CLASSIFICATION AND PITFALLS OF ATRIOVENTR ICULAR-BLOCK

Atrioventricular blocks may be classified according to their degree, t heir site and their aetiology. Assessing the degree of block is not al ways easy when the P waves are poorly Visible and/or masked by the Ven tricular complexes. Affirmation that a 2nd degree block is a Mobitz II block requires examination of the ECG to differentiate it from ''fals e'' Mobitz II due to variable PP intervals or concealed hisian extrasy stoles. Complete atrioventricular block is easy to define on the ECG b ut not always synonymous with totally blocked conduction and should be interpreted taking into account the frequency of escape beats. Determ ining the site of block is important as it has therapeutic implication s; the type of block evaluated from the surface ECG also provides usef ul but not always decisive information. The investigation of the aetio logy of the block is valuable for differentiating acute, transient blo cks from chronic (permanent or paroxysmal) blocks, the former sometime s requiring temporary but rarely permanent cardiac pacing.