Definitions-accessory pathways (wolff-parkinson-white)

• Accessory pathway (bypass tract) of conducting myocardium connecting atria & ventricles, allowing impulses to bypass normal AVN delay
• Pre-excitation (WPW) pattern: ↓ PR interval, ↑ QRS width w/ δ wave (slurred onset, can be subtle). ST & Tw abnl (can mimic old IMI). Only seen w/ pathways that conduct antegrade (if pathway only conducts retrograde, then ECG will be normal during SR; “concealed” bypass tract).
• PAC can exaggerate pre-excitation if AV node conduction slowed
• WPW syndrome: WPW accessory pathway + paroxysmal tachycardia