Figure 21. Third-degree (complete) heart (AV) block. There is no relationship between P waves and QRS complexes: QRS rate is slower than P wave rate. Impulses originate at both the SA node (P waves) and below the site of block in the AV node (junctional rhythm) conducting to the ventricles. Atria and ventricles depolarize independently, QRS complexes are less frequent; regular at 20 to 40/min but normal in shape.
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