Pacemaker (SA Node) — ECG/EKG Terminology

Definition: Specialized nervous tissue in the right atrium that begins the heartbeat. An artificial pacemaker is an electronic apparatus implanted to stimulate weak heart muscle.

Key Facts

• The SA node is the dominant intrinsic pacemaker in normal hearts.
• Automatic firing rate is typically 60 to 100 bpm at rest in adults.
• Suppression of SA activity allows slower subsidiary pacemakers to emerge.

ECG Connection: Sinus pacing generates upright P waves in lead II with consistent PR conduction.

Why It Matters: Loss of sinus pattern can be an early warning of conduction disease or medication effects.