see also:

• cardiology
• The basics of reading an ECG
• Fascicular heart blocks
• Left Bundle Branch Block (LBBB)
• Right Bundle Branch Block (RBBB)
• sick sinus syndrome (SSS) / tachycardia-bradycardia syndrome

• cardiac conduction blocks are common and often found co-incidentally on ECGs taken for other reasons
• most have a low probability of serious adverse events although some will result in syncopal episodes and warrant investigation and possible pacemaker placement

• acute increased vagal tone events
  • vaso-vagal syncope
• medications
  • beta adrenergic blockers
  • calcium channel blockers
• electrolyte disturbances
• ischaemic heart disease
• diabetes
• ageing
• myocarditis
  • viral infections
• cardiomyopathies
• RV strain may result in Right Bundle Branch Block (RBBB)
• infiltrative diseases
  • haemochromatosis
  • amyloidosis
  • sarcoidosis
• congenital

• prolonged PR interval:
  • no dropped beats ⇒ 1st degree heart block
• dropped beats:
  • dropped beat after successive increasingly long PR interval ⇒ Wenckebach (Mobitz type I)
  • at least 2 regular, consecutive impulses conducted with same PR ⇒ Mobitz type II
  • no conduction ⇒ complete HB

• see Fascicular heart blocks

• see Right Bundle Branch Block (RBBB) and Left Bundle Branch Block (LBBB)

• irreversible blocks causing syncope or hypotension, usually:
  • complete A-V block
  • trifascicular blocks
• sick sinus syndrome (SSS) / tachycardia-bradycardia syndrome