
- Partial: AV filtering (placeholder)
- Variable: Vent. rate (placeholder)
- Irregularly irregular: Pulse (placeholder)
- Lost: Atrial kick (placeholder)
Irregular ventricular conduction
Placeholder: only some impulses cross the AV node randomly.